Controlled release of IGF-1 and HGF from a biodegradable polyurethane scaffold

Abstract

Purpose: Biodegradable elastomers, which can possess favorable mechanical properties and degradation rates for soft tissue engineering applications, are more recently being explored as depots for biomolecule delivery. The objective of this study was to synthesize and process biodegradable, elastomeric poly(ester urethane)urea (PEUU) scaffolds and to characterize their ability to incorporate and release bioactive insulin-like growth factor-1 (IGF-1) and hepatocyte growth factor (HGF).

Methods: Porous PEUU scaffolds made from either 5 or 8 wt% PEUU were prepared with direct growth-factor incorporation. Long-term in vitro IGF-1 release kinetics were investigated in saline or saline with 100 units/ml lipase to simulate in vivo degradation. Cellular assays were used to confirm released IGF-1 and HGF bioactivity.

Results: IGF-1 release into saline occurred in a complex multi-phasic manner for up to 440 days. Scaffolds generated from 5 wt% PEUU delivered protein faster than 8 wt% scaffolds. Lipase-accelerated scaffold degradation led to delivery of >90% protein over 9 weeks for both polymer concentrations. IGF-1 and HGF bioactivity in the first 3 weeks was confirmed.

Conclusions: The capacity of a biodegradable elastomeric scaffold to provide long-term growth-factor delivery was demonstrated. Such a system might provide functional benefit in cardiovascular and other soft tissue engineering applications.

Figure 1

Synthesis of PEUU. Poly(caprolactone) diol reacts with 1,4 diisocyanatobutane to form the prepolymer. The final product is formed by chain extension of prepolymer with putrescine.

Figure 2

The mass loss of PEUU scaffolds was determined over time for 5 and 8 wt% scaffolds soaked in PBS or with 100 units/ml lipase enzyme. * denotes p<0.05 between scaffold polymer concentrations

Figure 3

Electron micrographs of TIPS scaffolds (5wt% A and C, 8 wt% B and D) incubated in PBS (top panels) or lipase solution (bottom panels) for 1 week. Scaffolds maintained an organized pore structure after one week in PBS (top panels). After one week of incubation with lipase, scaffold surfaces were noticeably broken apart. Scale bar = 100 µm.

Figure 4

DSC heating curves of 5 wt % (A) and 8 wt% (B) scaffolds during degradation with lipase enzyme. In all situations the initial primary melting temperature near 50°C is lost as a new substantial peak near 30°C is formed. Scaffolds with 8 wt% PEUU maintain the first peak for 7 days (black arrow) suggesting a slower degradation than 5 wt% scaffolds which have lost that peak by 7 days.

Figure 5

A) Scaffolds in PBS demonstrated a tri-phasic release profile for IGF-1 over the time period studied. Alternating periods of slow, steady protein release (latent phases) and more rapid release (diffusion phases) followed an initial burst release. B) Both scaffold types incubated with 100 units/ml lipase enzyme released IGF-1 at a much faster rate than those without enzyme.

Figure 6

MG-63 (A) and Balb/3T3 (B) cells cultured in releasate from polymer containing IGF-1 demonstrated significantly greater cell metabolic activity (as an index of cell number) compared to cells cultured in releasate from polymer without growth factor (*p<0.05). IGF-1 added at 150 ng/ml to releasate from polymer without growth factor served as a positive control.

Figure 7

HUVECs maintained in releasate from scaffolds containing HGF grew into and repopulated the artificial wound area more extensively than those maintained in growth medium or in releasate from scaffolds without growth factor (*p<0.05). HGF added at 100 ng/ml to releasate from polymer without growth factor served as a positive control.