# Poly(vinyl alcohol)/Gelatin Scaffolds Allow Regeneration of Nasal Tissues
## 4 Discussion  
The nose is a complex organ consisting of several tissue types that are mechanically and functionally interconnected with each other to prime the respiratory function: cartilaginous, bony, epithelial, adipose and fibromuscular tissues, among others. The shape and integrity of all the nasal tissues are fundamental for its physiology. Due to its exposed position, the nose is affected by several pathologies, mainly derived from allergy, infections, traumas, burns, chemical agents, drugs, and tumors [1; 2; 3; 4]. In particular, tumor resection leads to deformation of the nasal structures with impairment of its function and aesthetics, thus necessitating reconstructive surgery, which is expensive and complex, as it requires several interventions. Due to its specific function and location, and for environmental factors like air pollution, the nose is challenged by inflammatory processes. Therefore, novel biomaterial approaches able to provide safe repair and reconstruction are greatly needed. Having a biomaterial suitable for reconstructing different nasal tissues would offer a better versatile platform for rhinoplasty. Recently, the problem of nasal tissue regeneration has been addressed from a TE point of view. In recent decades, the TE paradigm, comprising cells, 3D biomaterial scaffolds and appropriate stimuli, has been explored in many medical fields, including nose reconstruction, albeit in limited studies. Although good results have been obtained, recently also in humans, no TE construct has yet been found to regenerate damaged nose in all its components [28]. Starting from these assumptions, we generated in vitro constructs made of PVA/G scaffolds and stem cells differentiated towards different lineages and we performed a morpho-functional investigation to assess potential to obtain cartilage tissue for repairing septum and lateral cartilages, bone tissue for the vomer and other bone structures, fibrous tissue for the regeneration of the connective ligaments and alae. PVA is a very versatile and widely known biocompatible material, used in many TE studies, but not yet evaluated for nasal structures [44]. G is a natural protein obtained from collagen denaturation. As the denaturation process preserves many functional groups of native collagen, G is able to interact with cells and facilitate their adhesion [45]. Moreover, we demonstrated that the addition of G during the emulsion process helps the foam porogenesis, which ultimately leads to pore size distribution in the range of cellular size [35]. Overall, G affects pore formation, size and interconnectivity via foaming, is responsible for sponge stability via GTA crosslinking, and modulates the surface properties of PVA to trigger cell adhesion. Considering our previous studies on PVA/G sponges, we observed that G within 20-30% by weight with respect to PVA led to sponges suitable for the growth of several cell types [30; 34; 35; 40]. In fact, as we showed here, both 80/20 and 70/30 (w/w%) PVA/G sponges displayed a highly porous architecture, with round-shaped pores and quite smooth surfaces. The sponges demonstrated a volumetric porosity of \(\sim\) 85% and pore interconnectivity of \(\sim\)97%, measured by considering minimum pore-pore openings of 52 \(\upmu\)m. This evidence indicates that only \(\sim\)3% of the scaffold volume is either inaccessible or connected through lower size openings, which, however, can contribute to oxygen and nutrient diffusion across the scaffold. Upon wetting, both sponge types almost doubled their volume, ultimately reaching a water content similar to that of cartilage [29]. Wet sponges were extremely soft in nature, as corroborated by compressive mechanical tests, and were provided with shape recovery, which is a remarkable feature for minimally invasive surgery. Both formulations thus showed very similar behavior, which was considered to fit nasal applications.