Mechanical evaluation of bacterial nanocellulose as an implant material for ear cartilage replacement

Bacterial nanocellulose (BNC) is a novel non-degradable biocompatible material that promotes chondrocyte adhesion and proliferation. In this work, its potential use in ear cartilage tissue engineering (TE) is investigated. Firstly, the mechanical properties of native ear cartilage are measured in order to set a preliminary benchmark for ear cartilage replacement materials. Secondly, the capacity of BNC to match these requirements is assessed. Finally, a biofabrication process to produce patient-specific BNC auricular implants is demonstrated. BNC samples (n=78) with varying cellulose content (2.5-15%) were compared using stress-relaxation indentation with human ear cartilage (n=17, from 4 males, aged 49-93 years old). Additionally, an auricle from a volunteer was scanned using a 3T MRI with a spoiled gradient-echo sequence. A negative ear mold was produced from the MRI data in order to investigate if an ear-shaped BNC prototype could be produced from this mold. The results show that the instantaneous modulus Ein, equilibrium modulus Eeq, and maximum stress σmax of the BNC samples are correlated to effective cellulose content. Despite significantly different relaxation kinetics, the Ein, Eeq and σmax of BNC at 14% effective cellulose content reached values equivalent to ear cartilage (for Eeq, BNC: 2.4±0.4MPa and ear cartilage: 3.3±1.3MPa). Additionally, this work shows that BNC can be fabricated into patient-specific auricular shapes. In conclusion, BNC has the capability to reach mechanical properties of relevance for ear cartilage replacement, and can be produced in patient-specific ear shapes.