Development of Photopolymer Hydroxyapatite Suspensions for 3D Printing in Medicine

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Abstract
Introduction. Additive manufacturing of hydroxyapatite (HA) ceramics is considered a promising approach to creating personalized bone implants. However, highly loaded photopolymer suspensions assume precise composition and exposure conditions to ensure stable printing and product quality. The present study aims to develop a photopolymer suspension based on HA of in-house synthesis for the additive production of ceramic implants using DLP 3D printing. Materials and methods. HA is synthesized by coprecipitation and hydrothermal synthesis methods in aqueous solutions of calcium and phosphate salts. The powder is milled and fractionated for assessing the morphology and element composition using scanning electron microscopy and energy-dispersive X-ray fluorescence analysis, respectively. A photopolymer suspension with 60 wt. % of the inorganic phase, developed based on the synthesized HA, contains acrylate monomers, photoinitiating system and dispersing additives. In addition, photopolymerization is studied on a DLP 3D printer at different UV radiation powers and exposure times. Results and discussion. The synthesized well-crystallized HA has lamellar and nanostructured morphology, as well as developed porosity; the predominance of calcium and phosphorus without significant toxic impurities is confirmed. At a radiation power of 40 mW/cm², the optimal exposure time of 6–10 s ensures the formation of uniformly hardened layers with a thickness of about 0.7–0.9 mm and a thickness plateau at a further increase in exposure time. Conclusion. The obtained data indicate that the combination of controlled HA morphology and specially selected photopolymer matrix provides sufficient polymerization depth and layer stability required for DLP printing of complex geometries. High specific surface area and porosity of HA further enhance its potential in tissue engineering. The developed photopolymer suspension based on HA of in-house synthesis demonstrates suitability for DLP 3D printing and can be used as a basis for creating personalized ceramic implants in traumatology, orthopedics, neurosurgery, and maxillofacial surgery.

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