Mineralizing Elastin-Like Protein Microgels

Mineralized tissues, such as bone and enamel are fundamental to the structure and function of organisms, with a complex interplay between their organic and inorganic components. Organized mineralization is crucial for both the tissues of living organisms and engineered materials. Elastin-like recombinamers (ELRs) have been successfully employed in tissue engineering, primarily as macroscopic coatings and membranes capable of mediating the nucleation and growth of hierarchically ordered mineralized structures. However, their adaptation into microgels has not been previously reported. To address this gap, our study presents a simple fabrication approach to produce injectable ELR microgels that retain the capacity for organized apatite-like mineralization. Converting the ELR platform into a microgel format offers distinct advantages, including an increased surface area-to-volume ratio, tuneable particle size, and improved handling. These features broaden the material's potential applications, such as its use as minimally invasive injectable scaffolds or as bioink formulations for 3D bioprinting in hard tissue repair. Here, we report on a straightforward and reproducible water-in-oil emulsification method to fabricate injectable mineralizing ELR microgels. Following mineralization, microgels supported the growth of apatite-like crystals, achieving a mineral content of approximately 20 wt%. The hierarchical organization of the mineral phase was confirmed by SEM and TEM imaging, while FTIR and XRD analyses verified that the mineral phase corresponds to the characteristic structural parameters of hydroxyapatite. ELR microgels demonstrated low cytotoxicity, maintaining over 90% viability of human mesenchymal stem cells (hMSCs) after 14 days in culture. As a proof of concept, the osteogenic potential of ELR microgels was evaluated by assessing alkaline phosphatase (ALP) activity, which demonstrated an approximate 40% increase relative to controls at day 14, with elevated levels sustained in the presence of mineralized microgels through day 28. We envision that the versatile ELR microgel platform will offer new opportunities for its application in mineralized tissue engineering.