Bacterial Cellulose as a new biomaterial for bioprosthetic heart valves

Abstract

As the population ages and the know-how of the medical field progresses, the number of surgical interventions is rapidly expanding. Heart valve replacement surgery is no exception to this phenomenon; every year 280 000 heart valve replacement surgeries are performed worldwide.Despite the success of heart valve replacement surgeries, various notable drawbacks hinder its advancement. Mechanical heart valves require anticoagulant therapy to reduce the risk of thromboembolisms, thereby also introducing anticoagulant-induced haemorrhage. Further-more, the need for anticoagulant therapy makes the mechanical valve undesirable for woman who desire a pregnancy. Bioprosthetic heart valves suffer from structural valve deterioration and therefore need to be replaced after less than 15 years. Replacement surgery is dangerous,with an increased mortality rate of up to 20%. Furthermore, heart valve prosthetics do not allow for native cell tissue ingrowth, limiting their ability to self-repair and grow, the latter being of especially high importance in pediatric heart valve surgeries.A promising new concept is the tissue engineered prosthetic heart valve, which would hypothetically remove the need for anticoagulent use, allow for self-repair and growth and increase the durability of heart valve prosthetics. The process of creating a Tissue Engineered Heart Valve (TEHV) is, however, complex, and an optimal scaffold is yet to be found.Bacterial Cellulose (BC) is hypothesised to be a feasible scaffold and material for use in heart valve prostheses. BC is a biogenic polymer with a chemical structure not unlike collagen. The material is produced by, among others, the bacterium Acetobacter Xylinus. BC has been shown to have considerable mechanical strength and low thrombogenicity. Furthermore,a study in rat models has indicated no inflammatory or foreign body response to implanted cellulose. Bacterial cellulose is already successfully in use as wound dressing, and has been utilised to produce feasible vascular grafts. However, to the knowledge of the author, pure BC has not yet been used for the production of prosthetic heart valves.BC has been cultured statically with a novel method of automatic medium exchange, and rotational with a specially designed rotation device.The BC cultured with the novel method of automatic medium exchange, is more stable and stronger than patches cultured with the previous culturing protocol. However, BC cultured using the rotary device is unstable and fragile. The rotary culturing protocol needs to be improved in order to result in feasible BC tubes for the production of heart valves.The BC shows strain levels slightly stiffer, but relatively similar to those of human pericardium. Furthermore, creep behaviour is, as with pericardium, insignificant under cyclic loading conditions.More patches need to be cultured in order to increase the sample size, and thereby produce more conclusive results. The results already gathered in this master thesis research, show that BC material has promising mechanical characteristics, possibly rendering it a feasible option for the use in bioprosthetic heart valves