Biomedical Applications of Bacterial Cellulose Fermentation, Morphology and Surface Properties

Doktorsavhandling, 2007

Because average life expectancy has increased and people’s lifestyles have changed, degenerative diseases have become a critical issue. The demand for biomedical materials to replace or improve major body systems (skeletal, circulatory and nervous, etc.) will increase as people strive to maintain good quality of life. Cellulose is the most abundant naturally occurring polymer and is an inexhaustible resource for raw materials. Bacterial cellulose (BC) resembles human tissue in the sense that it is soft and is composed of highly hydrated nano fibrils with high mechanical strength. The material is versatile and can be manufactured in various sizes and shapes depending on the product requirements. This makes it interesting to explore BC for use in several biomedical applications. In this work bacterial cellulose was fermented into tubular and meniscus form. The material properties were evaluated with a focus on mechanical, morphological and surface properties for applications such as blood vessels and meniscus substitutes. Bacterial cellulose tubes with asymmetric morphology and an “onion like” multilayer structure were produced by optimizing the oxygen ratio during fermentation. The inner lumen of the tube was smooth and promoted the adhesion and formation of a confluent layer of endothelial cells. The outer layer was more open, to allow cell ingrowth. The mechanical properties were improved by an increase in the oxygen ratio. A maximal burst pressure value of 880mmHg was recorded for tubes produced at 100% oxygen ratio, which is far higher than physiological blood pressure. The material was proven to be biocompatible, subcutaneous in rats. There were no foreign body reactions or encapsulation of the material. Instead newly formed blood vessels could be seen as well as ingrowth of cells and production of tissue in the material. Modification of the cellulose with xyloglucan bearing an adhesion peptide improved the adhesion of endothelial cells with an unaffected morphology of the cellulose network. The nano fibrils were also surface modified with ionic groups and decorated with calcium phosphate to improve bone adhesion and later fixation of the material as a future meniscus substitute. Initial mechanical properties of BC in compression and tensile load revealed that BC has advantageous mechanical properties compared to collagen material and has the same Young’s modulus in compression load as a pig meniscus. This research contributes to knowledge of tubular fermentation and the mechanical, morphological properties thereof and has developed two novel surface modifications to improve cell adhesion to the nano cellulose. The results can be used as a starting point for new optimization and developments of new generations of cardiovascular and orthopaedic implants using microbially derived cellulose.