(5dg) Hydrolytically Degradable Poly(ethylene glycol) Hydrogel as a Tunable Scaffold for Neural Tissue Engineering

The generation of replacement organs and tissues relies on the design of components that replicate the three-dimensional (3D) structures and physiologies found in the body. While great strides have been made in developing new biomaterials, the tissue engineering efforts focused on nerve repair have been limited by a rudimentary understanding of how neurons interact with their 3D environment. Our overall goal is to develop new 3D matrices that are specifically designed to a) mimic the properties of soft nervous tissues and b) enable new fundamental investigations of how scaffold physical properties (e.g., porosity and mechanical properties) impact neuronal response. Our hydrogel of choice is poly(ethylene glycol) (PEG), because it fulfills most of the requirements imposed on the scaffold's design such as biocompatibility, biodegradability, as well as, resistance to non-specific protein adsorption.

In this study we use PEG vinyl sulfone gels, cross-linked with PEG-dithiol ester cross-linkers. One benefit of this hydrogel is that it can be formed in physiological conditions and thus can be seeded with cells prior to gelation. Further, we explore the change in diffusion, mechanical properties and porosity with degradation by utilizing PEG polymers of varying molecular weight, varying location of the hydrolysable group and by manipulating polymer density. Thus far, we have synthesized PEG hydrogels that span a range of mechanical properties (G', 0.4-5 kPa) that mimics human nervous tissue (e.g., brain and spinal cord).

We will present current work with a focus on: (a) characterization of gel porosity and stiffness with gel degradation (degradation times spanned from several hours to several days and 20-fold change in gel physical properties was observed over time), (b) characterization of diffusion of various model solutes in the gels (De/Do=0.58 for Lysozyme; 0.18 for BSA; 0.1 for Ig), (c) addition of common adhesive ligands to the scaffolds to promote neuronal outgrowth and the associated change in gel mechanical properties (addition of RGDS or YIGSR lead to an increase in G' and decrease in swelling ratio and mesh size), and (d) investigation of neuronal and PC12 cells response to these novel scaffolding biomaterials with varying tunable properties (an average of 90% viability was achieved with all gel types).

This work will ultimately lead to a fundamental quantitative understanding of how to more effectively design tissue engineering scaffolds for directed neuronal response and may result in advanced model systems for in vitro neurobiology studies as well as improved materials to treat neural injuries.