Charles R. Nuttelman

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 (6 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 ~ 50% lower than a control. In the presence of low intensity initiating light (~ 6 mW cm-2 of 365 nm UV light and ~ 60 mW cm-2 of 470-490 nm visible light) and initiating radicals, Darocur 2959 at concentrations 6 0.05% (w/w) and CQ at concentrations 6 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 ~ 8 mW cm-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.

A Versatile Synthetic Extracellular Matrix Mimic via Thiol‐Norbornene Photopolymerization

Step-growth, radically mediated thiol-norbornene photopolymerization is used to create versatile, stimuli-responsive poly(ethylene glycol)-co-peptide hydrogels The reaction is cytocompatible and allows for the encapsulation of human mesenchymal stem cells with a viability greater than 95%. Cellular spreading is dictated via three-dimensional biochemical photopatterning.

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 PVAs 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.

Synthesis and characterization of photocrosslinkable, degradable poly(vinyl alcohol)-based tissue engineering scaffolds

Hydrogels have many advantages that make them prime candidates for tissue engineering applications: high water content, tissue-like elasticity, and relative biocompatibility. We aim to tissue engineer heart valves using a hydrogel scaffold based on poly(vinyl alcohol) (PVA), and the design parameters for a suitable tissue engineering scaffold are quite stringent. In this research, we develop degradable and photocrosslinkable poly(lactic acid)-g-PVA multifunctional macromers that can be reacted in solution to form degradable networks. The mass loss profiles and bulk properties of the resulting scaffolds are easily tailored by modifying the structure of the starting macromers. Specifically, altering the number of lactide repeat units per crosslinking side chain, percent substitution, molecular weight of PVA backbone, and macromer solution concentration, the rate of mass loss from these degradable networks is controlled. In addition, by increasing the networks hydrophobicity, valve interstitial cell adhesion is improved.

Temporal changes in peg hydrogel structure influence human mesenchymal stem cell proliferation and matrix mineralization

Preventing bone resorption or facilitating bone regeneration are major clinical challenges for several dental procedures, including ridge preservation after tooth extractions, integration of tooth implants, and the treatment of severe periodontal disease1, 2. Many of the current treatments fail because of the inability of the materials and methods to heal osseous defects. Thus, recent directions in tissue engineering suggest strategies to design synthetic carriers for cell-based therapies that are targeted towards bone regeneration. For example, several groups3, 4, 5 are interested in the development of injectable gel carriers that would allow simple and reproducible clinical delivery of human mesenchymal stem cells (hMSCs) to treat bone defects. From a bone tissue engineering perspective, hMSCs have many advantages. A large number of hMSCs can be easily obtained by aspiration of adult bone marrow6, and these multipotent cells can then be coaxed to differentiate into osteoblasts by exposure to specific growth factors or hormones at the right time and with the right dose (e.g., dexamethasone, BMPs, others)7, 8, 9. During their differentiation to osteoblasts, hMSCs secrete significant amounts of extracellular matrix molecules, providing further advantages for tissue regeneration. Because of these properties, numerous groups are exploring the development of hydrogels for three-dimensional culture and expansion of hMSCs; controlled differentiation of hMSCs to osteoblasts10, chondrocytes11, and other cell types12; and the targeted delivery of hMSCs to bone defects13.