Radiopaque, Iodine Functionalized, Phenylalanine-Based Poly(ester urea)s

Tunable shape memory properties of highly stretchable poly(ester urea) random copolymers based on α-amino acids

The exploration of biodegradable polymers with shape memory effects (SMEs) holds great promise in biomedical fields. Revealing the relationship between the SMEs and polymer structures not only contributes to interpreting the SME mechanisms, but also prompts the customization of materials properties for specific requirements. Herein, we developed a series of poly(ester urea) (PEU) random copolymers composed of two different diamine monomers based on L-alanine and L-valine, respectively. It was shown that the shape memory performance of the PEU copolymers strongly depended on the composition of two different diamine monomers in the PEU copolymers and other physical properties. This tunability likely arose from the change of polymer chain mobility and crystallinity, which were impacted by the choice of α-amino acids. Intriguingly, thin films of the PEU copolymers exhibited a high strain at break of 347-743% around the physiological temperature (35 °C). Moreover, the random copolymerization of two different sorts of diamine monomers has been demonstrated as a facile approach to precisely tailor the physical properties of the PEUs according to custom needs.

Radiopaque scaffolds based on electrospun iodixanol/polycaprolactone fibrous composites

Grafts based on biodegradable polymer scaffolds are increasingly used in tissue-engineering applications as they facilitate natural tissue regeneration. However, monitoring the position and integrity of these scaffolds over time is challenging due to radiolucency. In this study, we used an electrospinning method to fabricate biodegradable scaffolds based on polycaprolactone (PCL) and iodixanol, a clinical contrast agent. Scaffolds were implanted subcutaneously into C57BL/6 mice and monitored in vivo using longitudinal X-ray imaging and micro-computed tomography (CT). The addition of iodixanol altered the physicochemical properties of the PCL scaffold; notably, as the iodixanol concentration increased, the fiber diameter decreased. Radiopacity was achieved with corresponding signal enhancement as iodine concentration increased while exhibiting a steady time-dependent decrease of 0.96% per day in vivo. The electrospun scaffolds had similar performance with tissue culture-treated polystyrene in supporting the attachment, viability, and proliferation of human mesenchymal stem cells. Furthermore, implanted PCL-I scaffolds had more intense acute inflammatory infiltrate and thicker layers of maturing fibrous tissue. In conclusion, we developed radiopaque, biodegradable, biocompatible scaffolds whose position and integrity can be monitored noninvasively. The successful development of other imaging enhancers may further expand the use of biodegradable scaffolds in tissue engineering applications.

Antibiotic eluting poly(ester urea) films for control of a model cardiac implantable electronic device infection

Cardiac implantable electronic device (CIED) infections acquired during or after surgical procedures are a major complication that are challenging to treat therapeutically, resulting in chronic and sometimes fatal infections. Localized delivery of antibiotics at the surgical site could be used to supplement traditional systemic administration as a preventative measure. Herein, we investigate a cefazolin-eluting l-valine poly(ester urea) (PEU) films as a model system for localized antibiotic delivery for CIEDs. Poly(1-VAL-8) PEU was used to fabricate a series of antibiotic-loaded films with varied loading concentrations (2%, 5%, 10% wt/wt) and thicknesses (40 µm, 80 µm, 140 µm). In vitro release measurements show thickness and loading concentration influence the amount and rate of cefazolin release. Group 10%-140 µm (load-thickness) showed 22.5% release of active pharmaceutical ingredient (API) in the first 24 h and 81.2% of cumulative percent release through day 14 and was found most effective in bacterial clearance in vitro. This group was also effective in clearing a bacterial infection in a model in vivo rat study while eliciting a limited inflammatory response. Our results suggest the feasibility of cefazolin-loaded PEU films as an effective sustained release matrix for localized delivery of antibiotics. SIGNIFICANCE STATEMENT: Implant-associated infections acquired during surgical procedures are a major complication that have proven a challenge to treat clinically, resulting in chronic and sometimes fatal infections. In this manuscript, we investigate an antibiotic-eluting L-valine poly(ester urea) (PEU) films as a model system for localized delivery of cefazolin. Significantly, we demonstrate a wide variation in temporal delivery and dosing within this family of PEUs and show that the delivery can be extended by varying the film thickness. The in vivo results show efficacy in an infected wound model and suggest antibiotic loaded PEU films function as an effective sustained release matrix for localized delivery of antibiotics across a number of clinical indications.

Highly Cross-Linked Shape Memory Polymers with Tunable Oxidative and Hydrolytic Degradation Rates and Selected Products Based on Succinic Acid

Minimally invasive medical devices are of great interest, with shape memory polymers (SMPs) representing one such possibility for producing these devices. Previous work with low density, highly porous SMPs has demonstrated oxidative degradation, while attempts to incorporate hydrolytic degradation have resulted in rapidly decreasing glass transition temperature (T _g ), ultimately preventing strain fixity of the materials at clinically relevant temperatures. Through esterification of the amino alcohol triethanolamine, an alcohol containing network was synthesized and incorporated into SMPs. These ester networks were used to control the bulk morphology of the SMP, with the T _g remaining above 37 °C when 50% of the alcohol was contributed by the ester network. This methodology also yielded SMPs that could degrade through both hydrolysis and oxidation; by oxidation, the SMPs degrade at a similar rate as the control materials (0.2%/day mass) for the first 30 days, at which point the rate changes to 3.5%/day until the samples become too fragile to examine at 80 days. By comparison, control materials have lost approximately 30% of mass by 140 days, at a constant rate of degradation, demonstrating that the ester SMPs are a promising material system for producing more rapidly degradable, soft, porous biomaterials.

Three-Dimensional Printing of Nano Hydroxyapatite/Poly(ester urea) Composite Scaffolds with Enhanced Bioactivity

Polymer-bioceramic composites incorporate the desirable properties of each material while mitigating the limiting characteristics of each component. 1,6-Hexanediol l-phenylalanine-based poly(ester urea) (PEU) blended with hydroxyapatite (HA) nanocrystals were three-dimensional (3D) printed into porous scaffolds (75% porosity) via fused deposition modeling and seeded with MC3T3-E1 preosteoblast cells in vitro to examine their bioactivity. The resulting 3D printed scaffolds exhibited a compressive modulus of ∼50 MPa after a 1-week incubation in PBS at 37 °C, cell viability >95%, and a composition-dependent enhancement of radio-contrast. The influence of HA on MC3T3-E1 proliferation and differentiation was measured using quantitative real-time polymerase chain reaction, immunohistochemistry and biochemical assays. After 4 weeks, alkaline phosphatase activity increased significantly for the 30% HA composite with values reaching 2.5-fold greater than the control. Bone sialoprotein showed approximately 880-fold higher expression and 15-fold higher expression of osteocalcin on the 30% HA composite compared to those of the control. Calcium quantification results demonstrated a 185-fold increase of calcium concentration in mineralized extracellular matrix deposition after 4 weeks of cell culture in samples with higher HA content. 3D printed HA-containing PEU composites promote bone regeneration and have the potential to be used in orthopedic applications.

α-Amino Acid-Based Poly(Ester urea)s as Multishape Memory Polymers for Biomedical Applications

The thermal shape memory behavior of a series of α-amino acid-based poly(ester urea)s has been explored. We demonstrate that these materials exhibit excellent shape memory performance in dual- and triple-shape thermomechanical testing. Significant activation of chain mobility above the T_g as well as a hydrogen bonding network provide the basis for shape transformations and recovery. Additionally, we tuned the shape memory properties of these materials with polymer blending, enabling the demonstration of quadruple-shape memory cycles.