3.1.7. Hyaluronic Acid

HyA, a natural linear glycosaminoglycan, is one of the components of the extracellular matrix, and its presence has been documented in skin, aorta, cartilage, and brain [87]. The HyA has hygroscopic, viscoelastic, biocompatible, biodegradable, anti-inflammatory, and bacteriostatic properties [88,89]. Furthermore, it has been reported to induce and enhance cell proliferation, migration, adhesion, and angiogenesis [90,91]. For its ideal regeneration properties, HyA has been widely used in the medical field for orthopedic surgery in the form of intraarticular injection into the osteoarthritic joint and in plastic surgery for dermal regeneration and soft tissue augmentation [87]. In dentistry, HyA has been applied for the treatment of osteoarthritic temporomandibular joint disease and periodontitis [40,92,93].

In 2017, Silva et al. reported that a HyA-coated collagen membrane by using the soaking coating technique did not show a significant difference in new bone formation compared to the non-coated collagen membrane group in rats [40]. However, other studies demonstrated that HyA coated with CaP and chitosan into a collagen membrane through a spraying technique or a HyA- and TCP-modified PCL membrane by the spin-coating technique showed significantly different results in in vitro experiments [16,19]. Dubus et al. [16] reported that a HyA-, CaP-, and chitosan-coated collagen membrane enhanced the proliferation of MSCs and the secretion of cytokines and growth factors. However, further in vivo studies are needed to confirm the effective role of HyA in bone regeneration.

## 3.1.8. Other Coating Materials—Tantalum, Copper

Ta is known to increase osteoconductivity by promoting the formation of CaP surface layers and is also known to have superior biocompatibility and mechanical properties [94–96]. In 2020, Hwang et al. reported a Ta coated-PLA membrane using sputtered Ta ions using a DC magnetron sputterer to enhance the bioactivity of the PLA membrane [41]. In the reported study, the Ta-coated PLA membrane showed more advanced osteoconductivity than the uncoated PLA membrane in both in vitro and in vivo experiments.

Copper has been known to have attractive dual functions in regenerative medicine [32,97]. Cuprous oxide (CuO2) nanoparticles have a high efficiency and broad-spectrum antibacterial properties [98]. In addition, Cu2+ has been reported to induce the osteogenic differentiation of BMSCs [97]. In 2020, Xu et al. reported a sodium alginate hydrogel composite (CTP-SA) doped with cubic CuO2 and PDA-coated titanium dioxide (TiO2) nanoparticles

for guided tissue regeneration [32]. In this study, CuO2 PDA/TiO2-modified CTP-SA showed improved antibacterial and osteogenic properties according to dual light controls [32].
