Biomimetic mineralization of electrospun elastin-like recombinamer nanofibers

One of the key factors for hard tissue regeneration is to develop mineralized fibrous scaffolds. These scaffolds can provide a micro-environment resembling the structure and mechanical properties of the extracellular matrix (ECM) of hard tissues favorable for subsequent cell responses and tissue regeneration. During biomineralization, amorphous precursor phases of calcium phosphate infiltrate into preformed collagen fibrils, and upon crystallization, the collagen fibrils are embedded with oriented hydroxyapatite (HA) nanocrystals. We previously demonstrated that hydrogels made of elastin-like recombinamers (ELRs) can template mineralization where minerals were selectively deposited into their frameworks. In this work, we focus on mimicking the nanostructure of the mineralized tissues, namely the intra- and extrafibrillar mineralized collagen fibrils, using the synthetic ELRs. We first electrospun the ELRs into nanofibers and then biomimetically mineralized them via the polymer-induced liquid-precursor (PILP) process. We tested two different ELRs one with a peptide sequence derived from the salivary protein statherin (st-ELR) and a reference one lacking the statherin sequence (ref-ELR). X-ray diffractometry (XRD) and Energy-dispersive X-Ray Spectroscopy (EDS) verified the mineral phase in the ELR nanofibers was HA. Scanning and Transmission Electorn Microscopy (SEM and TEM) analyses revealed that HA nanocrystals were infiltrated into and randomly oriented within the ELR nanofibers. The elastic modulus and hardness of the mineralized ELR nanofibers was increased significantly compared to unmineralized ELR. The mineralized nanofibers promoted the proliferation and osteogenic differentiation of pre-osteoblasts. These results support that a scaffold obtained using this biomimetic strategy and made of mineralized ELR electrospun nanofibers with controlled mineralization and improved mechanical properties has great potential for being used in hard tissue regeneration, such as craniofacial and periodontal and perimplant regeneration as well as tertiary dentin regeneration, as it mimics the structure and mechanical properties of collagen-HA nanocomposites.