Evaluation of MMP substrate concentration and specificity for neovascularization of hydrogel scaffolds

Abstract

Controlled vascular response in scaffolds following implantation remains a significant clinical challenge. A critical biomaterial design criterion is the synchronization of the rates of scaffold degradation and vascularized tissue formation. Matrix metalloproteinases (MMPs) are key enzymes that regulate neovascularization and extracellular matrix remodelling. Synthetic protease-sensitive hydrogels offer controllable environments for investigating the role of matrix degradation on neovascularization. In this study, PEG hydrogels containing MMP-sensitive peptides with increased catalytic activity for MMPs expressed during neovascularization were investigated. Scaffolds were functionalized with MMP-2-, MMP-14- or general collagenase-sensitive peptides and with varying peptide concentration using crosslinkers containing one (SSite) or multiple (TSite) repeats of each protease-sensitive sequence. Increasing peptide concentration enhanced the degradation kinetics of scaffolds functionalized with MMP-specific sequences while 80% of the collagenase-sensitive scaffolds remained upon exposure to MMP-2 and MMP-14. In vitro neovascularization was consistent with in vivo tissue invasion with significantly increased invasion occurring within SSite MMP-specific as compared to collagenase-sensitive hydrogels and with further invasion in TSite as compared to SSite hydrogels regardless of peptide specificity. All scaffolds supported in vivo neovascularization; however, this was not dependent on peptide specificity. These findings demonstrate that peptide concentration and specificity regulate in vivo scaffold degradation, neovascularization and matrix remodelling.

Regulation of tissue ingrowth into proteolytically degradable hydrogels

“…MMP-2 and MMP-14 were shown to increase invasion rates when multiple repeats of each protease-sensitive sequence was used compared to crosslinkers only containing one site [22,30]. Although, proteolytic degradation was promoted, no difference was observed in vivo between the different MMP recognition sequences over a 3 week period.…”

“…In a recent study [22], the effect of MMP substrate concentration and specificity for neovascularization within a hydrogel scaffold was evaluated.…”

“…Very recently, a system for regulating ingrowth was formulated whereby peptides were designed that separately incorporated cleavage sequences for either MMP-2, MMP-14 or collagenase in single or triple repeats and these were used to photo-crosslink PEG hydrogels [22]. These hydrogels were shown to be similar biomechanically as determined by compression testing.…”

Tailoring Collagen to Engineer the Cellular Microenvironment

“…This ability to modulate degradation of ECM is important for tissue engineering applications . For example, increased vascular invasion depth within hydrogels with increased concentration of MMP‐sensitive substrates has been observed . However, that study utilized peptides of different lengths to increase the concentration of MMP sites, with increasing peptide length corresponding to increased number of MMP sites.…”

“…Collagens, due to their triple‐helical nature, are resistant to proteases that are not part of the MMP family . Since MMPs have been implicated in many physiological properties such as angiogenesis, sites sensitive to MMPs have been included in biomimetic tissue engineering scaffolds . Scaffold degradation rate has been shown to influence cellular fate; therefore, we investigated the ability to control the number of MMP cleavage sites within recombinant collagen to control degradation characteristics.…”