Isotropic and anisotropic polyvinyl alcohol based hydrogels for biomedical applications.

摘要

One important criterion in the design of biomaterials suitable for soft tissue replacement is to closely match the orientation dependent mechanical properties between the targeted tissue and its replacement. 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 a low temperature thermal cycling process.;Most polymeric materials, including PVA and PVA-BC nanocomposite, are isotropic, as oppose to most soft tissues, which are anisotropic. By applying a controlled strain to the PVA samples, while undergoing low temperature thermal cycling, anisotropic PVA was successfully created. The oriented stress-strain properties of porcine aorta were matched simultaneously by a PVA hydrogel prepared. This novel technique allows the controlled introduction of anisotropy into PVA hydrogel, and gives a broad range of control of its mechanical properties, for specific medical device applications.;An anisotropic PVA-BC nanocomposite, with improved mechanical properties and degree of anisotropy than PVA, was successfully developed following a similar approach. By adding small amounts of BC to PVA, improved anisotropic properties were obtained. The anisotropy of porcine aorta was closely matched by one type of anisotropic PVA-BC nanocomposite within physiological range, with improved resistance to further stretch. The PVA-BC nanocomposite gives a broader range of control of mechanical properties, including anisotropy.;The structure of the physically crosslinked isotropic and anisotropic PVA was characterized using small angle neutron scattering (SANS). SANS results revealed the presence of crystallites of about 3 nm, with amorphous regions of the order of 16-9 nm, and that the anisotropic mechanical properties are mainly due to orientation of the large scale structures (>100 nm).;Bacterial cellulose (BC) fibers with an average diameter of 50 nm were produced by the bacterium Acetobacter xylinum using a fermentation process. These fibers were incorporated into PVA to create a PVA-BC nanocomposite with a broad range of mechanical properties. The stress-strain properties for porcine aorta were matched by at least one type of PVA-BC nanocomposite in either circumferential or axial directions. PVA-BC nanocomposites with similar properties as heart valve tissue were also developed. The new PVA-BC nanocomposite is a promising material for cardiovascular soft tissue replacement applications.;Keywords: Polyvinyl alcohol (PVA), bacterial cellulose (BC), hydrogel, nanocomposites, anisotropy, cardiovascular tissue, mechanical properties, vascular prosthesis, heart valve, biomedical devices.