There is a great need to treat defects in bone that result from either trauma, disease, or reconstructive surgery. Autologous bone or cadaver bone are the traditional graft materials used to replace bone in these circumstances; however, the use of these particular graft materials can increase the morbidity associated with the surgical management of the condition. As a result, synthetic materials are being developed to function as either bone grafts or templates containing isolated cells that foster bone regeneration. A major limitation with current materials used as artificial grafts or templates for tissue regeneration is the invasive procedures needed for placement of the device and the lack of designed interaction between the material and the isolated cells. This proposal details -the synthesis and characterization of loosely crosslinked Poly(N-isopropylacrylamideco-acrylic acid) hydrogels that are extremely pliable and fluid-like at room temperature (RT), but demonstrate a phase transition as the matrix warms from RT to body temperature, yielding more rigid structures. Thus, these hydrogels offer the benefit of in situ stabilization without the potential adverse effects of in situ polymerization (e.g., residual monomers, initiators, catalysts, etc.). We envision exploiting this thermoreversible behavior by incorporating autogenous cells (e.g., osteoblasts) into the hydrogel at room temperature when the matrix is pliable and the cells can be easily distributed throughout the matrix, and then allowing the phase behavior of the hydrogel to entrain the cells and stabilize when implanted. The hydrogels are also amenable to modification with biological ligands that interact with integrin cell surface receptors, such as the -RGD- and-FHRRIKA- signals previously identified in the P.I.'s laboratory.
We aim to synthesize hydrogels that incorporate these biomimetic peptides that facilitate proliferation and differentiation of osteogenic cells (e.g., osteoblasts), and incorporate peptide crosslinkers that are cleaved by matrix metalloproteinases (e.g., MMP-13) synthesized by these cells. This application has three parts in which two major hypotheses will be tested. In Part 1 the investigators will characterize the physical, chemical, and degradation properties of these gels. In Part 2 the investigators will evaluate their ability to promote proliferation and phenotypic expression of either rat or human derived osteoblasts in vitro. In Part 3 they will assess the ability of the biomimetic and degradable hydrogels, seeded with human derived osteoblasts, to foster the formation of tissue with the histoarchitecture of bone in vivo, in an ectopic site in an athymic mouse model.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR047304-04
Application #
6628112
Study Section
Special Emphasis Panel (ZRG1-SSS-M (01))
Program Officer
Panagis, James S
Project Start
2000-04-01
Project End
2005-01-31
Budget Start
2003-02-01
Budget End
2004-01-31
Support Year
4
Fiscal Year
2003
Total Cost
$256,531
Indirect Cost
Name
University of California Berkeley
Department
Biomedical Engineering
Type
Schools of Engineering
DUNS #
124726725
City
Berkeley
State
CA
Country
United States
Zip Code
94704
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Kim, Soyeon; Healy, Kevin E (2003) Synthesis and characterization of injectable poly(N-isopropylacrylamide-co-acrylic acid) hydrogels with proteolytically degradable cross-links. Biomacromolecules 4:1214-23
Stile, Ranee A; Healy, Kevin E (2002) Poly(N-isopropylacrylamide)-based semi-interpenetrating polymer networks for tissue engineering applications. 1. Effects of linear poly(acrylic acid) chains on phase behavior. Biomacromolecules 3:591-600
Stile, R A; Healy, K E (2001) Thermo-responsive peptide-modified hydrogels for tissue regeneration. Biomacromolecules 2:185-94