Improved Oxidative Biostability of Porous Shape Memory Polymers by Substituting Triethanolamine for Glycerol

In vitro and in vivo degradation correlations for polyurethane foams with tunable degradation rates

Polyurethane foams present a tunable biomaterial platform with potential for use in a range of regenerative medicine applications. Achieving a balance between scaffold degradation rates and tissue ingrowth is vital for successful wound healing, and significant in vivo testing is required to understand these processes. Vigorous in vitro testing can minimize the number of animals that are required to gather reliable data; however, it is difficult to accurately select in vitro degradation conditions that can effectively mimic in vivo results. To that end, we performed a comprehensive in vitro assessment of the degradation of porous shape memory polyurethane foams with tunable degradation rates using varying concentrations of hydrogen peroxide to identify the medium that closely mimics measured in vivo degradation rates. Material degradation was studied over 12 weeks in vitro in 1%, 2%, or 3% hydrogen peroxide and in vivo in subcutaneous pockets in Sprague Dawley rats. We found that the in vitro degradation conditions that best predicted in vivo degradation rates varied based on the number of mechanisms by which the polymer degraded and the polymer hydrophilicity. Namely, more hydrophilic materials that degrade by both hydrolysis and oxidation require lower concentrations of hydrogen peroxide (1%) to mimic in vivo rates, while more hydrophobic scaffolds that degrade by oxidation alone require higher concentrations of hydrogen peroxide (3%) to model in vivo degradation. This information can be used to rationally select in vitro degradation conditions that accurately identify in vivo degradation rates prior to characterization in an animal model.

Shape Memory Poly(β-hydroxythioether) Foams for Oil Remediation in Aquatic Environments

Shape memory poly(β-hydroxythioether) foams were produced using organobase catalyzed reactions between epoxide and thiol monomers, allowing for the rapid formation of porous media within approximately 5 min, confirmed using both rheology and physical foam blowing. The porous materials possess ultralow densities (0.022 g × cm^-3) and gel fractions of approximately 93%. Thermomechanical characterizations of the materials revealed glass transition temperatures tunable from approximately 50 to 100 °C, elastic moduli of approximately 2 kPa, and complete strain recovery upon heating of the sample above its glass transition temperature. The foams were characterized for their ability to take up oil from an aqueous multilayered ideal environment, revealing more than 2000% mass of oil (relative to the foam mass) could be collected. Importantly, while post-fabrication functionalization was possible with isocyanate chemistry followed by addition of hexadecanethiol or 3,3-bis(hexadecylthio)propan-1-ol, the oil collection efficiency of the system was not significantly enhanced, indicating that these materials, as porous media, possess unique attributes that make them appealing for environmental remediation without the need for costly modifications or manipulations.

Biobased polyurethanes for biomedical applications

Polyurethanes (PUs) are a major family of polymers displaying a wide spectrum of physico-chemical, mechanical and structural properties for a large range of fields. They have shown suitable for biomedical applications and are used in this domain since decades. The current variety of biomass available has extended the diversity of starting materials for the elaboration of new biobased macromolecular architectures, allowing the development of biobased PUs with advanced properties such as controlled biotic and abiotic degradation. In this frame, new tunable biomedical devices have been successfully designed. PU structures with precise tissue biomimicking can be obtained and are adequate for adhesion, proliferation and differentiation of many cell's types. Moreover, new smart shape-memory PUs with adjustable shape-recovery properties have demonstrated promising results for biomedical applications such as wound healing. The fossil-based starting materials substitution for biomedical implants is slowly improving, nonetheless better renewable contents need to be achieved for most PUs to obtain biobased certifications. After a presentation of some PU generalities and an understanding of a biomaterial structure-biocompatibility relationship, recent developments of biobased PUs for non-implantable devices as well as short- and long-term implants are described in detail in this review and compared to more conventional PU structures.

The Difference in Molecular Orientation and Interphase Structure of SiO2/Shape Memory Polyurethane in Original, Programmed and Recovered States during Shape Memory Process

In order to further understand the shape memory mechanism of a silicon dioxide/shape memory polyurethane (SiO₂/SMPU) composite, the thermodynamic properties and shape memory behaviors of prepared SiO₂/SMPU were characterized. Dynamic changes in the molecular orientation and interphase structures of SiO₂/SMPU during a shape memory cycle were then discussed according to the small angle X-ray scattering theory, Guinier’s law, Porod approximation, and fractal dimension theorem. In this paper, a dynamic mechanical analyzer (DMA) helped to determine the glass transition start temperature (T_g) by taking the onset point of the sigmoidal change in the storage modulus, while transition temperature (T_trans) was defined by the peak of tan δ, then the test and the calculated results indicated that the T_g of SiO₂/SMPU was 50.4 °C, and the T_trans of SiO₂/SMPU was 72.18 °C. SiO₂/SMPU showed good shape memory performance. The programmed SiO₂/SMPU showed quite obvious microphase separation and molecular orientation. Large-size sheets and long-period structures were formed in the programmed SiO₂/SMPU, which increases the electron density difference. Furthermore, some hard segments had been rearranged, and their gyration radii decreased. In addition, several defects formed at the interfaces of SiO₂/SMPU, which caused the generation of space charges, thus leading to local electron density fluctuations. The blurred interphase structure and the intermediate layer formed in the programmed SiO₂/SMPU and there was evident crystal damage and chemical bond breakage in the recovered SiO₂/SMPU. Finally, the original and recovered SiO₂/SMPU samples belong to the surface fractal system, but the programmed sample belongs to the mass fractal and reforms two-phase structures. This study provides an insight into the shape memory mechanism of the SiO₂/SMPU composite.

Biodegradable shape memory polymer foams with appropriate thermal properties for hemostatic applications

Shape memory polymer (SMP) foams are a promising material for hemostatic dressings due to their biocompatibility, high surface area, excellent shape recovery, and ability to quickly initiate blood clotting. Biodegradable SMP foams could eliminate the need for a secondary removal procedure of hemostatic material from the patients' wound, further facilitating wound healing. In this study, we developed hydrolytically and oxidatively biodegradable SMP foams by reacting polyols (triethanolamine or glycerol) with 6-aminocaproic acid or glycine to generate foaming monomers with degradable ester bonds. These monomers were used in foam synthesis to provide highly crosslinked SMP foam structures. The ester-containing foams showed clinically relevant thermal properties that were comparable to controls and excellent shape recovery within eight min. Triethanolamine-based ester-containing foams showed interconnected porous structure along with increased mechanical strength. Faster hydrolytic and oxidative biodegradation rates were achieved in ester-containing foams in comparison to controls. These biodegradable SMP foams with clinically applicable thermal properties possess great potential as an effective hemostatic device for use in hospitals or on battlefields.

Terpene- and terpenoid-based polymeric resins for stereolithography 3D printing

Thiol–ene ‘click’ reactions between terpenes and a four-arm thiol were utilized to produced thermoset 3D printed structures using vat photopolymerisation.