Novel Metformin-Releasing Calcium Phosphate Pulp-Capping Cement to Enhance Dental Pulp Stem Cells for Dentin Regeneration

Abstract

Preserving pulp vitality is crucial for maintaining tooth function and ensuring proper root development, particularly in young patients with immature permanent teeth. Direct pulp capping (DPC) is a conservative treatment designed to protect exposed pulp tissue and stimulate reparative dentin formation. Although mineral trioxide aggregate (MTA) is widely used for DPC because of its biocompatibility and sealing ability, its clinical application is limited by prolonged setting time, high cost, handling difficulties, and potential tooth discoloration. Metformin, an FDA-approved drug for type 2 diabetes, has been shown to promote odontoblastic differentiation and mineralized tissue formation in dental pulp stem cells (DPSCs). This dissertation aims to develop a novel pulp-capping material by incorporating metformin into a calcium phosphate cement–chitosan (CPCC) system, providing improved physico-mechanical properties, a shorter setting time, and enhanced biological performance through local metformin delivery. In the first part of this PhD project, different CPCC powder-to-liquid (P:L) ratios were evaluated against the gold standard MTA with respect to physical and mechanical properties. CPCC at a 3.25:1 ratio performed better than MTA, with an approximately threefold reduction in setting time. This optimized formulation was then loaded with metformin in the liquid chitosan phase at 50, 100, and 150 µg, and metformin release as well as cellular compatibility were assessed. Metformin showed burst release within 24 hrs, and the amount released was proportional to the loading dose. All metformin concentrations supported excellent cell attachment and proliferation similar to MTA and CPCC without metformin. In the second part of this PhD project, metformin was encapsulated within poly(lactic-co-glycolic acid) (PLGA) to extend its release. The encapsulated metformin within PLGA (Met-PLGA) was mixed with CPCC at concentrations ranging from 5% to 20%. Met-PLGA microsphere characterization, physico-mechanical properties, metformin release, and cytocompatibility were evaluated. The Met-PLGA microspheres were uniformly spherical with a mean diameter of (5.43 ± 0.17) µm. Successful incorporation of metformin into PLGA was evidenced by an encapsulation efficiency of 51% and changes in characteristic bands of Met-PLGA compared with PLGA alone. The 15% Met-PLGA-CPCC group showed physico-mechanical properties comparable to CPCC and MTA, with approximately five-folds reduction in setting time compared with MTA. Metformin release was extended to four days relative to non-encapsulated metformin. In addition, the incorporation of Met-PLGA did not alter the excellent compatibility with DPSCs. In conclusion, metformin was successfully incorporated into CPCC, yielding formulations with improved physico-mechanical properties and extended local metformin release to the pulp, with the potential to induce cell differentiation and promote odontogenesis.