Abstract
Tissue engineering strategies for repairing and regenerating articular cartilage face critical challenges to recapitulate the dynamic and complex biochemical microenvironment of native tissues. One approach to mimic the biochemical complexity of articular cartilage is through the use of recombinant bacterial collagens as they provide a well–defined biological ‘blank template’ that can be modified to incorporate bioactive and biodegradable peptide sequences within a precisely defined three–dimensional system. We customized the backbone of a Streptococcal collagen–like 2 (Scl2) protein with heparin–binding, integrin–binding, and hyaluronic acid–binding peptide sequences previously shown to modulate chondrogenesis and then cross–linked the recombinant Scl2 protein with a combination of matrix metalloproteinase 7 (MMP7)– and aggrecanase (ADAMTS4)–cleavable peptides at varying ratios to form biodegradable hydrogels with degradation characteristics matching the temporal expression pattern of these enzymes in human mesenchymal stem cells (hMSCs) during chondrogenesis. hMSCs encapsulated within the hydrogels cross–linked with both degradable peptides exhibited enhanced chondrogenic characteristics as demonstrated by gene expression and extracellular matrix deposition compared to the hydrogels cross–linked with a single peptide. Additionally, these combined peptide hydrogels displayed increased MMP7 and ADAMTS4 activities and yet increased compression moduli after 6 weeks, suggesting a positive correlation between the degradation of the hydrogels and the accumulation of matrix by hMSCs undergoing chondrogenesis. Our results suggest that including dual degradation motifs designed to respond to enzymatic activity of hMSCs going through chondrogenic differentiation led to improvements in chondrogenesis. Our hydrogel system demonstrates a bimodal enzymatically degradable biological platform that can mimic native cellular processes in a temporal manner. As such, this novel collagen–mimetic protein, cross–linked via multiple enzymatically degradable peptides, provides a highly adaptable and well defined platform to recapitulate a high degree of biological complexity, which could be applicable to numerous tissue engineering and regenerative medicine applications.
Highlights
Developing bioengineered constructs for cartilage tissue engineering that promote neocartilage regeneration by encapsulatedP.A
Confirming these observations, the compression moduli of the hydrogels determined using unconfined dynamic mechanical analysis (DMA) were found to range between ~4 and 5 kPa at 1 Hz, and there were no statistical differences in compression moduli between samples
Unlike poly(ethylene glycol) (PEG), a commonly used hydrogel platform in cartilage tissue engineering, the Streptococcal collagenelike 2 (Scl2) hydrogels exhibited viscoelastic behavior, which may be a more suitable replacement for tissues such as cartilage that behave as viscoelastic materials [29]
Summary
Developing bioengineered constructs for cartilage tissue engineering that promote neocartilage regeneration by encapsulatedP.A. Cellemediated degradation occurs in hydrogels made of naturally derived materials such as collagen and fibrin, and these native molecules present moieties that can enhance cellular adhesion and biorecognition [6]. The ability to tune the degradation of the hydrogel with the deposition of ECM by harnessing cellemediated processes has been shown to elicit advantages towards chondrogenesis. Hydrogels can be programmed to degrade by cellemediated mechanisms, such as PEG hydrogels formed with matrix metalloproteinase (MMP)edegradable crosselinks that were previously found to improve chondrogenesis of encapsulated hMSCs compared to noneenzymatically degradable PEG hydrogels [10]. Hydrogels can provide a welledefined system that increases their feasibility for clinical translation while recapitulating features of natural systems such as cellemediated degradation and adhesion to ECM molecules
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