Eric Appel

All Publications

• Lipid Nanodiscs via Ordered Copolymers CHEM Smith, A. A., Autzen, H. E., Faust, B., Mann, J. L., Muir, B. W., Howard, S., Postma, A., Spakowitz, A. J., Cheng, Y., Appel, E. A. 2020; 6 (10): 2782–95

  View details for DOI 10.1016/j.chempr.2020.08.004

  View details for Web of Science ID 000580615300022

• An ultrafast insulin formulation enabled by high-throughput screening of engineered polymeric excipients. Science translational medicine Mann, J. L., Maikawa, C. L., Smith, A. A., Grosskopf, A. K., Baker, S. W., Roth, G. A., Meis, C. M., Gale, E. C., Liong, C. S., Correa, S., Chan, D., Stapleton, L. M., Yu, A. C., Muir, B., Howard, S., Postma, A., Appel, E. A. 2020; 12 (550)

  Abstract

  Insulin has been used to treat diabetes for almost 100 years; yet, current rapid-acting insulin formulations do not have sufficiently fast pharmacokinetics to maintain tight glycemic control at mealtimes. Dissociation of the insulin hexamer, the primary association state of insulin in rapid-acting formulations, is the rate-limiting step that leads to delayed onset and extended duration of action. A formulation of insulin monomers would more closely mimic endogenous postprandial insulin secretion, but monomeric insulin is unstable in solution using present formulation strategies and rapidly aggregates into amyloid fibrils. Here, we implement high-throughput-controlled radical polymerization techniques to generate a large library of acrylamide carrier/dopant copolymer (AC/DC) excipients designed to reduce insulin aggregation. Our top-performing AC/DC excipient candidate enabled the development of an ultrafast-absorbing insulin lispro (UFAL) formulation, which remains stable under stressed aging conditions for 25 ± 1 hours compared to 5 ± 2 hours for commercial fast-acting insulin lispro formulations (Humalog). In a porcine model of insulin-deficient diabetes, UFAL exhibited peak action at 9 ± 4 min, whereas commercial Humalog exhibited peak action at 25 ± 10 min. These ultrafast kinetics make UFAL a promising candidate for improving glucose control and reducing burden for patients with diabetes.

  View details for DOI 10.1126/scitranslmed.aba6676

  View details for PubMedID 32611683

• Injectable Hydrogels for Sustained Codelivery of Subunit Vaccines Enhance Humoral Immunity. ACS central science Roth, G. A., Gale, E. C., Alcántara-Hernández, M., Luo, W., Axpe, E., Verma, R., Yin, Q., Yu, A. C., Lopez Hernandez, H., Maikawa, C. L., Smith, A. A., Davis, M. M., Pulendran, B., Idoyaga, J., Appel, E. A. 2020; 6 (10): 1800–1812

  Abstract

  Vaccines aim to elicit a robust, yet targeted, immune response. Failure of a vaccine to elicit such a response arises in part from inappropriate temporal control over antigen and adjuvant presentation to the immune system. In this work, we sought to exploit the immune system's natural response to extended pathogen exposure during infection by designing an easily administered slow-delivery vaccine platform. We utilized an injectable and self-healing polymer-nanoparticle (PNP) hydrogel platform to prolong the codelivery of vaccine components to the immune system. We demonstrated that these hydrogels exhibit unique delivery characteristics, whereby physicochemically distinct compounds (such as antigen and adjuvant) could be codelivered over the course of weeks. When administered in mice, hydrogel-based sustained vaccine exposure enhanced the magnitude, duration, and quality of the humoral immune response compared to standard PBS bolus administration of the same model vaccine. We report that the creation of a local inflammatory niche within the hydrogel, coupled with sustained exposure of vaccine cargo, enhanced the magnitude and duration of germinal center responses in the lymph nodes. This strengthened germinal center response promoted greater antibody affinity maturation, resulting in a more than 1000-fold increase in antigen-specific antibody affinity in comparison to bolus immunization. In summary, this work introduces a simple and effective vaccine delivery platform that increases the potency and durability of subunit vaccines.

  View details for DOI 10.1021/acscentsci.0c00732

  View details for PubMedID 33145416

  View details for PubMedCentralID PMC7596866

• A co-formulation of supramolecularly stabilized insulin and pramlintide enhances mealtime glucagon suppression in diabetic pigs. Nature biomedical engineering Maikawa, C. L., Smith, A. A., Zou, L., Roth, G. A., Gale, E. C., Stapleton, L. M., Baker, S. W., Mann, J. L., Yu, A. C., Correa, S., Grosskopf, A. K., Liong, C. S., Meis, C. M., Chan, D., Troxell, M., Maahs, D. M., Buckingham, B. A., Webber, M. J., Appel, E. A. 2020

  Abstract

  Treatment of patients with diabetes with insulin and pramlintide (an amylin analogue) is more effective than treatment with insulin only. However, because mixtures of insulin and pramlintide are unstable and have to be injected separately, amylin analogues are only used by 1.5% of people with diabetes needing rapid-acting insulin. Here, we show that the supramolecular modification of insulin and pramlintide with cucurbit[7]uril-conjugated polyethylene glycol improves the pharmacokinetics of the dual-hormone therapy and enhances postprandial glucagon suppression in diabetic pigs. The co-formulation is stable for over 100 h at 37 °C under continuous agitation, whereas commercial formulations of insulin analogues aggregate after 10 h under similar conditions. In diabetic rats, the administration of the stabilized co-formulation increased the area-of-overlap ratio of the pharmacokinetic curves of pramlintide and insulin from 0.4 ± 0.2 to 0.7 ± 0.1 (mean ± s.d.) for the separate administration of the hormones. The co-administration of supramolecularly stabilized insulin and pramlintide better mimics the endogenous kinetics of co-secreted insulin and amylin, and holds promise as a dual-hormone replacement therapy.

  View details for DOI 10.1038/s41551-020-0555-4

  View details for PubMedID 32393892

• Wildfire prevention through prophylactic treatment of high-risk landscapes using viscoelastic retardant fluids. Proceedings of the National Academy of Sciences of the United States of America Yu, A. C., Lopez Hernandez, H., Kim, A. H., Stapleton, L. M., Brand, R. J., Mellor, E. T., Bauer, C. P., McCurdy, G. D., Wolff, A. J., Chan, D., Criddle, C. S., Acosta, J. D., Appel, E. A. 2019

  Abstract

  Polyphosphate fire retardants are a critical tactical resource for fighting fires in the wildland and in the wildland-urban interface. Yet, application of these retardants is limited to emergency suppression strategies because current formulations cannot retain fire retardants on target vegetation for extended periods of time through environmental exposure and weathering. New retardant formulations with persistent retention to target vegetation throughout the peak fire season would enable methodical, prophylactic treatment strategies of landscapes at high risk of wildfires through prolonged prevention of ignition and continual impediment to active flaming fronts. Here we develop a sprayable, environmentally benign viscoelastic fluid comprising biopolymers and colloidal silica to enhance adherence and retention of polyphosphate retardants on common wildfire-prone vegetation. These viscoelastic fluids exhibit appropriate wetting and rheological responses to enable robust retardant adherence to vegetation following spray application. Further, laboratory and pilot-scale burn studies establish that these materials drastically reduce ignition probability before and after simulated weathering events. Overall, these studies demonstrate how these materials actualize opportunities to shift the approach of retardant-based wildfire management from reactive suppression to proactive prevention at the source of ignitions.

  View details for DOI 10.1073/pnas.1907855116

  View details for PubMedID 31570592

• Use of a supramolecular polymeric hydrogel as an effective post-operative pericardial adhesion barrier. Nature biomedical engineering Stapleton, L. M., Steele, A. N., Wang, H., Lopez Hernandez, H., Yu, A. C., Paulsen, M. J., Smith, A. A., Roth, G. A., Thakore, A. D., Lucian, H. J., Totherow, K. P., Baker, S. W., Tada, Y., Farry, J. M., Eskandari, A., Hironaka, C. E., Jaatinen, K. J., Williams, K. M., Bergamasco, H., Marschel, C., Chadwick, B., Grady, F., Ma, M., Appel, E. A., Woo, Y. J. 2019; 3 (8): 611–20

  Abstract

  Post-operative adhesions form as a result of normal wound healing processes following any type of surgery. In cardiac surgery, pericardial adhesions are particularly problematic during reoperations, as surgeons must release the adhesions from the surface of the heart before the intended procedure can begin, thereby substantially lengthening operation times and introducing risks of haemorrhage and injury to the heart and lungs during sternal re-entry and cardiac dissection. Here we show that a dynamically crosslinked supramolecular polymer-nanoparticle hydrogel, with viscoelastic and flow properties that enable spraying onto tissue as well as robust tissue adherence and local retention in vivo for two weeks, reduces the formation of pericardial adhesions. In a rat model of severe pericardial adhesions, the hydrogel markedly reduced the severity of the adhesions, whereas commercial adhesion barriers (including Seprafilm and Interceed) did not. The hydrogels also reduced the severity of cardiac adhesions (relative to untreated animals) in a clinically relevant cardiopulmonary-bypass model in sheep. This viscoelastic supramolecular polymeric hydrogel represents a promising clinical solution for the prevention of post-operative pericardial adhesions.

  View details for DOI 10.1038/s41551-019-0442-z

  View details for PubMedID 31391596

• Prolonged Codelivery of Hemagglutinin and a TLR7/8 Agonist in a Supramolecular Polymer-Nanoparticle Hydrogel Enhances Potency and Breadth of Influenza Vaccination. ACS biomaterials science & engineering Roth, G. A., Saouaf, O. M., Smith, A. A., Gale, E. C., Hernandez, M. A., Idoyaga, J., Appel, E. A. 2021

  Abstract

  The sustained release of vaccine cargo has been shown to improve humoral immune responses to challenging pathogens such as influenza. Extended codelivery of antigen and adjuvant prolongs germinal center reactions, thus improving antibody affinity maturation and the ability to neutralize the target pathogen. Here, we develop an injectable, physically cross-linked polymer-nanoparticle (PNP) hydrogel system to prolong the local codelivery of hemagglutinin and a toll-like receptor 7/8 agonist (TLR7/8a) adjuvant. By tethering the TLR7/8a to a NP motif within the hydrogels (TLR7/8a-NP), the dynamic mesh of the PNP hydrogels enables codiffusion of the adjuvant and protein antigen (hemagglutinin), therefore enabling sustained codelivery of these two physicochemically distinct molecules. We show that subcutaneous delivery of PNP hydrogels carrying hemagglutinin and TLR7/8a-NP in mice improves the magnitude and duration of antibody titers in response to a single injection vaccination compared to clinically used adjuvants. Furthermore, the PNP gel-based slow delivery of influenza vaccines led to increased breadth of antibody responses against future influenza variants, including a future pandemic variant, compared to clinical adjuvants. In summary, this work introduces a simple and effective vaccine delivery platform that increases the potency and durability of influenza subunit vaccines.

  View details for DOI 10.1021/acsbiomaterials.0c01496

  View details for PubMedID 33404236

• A fluorescence sandwich immunoassay for the real-time continuous detection of glucose and insulin in live animals. Nature biomedical engineering Poudineh, M., Maikawa, C. L., Ma, E. Y., Pan, J., Mamerow, D., Hang, Y., Baker, S. W., Beirami, A., Yoshikawa, A., Eisenstein, M., Kim, S., Vuckovic, J., Appel, E. A., Soh, H. T. 2020

  Abstract

  Biosensors that continuously measure circulating biomolecules in real time could provide insights into the health status of patients and their response to therapeutics. But biosensors for the continuous real-time monitoring of analytes in vivo have only reached nanomolar sensitivity and can measure only a handful of molecules, such as glucose and blood oxygen. Here we show that multiple analytes can be continuously and simultaneously measured with picomolar sensitivity and sub-second resolution via the integration of aptamers and antibodies into a bead-based fluorescence sandwich immunoassay implemented in a custom microfluidic chip. After an incubation time of 30s, bead fluorescence is measured using a high-speed camera under spatially multiplexed two-colour laser illumination. We used the assay for continuous quantification of glucose and insulin concentrations in the blood of live diabetic rats to resolve inter-animal differences in the pharmacokinetic response to insulin as well as discriminate pharmacokinetic profiles from different insulin formulations. The assay can be readily modified to continuously and simultaneously measure other blood analytes in vivo.

  View details for DOI 10.1038/s41551-020-00661-1

  View details for PubMedID 33349659

• A Quantitative Description for Designing the Extrudability of Shear-Thinning Physical Hydrogels. Macromolecular bioscience Lopez Hernandez, H., Souza, J. W., Appel, E. A. 2020: e2000295

  Abstract

  Physically associated hydrogels (PHs) capable of reversible transitions between solid and liquid-like states have enabled novel strategies for 3D printing, therapeutic drug and cell delivery, and regenerative medicine. Among the many design criteria (e.g., viscoelasticity, cargo diffusivity, biocompatibility) for these applications, engineering PHs for extrudability is a necessary and critical design criterion for the successful application of these materials. As the development of many distinct PH material systems continues, a strategy to determine the extrudability of PHs a priori will be exceedingly useful for reducing costly and time-consuming trial-and-error experimentation. Here, a strategy to determine the property-function relationships for PHs in injectable drug delivery applications at clinically relevant flow rates is presented. This strategy-validated with two chemically and physically distinct PHs-reveals material design spaces in the form of Ashby-style plots that highlight acceptable, application-specific material properties. It is shown that the flow behavior of PHs does not obey a single shear-thinning power law and the implications for injectable drug delivery are discussed. This approach for generating design criteria has potential for streamlining the screening of PHs and their utility in applications with varying geometrical (i.e., needle diameter) and process (i.e., flow rate) constraints.

  View details for DOI 10.1002/mabi.202000295

  View details for PubMedID 33164332

• Highly Branched Polydimethylacrylamide Copolymers as Functional Biomaterials. Biomacromolecules Mann, J. L., Grosskopf, A. K., Smith, A. A., Appel, E. A. 2020

  Abstract

  Controlled radical polymerization of vinyl monomers with multivinyl cross-linkers leads to the synthesis of highly branched polymers with controlled spatial density of functional chain ends. The resulting polymers synthesized in this manner have large dispersities resulting from a mixture of unreacted primary chains, low molecular weight branched species, and high molecular weight highly branched species. Through the use of fractional precipitation, we present a synthetic route to high molecular weight highly branched polymers that are absent of low molecular weight species and that contain reactivity toward amines for controlled postpolymerization modification. The controlled spatial density of functional moieties on these high molecular weight macromolecular constructs enable new functional biomaterials with the potential for application in regenerative medicine, immunoengineering, imaging, and controlled drug delivery.

  View details for DOI 10.1021/acs.biomac.0c00539

  View details for PubMedID 32786733

• Site-selective modification of proteins using cucurbit[7]uril as supramolecular protection for N-terminal aromatic amino acids. Organic & biomolecular chemistry Smith, A. A., Maikawa, C. L., Roth, G. A., Appel, E. A. 2020

  Abstract

  Cucurbit[7,8]urils are known to form inclusion complexes with aromatic amino acids, hosting the hydrohobic side chains within the cavity and adjacent cations within the portal of the macrocyclic host. Here we show that cucurbit[7]uril binding with N-terminal phenylalanine significantly reduces the nucleophilicity of the amine, likely due to an increase in stability of the ammonium ion, rendering it unreactive at neutral pH. Using insulin as a model protein, we show that this supramolecular protection strategy can drive selectivity of N-terminal amine conjugation away from the preferred B chain N-terminal phenylalanine towards the A chain N-terminal glycine. Cucurbit[7]uril can therefore be used as a supramolecular protecting group for site-selective protein modification.

  View details for DOI 10.1039/d0ob01004a

  View details for PubMedID 32459261

• Reply to Santin et al.: Viscoelastic retardant fluids enable treatments to prevent wildfire on landscapes subject to routine ignitions. Proceedings of the National Academy of Sciences of the United States of America Appel, E. A., Criddle, C. S., Acosta, J. D., Yu, A. C. 2020

  View details for DOI 10.1073/pnas.1922877117

  View details for PubMedID 32079729

• A human mission to Mars: Predicting the bone mineral density loss of astronauts. PloS one Axpe, E., Chan, D., Abegaz, M. F., Schreurs, A., Alwood, J. S., Globus, R. K., Appel, E. A. 2020; 15 (1): e0226434

  Abstract

  A round-trip human mission to Mars is anticipated to last roughly three years. Spaceflight conditions are known to cause loss of bone mineral density (BMD) in astronauts, increasing bone fracture risk. There is an urgent need to understand BMD progression as a function of spaceflight time to minimize associated health implications and ensure mission success. Here we introduce a nonlinear mathematical model of BMD loss for candidate human missions to Mars: (i) Opposition class trajectory (400-600 days), and (ii) Conjunction class trajectory (1000-1200 days). Using femoral neck BMD data (N = 69) from astronauts after 132-day and 228-day spaceflight and the World Health Organization's fracture risk recommendation, we predicted post-mission risk and associated osteopathology. Our model predicts 62% opposition class astronauts and 100% conjunction class astronauts will develop osteopenia, with 33% being at risk for osteoporosis. This model can help in implementing countermeasure strategies and inform space agencies' choice of crew candidates.

  View details for DOI 10.1371/journal.pone.0226434

  View details for PubMedID 31967993

• Nanoparticles Presenting Potent TLR7/8 Agonists Enhance Anti-PD-L1 Immunotherapy in Cancer Treatment. Biomacromolecules Smith, A. A., Gale, E. C., Roth, G. A., Maikawa, C. L., Correa, S., Yu, A. C., Appel, E. A. 2020

  Abstract

  Cancer immunotherapy can be augmented with toll-like receptor agonist (TLRa) adjuvants, which interact with immune cells to elicit potent immune activation. Despite their potential, use of many TLRa compounds has been limited clinically due to their extreme potency and lack of pharmacokinetic control, causing systemic toxicity from unregulated systemic cytokine release. Herein, we overcome these shortcomings by generating poly(ethylene glycol)-poly(lactic acid) (PEG-PLA) nanoparticles (NPs) presenting potent TLR7/8a moieties on their surface. The NP platform allows precise control of TLR7/8a valency and resulting surface presentation through self-assembly using nanoprecipitation. We hypothesize that the pharmacokinetic profile of the NPs minimizes systemic toxicity, localizing TLR7/8a presentation to the tumor bed and tumor-draining lymph nodes. In conjunction with antiprogrammed death-ligand 1 (anti-PD-L1) checkpoint blockade, peritumoral injection of TLR7/8a NPs slows tumor growth, extends survival, and decreases systemic toxicity in comparison to the free TLR7/8a in a murine colon adenocarcinoma model. These NPs constitute a modular platform for controlling pharmacokinetics of immunostimulatory molecules, resulting in increased potency and decreased toxicity.

  View details for DOI 10.1021/acs.biomac.0c00812

  View details for PubMedID 32816460

• Towards brain-tissue-like biomaterials. Nature communications Axpe, E., Orive, G., Franze, K., Appel, E. A. 2020; 11 (1): 3423

  View details for DOI 10.1038/s41467-020-17245-x

  View details for PubMedID 32647269

• Multi-phase catheter-injectable hydrogel enables dual-stage protein-engineered cytokine release to mitigate adverse left ventricular remodeling following myocardial infarction in a small animal model and a large animal model. Cytokine Steele, A. N., Paulsen, M. J., Wang, H., Stapleton, L. M., Lucian, H. J., Eskandari, A., Hironaka, C. E., Farry, J. M., Baker, S. W., Thakore, A. D., Jaatinen, K. J., Tada, Y., Hollander, M. J., Williams, K. M., Seymour, A. J., Totherow, K. P., Yu, A. C., Cochran, J. R., Appel, E. A., Woo, Y. J. 2020; 127: 154974

  Abstract

  Although ischemic heart disease is the leading cause of death worldwide, mainstay treatments ultimately fail because they do not adequately address disease pathophysiology. Restoring the microvascular perfusion deficit remains a significant unmet need and may be addressed via delivery of pro-angiogenic cytokines. The therapeutic effect of cytokines can be enhanced by encapsulation within hydrogels, but current hydrogels do not offer sufficient clinical translatability due to unfavorable viscoelastic mechanical behavior which directly impacts the ability for minimally-invasive catheter delivery. In this report, we examine the therapeutic implications of dual-stage cytokine release from a novel, highly shear-thinning biocompatible catheter-deliverable hydrogel. We chose to encapsulate two protein-engineered cytokines, namely dimeric fragment of hepatocyte growth factor (HGFdf) and engineered stromal cell-derived factor 1α (ESA), which target distinct disease pathways. The controlled release of HGFdf and ESA from separate phases of the hyaluronic acid-based hydrogel allows extended and pronounced beneficial effects due to the precise timing of release. We evaluated the therapeutic efficacy of this treatment strategy in a small animal model of myocardial ischemia and observed a significant benefit in biological and functional parameters. Given the encouraging results from the small animal experiment, we translated this treatment to a large animal preclinical model and observed a reduction in scar size, indicating this strategy could serve as a potential adjunct therapy for the millions of people suffering from ischemic heart disease.

  View details for DOI 10.1016/j.cyto.2019.154974

  View details for PubMedID 31978642

• Structural considerations for physical hydrogels based on polymer-nanoparticle interactions MOLECULAR SYSTEMS DESIGN & ENGINEERING Yu, A. C., Smith, A. A., Appel, E. A. 2020; 5 (1): 401–7

  View details for DOI 10.1039/c9me00120d

  View details for Web of Science ID 000508398900034

• Stable Monomeric Insulin Formulations Enabled by Supramolecular PEGylation of Insulin Analogues. Advanced therapeutics Maikawa, C. L., Smith, A. A., Zou, L., Meis, C. M., Mann, J. L., Webber, M. J., Appel, E. A. 2020; 3 (1)

  Abstract

  Current "fast-acting" insulin analogues contain amino acid modifications meant to inhibit dimer formation and shift the equilibrium of association states toward the monomeric state. However, the insulin monomer is highly unstable and current formulation techniques require insulin to primarily exist as hexamers to prevent aggregation into inactive and immunogenic amyloids. Insulin formulation excipients have thus been traditionally selected to promote insulin association into the hexameric form to enhance formulation stability. This study exploits a novel excipient for the supramolecular PEGylation of insulin analogues, including aspart and lispro, to enhance the stability and maximize the prevalence of insulin monomers in formulation. Using multiple techniques, it is demonstrated that judicious choice of formulation excipients (tonicity agents and parenteral preservatives) enables insulin analogue formulations with 70-80% monomer and supramolecular PEGylation imbued stability under stressed aging for over 100 h without altering the insulin association state. Comparatively, commercial "fast-acting" formulations contain less than 1% monomer and remain stable for only 10 h under the same stressed aging conditions. This simple and effective formulation approach shows promise for next-generation ultrafast insulin formulations with a short duration of action that can reduce the risk of post-prandial hypoglycemia in the treatment of diabetes.

  View details for DOI 10.1002/adtp.201900094

  View details for PubMedID 32190729

  View details for PubMedCentralID PMC7079736

• MRBLES 2.0: High-throughput generation of chemically functionalized spectrally and magnetically encoded hydrogel beads using a simple single-layer microfluidic device. Microsystems & nanoengineering Feng, Y., White, A. K., Hein, J. B., Appel, E. A., Fordyce, P. M. 2020; 6: 109

  Abstract

  The widespread adoption of bead-based multiplexed bioassays requires the ability to easily synthesize encoded microspheres and conjugate analytes of interest to their surface. Here, we present a simple method (MRBLEs 2.0) for the efficient high-throughput generation of microspheres with ratiometric barcode lanthanide encoding (MRBLEs) that bear functional groups for downstream surface bioconjugation. Bead production in MRBLEs 2.0 relies on the manual mixing of lanthanide/polymer mixtures (each of which comprises a unique spectral code) followed by droplet generation using single-layer, parallel flow-focusing devices and the off-chip batch polymerization of droplets into beads. To streamline downstream analyte coupling, MRBLEs 2.0 crosslinks copolymers bearing functional groups on the bead surface during bead generation. Using the MRBLEs 2.0 pipeline, we generate monodisperse MRBLEs containing 48 distinct well-resolved spectral codes with high throughput (>150,000/min and can be boosted to 450,000/min). We further demonstrate the efficient conjugation of oligonucleotides and entire proteins to carboxyl MRBLEs and of biotin to amino MRBLEs. Finally, we show that MRBLEs can also be magnetized via the simultaneous incorporation of magnetic nanoparticles with only a minor decrease in the potential code space. With the advantages of dramatically simplified device fabrication, elimination of the need for custom-made equipment, and the ability to produce spectrally and magnetically encoded beads with direct surface functionalization with high throughput, MRBLEs 2.0 can be directly applied by many labs towards a wide variety of downstream assays, from basic biology to diagnostics and other translational research.

  View details for DOI 10.1038/s41378-020-00220-3

  View details for PubMedID 33299601

• Engineered biomaterials for heart disease. Current opinion in biotechnology Stapleton, L., Zhu, Y., Woo, Y. J., Appel, E. 2020; 66: 246–54

  Abstract

  Ischemic heart disease is the most common type of heart disease, responsible for roughly 10 million deaths worldwide annually. While standard clinical interventions have resulted in improved patient outcomes, access to small diameter vessels required for cardiovascular interventions, and long-term patient mortality rates associated with eventual heart failure, remain critical challenges. In this current opinion piece we discuss novel methodologies for the advancement of vascular grafts, cardiac patches, and injectable drug delivery depot technologies as they relate to treatment of ischemic heart disease, including bilayered conduits, acellular bioactive extracellular matrix (ECM) scaffolds, and protease-responsive hydrogel delivery platforms. We address the motivation for innovation and current limitations in the field of engineered biomaterials for myocardial ischemia therapeutics and interventions.

  View details for DOI 10.1016/j.copbio.2020.08.008

  View details for PubMedID 33011453

• Injectable supramolecular polymer-nanoparticle hydrogels enhance human mesenchymal stem cell delivery. Bioengineering & translational medicine Grosskopf, A. K., Roth, G. A., Smith, A. A., Gale, E. C., Hernandez, H. L., Appel, E. A. 2020; 5 (1): e10147

  Abstract

  Stem cell therapies have emerged as promising treatments for injuries and diseases in regenerative medicine. Yet, delivering stem cells therapeutically can be complicated by invasive administration techniques, heterogeneity in the injection media, and/or poor cell retention at the injection site. Despite these issues, traditional administration protocols using bolus injections in a saline solution or surgical implants of cell-laden hydrogels have highlighted the promise of cell administration as a treatment strategy. To address these limitations, we have designed an injectable polymer-nanoparticle (PNP) hydrogel platform exploiting multivalent, noncovalent interactions between modified biopolymers and biodegradable nanoparticles for encapsulation and delivery of human mesenchymal stem cells (hMSCs). hMSC-based therapies have shown promise due to their broad differentiation capacities and production of therapeutic paracrine signaling molecules. In this work, the fundamental hydrogel mechanical properties that enhance hMSC delivery processes are elucidated using basic in vitro models. Further, in vivo studies in immunocompetent mice reveal that PNP hydrogels enhance hMSC retention at the injection site and retain administered hMSCs locally for upwards of 2 weeks. Through both in vitro and in vivo experiments, we demonstrate a novel scalable, synthetic, and biodegradable hydrogel system that overcomes current limitations and enables effective cell delivery.

  View details for DOI 10.1002/btm2.10147

  View details for PubMedID 31989036

  View details for PubMedCentralID PMC6971438

• Universal Scaling Behavior during Network Formation in Controlled Radical Polymerizations. Macromolecules Mann, J. L., Rossi, R. L., Smith, A. A., Appel, E. A. 2019; 52 (24): 9456–65

  Abstract

  Despite the ubiquity of branched and network polymers in biological, electronic, and rheological applications, it remains difficult to predict the network structure arising from polymerization of vinyl and multivinyl monomers. While controlled radical polymerization (CRP) techniques afford modularity and control in the synthesis of (hyper)branched polymers, a unifying understanding of network formation providing grounded predictive power is still lacking. A current limitation is the inability to predict the number and weight average molecular weights that arise during the synthesis of (hyper)branched polymers using CRP. This study addresses this literature gap through first building intuition via a growth boundary analysis on how certain environmental cues (concentration, monomer choice, and cross-linker choice) affect the cross-link efficiency during network formation through experimental gel point measurements. We then demonstrate, through experimental gel point normalization, universal scaling behavior of molecular weights in the synthesis of branched polymers corroborated by previous literature experiments. Moreover, the normalization employed in this analysis reveals trends in the macroscopic mechanical properties of networks synthesized using CRP techniques. Gel point normalization employed in this analysis both enables a polymer chemist to target specific number and weight average molecular weights of (hyper)branched polymers using CRP and demonstrates the utility of CRP for gel synthesis.

  View details for DOI 10.1021/acs.macromol.9b02109

  View details for PubMedID 31894160

• Stable Monomeric Insulin Formulations Enabled by Supramolecular PEGylation of Insulin Analogues ADVANCED THERAPEUTICS Maikawa, C. L., Smith, A. A., Zou, L., Meis, C. M., Mann, J. L., Webber, M. J., Appel, E. A. 2019

  View details for DOI 10.1002/adtp.201900094

  View details for Web of Science ID 000503161700001

• A Nanoparticle Platform for Improved Potency, Stability, and Adjuvanticity of Poly(I:C) ADVANCED THERAPEUTICS Gale, E. C., Roth, G. A., Smith, A. A., Alcantara-Hernandez, M., Idoyaga, J., Appel, E. A. 2019

  View details for DOI 10.1002/adtp.201900174

  View details for Web of Science ID 000502045100001

• Injectable supramolecular polymer-nanoparticle hydrogels enhance human mesenchymal stem cell delivery BIOENGINEERING & TRANSLATIONAL MEDICINE Grosskopf, A. K., Roth, G. A., Smith, A. A., Gale, E. C., Hernandez, H., Appel, E. A. 2019

  View details for DOI 10.1002/btm2.10147

  View details for Web of Science ID 000491537900001

• A Multiscale Model for Solute Diffusion in Hydrogels. Macromolecules Axpe, E., Chan, D., Offeddu, G. S., Chang, Y., Merida, D., Hernandez, H. L., Appel, E. A. 2019; 52 (18): 6889–97

  Abstract

  The number of biomedical applications of hydrogels is increasing rapidly on account of their unique physical, structural, and mechanical properties. The utility of hydrogels as drug delivery systems or tissue engineering scaffolds critically depends on the control of diffusion of solutes through the hydrogel matrix. Predicting or even modeling this diffusion is challenging due to the complex structure of hydrogels. Currently, the diffusivity of solutes in hydrogels is typically modeled by one of three main theories proceeding from distinct diffusion mechanisms: (i) hydrodynamic, (ii) free volume, and (iii) obstruction theory. Yet, a comprehensive predictive model is lacking. Thus, time and capital-intensive trial-and-error procedures are used to test the viability of hydrogel applications. In this work, we have developed a model for the diffusivity of solutes in hydrogels combining the three main theoretical frameworks, which we call the multiscale diffusion model (MSDM). We verified the MSDM by analyzing the diffusivity of dextran of different sizes in a series of poly(ethylene glycol) (PEG) hydrogels with distinct mesh sizes. We measured the subnanoscopic free volume by positron annihilation lifetime spectroscopy (PALS) to characterize the physical hierarchy of these materials. In addition, we performed a meta-analysis of literature data from previous studies on the diffusion of solutes in hydrogels. The model presented outperforms traditional models in predicting solute diffusivity in hydrogels and provides a practical approach to predicting the transport properties of solutes such as drugs through hydrogels used in many biomedical applications.

  View details for DOI 10.1021/acs.macromol.9b00753

  View details for PubMedID 31579160

• Block copolymer composition drives function of self-assembled nanoparticles for delivery of small-molecule cargo JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Maikawa, C. L., Sevit, A., Lin, B., Wallstrom, R. J., Mann, J. L., Yu, A. C., Waymouth, R. M., Appel, E. A. 2019; 57 (12): 1322–32

  View details for DOI 10.1002/pola.29393

  View details for Web of Science ID 000469938700008

• A Biocompatible Therapeutic Catheter-Deliverable Hydrogel for In Situ Tissue Engineering ADVANCED HEALTHCARE MATERIALS Steele, A. N., Stapleton, L. M., Farry, J. M., Lucian, H. J., Paulsen, M. J., Eskandari, A., Hironaka, C. E., Thakore, A. D., Wang, H., Yu, A. C., Chan, D., Appel, E. A., Woo, Y. 2019; 8 (5)

  View details for DOI 10.1002/adhm.201801147

  View details for Web of Science ID 000461575200003

• A Biocompatible Therapeutic Catheter-Deliverable Hydrogel for In Situ Tissue Engineering. Advanced healthcare materials Steele, A. N., Stapleton, L. M., Farry, J. M., Lucian, H. J., Paulsen, M. J., Eskandari, A., Hironaka, C. E., Thakore, A. D., Wang, H., Yu, A. C., Chan, D., Appel, E. A., Woo, Y. J. 2019: e1801147

  Abstract

  Hydrogels have emerged as a diverse class of biomaterials offering a broad range of biomedical applications. Specifically, injectable hydrogels are advantageous for minimally invasive delivery of various therapeutics and have great potential to treat a number of diseases. However, most current injectable hydrogels are limited by difficult and time-consuming fabrication techniques and are unable to be delivered through long, narrow catheters, preventing extensive clinical translation. Here, the development of an easily-scaled, catheter-injectable hydrogel utilizing a polymer-nanoparticle crosslinking mechanism is reported, which exhibits notable shear-thinning and self-healing behavior. Gelation of the hydrogel occurs immediately upon mixing the biochemically modified hyaluronic acid polymer with biodegradable nanoparticles and can be easily injected through a high-gauge syringe due to the dynamic nature of the strong, yet reversible crosslinks. Furthermore, the ability to deliver this novel hydrogel through a long, narrow, physiologically-relevant catheter affixed with a 28-G needle is highlighted, with hydrogel mechanics unchanged after delivery. Due to the composition of the gel, it is demonstrated that therapeutics can be differentially released with distinct elution profiles, allowing precise control over drug delivery. Finally, the cell-signaling and biocompatibility properties of this innovative hydrogel are demonstrated, revealing its wide range of therapeutic applications.

  View details for PubMedID 30714355

• Non-Newtonian Polymer-Nanoparticle Hydrogels Enhance Cell Viability during Injection MACROMOLECULAR BIOSCIENCE Hernandez, H., Grosskopf, A. K., Stapleton, L. M., Agmon, G., Appel, E. A. 2019; 19 (1)

  View details for DOI 10.1002/mabi.201800275

  View details for Web of Science ID 000458817700008

• Injectable Polymer-Nanoparticle Hydrogels for Local Immune Cell Recruitment. Biomacromolecules Fenton, O. S., Tibbitt, M. W., Appel, E. A., Jhunjhunwala, S., Webber, M. J., Langer, R. 2019

  Abstract

  The ability to engineer immune function has transformed modern medicine, highlighted by the success of vaccinations and recent efforts in cancer immunotherapy. Further directions in programming the immune system focus on the design of immunomodulatory biomaterials that can recruit, engage with, and program immune cells locally in vivo. Here, we synthesized shear-thinning and self-healing polymer-nanoparticle (PNP) hydrogels as a tunable and injectable biomaterial platform for local dendritic cell (DC) recruitment. PNP gels were formed from two populations of poly(ethylene glycol)-block-polylactide (PEG-b-PLA) NPs with the same diameter but different PEG brush length (2 or 5 kDa). PEG-b-PLA NPs with the longer PEG brush exhibited improved gel formation following self-assembly and faster recovery after shear-thinning. In all cases, model protein therapeutics were released via Fickian diffusion in vitro, and minor differences in the release rate between the gel formulations were observed. PNP hydrogels were loaded with the DC cytokine CCL21 and injected subcutaneously in a murine model. CCL21-loaded PNP hydrogels recruited DCs preferentially to the site of injection in vivo relative to non-CCL21-loaded hydrogels. Thus, PNP hydrogels comprise a simple and tunable platform biomaterial for in vivo immunomodulation following minimally invasive subcutaneous injection.

  View details for DOI 10.1021/acs.biomac.9b01129

  View details for PubMedID 31682423

• Non-Newtonian Polymer-Nanoparticle Hydrogels Enhance Cell Viability during Injection. Macromolecular bioscience Lopez Hernandez, H., Grosskopf, A. K., Stapleton, L. M., Agmon, G., Appel, E. A. 2018: e1800275

  Abstract

  Drug delivery and cell transplantation require minimally invasive deployment strategies such as injection through clinically relevant high-gauge needles. Supramolecular hydrogels comprising dodecyl-modified hydroxypropylmethylcellulose and poly(ethylene glycol)-block-poly(lactic acid) have been previously demonstrated for the delivery of drugs and proteins. Here, it is demonstrated that the rheological properties of these hydrogels allow for facile injectability, an increase of cell viability after injection when compared to cell viabilities of cells injected in phosphate-buffered saline, and homogeneous cell suspensions that do not settle. These hydrogels are injected at 1mL min-1 with pressures less than 400kPa, despite the solid-like properties of the gel when at rest. The cell viabilities immediately after injection are greater than 86% for adult human dermal fibroblasts, human umbilical vein cells, smooth muscle cells, and human mesenchymal stem cells. Cells are shown to remain suspended and proliferate in the hydrogel at the same rate as observed in cell media. The work expands on the versatility of these hydrogels and lays a foundation for the codelivery of drugs, proteins, and cells.

  View details for PubMedID 30369048

• Self-assembled biomaterials using host-guest interactions SELF-ASSEMBLING BIOMATERIALS: MOLECULAR DESIGN, CHARACTERIZATION AND APPLICATION IN BIOLOGY AND MEDICINE Yu, A. C., Stapleton, L. M., Mann, J. L., Appel, E. A., Azevedo, H. S., DaSilva, R. M. 2018: 205–31

  View details for DOI 10.1016/B978-0-08-102015-9.00010-1

  View details for Web of Science ID 000462711900010

• Engineering the Mechanical Properties of Polymer Networks with Precise Doping of Primary Defects. ACS applied materials & interfaces Chan, D., Ding, Y., Dauskardt, R. H., Appel, E. A. 2017

  Abstract

  Polymer networks are extensively utilized across numerous applications ranging from commodity superabsorbent polymers and coatings to high-performance microelectronics and biomaterials. For many applications, desirable properties are known; however, achieving them has been challenging. Additionally, the accurate prediction of elastic modulus has been a long-standing difficulty owing to the presence of loops. By tuning the prepolymer formulation through precise doping of monomers, specific primary network defects can be programmed into an elastomeric scaffold, without alteration of their resulting chemistry. The addition of these monomers that respond mechanically as primary defects is used both to understand their impact on the resulting mechanical properties of the materials and as a method to engineer the mechanical properties. Indeed, these materials exhibit identical bulk and surface chemistry, yet vastly different mechanical properties. Further, we have adapted the real elastic network theory (RENT) to the case of primary defects in the absence of loops, thus providing new insights into the mechanism for material strength and failure in polymer networks arising from primary network defects, and to accurately predict the elastic modulus of the polymer system. The versatility of the approach we describe and the fundamental knowledge gained from this study can lead to new advancements in the development of novel materials with precisely defined and predictable chemical, physical, and mechanical properties.

  View details for PubMedID 29135222

• Supramolecular polymeric biomaterials. Biomaterials science Mann, J. L., Yu, A. C., Agmon, G., Appel, E. A. 2017

  Abstract

  Polymeric chains crosslinked through supramolecular interactions-directional and reversible non-covalent interactions-compose an emerging class of modular and tunable biomaterials. The choice of chemical moiety utilized in the crosslink affords different thermodynamic and kinetic parameters of association, which in turn illustrate the connectivity and dynamics of the system. These parameters, coupled with the choice of polymeric architecture, can then be engineered to control environmental responsiveness, viscoelasticity, and cargo diffusion profiles, yielding advanced biomaterials which demonstrate rapid shear-thinning, self-healing, and extended release. In this review we examine the relationship between supramolecular crosslink chemistry and biomedically relevant macroscopic properties. We then describe how these properties are currently leveraged in the development of materials for drug delivery, immunology, regenerative medicine, and 3D-bioprinting (253 references).

  View details for PubMedID 29164196

• Decoupled Associative and Dissociative Processes in Strong yet Highly Dynamic Host-Guest Complexes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Appel, E. A., Biedermann, F., Hoogland, D., del Barrio, J., Driscoll, M. D., Hay, S., Wales, D. J., Scherman, O. A. 2017; 139 (37): 12985–93

  Abstract

  Kinetics and thermodynamics in supramolecular systems are intimately linked, yet both are independently important for application in sensing assays and stimuli-responsive switching/self-healing of materials. Host-guest interactions are of particular interest in many water-based materials, sensing, and drug delivery applications. Herein we investigate the binding dynamics of a variety of electron-rich aromatic moieties forming hetero-ternary complexes with the macrocycle cucurbit[8]uril (CB[8]) and an auxiliary guest, dimethyl viologen, with high selectivity and equilibrium binding constants (Keq up to 1014 M-2). Using stopped-flow spectrofluorimetry, association rate constants were observed to approach the diffusion limit and were found to be insensitive to the structure of the guest. Conversely, the dissociation rate constants of the ternary complexes varied dramatically with the guest structure and were correlated with the thermodynamic binding selectivity. Hence differing molecular features were found to contribute to the associative and dissociative processes, mimicking naturally occurring reactions and giving rise to a decoupling of these kinetic parameters. Moreover, we demonstrate the ability to exploit these phenomena and selectively perturb the associative process with external stimuli (e.g., viscosity and pressure). Significantly, these complexes exhibit increased binding equilibria with increasing pressure, with important implications for the application of the CB[8] ternary complex for the formation of hydrogels, as these gels exhibit unprecedented pressure-insensitive rheological properties. A high degree of flexibility therefore exists in the design of host-guest systems with tunable kinetic and thermodynamic parameters for tailor-made applications across a broad range of fields.

  View details for PubMedID 28661667

• Mixed Reversible Covalent Crosslink Kinetics Enable Precise, Hierarchical Mechanical Tuning of Hydrogel Networks ADVANCED MATERIALS Yesilyurt, V., Ayoob, A. M., Appel, E. A., Borenstein, J. T., Langer, R., Anderson, D. G. 2017; 29 (19)

  Abstract

  Hydrogels play a central role in a number of medical applications and new research aims to engineer their mechanical properties to improve their capacity to mimic the functional dynamics of native tissues. This study shows hierarchical mechanical tuning of hydrogel networks by utilizing mixtures of kinetically distinct reversible covalent crosslinks. A methodology is described to precisely tune stress relaxation in PEG networks formed from mixtures of two different phenylboronic acid derivatives with unique diol complexation rates, 4-carboxyphenylboronic acid, and o-aminomethylphenylboronic acid. Gel relaxation time and the mechanical response to dynamic shear are exquisitely controlled by the relative concentrations of the phenylboronic acid derivatives. The differences observed in the crossover frequencies corresponding to pKa differences in the phenylboronic acid derivatives directly connect the molecular kinetics of the reversible crosslinks to the macroscopic dynamic mechanical behavior. Mechanical tuning by mixing reversible covalent crosslinking kinetics is found to be independent of other attributes of network architecture, such as molecular weight between crosslinks.

  View details for DOI 10.1002/adma.201605947

  View details for Web of Science ID 000401170600014

  View details for PubMedID 28295624

• Single-Chain Polymeric Nanocarriers: A Platform for Determining Structure-Function Correlations in the Delivery of Molecular Cargo BIOMACROMOLECULES Chan, D., Yu, A. C., Appel, E. A. 2017; 18 (4): 1434-1439

  Abstract

  There has been growing interest in producing stable, biocompatible nanocarriers for the controlled delivery of therapeutics. With micelles, it remains a challenge to predict a priori the size, aggregation number, and functionality of the self-assembled aggregates. Utilizing controlled radical polymerization techniques, we have prepared tunable high molecular weight amphiphilic comb copolymers that self-assemble into unimolecular "micelle-like" nanocarriers of predictable size and functionality. Excellent control over self-assembly behavior and structure allows for systematic determination of the role of important polymeric material properties (i.e., glass transition) on the release of model therapeutics while simultaneously controlling for size, dispersity, structural, and functionality effects. Moreover, these single-chain polymeric nanocarriers represent a class of drug delivery systems allowing for interrogation of the limitations of standard methods for characterization of micellar aggregates.

  View details for DOI 10.1021/acs.biomac.7b00249

  View details for Web of Science ID 000399061100040

  View details for PubMedID 28263572

• Engineering the Mechanical Properties of Polymer Networks with Precise Doping of Primary Defects ACS Applied Materials and Interfaces Chan, D., Ding, Y., Dauskardt, R., Appel, E. A. 2017; 9: 42217-42224
• Mechanistic understanding of in vivo protein corona formation on polymeric nanoparticles and impact on pharmacokinetics. Nature communications Bertrand, N., Grenier, P., Mahmoudi, M., Lima, E. M., Appel, E. A., Dormont, F., Lim, J. M., Karnik, R., Langer, R., Farokhzad, O. C. 2017; 8 (1): 777

  Abstract

  In vitro incubation of nanomaterials with plasma offer insights on biological interactions, but cannot fully explain the in vivo fate of nanomaterials. Here, we use a library of polymer nanoparticles to show how physicochemical characteristics influence blood circulation and early distribution. For particles with different diameters, surface hydrophilicity appears to mediate early clearance. Densities above a critical value of approximately 20 poly(ethylene glycol) chains (MW 5 kDa) per 100 nm2 prolong circulation times, irrespective of size. In knockout mice, clearance mechanisms are identified for nanoparticles with low and high steric protection. Studies in animals deficient in the C3 protein showed that complement activation could not explain differences in the clearance of nanoparticles. In nanoparticles with low poly(ethylene glycol) coverage, adsorption of apolipoproteins can prolong circulation times. In parallel, the low-density-lipoprotein receptor plays a predominant role in the clearance of nanoparticles, irrespective of poly(ethylene glycol) density. These results further our understanding of nanopharmacology.Understanding the interaction between nanoparticles and biomolecules is crucial for improving current drug-delivery systems. Here, the authors shed light on the essential role of the surface and other physicochemical properties of a library of nanoparticles on their in vivo pharmacokinetics.

  View details for PubMedID 28974673

  View details for PubMedCentralID PMC5626760

• Synthesis and Biological Evaluation of Ionizable Lipid Materials for the In Vivo Delivery of Messenger RNA to B Lymphocytes Advanced Materials Fenton, O. S., et al 2017; 29: e1606944
• Distinguishing the Respective Mechanical Contributions of Polymer and Supramolecular Dynamics in Transiently Crosslinked Polymeric Networks Polymer Chemistry Tan, C. S., Agmon, G., Hoogland, D., Janecek, E., Toprakcioglu, C., Appel, E. A., Scherman, O. A. 2017; 8: 5336-5343
• Decoupled Associative and Dissociative Processes in Strong yet Highly Dynamic Host-Guest Complexes Journal of the American Chemical Society Appel, E. A., Biedermann, F., Driscoll, M. D., Hay, S., Wales, D. J., Scherman, O. A. 2017; 139: 12985-12993
• Supramolecular Polymeric Biomaterials Biomaterials Science Mann, J. L., Yu, A. C., Agmon, G., Appel, E. A. 2017; 6: 10-37
• Mechanistic understanding of in vivo protein corona formation on polymeric nanoparticles and impact on pharmacokinetics Nature Communication Bertrand, N., et al 2017; 8: e777
• Supramolecular PEGylation of biopharmaceuticals PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Webber, M. J., Appel, E. A., Vinciguerra, B., Cortinas, A. B., Thapa, L. S., Jhunjhunwala, S., Isaacs, L., Langer, R., Anderson, D. G. 2016; 113 (50): 14189-14194

  Abstract

  The covalent modification of therapeutic biomolecules has been broadly explored, leading to a number of clinically approved modified protein drugs. These modifications are typically intended to address challenges arising in biopharmaceutical practice by promoting improved stability and shelf life of therapeutic proteins in formulation, or modifying pharmacokinetics in the body. Toward these objectives, covalent modification with poly(ethylene glycol) (PEG) has been a common direction. Here, a platform approach to biopharmaceutical modification is described that relies on noncovalent, supramolecular host-guest interactions to endow proteins with prosthetic functionality. Specifically, a series of cucurbit[7]uril (CB[7])-PEG conjugates are shown to substantially increase the stability of three distinct protein drugs in formulation. Leveraging the known and high-affinity interaction between CB[7] and an N-terminal aromatic residue on one specific protein drug, insulin, further results in altering of its pharmacological properties in vivo by extending activity in a manner dependent on molecular weight of the attached PEG chain. Supramolecular modification of therapeutic proteins affords a noncovalent route to modify its properties, improving protein stability and activity as a formulation excipient. Furthermore, this offers a modular approach to append functionality to biopharmaceuticals by noncovalent modification with other molecules or polymers, for applications in formulation or therapy.

  View details for DOI 10.1073/pnas.1616639113

  View details for Web of Science ID 000389696700033

  View details for PubMedID 27911829

• Scalable manufacturing of biomimetic moldable hydrogels for industrial applications PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Yu, A. C., Chen, H., Chan, D., Agmon, G., Stapleton, L. M., Sevit, A. M., Tibbitt, M. W., Acosta, J. D., Zhang, T., Franzia, P. W., Langer, R., Appel, E. A. 2016; 113 (50): 14255-14260

  Abstract

  Hydrogels are a class of soft material that is exploited in many, often completely disparate, industrial applications, on account of their unique and tunable properties. Advances in soft material design are yielding next-generation moldable hydrogels that address engineering criteria in several industrial settings such as complex viscosity modifiers, hydraulic or injection fluids, and sprayable carriers. Industrial implementation of these viscoelastic materials requires extreme volumes of material, upwards of several hundred million gallons per year. Here, we demonstrate a paradigm for the scalable fabrication of self-assembled moldable hydrogels using rationally engineered, biomimetic polymer-nanoparticle interactions. Cellulose derivatives are linked together by selective adsorption to silica nanoparticles via dynamic and multivalent interactions. We show that the self-assembly process for gel formation is easily scaled in a linear fashion from 0.5 mL to over 15 L without alteration of the mechanical properties of the resultant materials. The facile and scalable preparation of these materials leveraging self-assembly of inexpensive, renewable, and environmentally benign starting materials, coupled with the tunability of their properties, make them amenable to a range of industrial applications. In particular, we demonstrate their utility as injectable materials for pipeline maintenance and product recovery in industrial food manufacturing as well as their use as sprayable carriers for robust application of fire retardants in preventing wildland fires.

  View details for DOI 10.1073/pnas.1618156113

  View details for Web of Science ID 000389696700044

  View details for PubMedID 27911849

  View details for PubMedCentralID PMC5167152

• Injectable and Glucose-Responsive Hydrogels Based on Boronic Acid-Glucose Complexation LANGMUIR Dong, Y., Wang, W., Veiseh, O., Appel, E. A., Xue, K., Webber, M. J., Tang, B. C., Yang, X., Weir, G. C., Langer, R., Anderson, D. G. 2016; 32 (34): 8743-8747

  Abstract

  Injectable hydrogels have been widely used for a number of biomedical applications. Here, we report a new strategy to form an injectable and glucose-responsive hydrogel using the boronic acid-glucose complexation. The ratio of boronic acid and glucose functional groups is critical for hydrogel formation. In our system, polymers with 10-60% boronic acid, with the balance being glucose-modified, are favorable to form hydrogels. These hydrogels are shear-thinning and self-healing, recovering from shear-induced flow to a gel state within seconds. More importantly, these polymers displayed glucose-responsive release of an encapsulated model drug. The hydrogel reported here is an injectable and glucose-responsive hydrogel constructed from the complexation of boronic acid and glucose within a single component polymeric material.

  View details for DOI 10.1021/acs.langmuir.5b04755

  View details for Web of Science ID 000382513900022

  View details for PubMedID 27455412

  View details for PubMedCentralID PMC5242094

• Bioinspired Alkenyl Amino Alcohol Ionizable Lipid Materials for Highly Potent In Vivo mRNA Delivery ADVANCED MATERIALS Fenton, O. S., Kauffman, K. J., McClellan, R. L., Appel, E. A., Dorkin, J. R., Tibbitt, M. W., Heartlein, M. W., DeRosa, F., Langer, R., Anderson, D. G. 2016; 28 (15): 2939-2943

  Abstract

  Thousands of human diseases could be treated by selectively controlling the expression of specific proteins in vivo. A new series of alkenyl amino alcohol (AAA) ionizable lipid nanoparticles (LNPs) capable of delivering human mRNA with unprecedented levels of in vivo efficacy is demonstrated. This study highlights the importance of utilizing synthesis tools in tandem with biological inspiration to understand and improve nucleic acid delivery in vivo.

  View details for DOI 10.1002/adma.201505822

  View details for Web of Science ID 000374336700011

  View details for PubMedID 26889757

  View details for PubMedCentralID PMC5245883

• Supramolecular biomaterials NATURE MATERIALS Webber, M. J., Appel, E. A., Meijer, E. W., Langer, R. 2016; 15 (1): 13-26

  View details for DOI 10.1038/NMAT4474

  View details for Web of Science ID 000366690600014

• Injectable Self-Healing Glucose Responsive Hydrogels with pH-Regulated Mechanical Properties Advanced Materials Yesilyurt, V., Webber, M. J., Appel, E. A., Godwin, C., Langer, R., Anderson, D. G. 2016; 28: 86-91
• Water soluble, biodegradable amphiphilic polymeric nanoparticles and the molecular environment of hydrophobic encapsulates: Consistency between simulation and experiment POLYMER Miller, R. D., Yusoff, R. M., Swope, W. C., Rice, J. E., Carr, A. C., Parker, A. J., Sly, J., Appel, E. A., Nguyen, T., Piunova, V. 2015; 79: 255-261

  View details for DOI 10.1016/j.polymer.2015.10.008

  View details for Web of Science ID 000365042500028

• Formation of Cucurbit[8]uril-Based Supramolecular Hydrogel Beads Using Droplet-Based Microfluidics BIOMACROMOLECULES Xu, X., Appel, E. A., Liu, X., Parker, R. M., Scherman, O. A., Abell, C. 2015; 16 (9): 2743-2749

  Abstract

  Herein we describe the use of microdroplets as templates for the fabrication of uniform-sized supramolecular hydrogel beads, assembled by supramolecular cross-linking of functional biopolymers with the macrocyclic host molecule, cucurbit[8]uril (CB[8]). The microdroplets were formed containing diluted hydrogel precursors in solution, including the functional polymers and CB[8], in a microfluidic device. Subsequent evaporation of water from collected microdroplets concentrated the contents, driving the formation of the CB[8]-mediated host-guest ternary complex interactions and leading to the assembly of condensed three-dimensional polymeric scaffolds. Rehydration of the dried particles gave monodisperse hydrogel beads. Their equilibrium size was shown to be dependent on both the quantity of material loaded and the dimensions of the microfluidic flow focus. Fluorescein-labeled dextran was used to evaluate the efficacy of the hydrogel beads as a vector for controlled cargo release. Both passive, sustained release (hours) and triggered, fast release (minutes) of the FITC-dextran was observed, with the rate of sustained release dependent on the formulation. The kinetics of release was fitted to the Ritger-Peppas controlled release equation and shown to follow an anomalous (non-Fickian) transport mechanism.

  View details for DOI 10.1021/acs.biomac.5b01048

  View details for Web of Science ID 000361341700020

  View details for PubMedID 26256409

• Exploiting Electrostatic Interactions in Polymer-Nanoparticle Hydrogels ACS MACRO LETTERS Appel, E. A., Tibbitt, M. W., Greer, J. M., Fenton, O. S., Kreuels, K., Anderson, D. G., Langer, R. 2015; 4 (8): 848-852

  View details for DOI 10.1021/acsmacrolett.5b00416

  View details for Web of Science ID 000359891200009

• A Facile Method for the Stain-Free Visualization of Hierarchical Structures with Electron Microscopy JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Williams, P. E., Appel, E. A., Jones, S. T., del Barrio, J., Lan, Y., Scherman, O. A. 2015; 53 (7): 842-845

  View details for DOI 10.1002/pola.27517

  View details for Web of Science ID 000350278400002

• Non-Cell-Adhesive Substrates for Printing of Arrayed Biomaterials ADVANCED HEALTHCARE MATERIALS Appel, E. A., Larson, B. L., Luly, K. M., Kim, J. D., Langer, R. 2015; 4 (4): 501-505

  Abstract

  Cellular microarrays have become extremely useful in expediting the investigation of large libraries of (bio)materials for both in vitro and in vivo biomedical applications. An exceedingly simple strategy is developed for the fabrication of non-cell-adhesive substrates supporting the immobilization of diverse (bio)material features, including both monomeric and polymeric adhesion molecules (e.g., RGD and polylysine), hydrogels, and polymers.

  View details for DOI 10.1002/adhm.201400594

  View details for Web of Science ID 000351225700002

  View details for PubMedID 25430948

  View details for PubMedCentralID PMC4447497

• Self-Assembled Hydrogels Utilising Polymer-Nanoparticle Interactions Nature Communications Appel, E. A., Tibbitt, M. W., Webber, M. J., Mattix, B. A., Veiseh, O., Langer, R. 2015; 6: e6295
• The control of cargo release from physically crosslinked hydrogels by crosslink dynamics BIOMATERIALS Appel, E. A., Forster, R. A., Rowland, M. J., Scherman, O. A. 2014; 35 (37): 9897-9903

  Abstract

  Controlled release of drugs and other cargo from hydrogels has been an important target for the development of next generation therapies. Despite the increasingly strong focus in this area of research, very little of the published literature has sought to develop a fundamental understanding of the role of molecular parameters in determining the mechanism and rate of cargo release. Herein, a series of physically crosslinked hydrogels have been prepared utilizing host-guest binding interactions of cucurbit[8]uril that are identical in strength (plateau modulus), concentration and structure, yet exhibit varying network dynamics on account of the use of different guests for supramolecular crosslinking. The diffusion of molecular cargo through the hydrogel matrix and the release characteristics from these hydrogels were investigated. It was determined that the release processes of the hydrogels could be directly correlated with the dynamics of the physical interactions responsible for crosslinking and corresponding time-dependent mesh size. These observations highlight that network dynamics play an indispensable role in determining the release mechanism of therapeutic cargo from a hydrogel, identifying that fine-tuning of the release characteristics can be gained through rational design of the molecular processes responsible for crosslinking in the carrier hydrogels.

  View details for DOI 10.1016/j.biomaterials.2014.08.001

  View details for Web of Science ID 000343639700015

  View details for PubMedID 25239043

• GLUING GELS A nanoparticle solution NATURE MATERIALS Appel, E. A., Scherman, O. A. 2014; 13 (3): 231-232

  View details for DOI 10.1038/nmat3893

  View details for Web of Science ID 000331945200014

  View details for PubMedID 24553651

• Activation Energies Control Macroscopic Properties of Supramolecular Crosslinked Materials Angewandte Chemie International Edition Appel, E. A., Forster, R. A., Koutsioumpas, A., , Scherman, O. A. 2014; 53: 10038-10043
• Rapidly Healable, Temporally Stable and Stiff Hydrogels: Combining Conflicting Properties Using Highly Dynamic and Selective Three-Component Recognition with Reinforcing Cellulose Nanorods Advanced Functional Materials Jason, M., Appel, E. A., Seitsonen, J., Kontturi, E., Scherman, O. A., Ikkala, O. 2014; 24: 2706-2713
• Dynamically crosslinked materials via recognition of amino acids by cucurbit[8]uril JOURNAL OF MATERIALS CHEMISTRY B Rowland, M. J., Appel, E. A., Coulston, R. J., Scherman, O. A. 2013; 1 (23): 2904-2910

  View details for DOI 10.1039/c3tb20180e

  View details for Web of Science ID 000319273100002

• Triggered insulin release studies of triply responsive supramolecular micelles POLYMER CHEMISTRY Loh, X. J., Tsai, M., del Barrio, J., Appel, E. A., Lee, T., Scherman, O. A. 2012; 3 (11): 3180-3188

  View details for DOI 10.1039/c2py20380d

  View details for Web of Science ID 000310421200021

• Ultra-High Water-Content Hydrogels from Renewable Resources Exhibiting Multi-Stimuli Responsiveness J. Am. Chem. Soc. Appel, E. A., Loh, X., Jones, S. T., Biedermann, F., Dreiss, C. A., Scherman, O. A. 2012; 134: 11767-11773
• Triply Triggered Doxorubicin Release From Supramolecular Nanocontainers BIOMACROMOLECULES Loh, X. J., del Barrio, J., Toh, P. P., Lee, T., Jiao, D., Rauwald, U., Appel, E. A., Scherman, O. A. 2012; 13 (1): 84-91

  Abstract

  The synthesis of a supramolecular double hydrophilic block copolymer (DHBC) held together by cucurbit[8]uril (CB[8]) ternary complexation and its subsequent self-assembly into micelles is described. This system is responsive to multiple external triggers including temperature, pH and the addition of a competitive guest. The supramolecular block copolymer assembly consists of poly(N-isopropylacrylamide) (PNIPAAm) as a thermoresponsive block and poly(dimethylaminoethylmethacrylate) (PDMAEMA) as a pH-responsive block. Moreover, encapsulation and controlled drug release was demonstrated with this system using the chemotherapeutic drug doxorubicin (DOX). This triple stimuli-responsive DHBC micelle system represents an evolution over conventional double stimuli-responsive covalent diblock copolymer systems and displayed a significant reduction in the viability of HeLa cells upon triggered release of DOX from the supramolecular micellar nanocontainers.

  View details for DOI 10.1021/bm201588m

  View details for Web of Science ID 000298897300009

  View details for PubMedID 22148638

• Toward biodegradable nanogel star polymers via organocatalytic ROP CHEMICAL COMMUNICATIONS Appel, E. A., Lee, V. Y., Nguyen, T. T., McNeil, M., Nederberg, F., Hedrick, J. L., Swope, W. C., Rice, J. E., Miller, R. D., Sly, J. 2012; 48 (49): 6163-6165

  Abstract

  Organocatalytic ring opening polymerization (OROP) is used to effect the rapid, scalable, room temperature formation of size-controlled, highly uniform, polyvalent, nanogel star polymer nanoparticles of biodegradable composition.

  View details for DOI 10.1039/c2cc31406a

  View details for Web of Science ID 000304363500028

  View details for PubMedID 22590707

• High Molecular Weight Polyacrylamides by ATRP: Enabling Advancements in Water-based Applications J. Poly. Sci. Part A: Polym. Chem. Appel, E. A., del Barrio, J., Loh, X., Dyson, J., Scherman, O. A. 2012; 50: 181-186
• Metastable single-chain polymer nanoparticles prepared by dynamic cross-linking with nor-seco-cucurbit[10]uril CHEMICAL SCIENCE Appel, E. A., del Barrio, J., Dyson, J., Isaacs, L., Scherman, O. A. 2012; 3 (7): 2278-2281

  View details for DOI 10.1039/c2sc20285a

  View details for Web of Science ID 000304919200014

• Enhanced Stability and Activity of Temozolomide in Primary GBM Cells with Cucurbit[n]uril Chemical Communications Appel, E. A., Rowland, M. J., Loh, X., Heywood, R. M., Watts, C., Scherman, O. A. 2012: 9843-9845
• Supramolecular polymeric hydrogels CHEMICAL SOCIETY REVIEWS Appel, E. A., del Barrio, J., Loh, X. J., Scherman, O. A. 2012; 41 (18): 6195-6214

  Abstract

  The supramolecular crosslinking of polymer chains in water by specific, directional and dynamic non-covalent interactions has led to the development of novel supramolecular polymeric hydrogels. These aqueous polymeric networks constitute an interesting class of soft materials exhibiting attractive properties such as stimuli-responsiveness and self-healing arising from their dynamic behaviour and that are crucial for a wide variety of emerging applications. We present here a critical review summarising the formation of dynamic polymeric networks through specific non-covalent interactions, with a particular emphasis on those systems based on host-guest complex formation, as well as the characterisation of their physical characteristics. Aqueous supramolecular chemistry has unlocked a versatile toolbox for the design and fine-tuning of the material properties of these hydrogels (264 references).

  View details for DOI 10.1039/c2cs35264h

  View details for Web of Science ID 000307779600021

  View details for PubMedID 22890548

• Formation of Single-Chain Polymer Nanoparticles in Water through Host-Guest Interactions ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Appel, E. A., Dyson, J., del Barrio, J., Walsh, Z., Scherman, O. A. 2012; 51 (17): 4185-4189

  View details for DOI 10.1002/anie.201108659

  View details for Web of Science ID 000303001000037

  View details for PubMedID 22422662

• Sustained Release of Proteins from a High-Water-Content Supramolecular Polymer Hydrogel Biomaterials Appel, E. A., Loh, X., Jones, S. T., Dreiss, C. A., Scherman, O. A. 2012; 33: 4646-4652
• Postpolymerization Modification of Hydroxyl-Functionalized Polymers with Isocyanates MACROMOLECULES Biedermann, F., Appel, E. A., del Barrio, J., Gruendling, T., Barner-Kowollik, C., Scherman, O. A. 2011; 44 (12): 4828-4835

  View details for DOI 10.1021/ma2008018

  View details for Web of Science ID 000291895700037

• Supramolecular gold nanoparticle-polymer composites formed in water with cucurbit[8]uril CHEMICAL COMMUNICATIONS Coulston, R. J., Jones, S. T., Lee, T., Appel, E. A., Scherman, O. A. 2011; 47 (1): 164-166

  Abstract

  A gold nanoparticle-polymer composite material has been prepared in water using cucurbit[8]uril as a supramolecular "handcuff" to hold together viologen-functionalised gold nanoparticles and a naphthol-functionalised acrylamide copolymer.

  View details for DOI 10.1039/c0cc03250f

  View details for Web of Science ID 000285068300008

  View details for PubMedID 20842297

• Supramolecular Cross-Linked Networks via Host-Guest Complexation with Cucurbit[8]uril JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Appel, E. A., Biedermann, F., Rauwald, U., Jones, S. T., Zayed, J. M., Scherman, O. A. 2010; 132 (40): 14251-14260

  Abstract

  The ability to finely tune the solution viscosity of an aqueous system is critical in many applications ranging from large-scale fluid-based industrial processes to free-standing hydrogels important in regenerative medicine, controlled drug delivery, and 'green' self-healing materials. Herein we demonstrate the use of the macrocyclic host molecule cucurbit[8]uril (CB[8]) to facilitate reversible cross-linking of multivalent copolymers with high binding constants (K(a) > 10(11)-10(12) M(-2)) leading to a supramolecular hydrogel. Multivalent copolymers were prepared by free radical polymerization techniques and contained either pendant methyl viologen (a good first guest for CB[8]) or naphthoxy derivatives (good second guests for CB[8]). A colorless solution of the two multivalent copolymers bearing first and second guests, respectively, can be transformed into a highly viscous, colored supramolecular hydrogel with the cross-link density being easily controlled through CB[8] addition. Moreover, the cross-links (1:1:1 supramolecular ternary complexes of CB[8]/viologen/naphthoxy) are dynamic and stimuli-responsive, and the material properties can be modulated by temperature or other external stimuli. Rheological characterization of the bulk material properties of these dynamically cross-linked networks provided insight into the kinetics of CB[8] ternary complexation responsible for elastically active cross-linking with a second guest dissociation rate constant (k(d)) of 1200 s(-1) for the ternary complex. These materials exhibited intermediate mechanical properties at 5 wt % in water (plateau modulus = 350-600 Pa and zero-shear viscosity = 5-55 Pa·s), which is complementary to existing supramolecular hydrogels. Additionally, these supramolecular hydrogels exhibited thermal reversibility and subsequent facile modulation of microstructure upon further addition of CB[8] and thermal treatment. The fundamental knowledge gained from the study of these dynamic materials will facilitate progress in the field of smart, self-healing materials, self-assembled hydrogels, and controlled solution viscosity.

  View details for DOI 10.1021/ja106362w

  View details for Web of Science ID 000282660100064

  View details for PubMedID 20845973

• Hierarchical Supermolecular Structures for Sustained Drug Release SMALL Tan, J. P., Kim, S. H., Nederberg, F., Appel, E. A., Waymouth, R. M., Zhang, Y., Hedrick, J. L., Yang, Y. Y. 2009; 5 (13): 1504-1507

  View details for DOI 10.1002/smll.200801756

  View details for Web of Science ID 000267903200003

  View details for PubMedID 19326354

• Simple Approach to Stabilized Micelles Employing Miktoarm Terpolymers and Stereocomplexes with Application in Paclitaxel Delivery BIOMACROMOLECULES Nederberg, F., Appel, E., Tan, J. P., Kim, S. H., Fukushima, K., Sly, J., Miller, R. D., Waymouth, R. M., Yang, Y. Y., Hedrick, J. L. 2009; 10 (6): 1460-1468

  Abstract

  A simple and versatile approach to miktoarm co- and terpolymers from carbonate functional oligomers is described. The key building block employed is a carboxylic acid functional cyclic carbonate, derived from 2,2-bis(methylol)propionic acid, that was readily coupled to a hydroxyl functional monomethylether poly(ethylene glycol) oligomer. Ring-opening of the cyclic carbonate using functional amines generates a carbamate linkage bearing a functional group capable of initiating either controlled radical or ring-opening polymerization, together with a primary hydroxyl group for ring-opening polymerization. Two tandem polymerization steps were possible which add the second two arms, thus generating the targeted ABC miktoarm terpolymer. The resulting amphiphilic miktoarm terpolymers containing poly(D- and L-lactide) formed polylactide stereocomplexes in the bulk. In aqueous solution, the stereocomplex mixture of Y-shaped miktoarm copolymers, poly(ethylene glycol)-poly(D-lactide)-poly(D-lactide) and poly(ethylene glycol)-poly(L-lactide)-poly(L-lactide), or the stereoblock miktoarm poly(ethylene glycol)-poly(D-lactide)-poly(L-lactide) form stabilized micelles with a significantly lower critical micelle concentration than those derived from conventional stereo regular linear or Y-shaped amphiphiles. This simple and versatile approach provides a useful synthetic route to complex macromolecular architectures that can assemble into stable micelles. These micelles provide high capacity for loading of the anticancer drug paclitaxel and possess narrow size distribution as well as unique structure, leading to sustained and near zero-ordered release of drug without significant initial burst.

  View details for DOI 10.1021/bm900056g

  View details for Web of Science ID 000266860700018

  View details for PubMedID 19385659