In SituCrosslinking Elastin-Like Polypeptide Gels for Application to Articular Cartilage Repair in a Goat Osteochondral Defect Model^*

Abstract

The objective of this study was to evaluate an injectable, in situ crosslinkable elastin-like polypeptide (ELP) gel for application to cartilage matrix repair in critically sized defects in goat knees. One cylindrical, osteochondral defect in each of seven animals was filled with an aqueous solution of ELP and a biocompatible, chemical crosslinker, while the contralateral defect remained unfilled and served as an internal control. Joints were sacrificed at 3 (n = 3) or 6 (n = 4) months for MRI, histological, and gross evaluation of features of biomaterial performance, including integration, cellular infiltration, surrounding matrix quality, and new matrix in the defect. At 3 months, ELP-filled defects scored significantly higher for integration by histological and gross grading compared to unfilled defects. ELP did not impede cell infiltration but appeared to be partly degraded. At 6 months, new matrix in unfilled defects outpaced that in ELP-filled defects and scored significantly better for MRI evidence of adverse changes, as well as integration and proteoglycan-containing matrix via gross and histological grading. The ELP-crosslinker solution was easily delivered and formed stable, well-integrated gels that supported cell infiltration and matrix synthesis; however, rapid degradation suggests that ELP formulation modifications should be optimized for longer-term benefits in cartilage repair applications.

Rapid Cross-Linking of Elastin-like Polypeptides with (Hydroxymethyl)phosphines in Aqueous Solution

“…In addition, the integrity and survival of THPP-crosslinked ELPs following injection into a tissue site in a goat model were evaluated as injectable hydrogels for articular cartilage repair of an osteochondral defect. 56 We observed that the solution mixture of THPP and ELP became turbid within one minute solid after 5 minutes. Thus, all surgical sites were closed at 5 minutes after injection into the cartilage defect site.…”

Elastomeric recombinant protein-based biomaterials

“…ELPs could be enzymatically crosslinked by transglutaminase to form elastic gels with improved mechanical properties but the clinical applications of these gels was hampered due to the length of time required for the crosslinking reaction to take place [88]. To solve this problem, Setton and Chilkoti synthesized an ELP containing lysine, ELP[V 6 K 1 -224], which could chemically crosslink in less than 5 min by using β-[tris(hydroxymethyl)phosphino]propionic acid (THPP) as a crosslinking agent under physiological conditions [89–92]. The fabricated hydrogel was injected into an osteochondral defect in a goat model.…”

Modular enzymatically crosslinked protein polymer hydrogels for in situ gelation

“…Often additional chemical crosslinking schemes have been used to form more rigid and stable gels. For example, elastin-like protein polymers have been chemically crosslinked by tris-succinimidyl aminotriacetate [14], disuccinimidyl suberate [15], and hydroxymethylphosphine crosslinking chemistries [16], greatly improving gel mechanical properties. Chemical crosslinking, however, is not ideal for in situ gelation due to possible crosslinker toxicity in vivo .…”