Hengchong Shi

Surface modification of poly(styrene-b-(ethylene-co-butylene)-b-styrene) elastomer via UV-induced graft polymerization of N-vinyl pyrrolidone

Poly(N-vinyl pyrrolidone) (PNVP) was covalently grafted onto the surface of biomedical poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) elastomer via a technique of UV-induced graft polymerization combined with plasma pre-treatment. The surface graft polymerization of N-vinyl pyrrolidone (NVP) was confirmed by ATR-FTIR and XPS. Effect of the parameters of graft polymerization, i.e., the initiator concentration, the UV irradiation time and the monomer concentration on the grafting density was investigated. The morphology and the wettability of the PNVP-modified surfaces were characterized by AFM and DSA, respectively. Protein adsorption and platelet adhesion were obviously suppressed after PNVP was grafted onto the SEBS substrates.

Fabricating a Cycloolefin Polymer Immunoassay Platform with a Dual-Function Polymer Brush via a Surface-Initiated Photoiniferter-Mediated Polymerization Strategy

The development of technologies for a biomedical detection platform is critical to meet the global challenges of various disease diagnoses. In this study, an inert cycloolefin polymer (COP) support was modified with two-layer polymer brushes possessing dual functions, i.e., a low fouling poly[poly(ethylene glycol) methacrylate] [p(PEGMA)] bottom layer and a poly(acrylic acid) (PAA) upper layer for antibody loading, via a surface-initiated photoiniferter-mediated polymerization strategy for fluorescence-based immunoassay. It was demonstrated through a confocal laser scanner that, for the as-prepared COP-g-PEG-b-PAA-IgG supports, nonspecific protein adsorption was suppressed, and the resistance to nonspecific protein interference on antigen recognition was significantly improved, relative to the COP-g-PAA-IgG references. This strategy for surface modification of a polymeric platform is also applicable to the fabrication of other biosensors.

Improved biocompatibility of poly (styrene-b-(ethylene-co-butylene)-b-styrene) elastomer by a surface graft polymerization of hyaluronic acid

Hyaluronic acid (HA) is an important component of extracellular matrix (ECM) in many tissues, providing a hemocompatible and supportive environment for cell growth. In this study, glycidyl methacrylate-hyaluronic acid (GMHA) was first synthesized and verified by proton nuclear magnetic resonance ((1)H NMR) spectroscopy. GMHA was then grafted to the surface of biomedical elastomer poly (styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) via an UV-initiated polymerization, monitored by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The further improvement of biocompatibility of the GMHA-modified SEBS films was assessed by platelet adhesion experiments and in vitro response of murine osteoblastic cell line MC-3T3-E1 with the virgin SEBS surface as the reference. It showed that the surface modification with HA strongly resisted platelet adhesion whereas improved cell-substrate interactions.

Facile Fabrication of Lubricant-Infused Wrinkling Surface for Preventing Thrombus Formation and Infection

Despite the advanced modern biotechniques, thrombosis and bacterial infection of biomedical devices remain common complications that are associated with morbidity and mortality. Most antifouling surfaces are in solid form and cannot simultaneously fulfill the requirements for antithrombosis and antibacterial efficacy. In this work, we present a facile strategy to fabricate a slippery surface. This surface is created by combining photografting polymerization with osmotically driven wrinkling that can generate a coarse morphology, and followed by infusing with fluorocarbon liquid. The lubricant-infused wrinkling slippery surface can greatly prevent protein attachment, reduce platelet adhesion, and suppress thrombus formation in vitro. Furthermore, E. coli and S. aureus attachment on the slippery surfaces is reduced by ∼98.8% and ∼96.9% after 24 h incubation, relative to poly(styrene-b-isobutylene-b-styrene) (SIBS) references. This slippery surface is biocompatible and has no toxicity to L929 cells. This surface-coating strategy that effectively reduces thrombosis and the incidence of infection will greatly decrease healthcare costs.

Nonleaching Bacteria-Responsive Antibacterial Surface Based on a Unique Hierarchical Architecture

Bacteria-responsive surfaces popularly exert their smart antibacterial activities by bacteria-triggered delivery of antibacterial agents; however, the antibacterial agents should be additionally reloaded for the renewal of these surfaces. Herein, a reversible, nonleaching bacteria-responsive antibacterial surface is prepared by taking advantage of a hierarchical polymer brush architecture. In this hierarchical surface, a pH-responsive poly(methacrylic acid) (PMAA) outer layer serves as an actuator modulating the surface behavior on demand, while antimicrobial peptides (AMP) are covalently immobilized on the inner layer. The PMAA hydration layer renders the hierarchical surface resistant to initial bacterial attachment and biocompatible under physiological conditions. When bacteria colonize the surface, the bacteria-triggered acidification allows the outermost PMAA chains to collapse, therefore exposing the underlying bactericidal AMP to on-demand kill bacteria. In addition, the dead bacteria can be released once the PMAA chains resume their hydrophilicity because of the environmental pH increase. The functionality of the nonleaching surface is reversible without additional reloading of the antibacterial agents. This approach provides a new methodology for the development of smart surfaces in a variety of practical biomedical applications.

Core/shell rubber toughened polyamide 6: an effective way to get good balance between toughness and yield strength

We have recently shown that by adding 10 to 30 wt% core/shell toughener with a low density polyethylene (LDPE) core and a polybutadiene-g-maleic anhydride (PB-g-MAH) rubber shell to polyamide 6 (PA6), the impact strength of PA6 matrix can be significantly increased by 600–1000%. However, this is at the expense of quite large losses in elastic modulus of 10–25% and tensile yield strength of 30–55%, especially at high core/shell rubber loading (e.g., 30 wt%). In this study, we have redressed this problem by replacing the LDPE core with a polypropylene (PP) core, which has both higher elastic modulus and yield strength than that of LDPE, forming a new core/shell (PP/PB-g-MAH) toughener. When this core/shell toughener containing 5 wt% PB-g-MAH is blended with PA6 in the weight ratios of 10/90 and 30/70, the Izod impact strengths are 390 and 480 J m−1 (which are 330 and 550% increases compared to neat PA6), and the modulus are 2.37 and 2.13 GPa, and yield strength are 60.2 and 54 MPa, respectively (which represent only 6 and 15% loss of modulus, and 5 and 13% decrease in yield strength relative to neat PA6). These improved results confirm that although the decrease of tensile modulus cannot be avoided with increasing impact strength, increasing the elastic modulus and yield strength of the core material in the rigid core/soft rubber shell toughener is an effective way to obtain a good balance of elastic modulus, tensile yield strength and impact strength.

Liquid-Infused Poly(styrene-b-isobutylene-b-styrene) Microfiber Coating Prevents Bacterial Attachment and Thrombosis

Infection and thrombosis associated with medical implants cause significant morbidity and mortality worldwide. As we know, current technologies to prevent infection and thrombosis may cause severe side effects. To overcome these complications without using antimicrobial and anticoagulant drugs, we attempt to prepare a liquid-infused poly(styrene-b-isobutylene-b-styrene) (SIBS) microfiber coating, which can be directly coated onto medical devices. Notably, the SIBS microfiber was fabricated through solution blow spinning. Compared to electrospinning, the solution blow spinning method is faster and less expensive, and it is easy to spray fibers onto different targets. The lubricating liquids then wick into and strongly adhere the microfiber coating. These slippery coatings can effectively suppress blood cell adhesion, reduce hemolysis, and inhibit blood coagulation in vitro. In addition, Pseudomonas aeruginosa (P. aeruginosa) on the lubricant infused coatings slides readily, and no visible residue is left after tilting. We furthermore confirm that the lubricants have no effects on bacterial growth. The slippery coatings are also not cytotoxic to L929 cells. This liquid-infused SIBS microfiber coating could reduce the infection and thrombosis of medical devices, thus benefiting human health.

Patterning surfaces for controlled platelet adhesion and detection of dysfunctional platelets.

Platelets play a fundamental role in thrombus formation and in the pathogenesis of arterial thrombosis. Patterning surfaces for controlled platelet adhesion paves the way for adhesion and activation mechanisms in platelets and detection of platelet functional defects. Here, a new and simple method based on controlled polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) on the surface of styrene-block-(ethylene-co-butylene)-block-styrene (SEBS) is shown. The competition between polymerization and degradation enables platelet adhesion on SEBS to be switched on and off. The adhesive sites of the platelets can be down to single cell level, and the dysfunctional platelets can be quantitatively detected.

Enhanced biocompatibility of biostable poly(styrene-b-isobutylene-b-styrene) elastomer via poly(dopamine)-assisted chitosan/hyaluronic acid immobilization

The biostable poly(styrene-b-isobutylene-b-styrene) (SIBS) elastomers are well-known for their large-scale in vivo application as drug-eluting coatings in coronary stents. In this study, the SIBS elastomers were modified with a poly(dopamine) (PDA) adherent layer, followed by integrating both chitosan (CS) and hyaluronic acid (HA) onto their surfaces. The as-prepared samples (SIBS-CS-g-HA) presented excellent cytocompatibility because CS facilitates cell attachment and HA enhances cell proliferation. The initial adhesion test of E. coli on SIBS-CS-g-HA showed effective antiadhesive properties. The in vitro antibacterial test confirmed that SIBS-CS-g-HA has good antibacterial activity.

Infection-resistant styrenic thermoplastic elastomers that can switch from bactericidal capability to anti-adhesion

Styrenic thermoplastic elastomers (STPEs), particularly for poly(styrene-b-isobutylene-b-styrene) (SIBS), have aroused great interest in the indwelling and implant applications. However, the biomaterial-associated infection is a great challenge for these hydrophobic elastomers. Here, benzyl chloride (BnCl) groups are initially introduced into the SIBS backbone via Friedel-Crafts chemistry, followed by reaction with methyl 3-(dimethylamino) propionate (MAP) to obtain a cationic carboxybetaine ester-modified elastomer. The as-prepared elastomer is able to kill bacteria efficiently, while upon the hydrolysis of carboxybetaine esters into zwitterionic groups, the resultant surface has antifouling performances against proteins, platelets, erythrocytes, and bacteria. This STPE that switches from bactericidal efficacy during storage to the antifouling property in service has great potential in biomedical applications, and is generally applicable to the other styrene-based polymers.