Enhanced Flame Retardancy of Rigid Polyurethane Foams by Polyacrylamide/MXene Hydrogel Nanocomposite Coating.

Rigid polyurethane foam (RPUF) has been widely used in many fields, but its high flammability and frequent release of large amounts of toxic smoke during combustion limit its application. Hydrogel coatings, as a kind of environmentally friendly material, contain large amounts of water, which is beneficial to flame retardance of RPUF. MXene, as a two-dimensional inorganic nanomaterial, possesses a large specific surface area and good thermal stability, performing well in smoke suppression and as a physical barrier for flammable gas products and heat. Herein, to address the fire hazards of RPUF, MXene nanosheets were first grafted with double bonds, and then introduced into a polyacrylamide hydrogel system by radical polymerization to prepare MXene-based hydrogel coating (PAAm-MXene). The flame-retardant RPUF (coated RPUF) was prepared by painting the PAAm-MXene coating onto RPUF surface. The dispersion of modified MXene nanosheets (m-MXene) in hydrogels is improved compared with pristine MXene, and the addition of m-MXene contributes to the thermal stability enhancement of PAAm-MXene. Cone calorimetry, water retention test, and open flame combustion test were used to study the flame retardancy, smoke suppression, and water retention of flame-retardant RPUF. The coated RPUF exhibited significant flame retardancy, including reduced peak heat release rate (pHRR) at a maximum by 25.8%, and total heat release rate (THR) at a maximum by 24.6%, and total smoke production at a maximum by 38.9%. The results show that both MXene and m-MXene can improve the flame retardancy, smoke suppression, and water retention of hydrogels, but m-MXene has a better smoke suppression effect than MXene. That can be ascribed to the better dispersion of m-MXene than pristine MXene. The detailed performance improvement mechanisms are proposed. This work will not only improve the flame retardancy of RPUF, but also promotes the exploration of new flame-retardant strategies for RPUF.

Impact of surface biofunctionalization strategies on key effector cells response in polyacrylamide hydrogels for bone regeneration.

Despite the clinical prevalence of various bone defect repair materials, a full understanding of their influence on bone repair and regeneration remains elusive. This study focuses on poly(acrylamide) (PAAm) hydrogels, popular 2D model substrates, which have regulable mechanical properties within physiological. However, their bio-inert nature requires surface biofunctionalization to enhance cell-material interactions and facilitate the study of bone repair mechanisms. We utilized PAAm hydrogels of varying stiffness (18, 76 and 295 kPa), employed sulfosuccinimidyl-6-(4'-azido-2'-nitropheny-lamino) hexanoate (sulfo-SANPAH) and N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride/N-hydroxysuccinimidyl acrylate (EDC/NHS) as crosslinkers, and cultured macrophages, endothelial cells, and bone mesenchymal stem cells on these hydrogels. Our findings indicated that sulfo-SANPAH's crosslinking efficiency surpassed that of EDC/NHS, irrespective of pore size and stiffness. Importantly, we observed that the stiffness and surface biofunctionalization method of hydrogels significantly impacted cell adhesion and proliferation. The collagen-modified hydrogels by EDC/NHS strategy failed to support the normal biological behavior of bone mesenchymal stem cells and hindered endothelial cell spreading. In contrast, these modified hydrogels by the sulfo-SANPAH method showed good cytocompatibility with the three types of cells. This study underscores the critical role of appropriate conjugation strategies for PAAm hydrogels, providing valuable insights for hydrogel surface modification in bone repair and regeneration research.

In Situ Photopolymerization of Acrylamide Hydrogel to Coat Cellulose Acetate Nanofibers for Drug Delivery System.

In this study we developed electrospun cellulose acetate nanofibers (CANFs) that were loaded with a model non-steroidal anti-inflammatory drug (NSAID) (ibuprofen, Ib) and coated with poly(acrylamide) (poly-AAm) hydrogel polymer using two consecutive steps: an electrospinning process followed by photopolymerization of AAm. Coated and non-coated CANF formulations were characterized by several microscopic and spectroscopic techniques to evaluate their physicochemical properties. An analysis of the kinetic release profile of Ib showed noticeable differences due to the presence or absence of the poly-AAm hydrogel polymer. Poly-AAm coating facilitated a constant release rate of drug as opposed to a more conventional burst release. The non-coated CANFs showed low cumulative drug release concentrations (ca. 35 and 83% at 5 and 10% loading, respectively). Conversely, poly-AAm coated CANFs were found to promote the release of drug (ca. 84 and 99.8% at 5 and 10% loading, respectively). Finally, the CANFs were found to be superbly cytocompatible.