Rapid synthesis of degradable ester/thioether monomers and their incorporation into thermoset polyurethane foams for traumatic wound healing

Polyurethane (PUr) foam hemostatic dressings are highly effective at controlling bleeding in traumatic wounds, but their traditionally slow degradation rate requires dressing removal, which could result in wound rebleeding. Incorporating degradable linkages into the PUr network can provide a biodegradable dressing that could be left in place during healing, eliminating rebleeding upon removal and providing scaffolding for new tissue ingrowth with no remains of the applied dressing after healing. In this work, a library of degradable PUr foams was synthesized from degradable monomers based on hydrolytically labile esters and oxidatively labile thioethers using rapid click-chemistry reactions. In a twelve-week in vitro degradation study in 3% hydrogen peroxide and 0.1 M sodium hydroxide, incorporation of degradable monomers resulted in significantly increased PUr foam mass loss, offering biodegradable foam dressings that could better match the rate of traumatic wound healing. Changes to foam chemical, mechanical, thermal, and physical properties throughout degradation were also analyzed. Furthermore, the degradable PUr foams had increased platelet interactions, which could improve foam-induced clotting for a more effective hemostatic dressing. Overall, a biodegradable PUr foam hemostatic dressing could significantly improve healing outcomes in traumatic wounds. STATEMENT OF SIGNIFICANCE: A simple, solvent-free, rapid synthesis technique was developed to provide degradable polythiol monomers for use in polyurethane synthesis. The degradable monomers were incorporated into hemostatic polyurethane foams to provide materials with tunable degradation rates within clinically-relevant time frames. The resulting foams and their degradation byproducts were cytocompatible and hemocompatible, and foams made with the new degradable monomers had enhanced blood clotting, enabling their future use as hemostatic dressings.

A Nonclinical Safety Evaluation of Cold Atmospheric Plasma for Medical Applications: The Role of Genotoxicity and Mutagenicity Studies

Atmospheric nonthermal plasma (ANTP) has rapidly evolved as an innovative tool in biomedicine with various applications, especially in treating skin diseases. In particular, the formation of reactive oxygen species (ROS) and nitrogen species (RNS), which are generated by ANTP, plays an important role in the biological signaling pathways of human cells. Unfortunately, excessive amounts of these reactive species significantly result in cellular damage and cell death induction. To ensure the safe application of ANTP, preclinical in vitro studies must be conducted before proceeding to in vivo or clinical trials involving humans. Our study aimed to investigate adverse effects on genetic substances in murine fibroblast cells exposed to ANTP. Cell viability and proliferation were markedly reduced after exposing the cells with plasma. Both extracellular and intracellular reactive species, especially RNS, were significantly increased upon plasma exposure in the culture medium and the cells. Notably, significant DNA damage in the cells was observed in the cells exposed to plasma. However, plasma was not classified as a mutagen in the Ames test. This suggested that plasma led to the generation of both extracellular and intracellular reactive species, particularly nitrogen species, which affect cell proliferation and are also known to induce genetic damage in fibroblast cells. These results highlight the genotoxic and mutagenic effects of ANTP, emphasizing the need for the cautious selection of plasma intensity in specific applications to avoid adverse side effects resulting from reactive species production.

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.

Development and Characterization of Oxidatively Responsive Thiol-Ene Networks for Bone Graft Applications

First metatarsophalangeal joint (MPJ) arthroplasty procedures are a common podiatric procedure. However, almost one-third of cases require revision surgeries because of nonunions. Revision or salvage surgery requires more extensive hardware and bone grafts to recreate the first metatarsal. Unfortunately, salvage surgeries have a similar rate of failure attributed to delayed healing, bone graft dissolution, and the lack of bone ingrowth. Furthermore, patients who suffer from neuropathic comorbidities such as diabetes suffer from a diminished healing capacity. An increase in proinflammatory factors and the high presence of reactive oxygen species (ROS) present in diabetics are linked to lower fusion rates. To this end, there is a need for a clinically relevant bone graft to promote bone fusions in patients with neuropathic comorbidities. Incorporating thiol-ene networks for bone scaffolds has demonstrated increased osteogenic biomarkers over traditional polymeric materials. Furthermore, thiol-ene networks can act as antioxidants. Sulfide linkages within the network have an inherent ability to consume radical oxygen to create sulfoxide and sulfone groups. These unique properties of thiol-ene networks make them a promising candidate as bone grafts for diabetic patients. In this work, we propose a thiol-ene biomaterial to address the current limitations of MPJ fusion in diabetics by characterizing mechanical properties, degradation rates under accelerated conditions, and oxidative responsiveness under pathophysiologic conditions. We also demonstrated that thiol-ene-based materials could reduce the number of hydroxyl radicals associated with neuropathic comorbidities.

Controlling Morphology and Physio-Chemical Properties of Stimulus-Responsive Polyurethane Foams by Altering Chemical Blowing Agent Content

Amorphous shape memory polymer foams are currently used as components in vascular occlusion medical devices such as the IMPEDE and IMPEDE-FX Embolization Plugs. Body temperature and moisture-driven actuation of the polymeric foam is necessary for vessel occlusion and the rate of expansion is a function of physio-chemical material properties. In this study, concentrations of the chemical blowing agent for the foam were altered and the resulting effects on morphology, thermal and chemical properties, and actuation rates were studied. Lower concentration of chemical blowing agent yielded foams with thick foam struts due to less bubble formation during the foaming process. Foams with thicker struts also had high tensile modulus and lower strain at break values compared to the foams made with higher blowing agent concentration. Additionally, less blowing agent resulted in foams with a lower glass transition temperature due to less urea formation during the foaming reaction. This exploratory study provides an approach to control thermo-mechanical foam properties and morphology by tuning concentrations of a foaming additive. This work aims to broaden the applications of shape memory polymer foams for medical use.