The overarching goal is to enable the design of tailored fibrin biomaterials with predictable mechanical, biological and biochemical properties for treatment of dermal injuries based on a fundamental understanding of their structure-function relationships. We hypothesize that the extent of protease and collagen expression in fibroblast - fibrin or keratinocyte - fibrin constructs may be quantitatively correlated with time-dependent changes in construct structure: the average (i) fibril diameter and (ii) fibril network pore size over 15 days. We further hypothesize that these changes in structure may be correlated with changes in mechanical function: namely, mechanical stiffness. Therefore, a major outcome of this work will be the development and validation of rigorous, physics-based models, coupled with heuristic analyses, for the underlying structure- function relationships of tailored fibrin biomaterials. We base these hypotheses on the following observations: First, fibroblast-seeded fibrin constructs exhibit an invariant or decreasing mechanical stiffness after 10 days in vitro [Mooney et al., 2004]. Second, fibrin constructs exhibit a mechanical stiffness that is proportional to fibrinogen concentration [Mooney et al., 2004]. Third, the fibrinogen and thrombin concentrations in 3-D fibrin/cell constructs affect: (i) fibroblast and keratinocyte proliferation, morphology, and, qualitatively, their structural integrity [Cox et al., 2004] and (ii) differential expression of IL-8, PDGF receptor and specific integrins. Fourth, preliminary analysis reveals that physics-based models may be developed for the underlying structure-function relationships for mechanical stiffness.
The specific aims are: I. Experimentally characterize the effects of time in vitro on fibril structure, mechanical stiffness and cell biology in fibrin-based clot constructs. For constructs of eleven fibrin/thrombin ratios, each seeded with/without cells of two densities of either fibroblasts or keratinocytes, at intervals of 1, 5, 10 and 15 days, we will: 1) Measure the mechanical stiffness parameters;2) Measure the average fibrin fibril diameter and fibril network pore size;3) Determine protein expression levels for various proteases and collagen types and 4) Determine cell proliferation. II. Based on the data from SA I, develop and critically validate physics-based and heuristic models for the structure-function relationships between i) the mechanical stiffness and ii) fibril diameter and average fibril network pore size. Key independent variables: i) fibrin/thrombin ratio, ii) with/without cells, iii) cell density (50,000 cells/ml or 100,000 cells/ml);iv) cell type (fibroblasts or keratinocytes) and v) time (1, 5, 10 and 15 days). Key dependent variables: i) mechanical stiffness, ii) fibril diameter and fibril network pore size, iii) protein level, iv) cell number.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR053250-05
Application #
7893132
Study Section
Musculoskeletal Tissue Engineering Study Section (MTE)
Program Officer
Tseng, Hung H
Project Start
2006-08-01
Project End
2013-07-31
Budget Start
2010-08-01
Budget End
2013-07-31
Support Year
5
Fiscal Year
2010
Total Cost
$160,102
Indirect Cost
Name
University of California Los Angeles
Department
Biomedical Engineering
Type
Schools of Engineering
DUNS #
092530369
City
Los Angeles
State
CA
Country
United States
Zip Code
90095