A biodegradable slotted tube stent based on poly(L-lactide) and poly(4-hydroxybutyrate) for rapid balloon-expansion.

Safe vascular stent application requires rapid expansion of the stent to minimize the risk of procedural ischemia. While high expansion speeds can be achieved with metallic stents, they are not necessarily feasible with biodegradable polymeric stents due to the viscoelastic material behavior. This study reports on a novel biodegradable polymer blend material based on poly(L-lactide) (PLLA) and poly(4-hydroxybutyrate) (P4HB), and describes the mechanical properties and in vitro degradation behavior of a balloon-expandable slotted tube stent concept. The stent prototypes with nominal dimensions of 6.0 x 25 mm were manufactured by laser machining of solution cast PLLA/P4HB tubes (I.D. = 2.8 mm, d = 300 microm). The stents were expanded within 1 min by balloon inflation to 8 bar, after 5 min preconditioning in 37 degrees C water. Recoil and collapse pressure were 4.2% and 1.1 bar, respectively. During in vitro degradation collapse pressure initially increased to a maximum at 4 w and then decreased thereafter. After 48 w, molecular weight was decreased by 82%. In summary, the PLLA/P4HB slotted tube stents allowed for rapid balloon-expansion and exhibited adequate mechanical scaffolding properties suitable for a broad range of vascular and non-vascular applications.

Biomatrix/polymer composite material for heart valve tissue engineering.

BACKGROUND: Decellularized extracellular matrix has been suggested as a scaffold for heart valve tissue engineering or direct implantation. However, cell removal impairs the physical properties of the valve structure and exposes bare collagen fibers that are highly thrombogenic. Matrix/polymer hybrid valves with improved biological and mechanical characteristics may be advantageous. METHODS: Porcine aortic valves were decellularized enzymatically and impregnated with biodegradable poly(hydroxybutyrate) by a stepwise solvent exchange process. Biocompatibility was tested in vitro using cell proliferation and coagulation assays. Proinflammatory activity was assessed in vivo by implantation of matrix/polymer patches in the rabbit aorta. Biomechanic valve properties and fluid dynamics were tested in a pressure/flow-controlled pulse duplicating system. Matrix/polymer hybrid valves were implanted in pulmonary and aortic position in sheep. RESULTS: Biocompatibility assays indicated that human blood vessel cells survive and proliferate on matrix/polymer hybrid tissue. In vitro activation of cellular and plasmatic coagulation cascades was lower than with uncoated control tissue. After implantation in the rabbit aorta, matrix/polymer hybrid patches healed well, with complete endothelialization, mild leukocyte infiltration, and less calcification than control tissue. Matrix/polymer hybrid tissue had superior tensile strength and suture retention strength, and hybrid valves showed good fluid dynamic performance. The two valves in aortic position performed well, with complete endothelialization and limited inflammatory cell invasion after 12 weeks. Of the two valves in pulmonary position, one failed. CONCLUSIONS: Matrix/polymer hybrid tissue valves have good biological and biomechanic characteristics and may provide superior replacement valves.

Mechanical and structural properties of a novel hybrid heart valve scaffold for tissue engineering.

Hybrid heart valve scaffolds were fabricated from decellularized porcine aortic heart valve matrices and enhanced with bioresorbable polymers using different protocols: (i) dip coating of lyophilized decellularized matrices, and (ii) impregnation of wet decellularized matrices. The following polymers were evaluated: poly(4-hydroxybutyrate) and poly(3-hydroxybutyrate-co4-hydroxybutyrate). Tensile tests were conducted to assess the biomechanical behavior of valve leaflet strips. Suture retention strength was evaluated for the adjacent conduit. A pulse duplicator system was used for functional testing of the valves under physiological systemic load conditions. The properties of the hybrid structures were compared with native, decellularized, and glutaraldehyde-fixed specimens. Mechanisms of the polymer impregnation process were studied with IR spectroscopy, fluorescent microscopic imaging, and SEM. Altogether this study demonstrates the feasibility and improved biomechanical function of a novel hybrid heart valve scaffold for an application in tissue engineering.