Objective Self-healing of bone from damage caused by infection, trauma, or surgical removal of cysts is limited. Generally, external intervention is needed to increase bone repair and regeneration. In this study, biocompatible light-cured hyaluronic acid hydrogels loaded with nano-hydroxyapatite and chitosan were prepared using a new photoinitiating system based on riboflavin for bone regeneration applications. Method Four light-cured hydrogel groups were prepared as follows: Group I, a control group with no additions; Group II, loaded with nano-hydroxyapatite; Group III, loaded with chitosan; and Group IV, loaded with both nano-hydroxyapatite and chitosan. The new photoinitiating system consisted of riboflavin as a photoinitiator, dimethylaminoethyl methacrylate (DMAEMA) as a coinitiator (being used with riboflavin for the first time), and diphenyliodonium chloride as an accelerator. For each group, X-ray-diffraction, surface morphology by scanning electron microscope, mechanical properties, water uptake (%), and cell viability (%) were tested. The osteogenic potential was then tested in a rabbit model, and histomorphometric assessment was conducted. Results In the four groups, the light-cured hydrogels were obtained after a short irradiation time of 10 s using a dental light-curing unit. The prepared hydrogels were biocompatible. Simultaneous addition of nano-hydroxyapatite and chitosan increased the mechanical properties threefold and the osteogenic potential, twofold, with a statistically significant difference compared with the control group. Conclusions Light-cured hyaluronic acid composite hydrogels loaded with nano-hydroxyapatite and chitosan—prepared by using the new photoinitiating system—are promising materials that can be used in bone regeneration applications.

Biocompatibility of materials used in dental and biomaterials applications is very important and depends on the components of these materials. Photopolymerized materials for dental and biomaterials applications have been progressively used since the 1970s. One of the crucial components in these materials is the photoinitiator (PI) that initiates the polymerization reaction. Synthetic PIs are the most commonly used types, but owing to their drawbacks such as cytotoxicity, insolubility in water, and high cost, research on naturally derived (bio-sourced) PIs is growing, to find an alternative to these synthetic types, especially in the growing field of three-dimensional (3D) printing and bioprinting of biomaterials for tissue engineering applications. Naturally derived PIs are biocompatible, highly water-soluble, and abundant. Naturally derived PIs have been used to prepare experimental dentine bonding agents, dentine primers, photo-crosslinked hydrogels for tissue engineering applications, antibacterial coatings, guided tissue regeneration membranes, and 3D printed biomaterials. An electronic search was done using MEDLINE/PubMed and Scopus databases using the keywords naturally derived, bio-sourced, PIs, dental, biomaterials, 3D printing, and 3D bioprinting, to review potential naturally derived PIs for dental and biomaterials applications. There are a variety of naturally derived PIs with various colors and absorption spectra to choose from, according to the intended application. Most of naturally derived PIs can be used with modern conventional dental light curing units, making them applicable for experimental studies for potential dental and biomaterials applications. Due to their biocompatibility and availability it is expected that in the upcoming years, research on naturally derived PIs and their dental and biomaterials applications will increase especially in the growing field of 3D bioprinting in which cell viability is essential; thus this review was done.

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Introduction: In-situ photo-cured hydrogels for bone regeneration offer an advantage compared to solid scaffolds or membranes is that it can be used by minimally invasive techniques and can fill irregularly shaped defects easily. Objective: was to prepare an injectable photo-curable hyaluronic acid hydrogel scaffold loaded with bioactive nano-hydroxyapatite using riboflavin as a natural source photoinitiator for bone regeneration and to investigate the effect of addition of nano-hydroxyapatite on the physiochemical and mechanical properties of the prepared hydrogel. Also, the osteogenic potential of the prepared hydrogels was assessed in a rabbit model. Materials and methods: Two groups were prepared, (Group I) photo-cured hyaluronic acid as a control group and (Group II) photo-cured hyaluronic acid/nano-hydroxyapatite. Laboratory Alexandria Dental Journal Volume XX. Issue X ii characterization tests: FTIR, XRD, SEM, mechanical, swelling and degradation rate tests were performed. Cell viability % using the MTT assay was used to assess the biocompatibility. In vivo bioactivity was assessed in a rabbit model and histomorphometric analysis was done. Results: Statistical analysis of results revealed that the addition of nano-hydroxyapatite increased significantly the mechanical properties of the hydrogels. SEM images demonstrated that the addition of nano-hydroxyapatite caused the formation of interconnected pores. MTT assay showed that hydrogel extract didn't affect cell viability after 48h. Histomorphometric analysis results revealed that the photo-cured (GMA-HA/HAP) hydrogel increased the osteogenic potential by one and a half folds compared to the control group and this proved its bioactivity. Conclusion: Results suggest that the prepared photo-cured hyaluronic hydrogel is a promising biomaterial to deliver bioactive nano-hydroxyapatite and has an osteogenic potential.