^{Bone Regeneration Mediated by a Bioactive and Biodegradable Extracellular Matrix-Like Hydrogel Based on Elastin-Like Recombinamers}

Abstract

The morbidity of bone fractures and defects is steadily increasing due to changes in the age pyramid. As such, novel biomaterials that are able to promote the healing and regeneration of injured bones are needed to overcome the limitations of auto-, allo-, and xenografts, while providing a ready-to-use product that may help to minimize surgical invasiveness and duration. In this regard, recombinant biomaterials, such as elastin-like recombinamers (ELRs), are very promising as their design can be tailored by genetic engineering, thus allowing scalable production and batch-to-batch consistency, among others. Furthermore, they can self-assemble into physically crosslinked hydrogels above a certain transition temperature, in this case body temperature, but are injectable below this temperature, thereby markedly reducing surgical invasiveness. In this study, we have developed two bioactive hydrogel-forming ELRs, one including the osteogenic and osteoinductive bone morphogenetic protein-2 (BMP-2) and the other the Arg-Gly-Asp (RGD) cell adhesion motif. The combination of these two novel ELRs results in a BMP-2-loaded extracellular matrix-like hydrogel. Moreover, elastase-sensitive domains were included in both ELR molecules, thereby conferring biodegradation as a result of enzymatic cleavage and avoiding the need for scaffold removal after bone regeneration. Both ELRs and their combination showed excellent cytocompatibility, and the culture of cells on RGD-containing ELRs resulted in optimal cell adhesion. In addition, hydrogels based on a mixture of both ELRs were implanted in a pilot study involving a femoral bone injury model in New Zealand white rabbits, showing complete regeneration in six out of seven cases, with the other showing partial closure of the defect. Moreover, bone neoformation was confirmed using different techniques, such as radiography, computed tomography, and histology. This hydrogel system therefore displays significant potential in the regeneration of bone defects, promoting self-regeneration by the surrounding tissue with no involvement of stem cells or osteogenic factors other than BMP-2, which is released in a controlled manner by elastase-mediated cleavage from the ELR backbone.

Use of proteolytic sequences with different cleavage kinetics as a way to generate hydrogels with preprogrammed cell-infiltration patterns imparted over their given 3D spatial structure

“…With regard to their physicochemical characterization (morphological features, mechanical properties and cytocompatibility), these ELR-based hydrogels proved to be effective as biological substitutes for future applications in tissue engineering. [50][51][52] [53] [54] The degradation rate of these systems was initially studied in vitro using a human recombinant uPA enzyme, with a clear difference in terms of degradation being found.…”

Biocompatibility of two model elastin‐like recombinamer‐based hydrogels formed through physical or chemical cross‐linking for various applications in tissue engineering and regenerative medicine

“…Herein, we aim to investigate the cytocompatibility and biocompatibility of two recently developed families of hydrogels based on elastin‐like recombinamers (ELRs) (Rodríguez‐Cabello, Martín, Alonso, Arias, & Testera, ), both of which are designed as a multipurpose approach for different TERM applications, such as bone (Coletta et al, ) and osteochondral regeneration (Pescador et al, ), or to improve the traceability of ELR‐based hydrogels through the recombinant conjugation of fluorescent proteins (Ibáñez‐Fonseca, Alonso, Arias, & Rodríguez‐Cabello, ), among others. ELRs are genetically engineered protein‐based materials whose composition is inspired by the primary sequence found in natural elastin, specifically the VPGXG pentapeptide, where X can be any amino acid except L‐proline.…”

Elastin‐Like Recombinamers: Deconstructing and Recapitulating the Functionality of Extracellular Matrix Proteins Using Recombinant Protein Polymers

“…Soft and hard tissues regeneration [214,222,237] Interspersed hydroxyphenylalanines groups in the ELR regeneration of different tissues. [244][245][246][247] They used an RGD-ELR with a simple modular design in which RGD sequences were interspersed with tandem VPGVG repeats.…”