Richard J. Zdrahala

Biomedical Applications of Polyurethanes: A Review of Past Promises, Present Realities, and a Vibrant Future

Polyurethanes, having extensive structure/property diversity, are one of the most bio- and blood-compatible materials known today. These materials played a major role in the development of many medical devices ranging from catheters to total artificial heart. Properties such as durability, elasticity, elastomer-like character, fatigue resistance, compliance, and acceptance or tolerance in the body during the healing, became often associated with polyurethanes. Furthermore, propensity for bulk and surface modification via hydrophilic/hydrophobic balance or by attachments of biologically active species such as anticoagulants or biorecognizable groups are possible via chemical groups typical for polyurethane structure. These modifications are designed to mediate and enhance the acceptance and healing of the device or implant. Many innovative processing technologies are used to fabricate functional devices, feeling and often behaving like natural tissue. The hydrolytically unstable polyester polyurethanes were replaced by more resistant but oxidation-sensitive polyether polyols based polyurethanes and their clones containing silicone and other modifying polymeric intermediates. Chronic in vivo instability, however, observed on prolonged implantation, became a major roadblock for many applications. Presently, utilization of more oxidation resistant polycarbonate polyols as soft segments, in combination with antioxidants such as Vitamin E, offer materials which can endure in the body for several years. The applications cover cardiovascular devices, artificial organs, tissue replacement and augmentation, performance enhancing coatings and many others. In situ polymerized, cross-linked systems could extend this biodurability even further. The future will expand this field by revisiting chemically-controlled biodegradation, in combination with a mini-version of RIM technology and minimally invasive surgical procedures, to form, in vivo, a scaffold, by delivery of reacting materials to the specific site in the body and polymerizing the mass in situ. This scaffold will provide anchor for tissue regeneration via cell attachment, proliferation, control of inflammation, and healing.

Bulk, surface, and blood-contacting properties of polyetherurethanes modified with polyethylene oxide

The bulk, surface, and blood-contacting properties of a series of polyether polyurethanes based on polyethylene oxide (PEO) (MW = 1450), polytetramethylene oxide (PTMO) (MW = 1000), and mixed PEO/PTMO soft segments were evaluated. The effect of varying the weight percentage of PEO, and thus the overall polarity of the mixed soft segment phase, was investigated. Two polymer blends prepared from a PTMO-based and a PEO-based polyurethane were also studied. Differential scanning calorimetry (DSC) and dynamic mechanical analysis indicated that the polyurethanes based on either the PEO or the PTMO soft segments are relatively phase mixed. The degree of phase mixing in the polymers increased with increasing weight fraction of PEO. As expected, water absorption and the hydrophilicity of the polymer increased with increasing PEO soft segment content. In vacuum, the PEO-rich polymers have a lower concentration of soft segment at the surface, possibly due to the migration of the polar PEO segments away from the polymer/vacuum interface. The blood-contacting results indicated that the higher PEO-containing polymers were more thrombogenic than the pure PTMO-based polyurethane. A threshold concentration of PEO in the polyurethane appeared to be required before the blood-contacting properties were significantly affected.

Bulk, surface and blood-contacting properties of polyether polyurethanes modified with polydimetnylsiloxane macroglycols

The bulk, surface and blood-contacting properties of a series of polyether polyurethanes, modified with three different polydimethylsiloxane (PDMS) macroglycol segments, were evaluated. The PDMS oligomers were terminated with hydroxy-tipped end groups of varying polarity. The effect of substituting the polytetramethylene oxide (PTMO) soft segment of a base polyurethane with 5 and 15 wt% of these PDMS-containing polyols was investigated. The ultimate tensile strength and elongation at break appeared to be the bulk properties most significantly affected by the addition of the PDMS-containing polyols. Underwater contact angle data indicate that the block copolymer surface became more hydrophilic with increasing PDMS content. In a vacuum, as determined from the ESCA data, the relatively non-polar PDMS soft segments preferentially oriented at the surface with increasing PDMS incorporation. Despite the variation in the surface properties, the blood compatibility of these polymers was not significantly affected by the addition of the PDMS-containing polyols.

Membranes for biomedical applications: Utilization of plasma polymerization for dimensionally stable hydrophilic membranes☆

Abstract Plasma polymerization techniques were utilized in the development of hydrophilic composite membranes having high hydrogen ion permeability and excellent dimensional stability. These membranes were prepared by using plasma polymerization of acrylic acid on porous polypropylene (PPA/PP) and plasma-initiated interpenetrating polymer network (IPN)-type polymerization of acrylic acid in porous polypropylene (PIPA/PP IPN). Hydrogen ion permeabilities of these membranes were determined. A hydrophilic composite membrane with high hydrogen ion permeability of acrylic acid polymer and excellent dimensional stability and mechanical strength of porous polypropylene was developed based on plasma IPN technique.