Attachment of fibronectin to poly(vinyl alcohol) hydrogels promotes NIH3T3 cell adhesion, proliferation, and migration.

Hydrogels have been used in biology and medicine for many years, and they possess many properties that make them advantageous for tissue engineering applications. Their high water content and tissue-like elasticity are similar to the native extracellular matrix of many tissues. In this work, we investigated the potential of a modified poly(vinyl alcohol) (PVA) hydrogel as a biomaterial for tissue engineering applications. First, the ability of NIH3T3 fibroblast cells to attach to PVA hydrogels was evaluated. Because of PVA's extremely hydrophilic nature, important cell adhesion proteins do not adsorb to PVA hydrogels, and consequently, cells are unable to adhere to the hydrogel. By covalently attaching the important cell adhesion protein fibronectin onto the PVA hydrogel surface, the rate of fibroblast attachment and proliferation was dramatically improved, and promoted two-dimensional cell migration. These studies illustrate that a fibronectin-modified PVA hydrogel is a potential biomaterial for tissue engineering applications.

Cytocompatibility of UV and visible light photoinitiating systems on cultured NIH/3T3 fibroblasts in vitro.

This work investigates the cytocompatibility of several photoinitiating systems for potential cell encapsulation applications. Both UV and visible light initiating schemes were examined. The UV photoinitiators included 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651), 1-hydroxycyclohexyl phenyl ketone (Irgacure 184), 2-methyl-1-[4-(methylthio) phenyl]-2-(4-morpholinyl)-1-propanone (Irgacure 907), and 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Darocur 2959). The visible light initiating systems included camphorquinone (CQ) with ethyl 4-N,N-dimethylaminobenzoate (4EDMAB) and triethanolamine (TEA) and the photosensitizer isopropyl thioxanthone. A cultured fibroblast cell line, NIH/3T3, was exposed to the photoinitiators at varying concentrations from 0.01% (w/w) to 0.1% (w/w) with and without the presence of initiating light. The results demonstrated that at low photoinitiator concentrations (< or = 0.01% (w/w)), all of the initiator molecules were cytocompatible with the exception of CQ, Irgacure 651, and 4EDMAB which had a relative survival approximately 50% lower than a control. In the presence of low intensity initiating light (approximately 6 mWcm(-2) of 365 nm UV light and approximately 60 mWcm(-2) of 470-490 nm visible light) and initiating radicals, Darocur 2959 at concentrations < or = 0.05% (w/w) and CQ at concentrations < or = 0.01% (w/w) were the most promising cytocompatible UV and visible light initiating systems, respectively. To demonstrate the potential use of cytocompatible photoinitiating systems in cell encapsulation applications, chondrocytes were encapsulated in a photocrosslinked hydrogel using 0.05% (w/w) Darocur 2959 (cytocompatible) and 0.01% (w/w) Irgacure 651 (cyto-incompatible). After photopolymerizing for 10 minutes with approximately 8 mWcm(-2) of 365 nm light, nearly all the chondrocytes survived the process with Darocur 2959 while very few of the chondrocytes survived the process with Irgacure 651.

The effects of crosslinking density on cartilage formation in photocrosslinkable hydrogels.

Photoencapsulation of chondrocytes to produce tissue engineered cartilage provides many benefits including rapid polymerization times, the ability to fabricate complex architectures in vivo, and spatial and temporal control during polymerization. Recently, we have examined the cytocompatibility of several photoinitiation schemes and found that low photoinitiator concentrations and light intensities in the ultraviolet and visible range are cytocompatible. In this work, we are currently investigating photocrosslinkable hydrogels based on poly(vinyl alcohol) (PVA) and poly(ethylene oxide) (PEO) as scaffolds for tissue engineering cartilage. In particular, the influence of the network crosslinking density, swelling ratio, and chemical composition on the ability of encapsulated chondrocytes to form extracellular matrix is examined. The cartilage produced in these hydrogels will be quantified using biochemical assays that measure DNA content and the amount of sulfated glycosaminoglycans and total collagen in the extracellular matrix. We have demonstrated that chondrocytes encapsulated in a polymer scaffold made from a 20 wt% solution of PEODM/PEO (40 wt% dimethacrylated PEO (MW 3400)/60 wt% PEO (MW 100 K)) form cartilage, and after four weeks the results based on the wet weight of cartilage were approximately 0.03 million cells/mg cartilage, approximately 1.5% glycosaminoglycans and approximately 4.5% total collagen.