Bio

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  • A Thermal and Biological Analysis of Bone Drilling. Journal of biomechanical engineering Aghvami, M., Brunski, J. B., Serdar Tulu, U., Chen, C., Helms, J. A. 2018; 140 (10)

    Abstract

    With the introduction of high-speed cutting tools, clinicians have recognized the potential for thermal damage to the material being cut. Here, we developed a mathematical model of heat transfer caused by drilling bones of different densities and validated it with respect to experimentally measured temperatures in bone. We then coupled these computational results with a biological assessment of cell death following osteotomy site preparation. Parameters under clinical control, e.g., drill diameter, rotational speed, and irrigation, along with patient-specific variables such as bone density were evaluated in order to understand their contributions to thermal damage. Predictions from our models provide insights into temperatures and thresholds that cause osteocyte death and that can ultimately compromise stability of an implant.

    View details for DOI 10.1115/1.4040312

    View details for PubMedID 30029243

  • Fiber Network Models Predict Enhanced Cell Mechanosensing on Fibrous Gels JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Aghvami, M., Billiar, K. L., Sander, E. A. 2016; 138 (10)

    Abstract

    The propagation of mechanical signals through nonlinear fibrous tissues is much more extensive than through continuous synthetic hydrogels. Results from recent studies indicate that increased mechanical propagation arises from the fibrous nature of the material rather than the strain-stiffening property. The relative importance of different parameters of the fibrous network structure to this propagation, however, remains unclear. In this work, we directly compared the mechanical response of substrates of varying thickness subjected to a constant cell traction force using either a nonfibrous strain-stiffening continuum-based model or a volume-averaged fiber network model consisting of two different types of fiber network structures: one with low fiber connectivity (growth networks) and one with high fiber connectivity (Delaunay networks). The growth network fiber models predicted a greater propagation of substrate displacements through the model and a greater sensitivity to gel thickness compared to the more connected Delaunay networks and the nonlinear continuum model. Detailed analysis of the results indicates that rotational freedom of the fibers in a network with low fiber connectivity is critically important for enhanced, long-range mechanosensing. Our findings demonstrate the utility of multiscale models in predicting cells mechanosensing on fibrous gels, and they provide a more complete understanding of how cell traction forces propagate through fibrous tissues, which has implications for the design of engineered tissues and the stem cell niche.

    View details for DOI 10.1115/1.4034490

    View details for Web of Science ID 000383984000006

    View details for PubMedID 27548709

  • A Combined In Vitro Imaging and Multi-Scale Modeling System for Studying the Role of Cell Matrix Interactions in Cutaneous Wound Healing PLOS ONE De Jesus, A. M., Aghvami, M., Sander, E. A. 2016; 11 (2)

    Abstract

    Many cell types remodel the extracellular matrix of the tissues they inhabit in response to a wide range of environmental stimuli, including mechanical cues. Such is the case in dermal wound healing, where fibroblast migrate into and remodel the provisional fibrin matrix in a complex manner that depends in part on the local mechanical environment and the evolving multi-scale mechanical interactions of the system. In this study, we report on the development of an image-based multi-scale mechanical model that predicts the short-term (24 hours), structural reorganization of a fibrin gel by fibroblasts. These predictive models are based on an in vitro experimental system where clusters of fibroblasts (i.e., explants) were spatially arranged into a triangular geometry onto the surface of fibrin gels that were subjected to either Fixed or Free in-plane mechanical constraints. Experimentally, regional differences in short-term structural remodeling and cell migration were observed for the two gel boundary conditions. A pilot experiment indicated that these small differences in the short-term remodeling of the fibrin gel translate into substantial differences in long-term (4 weeks) remodeling, particularly in terms of collagen production. The multi-scale models were able to predict some regional differences in remodeling and qualitatively similar reorganization patterns for the two boundary conditions. However, other aspects of the model, such as the magnitudes and rates of deformation of gel, did not match the experiments. These discrepancies between model and experiment provide fertile ground for challenging model assumptions and devising new experiments to enhance our understanding of how this multi-scale system functions. These efforts will ultimately improve the predictions of the remodeling process, particularly as it relates to dermal wound healing and the reduction of patient scarring. Such models could be used to recommend patient-specific mechanical-based treatment dependent on parameters such as wound geometry, location, age, and health.

    View details for DOI 10.1371/journal.pone.0148254

    View details for Web of Science ID 000369550200112

    View details for PubMedID 26840835

  • Nonlinear Strain Stiffening Is Not Sufficient to Explain How Far Cells Can Feel on Fibrous Protein Gels BIOPHYSICAL JOURNAL Rudnicki, M. S., Cirka, H. A., Aghvami, M., Sander, E. A., Wen, Q., Billiar, K. L. 2013; 105 (1): 11-20

    Abstract

    Recent observations suggest that cells on fibrous extracellular matrix materials sense mechanical signals over much larger distances than they do on linearly elastic synthetic materials. In this work, we systematically investigate the distance fibroblasts can sense a rigid boundary through fibrous gels by quantifying the spread areas of human lung fibroblasts and 3T3 fibroblasts cultured on sloped collagen and fibrin gels. The cell areas gradually decrease as gel thickness increases from 0 to 150 μm, with characteristic sensing distances of >65 μm below fibrin and collagen gels, and spreading affected on gels as thick as 150 μm. These results demonstrate that fibroblasts sense deeper into collagen and fibrin gels than they do into polyacrylamide gels, with the latter exhibiting characteristic sensing distances of <5 μm. We apply finite-element analysis to explore the role of strain stiffening, a characteristic mechanical property of collagen and fibrin that is not observed in polyacrylamide, in facilitating mechanosensing over long distances. Our analysis shows that the effective stiffness of both linear and nonlinear materials sharply increases once the thickness is reduced below 5 μm, with only a slight enhancement in sensitivity to depth for the nonlinear material at very low thickness and high applied traction. Multiscale simulations with a simplified geometry predict changes in fiber alignment deep into the gel and a large increase in effective stiffness with a decrease in substrate thickness that is not predicted by nonlinear elasticity. These results suggest that the observed cell-spreading response to gel thickness is not explained by the nonlinear strain-stiffening behavior of the material alone and is likely due to the fibrous nature of the proteins.

    View details for DOI 10.1016/j.bpj.2013.05.032

    View details for Web of Science ID 000321241400004

    View details for PubMedID 23823219

  • Multiscale Mechanical Simulations of Cell Compacted Collagen Gels JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME Aghvami, M., Barocas, V. H., Sander, E. A. 2013; 135 (7)

    Abstract

    Engineered tissues are commonly stretched or compressed (i.e., conditioned) during culture to stimulate extracellular matrix (ECM) production and to improve the mechanical properties of the growing construct. The relationships between mechanical stimulation and ECM remodeling, however, are complex, interdependent, and dynamic. Thus, theoretical models are required for understanding the underlying phenomena so that the conditioning process can be optimized to produce functional engineered tissues. Here, we continue our development of multiscale mechanical models by simulating the effect of cell tractions on developing isometric tension and redistributing forces in the surrounding fibers of a collagen gel embedded with explants. The model predicted patterns of fiber reorganization that were similar to those observed experimentally. Furthermore, the inclusion of cell compaction also changed the distribution of fiber strains in the gel compared to the acellular case, particularly in the regions around the cells where the highest strains were found.

    View details for DOI 10.1115/1.4024460

    View details for Web of Science ID 000326084400005

    View details for PubMedID 23720151

  • Analysis of flat heat pipes with various heating and cooling configurations APPLIED THERMAL ENGINEERING Aghvami, M., Faghri, A. 2011; 31 (14-15): 2645-2655
  • A Comparative Assessment of Implant Site Viability in Humans and Rats. Journal of dental research Chen, C. H., Pei, X., Tulu, U. S., Aghvami, M., Chen, C. T., Gaudillière, D., Arioka, M., Maghazeh Moghim, M., Bahat, O., Kolinski, M., Crosby, T. R., Felderhoff, A., Brunski, J. B., Helms, J. A. 2017: 22034517742631

    Abstract

    Our long-term objective is to devise methods to improve osteotomy site preparation and, in doing so, facilitate implant osseointegration. As a first step in this process, we developed a standardized oral osteotomy model in ovariectomized rats. There were 2 unique features to this model: first, the rats exhibited an osteopenic phenotype, reminiscent of the bone health that has been reported for the average dental implant patient population. Second, osteotomies were produced in healed tooth extraction sites and therefore represented the placement of most implants in patients. Commercially available drills were then used to produce osteotomies in a patient cohort and in the rat model. Molecular, cellular, and histologic analyses demonstrated a close alignment between the responses of human and rodent alveolar bone to osteotomy site preparation. Most notably in both patients and rats, all drilling tools created a zone of dead and dying osteocytes around the osteotomy. In rat tissues, which could be collected at multiple time points after osteotomy, the fate of the dead alveolar bone was followed. Over the course of a week, osteoclast activity was responsible for resorbing the necrotic bone, which in turn stimulated the deposition of a new bone matrix by osteoblasts. Collectively, these analyses support the use of an ovariectomy surgery rat model to gain insights into the response of human bone to osteotomy site preparation. The data also suggest that reducing the zone of osteocyte death will improve osteotomy site viability, leading to faster new bone formation around implants.

    View details for DOI 10.1177/0022034517742631

    View details for PubMedID 29202640

  • FIBROBLAST-MEDIATED FIBER REALIGNMENT IN FIBRIN GELS PROCEEDINGS OF THE ASME SUMMER BIOENGINEERING CONFERENCE - 2013, PT B De Jesus, A. M., Aghvami, M., Sander, E. A. 2014
  • Numerical simulation of electrolyte particles trajectory to investigate battery cover design characteristics JOURNAL OF POWER SOURCES Esfahanian, V., Darian, H. M., Babazadeh, H., Aghvami, M., Pasandeh, R., Torabi, F., Ahmadi, G. 2009; 191 (1): 139-143
  • ROUGHNESS EFFECT ON PRESSURE DROP FOR ELECTROOSMOTIC (EO) FLOW IN MICROTUBES PROCEEDINGS OF THE 6TH INTERNATIONAL CONFERENCE ON NANOCHANNELS, MICROCHANNELS, AND MINICHANNELS, PTS A AND B Shokouhmand, H., Aghvami, M., Moghadami, M., Babazadeh, H. 2008: 437-440
  • PRESSURE DROP AND HEAT TRANSFER OF FULLY DEVELOPED, LAMINAR FLOW IN ROUGH, RECTANGULAR MICROCHANNELS PROCEEDINGS OF THE 6TH INTERNATIONAL CONFERENCE ON NANOCHANNELS, MICROCHANNELS, AND MINICHANNELS, PTS A AND B Shokouhmand, H., Aghvami, M., Afshin, M. J. 2008: 153-157