Biomaterials for implant-associated infections and bone tissue regeneration

Abstract

Millions of people suffer from bone fractures/injuries worldwide, leading to chronic pain, long-term disability, or death1. The accelerating number of bone fractures/disorders and implant failures due to osteoporosis, autoimmune diseases, fixation stability, and implant-related infections have resulted in high demand for bone-substitutes. The limitations associated with the gold standard, natural graft therapy, have generated a high demand for synthetic bone substitutes1. Although a variety of synthetic biomaterials, ranging from bioinert to biomimetic, have been investigated as synthetic bone substitutes, the infection associated with biomaterials and their poor osteogenic potential are major challenges in the field2–4. In the present work, we have made efforts to address key challenges associated with biomaterial-associated infections, bone mineralization, and tissue regeneration. We have developed a highly potent and proteolytically stable bactericidal gel from Fmoc-L-Arg-D-Phe-D-Phe-CONH2 (Rff) peptide in aqueous DMSO and investigated their surface morphology, rheological properties, self-healing characteristics, and swelling and degradation properties. It exhibited broad-spectrum antibacterial activities (up to 90%) against S. aureus and E. coli for up to 72 h, and no significant cytotoxicity towards the mammalian cell line (L929). The gel may have a strong potential in preventing biomaterial-associated infections5. In addition, we have also investigated the hydroxyapatite (HA) mineralization at the physiological pH and temperature in the presence of amino acids, L-Histidine (L-His) and L-Glutamic acid (L-Glu), along with the effect of organic buffers (Tris and Hepes) on their structural properties. L-His was found to regulate bone apatite-like, plate-shaped morphology of HA in different conditions, while the structural properties regulated by L-Glu were subject to experimental conditions6, and both buffers influenced the HA properties. The mouse osteoblast precursor (MC3T3-E1) cells showed highest proliferation on the plate-shaped HA synthesized in the presence of L-His, thus suggesting that the L-His can be used as an effective regulator of plate-shaped HA for designing biomaterials for mineralization and bone regeneration applications in place of large proteins. Finally, we have developed dexamethasone (Dex)-loaded injectable pullulan-PEG hydrogels for bone tissue engineering. The hydrogels were fabricated by crosslinking partially oxidized pullulan and 8-arm PEG hydrazine via biodegradable hydrazone linkages, and Dex, an anti-inflammatory corticosteroid used to induce mesenchymal stem cells differentiation in osteoblasts7 was loaded into hydrogels by covalently linking it to PEG hydrazine by hydrazone linkages. The hydrogels exhibited fast gelation, excellent mechanical properties, in vitro stability, and sustained release of Dex for up to 28 days, which is suitable for bone-regeneration applications. It exhibited cytocompatibility and in situ encapsulation of MC3T3-E1 cells within the matrix. The hydrogels showed antioxidant and anti-inflammatory properties and induced high early osteogenic differentiation of MC3T3-E1 cells, and enhanced mineralization that demonstrated their potential in in vitro bone regeneration. The biodegradable hydrogels show strong potential in addressing the challenges associated with dose control, frequency of drug administration, and osteogenic activities, and hold promise as an anti-inflammatory implantable depot for bone regeneration in chronic inflammation conditions. In conclusion, we developed biomaterials from peptides, ceramics, and polymers, which can be employed to overcome the challenges associated with implant-related infections and bone tissue regeneration. Overview of the thesis: Development of peptide, ceramic, and polymer-based biomaterials for potential applications in implant-associated infections and bone tissue regeneration. (A) Antibacterial self-assembled peptide gels. (B) Bone-like, plate-shaped hydroxyapatite (HA) fabricated using L-His. (C) Dexamethasone (Dex)-loaded pullulan-PEG hydrogels for bone regeneration.