# Antibacterial Bio-Based Polymers for Cranio-Maxillofacial Regeneration Applications
## 3 Scaffolds and Implanting Medical Devices for Soft and Hard Maxilofacial Tissues
### Hybrid Scaffolds  
Scaffolds are three-dimensional constructs that act as a substitute of the extracellular matrix, providing a supporting structure for cell colonization, proliferation, and subsequent new tissue formation [72]. Several polymeric, composite materials have been clinically employed for cranial and maxillary regenerative therapies (e.g., collagen-based sponge grafting for preventing oroantral fistulae, maxillary peri-implantitis, sinusitis of zygomatic and bone defects of dental implant origin) [33]. Polyesters are the main biodegradable polymers which have received more attention due to their physical characteristics, revealing a wide range of properties, from rigid-brittle to flexible plastics. In this sense, the combination of different polymers like PCL, PHB or PLGA has demonstrated good features for repairing damaged human tissues, as well as for developing devices for drug-release purposes, including antibiotics [73; 74]; or nanoparticles with antibacterial properties (Figure 3) [54; 75; 76]. In particular, PCL is a common choice for developing polymeric blends because of its low melting point, great mechanical properties and non-enzymatic degradation by hydrolysis. In contrast, it also presents some drawbacks such as its hydrophobicity, limited bioactivity and its neutral charge. For this reason, its combination with other bio-based polymers not only solves these limitations, but also the disadvantages of their counterparts. For instance, in chitosan/PCL blends, the former could supply a positive charge and biocompatibility, while the latter could enhance the poor mechanical properties of chitosan and control the overall degradation of the scaffold [77]. Recently, [PERSON] et al. studied drug incorporation into organic/inorganic hybrid scaffolds in contrast to pure polymeric or ceramic ones, which are more common in the field. The group developed two hybrid scaffolds made of PHB/PCL, containing or not a sol-gel-derived silica, and loaded levofloxacin as a model antibiotic. Their studies shown that these scaffolds exhibited antibacterial action against both Gram-positive _S. aureus_ and Gram-negative _E. coli_, while not affecting osteoblast viability. Moreover, the silica phase dissolution significantly increased the mineralization nodules after 4 weeks of culture, being the optimal choice for bone tissue regeneration [70]. In a similar way, [PERSON] et al. synthesized two-dimensional membranes and three-dimensional porous scaffolds to evaluate the antibacterial properties of chitosan blended with PCL matrices in different configurations against two pathogens _S. mutans and A. actinomycetemcomitans_. This study indicated that chitosan impaired the proliferation of microorganisms on its surface despite a certain loss of a activity after its blending with PCL [76]. The use of bio-based polymers has been widely investigated for the reconstruction of soft tissues such as palatal, gingival and periodontal tissues. Several studies have reported the clinical applicability of collagen-based scaffolds for oral soft tissue augmentation to support wound healing [78; 79]. However, many of such studies have recommended the modification of collagen to improve its regenerative and antimicrobial potential [23]. On the other hand, the antibacterial activity of chitosan-based scaffolds has been investigated by several authors reporting chitosan as a perfect wound dressing candidate for the treatment of defects of the maxillofacial region such as palatal, gingival and periodontal wounds [80; 81; 82; 83; 84]. In this way, according to [PERSON] et al., chitosan also seems to stimulate fibroblasts, and it could be considered as a biodegradable and non-toxic material, capable of activating macrophages and neutrophils, and, therefore, preventing infections, while accelerating wound healing. This could be particularly beneficial in the case of destructive diseases like periodontitis [80]. In addition, [PERSON] et al.