Mechanical Properties of Bacterial Cellulose Implants

Cellulose is a biopolymer that has long been used as a biomaterial and its different sources, as Bacterial Cellulose (BC), have shown to possess impressive mechanical properties, which can lead to the development of new biomedical implants. Bacterial Cellulose is a polysaccharide secreted by bacteria as Gluconacetobacter xylinus: BC is composed of highly hydrated nanofibrils and it is characterized by high mechanical strength, high water content, high cristallinity and an ultra-fine highly pure nano-fibril network structure. The reasons for the great mechanical properties of Bacterial Cellulose have to be searched in the nanoand microlevel morphology of the material. The nano-scale morphology shows the presence of nano-fibrils; however, it is more likely the structure of the entire network at a micro-level that can explain the extremely good mechanical properties of Bacterial Cellulose implants. Thanks to its biocompatibility, BC can be used in a wide range of applications, such as blood vessels, skin and meniscus replacements etc. BC is a highly effective wound-dressing material, as skin of patients with burns heals faster when covered with membranes of bacterial cellulose, than if conventional wound-dressings are applied. Another medical application of bacterial cellulose is in vascular surgery, where tubular pieces of BC serve as bypass grafts. BC has Young's modulus in compression similar to the meniscus one, and shows even better mechanical properties than the native collagen material. The low price for the production of BC and the possibility to manufacture BC implants in different shape and size give to the Bacterial Cellulose a great potential among the biomaterials of the future. Although the BC implants are having great success as biomaterials, it is still necessary to reach a deep understanding of the reasons behind such good mechanical properties of the material. The reasons have to be found through an analysis of the morphology of the BC at a nanoand micro-level. The present work has been based on the hypothesis that it is the network of fibrils at a micro-level which provides the mechanical performance of the material. The purpose of this work has been to study the effect of the BC networks on the mechanical properties of the implants. By changing the water content of the Bacterial Cellulose network, it was possible to produce BC materials with mechanical properties more similar to the native soft tissue that have to be replaced. The objective is to reach a prediction of the mechanical performances of the material, knowing the components, the morphology of the network and the amount of water content. Several mechanical tests were performed, with a focus on tensile testing, to evaluate the mechanical properties of the Bacterial Cellulose samples: strength, Young's modulus, strain of BC pellicles were determined and analyzed. Due to the lack of Standards for this kind of mechanical tests on hydrogel materials, it was necessary to develop a new Standard Operating Procedure for all the experiments performed.