Finding materials suitable for soft tissue replacement is an important aspect for medical devices design and fabrication. There is a need to develop a material that will not only display similar mechanical properties as the tissue it is replacing, but also shows improved life span, biocompatibility, nonthrombogenic, and low degree of calcification. Polyvinyl alcohol (PVA) is a hydrophilic biocompatible polymer with various characteristics desired for biomedical applications. PVA can be transformed into a solid hydrogel with good mechanical properties by physical crosslinking, using freeze-thaw cycles. Hydrophilic bacterial cellulose (BC) fibers of an average diameter of 50 nm are produced by the bacterium Acetobacter xylinum, using a fermentation process. They are used in combination with PVA to form biocompatible nanocomposites. The resulting nanocomposites possess a broad range of mechanical properties and can be made with mechanical properties similar to that of cardiovascular tissues, such as aorta and heart valve leaflets. The stress-strain properties for porcine aorta are matched by at least one type of PVA-BC nanocomposite in both the circumferential and the axial tissue directions. A PVA-BC nanocomposite with similar properties as heart valve tissue is also developed. Relaxation properties of all samples, which are important for cardiovascular applications, were also studied and found to relax at a faster rate and to a lower residual stress than the tissues they might replace. The new PVA-BC composite is a promising material for cardiovascular soft tissue replacement applications.

Polyvinyl alcohol (PVA) is a hydrophilic polymer with various characteristics desired for biomedical applications and can be transformed into a solid hydrogel by physical crosslinking, using a low-temperature thermal cycling process. As with most polymeric materials, the mechanical properties of the resultant PVA are isotropic, as oppose to most soft tissues, which are anisotropic. The objective of this research is to develop a PVA-based hydrogel that not only mimics the nonlinear mechanical properties displayed by cardiovascular tissues, but also their anisotropic behavior. By applying a controlled strain to the PVA samples, while undergoing low-temperature thermal cycling, we were able to create oriented mechanical properties in PVA hydrogels. The oriented stress-strain properties of porcine aorta were matched simultaneously by a PVA hydrogel prepared (10% PVA, cycle 3, 75% initial strain). This novel technique allows the controlled introduction of anisotropy to PVA hydrogel, and gives a broad range of control of its mechanical properties, for specific medical device applications.

Poly(vinyl alcohol) (PVA) hydrogels are formed by physical cross-linking through freeze/thaw cycles. By controlling the stress applied during the freeze/thaw process, anisotropic PVA hydrogels can be produced. An anisotropic PVA hydrogel conduit that mimics the nonlinear and anisotropic mechanical properties displayed by porcine aorta was developed. Preliminary structural characterization of isotropic and anisotropic PVA samples using small-angle neutron scattering reveals a polymer mesh cross-linked by crystallites spaced by about 18 nm and, most importantly, that the anisotropic properties are due to large-scale (>100 nm) structures alone; the geometry of the polymer mesh and crystallites remains largely unaltered. Controlling the properties of these anisotropic PVA hydrogels promises a broad range of potential applications in biomedical devices, such as coronary bypass grafts, where compliance mismatch between the implanted synthetic graft and the surrounding tissue has been identified as a major cause of failure.

Despite the established use of total joint replacement for the treatment of advanced degeneration of articular cartilage, component loosening due to wear and osteolysis limits the lifespan of these joint prostheses. In the present study, nanocomposites consisting of poly(vinyl alcohol) (PVA) and bacterial cellulose (BC) nanofibers were investigated as possible improved cartilage replacement materials. Nanocomposites were synthesized by adding small amounts (<1%) of BC to PVA, and subjecting the mixture to thermal cycling. The mechanical properties of the resulting material were evaluated using unconfined compression testing. By the addition of BC nanofibers to the PVA matrix, a nanocomposite with a wide range of compressive mechanical properties control was obtained, with elastic modulus values similar to those reported for native articular cartilage. The nanocomposite also showed improved strain-rate dependence and adequate viscoelastic properties. The PVA-BC nanocomposite is therefore a promising biomaterial to be considered as a possible replacement material for localized articular cartilage injuries and other orthopedic applications such as intervertebral discs.