Background: 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.
Questions/purposes: 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).
Methods: 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.
Results: 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.
Conclusions: 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.
Clinical relevance: 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.