Staphylococcus aureus is one of the representative foodborne pathogens which forms biofilm. Antibiotics are widely applied in livestock husbandry to maintain animal health and productivity, thus contribute to the dissemination of antimicrobial resistant livestock and human pathogens, and pose a significant public health threat. Effect of antibiotic pressure on S. aureus biofilm formation, as well as the mechanism, remains unclear. In this study, the regulatory mechanism of low concentration of ampicillin on S. aureus biofilm formation was elucidated. The viability and biomass of biofilm with and without 1/4 MIC ampicillin treatment for 8 h were determined by XTT and crystal violet straining assays, respectively. Transcriptomics analysis on ampicillin-induced and non-ampicillin-induced biofilms were performed by RNA-sequencing, differentially expressed genes identification and annotation, GO functional and KEGG pathway enrichment. The viability and biomass of ampicillin-induced biofilm showed dramatical increase compared to the non-ampicillin-induced biofilm. A total of 530 differentially expressed genes (DEGs) with 167 and 363 genes showing up- and down-regulation, respectively, were obtained. Upon GO functional enrichment, 183, 252, and 21 specific GO terms in biological process, molecular function and cellular component were identified, respectively. Eight KEGG pathways including “Microbial metabolism in diverse environments”, “S. aureus infection”, and “Monobactam biosynthesis” were significantly enriched. In addition, “beta-lactam resistance” pathway was also highly enriched. In ampicillin-induced biofilm, the significant up-regulation of genes encoding multidrug resistance efflux pump AbcA, penicillin binding proteins PBP1, PBP1a/2, and PBP3, and antimicrobial resistance proteins VraF, VraG, Dlt, and Aur indicated the positive response of S. aureus to ampicillin. The up-regulation of genes encoding surface proteins ClfB, IsdA, and SasG and genes (cap5B and cap5C) which promote the adhesion of S. aureus in ampicillin induced biofilm might explain the enhanced biofilm viability and biomass.
Shape-memory polymeric materials triggered by body temperature were fabricated via toughening sustainable poly(propylene carbonate) (PPC) with thermoplastic polyurethane (TPU). With an addition of TPU through melt blending, the ductility of PPC was dramatically enhanced, leading to the increase of shape recoverability but a deterioration of shape fixity. Remarkably, the blend containing 50 wt % TPU (PT50) presented the optimal shape-memory effect (SME) with balanced shape recovery and shape fixation performances because of the formation of the co-continuous structure promoting the synergy between PPC and TPU. Moreover, the PT50 sample exhibited significant improvement in not only the shape recovery ratio (∼95.0% recovery) but also the recovery speed and recovery stress, which enabled it to achieve an excellent SME when applied in practical use. After processed into a spiral-like stent, PT50 still showed a fast response to 37 °C, giving an efficient self-expansion within only 20 s. Besides, the blood and cell compatibility testing results revealed the good biocompatibility of PT50, further demonstrating the great potential of this material for development of biomedical stents.
Multilayered shape-memory composites composed of multiwalled carbon nanotube (MWCNT)-filled thermoplastic polyurethane (TPU) (denoted as cTPU) and polycaprolactone (PCL) were prepared through layer-multiplying coextrusion. The phase interfaces and conductive pathways in the multilayered structure which can be tailored by layer-multiplying endowed the materials with tunable thermo-and electro-responsive shapememory effects (TSME and ESME). Compared with the conventional blending composite having the same compositions, the cTPU/PCL multilayered system with high phase continuity and abundantly continuous interfaces exhibited better TSME, which could be further enhanced with increasing the layer number. It was revealed that the strain energy stored in cTPU layers would be balanced by adjacent PCL layers via interfacial shearing effect so that each domain could endow the maximum contribution to the shape-memory performance. Besides, the confined layer space allowed for a more compact connection between the MWCNTs than in the blending composite, while the original conductive network formed in cTPU tended to be gradually broken up during layer multiplying. Moreover, an excessive conductivity may induce local overheating and even the melting of permanent domains, leading to undesired deformation. Accordingly, the multilayered composite with a proper layer number which exhibited suitable conductivity and efficient TSME achieved balanced ESME with quick recovery speed, excellent recovery ratio, and good appearance retention. This work opened an avenue in preparing outstanding shape-memory materials with both thermal and electrical actuations, which showed great potential in applications of sensors, actuators, self-deployable devices, and so forth.
In this work, inspired by the hierarchical architecture of nacre, we have fabricated poly(propylene carbonate) (PPC)/thermoplastic polyurethane (TPU) alternating multilayer films via layer-multiplying coextrusion. Based on the glass transition at around 37 °C of PPC, the multilayer films exhibited an outstanding body heat-responsive shape-memory effect (SME) with high shape fixation and recovery ratios (96.1 and 93.6%), much better than the conventional cocontinuous blend with the same compositions. It was revealed that the high phase continuity and abundantly two-dimensional interfaces both capable of promoting stress transferring and load distribution maximally contributed to the SME. Furthermore, the multilayer films showed a superior recovery stress storage capacity and the force generated by shape recovery allowed automatic expansion of the spiral in 37 °C water and efficient lifting of a load 880 times its weight. Different from the opacity of the blend, a high optical transparence was observed in the multilayers because of the parallel assembly of transparent PPC and TPU enabling light to directly pass through the films. Besides, the nacre-like films had layer debonding and layer stepwise breaking during stretching, resulting in a 90% increase in tensile strength, a 70% increase in elongation at break, and onefold improvement in yield stress, compared with those of the blend. Our approach paves a new way for developing bioinspired structural materials with excellent optical, mechanical, and shape-memory properties, which can be extended to different amorphous polymers and elastomers. Also, the materials presented herein have great potential in applications of biomedical devices and soft robotics.
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