This review describes research on selected peptide sequences that affect cell adhesion as it applies in orthopedic applications. Of particular interest are the integrin-binding RGD peptides and heparin-binding peptides. The influence of these peptides on cell adhesion is described. Cell adhesion is defined as a sequence of four steps: cell attachment, cell spreading, organization of an actin cytoskeleton, and formation of focal adhesions. RGD sequences clearly influence cell attachment and spreading, whereas heparin-binding sequences appear to be less efficient. Collectively, these sequences appear to promote all steps of cell adhesion in certain cell types. This review also addresses issues related to peptide immobilization, as well as potential complexities that may develop as a result of using these versatile cell-binding sequences. Also described are future directions in the field concerning use of existing and more sophisticated peptide substrata.

We have previously identified a gene, beta ig-h3, which is highly induced in A549 cells (human lung adenocarcinoma) after growth arrest by transforming growth factor-beta. The beta ig-h3 gene encodes a 683-amino-acid secretory protein termed beta IG-H3, and treatment of several cell lines with transforming growth factor-beta results in increased secretion of beta IG-H3 into cell culture supernatants. In this report, we further characterize beta IG-H3 with respect to its synthesis and function. Primary human foreskin fibroblasts grown in monolayer culture produced beta IG-H3 mRNA and secreted beta IG-H3 protein into the growth media. Treatment of these cells with transforming growth factor-beta led to an increase in beta IG-H3 mRNA and protein. Cells grown on three-dimensional scaffolds secreted beta IG-H3 into the extracellular matrix, as judged by immunostaining with anti-beta IG-H3 antibodies. beta IG-H3 was also detected in normal human skin, especially in the papillary dermis. Finally, we show that recombinant beta IG-H3 supported attachment and spreading of dermal fibroblasts, suggesting that beta IG-H3 may function as an extracellular attachment protein in skin.

This study was designed to determine the effect of changes in poly(ethylene glycol) (PEG) molecular weight on swelling and mechanical properties of hydrogels made from a novel polymer, oligo(poly(ethylene glycol) fumarate) (OPF), recently developed in our laboratory. Properties of hydrogels made from OPF with initial PEG molecular weights of 860, 3900, and 9300 were examined. The PEG 3900 formulation had a tensile modulus of 23.1 +/- 12.4 kPa and percent elongation at fracture of 53.2 +/- 13.7%; the PEG 9300 formulation had similar tensile properties (modulus: 16.5 +/- 4.6 kPa, elongation: 76.0 +/- 26.4%). However, the PEG 860 gels had a significantly higher modulus (89.5 +/- 50.7 kPa) and a significantly smaller percent elongation at fracture (30.1 +/- 6.4%), when compared with other formulations. Additionally, there were significant differences in percent swelling between each of the formulations. Molecular weight between crosslinks (M(c)) and mesh size were calculated for each OPF formulation. M(c) increased from 2010 +/- 116 g/mol with PEG 860 to 6250 +/- 280 g/mol with PEG 9300. Mesh size calculations showed a similar trend (76 +/- 2 A for PEG 860 to 160 +/- 6 A for PEG 9300). It was also found that these hydrogels could be laminated if a second layer was added before the first had completely crosslinked. Mechanical testing of these laminated gels revealed that the presence of an interfacial area did not significantly alter their tensile properties. These results suggest that the material properties of OPF-based hydrogels can be altered by changing the molecular weight of PEG used in synthesis and that multilayered OPF hydrogel constructs can be produced, with each layer having distinct mechanical properties.

Novel hydrogel materials based on oligo(poly(ethylene glycol) fumarate) (OPF) crosslinked with a redox radical initiation system were recently developed in our laboratory as injectable cell carriers for orthopedic tissue engineering applications. The effect of OPF hydrogel material properties on in vitro osteogenic differentiation of encapsulated rat marrow stromal cells (MSCs) with and without the presence of osteogenic supplements (dexamethasone) was investigated. Two OPF formulations that resulted in hydrogels with different swelling properties were used to encapsulate rat MSCs (seeding density approximately 13 million cells/mL, samples 6 mm diameter x 0.5 mm thick before swelling) and osteogenic differentiation in these constructs over 28 days in vitro was determined via histology and biochemical assays for alkaline phosphatase, osteopontin and calcium. Evidence of MSC differentiation was apparent over the culture period for samples without dexamethasone, but there was large variability in calcium production between constructs using cells of the same source. Differentiation was also seen in samples cultured with osteogenic supplements, but calcium deposition varied depending on the source pool of MSCs. By day 28, osteopontin and calcium results suggested that, in the presence of dexamethasone, OPF hydrogels with greater swelling promoted embedded MSC differentiation over those that swelled less (43.7 +/- 16.5 microg calcium/sample and 16.4 +/- 2.8 microg calcium/sample, respectively). In histological sections, mineralized areas were apparent in all sample types many microns away from the cells. These experiments indicate that OPF hydrogels are promising materials for use as injectable MSC carriers and that hydrogel swelling properties can influence osteogenic differentiation of encapsulated progenitor cells.

Purpose:The purpose is to determine whether the levels of expression of extracellular matrix components in peritumoral stroma are predictive of disease outcome for women with node-negative breast cancer.Experimental Design: Tumor tissue from 86 patients with node-negative breast cancer was examined by immunohistochemical staining for the expression of versican, chondroitin sulfate (CS), tenascin, and hyaluronan (HA). With the exception of HA, the expression of the extracellular matrix components was measured by video image analysis. Statistical correlation of the immunohistochemical data with clinicopathological characteristics and disease outcome was performed.Results: All of the extracellular matrix components were present in the peritumoral stroma of the entire study cohort. In contrast, immunoreactivity within the cancer cell was observed in 82% of tumors for HA, 12% for CS, and 4% for tenascin; no immunostaining of cancer cells for versican was observed for any of the tumors. Cox regression and Kaplan-Meier analyses indicated that elevated expression of stromal versican predicted increased risk and rate of relapse in this cohort. Elevated expression of tenascin was predictive of increased risk and rate of death only. Although neither CS nor HA were predictive of disease outcome in this cohort, tumor size was predictive of increased risk and rate of both relapse and survival.Conclusions: Elevated expression within peritumoral stromal matrix of versican and tenascin was predictive of relapse-free and overall survival, respectively, in women with node-negative breast cancer.