Preparation and properties of artificial auricles based on PVA/BNC composites

With the increasing number of patients with ear defects caused by congenital microtia, trauma, and cancer, ear reconstruction has become an urgent problem to be solved. Due to the lack of blood vessels, nerves, and lymphatic support, as well as the extremely intricate three-dimensional structure of ear tissue, self-repair and reconstruction of the ear are difficult. Current treatment methods have many complications. So far, an ideal ear substitute that can match the biomechanical properties of human ear tissue and maintain long-term structural and mechanical stability at the transplantation site has not been found. Therefore, this study aims to explore and develop a PVA/BNC artificial ear material that combines high elasticity and toughness with high mechanical strength using bacterial nanocellulose (BNC) and polyvinyl alcohol (PVA) hydrogels, with the goal of applying it in the field of plastic and reconstructive surgery.

First, BNC membranes were prepared using the shallow dish static culture method. After multiple purifications and sterilizations, the BNC membranes were homogenized into a pulp-like state using a high-speed dispersion homogenizer (10,000 r/min, 15 min, 3 times). Then, the appropriate amount of PVA particles was taken and dissolved in a magnetic stirring water bath at 90°C for 2 hours to prepare 8%, 12%, 16%, and 20% (w/v) PVA aqueous solutions. The BNC pulp was centrifuged at 10,000 r/min for 10 minutes to remove excess moisture. The centrifuged BNC precipitate (with a moisture content of approximately 97.34 ± 0.57%) was added to the PVA solution in a 30% (w/v) ratio and thoroughly mixed. The mixture was then poured into a mold. It was frozen at -20°C for 36 hours and thawed at room temperature for 12 hours to obtain the PVA/BNC composite material. Finally, the PVA/BNC composite was characterized and evaluated as a potential artificial ear using SEM, FT-IR, XRD, density and mechanical property tests, as well as in vitro cell experiments.

By conducting physicochemical characterization of the PVA/BNC composite material, the following results were obtained: (1) The PVA/BNC material exhibited a porous honeycomb network structure under electron microscopy, with a porosity significantly higher than that of PVA hydrogel. (2) The moisture content and swelling rate of the PVA/BNC material were higher than those of the same concentration of PVA hydrogel. Among them, the 8% PVA/BNC reached water absorption equilibrium at 360 minutes with a saturated swelling rate of 463%. (3) The crystallinity of all samples ranged from 34% to 46%, and the crystallinity of the PVA/BNC composite material was higher than that of PVA hydrogel. (4) The compressive modulus and strength of the PVA/BNC composite material were significantly higher than those of PVA hydrogel. With the increase of PVA concentration, the modulus increased from 2.30 ± 0.29 MPa to 6.98 ± 0.49 MPa, which was similar to that of natural ear cartilage (1.66 ± 0.63 MPa). Meanwhile, after 5-20 cycles of compression, the energy loss of the 16% PVA/BNC decreased gradually from 1.82 MJ/m to 0.54 MJ/m, and the loss coefficient decreased from 50.53% to 14.92%. After 10 cycles of compression, the change became smaller and tended to stabilize, indicating that the 16% PVA/BNC had strong stress dispersion ability. (5) The tensile strength and modulus of the PVA/BNC composite material at different concentrations were significantly higher than those of PVA gel. The maximum tensile modulus (1.11 ± 0.17 MPa) was comparable to that of natural ear cartilage (2.02 ± 0.25 MPa). The fracture elongation (49.83% ± 4.02%) was similar to that of natural ear cartilage (40.62% ± 28%). The toughness of the 16% PVA/BNC in the first and fifth stretching cycles was 5.05 MJ/m and 3.70 MJ/m, respectively. In the 5th to 20th cycle process, the toughness gradually decreased to 3.04 MJ/m, and the energy dissipation coefficient increased from 26.75% to 39.80%, indicating that the PVA/BNC composite material had high toughness. (6) The addition of BNC significantly improved the suture strength of the composite material, with the highest suture strength of PVA/BNC reaching 7.06 ± 0.33 N, fully satisfying the requirements of clinical transplantation surgery. (7) The results of cell experiments showed that cells on low-concentration PVA/BNC materials had a more spread-out morphology, higher cell density, and vitality.Conclusions: The PVA/BNC composite material exhibits higher moisture content, swelling rate, and porosity compared to PVA hydrogel, which is attributed to the introduction of air during the stirring process of BNC and PVA. Additionally, the high moisture content (approximately 97.34 ± 0.57%) and water absorption capacity of BNC facilitate the formation of ice crystals during the freeze-thaw process. After thawing, the original positions of the ice crystals become pores, increasing the porosity. This promotes the penetration of nutrients and cells into the material, improving cell adhesion and growth on the material. The addition of BNC disrupts the network structure of PVA and participates in the crystallization process during reconstruction. Moreover, by increasing the solid content of the material, BNC significantly enhances compressive and tensile properties, making them compatible with natural ear tissue. Therefore, this study successfully prepared the PVA/BNC composite material using the freeze-thaw method, and subsequent animal experiments will be conducted to investigate its tissue compatibility. Furthermore, efforts will be made to improve the microstructure of the material by increasing pore size and porosity, aiming to enhance cell migration and tissue ingrowth, and further explore and develop a more application-promising artificial ear.