Growth factor delivery through self-assembling peptide scaffolds.

Abstract

The best strategy for delivering growth factors to cells for the purpose of cartilage tissue engineering remains an unmet challenge. Tethering biotinylated insulin-like growth factor-1 (bIGF-1) to the self-assembling peptide scaffold (RADA)(4) effectively delivers bioactive bIGF-1 to cardiac tissue. We therefore asked whether: (1) soluble bIGF-1 could stimulate proteoglycan production by chondrocytes; (2) bIGF-1 could be adsorbed or tethered to the self-assembling peptide scaffold (KLDL)(3); (3) adsorbed or tethered bIGF-1 could stimulate proteoglycan production; and (4) transforming growth factor-β1 (TGF-β1) could be adsorbed or tethered and stimulate proteoglycan production by bone marrow stromal cells (BMSCs). Chondrocytes or BMSCs were encapsulated in (KLDL)(3). The growth factors were (1) delivered solubly in the medium; (2) adsorbed to (KLDL)(3); or (3) tethered to (KLDL)(3) through biotin-streptavidin bonds. Fluorescently tagged streptavidin was used to determine IGF-1 kinetics; sGAG and DNA content was measured. Soluble bIGF-1 stimulated comparable sGAG accumulation as soluble IGF-1. Tethering IGF-1 to (KLDL)(3) increased retention of IGF-1 in (KLDL)(3) compared with adsorption, but neither method increased sGAG or DNA accumulation above control. Adsorbing TGF-β1 increased proteoglycan accumulation above control, but tethering did not affect sGAG levels. Although TGF-β1 can be effectively delivered by adsorption to (KLDL)(3), IGF-1 cannot. Additionally, although tethering these factors provided long-term sequestration, tethering did not stimulate proteoglycan production. Tethering growth factors to (KLDL)(3) results in long-term delivery, but tethering does not necessarily result in the same bioactivity as soluble delivery, indicating presentation of proteins is vital when considering a delivery strategy.