# Antibacterial Bio-Based Polymers for Cranio-Maxillofacial Regeneration Applications
## 2 Membranes for Guided Tissue/Bone Regeneration  
The use of guided tissue/bone regeneration (GTR/GBR) approaches has recently increased in the oral and maxillofacial fields, being widely used for the augmentation of alveolar bone in maxillofacial surgery or in the reconstruction of oral tissues such as during the placement of dental implants, or during  
Figure 1: Most clinically applied systems in oro-cranio-facial regeneration and areas of interest, including the skull, facial bones (e.g., maxillary bone), and the oral cavity. Applications are shown below the boxes. Abbreviations: Bioactive glasses (BGs), calcium phosphate cements (CPCs) glass ionomer cements (GICs), guided bone regeneration membranes (GBR Memb. ), polymethyl methacrylate cements (PMMA). the regeneration of periodontal and endodontic tissues. This procedure is based on the concept of employing a physical barrier (membrane) to exclude gingival epithelium and connective tissue ingrowth, while enhancing the formation of bone and/or periodontal tissues [28; 29; 30; 31; 44]. Regarding their design, different polymeric materials, bio-based or not, have been employed for GTR/GBR, including synthetic polymers like polytetrafluoroethylene (PTFE) or aliphatic polyesters such as PLA, polygalacturonic acid (PGA) or PCL; and natural ones like collagen or alginate [29; 45; 46; 47; 48; 49; 50; 51; 52; 53]. However, although these membranes are widely marketed today, they do not possess intrinsic antibacterial properties [31; 54; 55; 56; 57]. In this sense, during the past 20 years, chitosan has been one of the most attractive candidates for tissue regeneration due to its low cost, biocompatibility, appropriate degradation rate, and hemostatic activity, among other characteristics. This polysaccharide is obtained from the partial deacetylation of chitin, being mainly composed of D-glucosamine and partly of N-acetyl-D-glucosamine units. Moreover, this bio-based polymer has not only been reported to provide a better substrate for osteoblasts attachment and proliferation rather than for fibroblasts colonization, but also it inhibits some Gram-negative and Gram-positive bacterial infections such as _Actinobacillus actinomycetemcomitans_ and _Streptococcus mutans_, making it a good candidate for maxillofacial GBR applications [46; 58; 59; 60]. Nevertheless, there are several factors influencing its antibacterial properties like the molecular weight, degree of deacetylation and polymer concentration, as its bactericidal mechanism has not been completely elucidated yet [58; 61; 62; 63; 64]. Chitosan has been employed in different forms. For example, chitosan nanoparticles have been investigated due to their potential to adhere to mucosal surfaces for drug delivery purposes. It was reported that chitosan acted synergistically with chlorhexidine or minocycline in collagen membranes for periapical GTR [44; 46; 65], showing antibacterial properties as well as biocompatibility and barrier function against _Enterococcus faecalis_[44]. On the other hand, chitosan has been widely employed for GBR membranes blended with other polymers such as collagen, against _S. mutans_[66], and PCL and gelatin, against _Escherichia coli_ and _Staphylococcus aureus_ (Figure 2) [62]. As an alternative, [PERSON] et al. recently studied a composite-membrane combining chitosan and silver particles, which they hypothesized could release silver ions from the fibers in a controlled manner in order to achieve enough antibacterial effects without affecting the biocompatibility of the material [31; 67]. Figure 2: Antibacterial efficacies of the chitosan-polycaprolactone (PCL) samples against _S. aureus_ and _E. coli_ evaluated by zone of inhibition assay (**a,b**). Scanning electron micrographs of _S. aureus_ and _E. coli_ adhered on the samples after 6 and 72 h (**c–f**). Reproduced from [PERSON] et al. 2018 [62], with permission from Creative Commons CC BY International License.