3.3.3. Graphene Oxide

Graphene is a flat monolayer of carbon atoms that are tightly packed into a 2-dimensional honeycomb lattice [110]. Due to its solubility in water and biocompatibility, graphene oxide (GO) has been used as biomaterials [48,111]. De Marco et al. reported a GO-coated collagen membrane [48]. The GO-coated membrane showed a lower deformability with a higher stiffness, an increased roughness, and an increase in the total surface that was exposed to the cells [48].

#### *3.4. No Significant Difference*

There exist studies about coated membranes that showed no significant advanced effect compared to the control group.

In 2017, Byun et al. reported a HA-coated Mg membrane to improve biocompatibility [22]. In the result, there were no significant differences or new bone volume, bone volume fraction, or bone surface density between the HA-coated Mg group and the control group [22].

In 2020, Steigmann et al. reported an ion implantation (II) and physical vapor deposition (PVD)-treated Mg membrane to improve biocompatibility [50]. In this study, the PVD-coated membrane demonstrated the absence of a positive influence on the gas cavity formation and advanced immune response compared to the noncoated Mg membrane. The authors concluded that a pure Mg membrane represents a promising alternative to the non-resorbable membrane [50].

In 2020, Toyama et al. reported an atmospheric pressure plasma (APP)-treated Ti membrane and analyzed its effect on the differentiation of BMSCs [51]. In this study, the APP-coated Ti membrane was identified to increase cell migration and gene-level expression of osteogenic markers; however, the suppression of mineralization was observed in an in vitro experiment. Furthermore, in the in vivo experiment, the new bone formation was not significantly different between APP-coated and noncoated Ti membranes [51].

#### **4. Conclusions**

The paradigm of the barrier membrane is changing from only inert (or biocompatible) physical barriers to bioactive osteo-immunomodulatory for effective guided bone and tissue regeneration. For this purpose, numerous studies on coating various bioactive materials on the membrane to improve osteogenesis, antimicrobial properties, and physical/mechanical properties by various techniques have been performed. However, there is a limitation that there exists only a few clinical studies on humans to date. Efforts are needed to implement the use of coated membranes from the laboratory bench to the dental chair unit. Further clinical studies are needed in the patients' group for long-term follow-up to confirm the effect of various coating materials.

**Author Contributions:** Conceptualization, J.-Y.K. and J.-B.P.; methodology, J.-Y.K. and J.-B.P.; formal analysis, J.-Y.K. and J.-B.P.; writing—original draft preparation, J.-Y.K. and J.-B.P.; writing—review and editing. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All data analyzed during this study are included in this published article.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

