Novel polyurethanes with interconnected porous structure induce in vivo tissue remodeling and accompanied vascularization

In vitro degradation profiles and in vivo biomaterial-tissue interactions of microwell array delivery devices

To effectively apply microwell array cell delivery devices their biodegradation rate must be tailored towards their intended use and implantation location. Two microwell array devices with distinct degradation profiles, either suitable for the fabrication of retrievable systems in the case of slow degradation, or cell delivery systems capable of extensive remodeling using a fast degrading polymer, were compared in this study. Thin films of a poly(ethylene glycol)‐poly(butylene terephthalate) (PEOT‐PBT) and a poly(ester urethane) were evaluated for their in vitro degradation profiles over 34 weeks incubation in PBS at different pH values. The PEOT‐PBT films showed minimal in vitro degradation over time, while the poly(ester urethane) films showed extensive degradation and fragmentation over time. Subsequently, microwell array cell delivery devices were fabricated from these polymers and intraperitoneally implanted in Albino Oxford rats to study their biocompatibility over a 12‐week period. The PEOT‐PBT implants shown to be capable to maintain the microwell structure over time. Implants provoked a foreign body response resulting in multilayer fibrosis that integrated into the surrounding tissue. The poly(ester urethane) implants showed a loss of the microwell structures over time, as well as a fibrotic response until the onset of fragmentation, at least 4 weeks post implantation. It was concluded that the PEOT‐PBT implants could be used as retrievable cell delivery devices while the poly(ester urethane) implants could be used for cell delivery devices that require remodeling within a 4–12 week period.

A new waterborne chitosan-based polyurethane hydrogel as a vehicle to transplant bone marrow mesenchymal cells improved wound healing of ulcers in a diabetic rat model

Foot ulcers, a common complication of diabetes, can cause physical incapacity and are derived from several factors, including poor wound healing. New therapeutic strategies are needed to minimize this complication for the sake of patients' health. We therefore developed a new chitosan- polyurethane hydrogel membrane (HPUC) and the test results confirmed that HPUC present low cytotoxicity and improved wound healing when used with mononuclear bone marrow fraction cells in the diabetic rat model. The biodegradable hydrogels were produced in block copolymer networks with a combination of chitosan blocks and biodegradable polyurethane. The membranes were characterized by FTIR, ¹³C-NMR and thermogravimetry. Swelling and hydrolytic degradation were also evaluated. The non-solubility of the membranes in good solvents and the chemical characterization confirmed that the network structure was formed between the PU and the chitosan through urea/urethane bonds. The findings confirm that the HPUC have interesting properties that make them suitable for wound healing applications.

Characterization of biodegradable polyurethane nanoparticles and thermally induced self-assembly in water dispersion

Waterborne polyurethanes (PU) with different compositions of biodegradable oligodiols as the soft segment were synthesized as nanoparticles (NPs) in this study. Using dynamic light scattering (DLS), multiangle light scattering (MALS), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS), we demonstrated that these NPs were compact spheres with different shape factors. The temperature-dependent swelling of the PU NPs in water was distinct. In particular, PU NPs with 80 mol % polycaprolactone (PCL) diol and 20 mol % poly(L-lactide) (PLLA) diol as the soft segment had significant swelling (∼450%) at 37 °C. This was accompanied by a sol-gel transition observed in about 2 min for the NP dispersion. The thermally induced swelling and self-assembly of these NPs were associated with the secondary force (mainly hydrogen bonding) and degree of crystallinity, which depended on the soft segment compositions. The thermo-responsiveness of the PU NPs with mixed biodegradable oligodiols may be employed to design smart biodegradable carriers for delivery of cells or drugs near body temperature.

Obstacles in haemocompatibility testing

ISO 10993-4 is an international standard describing the methods of testing of medical devices for interactions with blood for regulatory purpose. The complexity of blood responses to biomaterial surfaces and the variability of blood functions in different individuals and species pose difficulties in standardisation. Moreover, in vivo or in vitro testing, as well as the clinical relevance of certain findings, is still matter of debate. This review deals with the major remaining problems, including a brief explanation of surface interactions with blood, the current ISO 10993 requirements for testing, and the role of in vitro test models. The literature is reviewed on anticoagulation, shear rate, blood-air interfaces, incubation time, and the importance of evaluation of the surface area after blood contact. Two test categories deserve further attention: complement and platelet function, including the effects on platelets from adhesion proteins, venipuncture, and animal derived- blood. The material properties, hydrophilicity, and roughness, as well as reference materials, are discussed. Finally this review calls for completing the acceptance criteria in the ISO standard based on a panel of test results.