A study of diffusion in poly(ethyleneglycol)-gelatin based semi-interpenetrating networks for use in wound healing

Abstract

Semi-interpenetrating networks (sIPNs) designed to mimic extracellular matrix via covalent crosslinking of poly(ethylene glycol) diacrylate in the presence of gelatin have been shown to aid in wound healing, particularly when loaded with soluble factors. Ideal systems for tissue repair permit an effective release of therapeutic agents and flow of nutrients to proliferating cells. Appropriate network characterization can, consequently, be used to convey an understanding of the mass transfer kinetics necessary for materials to aid in the wound healing process. Solute transport from and through sIPNs has not yet been thoroughly evaluated. In the current study, the diffusivity of growth factors and nutrients through the polymeric system was determined. Transport of keratinocyte growth factor was modeled by treating the sIPN as a plane sheet into which the protein was loaded. The diffusion coefficient was determined to be 4.86 × 10^-9 ± 1.86 × 10^-12 cm²/s. Glucose transport was modeled as flow through a semi-permeable membrane. Using lag-time analysis, the diffusion coefficient was calculated to be 2.25 × 10^-6 ± 1.98 × 10^-7 cm²/s. The results were evaluated in conjunction with previous studies on controlled drug release from sIPNs. As expected from Einstein-Stokes equation, diffusivity decreased as molecular size increased. The results offer insight into the structure-function design paradigm and show that release from the polymeric system is diffusion controlled, rather than dissolution controlled.

Keywords: Controlled release; Diffusion; Physical characterization; Semi-interpenetrating network; Transport.

Fig. 1

A representative plot of KGF release from a small sIPN. The KGF concentrations found experimentally (diamonds) were directly compared with those predicted using a diffusion coefficient D, estimated from the experimental data and Eq. (2) (squares)

Fig. 2

Glucose flow through a sIPN. Flux was unidirectional in the z direction from chamber 1 to chamber 2

Fig. 3

A representative plot of glucose flux through a sIPN membrane. The lag time t₀, was used to determine the diffusion coefficient D, of glucose