Showing papers by "En-Tang Kang published in 2018"

Dextran and Chitosan-based Antifouling, Antimicrobial Adhesion and Self-Polishing Multilayer Coatings from pH-Responsive Linkages-Enabled Layer-by-Layer Assembly

Abstract: To meet the demand for more environmentally-friendly antifouling coatings, and to improve the fouling-resistant coatings with both ‘offense’ and ‘defense’ functionalities, polysaccharides (PSa)-based self-polishing multilayer coatings were developed for combating biofouling. Dextran aldehyde (Dex-CHO) and carboxymethyl chitosan (CMCS) were synthesized and alternatively incorporated via imine linkage into the multilayer coating in layer-by-layer (LbL) deposition. Surface plasmon resonance (SPR) technique was utilized to monitor the LbL assembly process. With increasing number of assembled bilayers, the antifouling performances against bovine serum albumin (BSA) adsorption, bacterial (S. aureus and E. coli) adhesion, and alga (Amphora coffeaeformis) attachment improved steadily. The self-polishing ability of the multilayer coatings was achieved via cleavage of pH-responsive imine linkage under acidic environments. As such, dense bacterial adhesion induced detachment of the outmost layer of the coatings. The...

pH-Sensitive Zwitterionic Polymer as an Antimicrobial Agent with Effective Bacterial Targeting

Abstract: It is highly desirable to develop new and more potent biocompatible antimicrobial agents to reduce the increasing risk of bacterial infection worldwide. To address this problem, we prepared a smart pH-sensitive polymer, poly(N′-citraconyl-2-(3-aminopropyl-N,N-dimethylammonium)ethyl methacrylate), or P(CitAPDMAEMA), which can undergo change in functionality from a biocompatible zwitterionic polymer to an antimicrobial cationic polymer at acidic bacterial infection sites. The precursor polymer, poly(2-(3-aminopropyl-N,N-dimethylammonium)ethyl methacrylate) (P(APDMAEMA)), was first prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization, and then modified with citraconic anhydride to obtain the zwitterionic P(CitAPDMAEMA). P(CitAPDMAEMA) is zwitterionic at physiological pH and exhibits low hemotoxicity and good biocompatibility. However, P(CitAPDMAEMA) can change from neutral to cationic with decreasing pH because of the hydrolysis of citraconic amide under low pH conditions. This ...

Electrical stimulation of adipose-derived mesenchymal stem cells and endothelial cells co-cultured in a conductive scaffold for potential orthopaedic applications.

Abstract: Electrical stimulation (ES) has emerged as a useful tool to regulate cell behaviour, but the effect of ES on mesenchymal stem cell (MSC)/vasculogenic cell co-culture has not been investigated. Herein, human adipose-derived MSCs (AD-MSCs) and umbilical vein endothelial cells (HUVECs) were co-cultured in an electrically conductive polypyrrole/chitosan scaffold. Compared with AD-MSC monoculture, calcium deposition in the co-culture without and with ES (200 μA for 4 h/day) was 139% and 346% higher, respectively, after 7 days. As the application of ES to AD-MSC monoculture only increased calcium deposition by 56% compared with that without ES after 7 days, these results indicate that ES and co-culture with HUVECs have synergistic effects on AD-MSCs' osteogenic differentiation. ES application also significantly enhanced CD31 expression of HUVECs. In HUVEC monoculture, application of ES increased CD31 expression by 224%, whereas the corresponding increase in AD-MSC/HUVEC co-culture with ES application was 62%. The gene expression results indicate that ES enhanced the cellular functions in AD-MSC and HUVEC monoculture via autocrine bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF), respectively. In co-culture, crosstalk between AD-MSCs and HUVECs due to paracrine BMP-2 and VEGF enhanced the cellular functions compared with the respective monoculture. With application of ES to the AD-MSC/HUVEC co-culture, autocrine signalling was enhanced, resulting in further promotion of cellular functions. These findings illustrate that co-culturing AD-MSC/HUVEC in a conductive scaffold with ES offers potential benefits for bone defect therapy.

Tailoring Polyelectrolyte Architecture To Promote Cell Growth and Inhibit Bacterial Adhesion.

Abstract: An important challenge facing the application of implanted biomaterials for tissue engineering is the need to facilitate desirable tissue interactions with the implant while simultaneously inhibiting bacterial colonization, which can lead to implant-associated infection. In this study, we explore the relevance of the physical parameters of polyelectrolyte multilayers, such as surface charge, wettability, and stiffness, in tissue cell/surface and bacteria/surface interactions, and investigate the tuning of the multilayer architecture to differentially control such interactions. Polyions with different side-chain chemical structures were paired with polyethylenimine to assemble multilayers with parallel control over surface charge and wettability under controlled conditions. The multilayers can be successfully cross-linked to yield stiffer (the apparent Young’s modulus was increased more than three times its original value) and more stable films while maintaining parallel control over surface charge and wet...

pH-Sensitive Theranostic Nanoparticles for Targeting Bacteria with Fluorescence Imaging and Dual-Modal Antimicrobial Therapy

Abstract: Bacterial infections with severely damaging consequences are serious threats to the public healthcare system. A pH-sensitive theranostic system was fabricated for targeting bacteria with fluorescence imaging and dual-modal antimicrobial therapy (cationic and photodynamic therapies). Poly(poly(ethylene glycol) methyl ether methacrylate)-b-poly(2-(diisopropylamino) ethyl methacrylate-co-2-hydroxyethyl methacrylate)-chlorin e6 (PPEGMA-b-P(DPA-co-HEMA)-Ce6) was synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization and post-modification. The self-assembled PPEGMA-b-P(DPA-co-HEMA)-Ce6 nanoparticles (NPs) with a mean diameter of about 78 nm and polydispersity index of 0.27 were obtained through the dialysis method. The surface potential of PPEGMA-b-P(DPA-co-HEMA)-Ce6 NPs can undergo changes from negative (−1.45 mV) at pH 7.4 to highly positive (+11.6 mV) at pH 6.0, as characterized by the zetasizer. The extent of interaction between the PPEGMA-b-P(DPA-co-HEMA)-Ce6 NPs and bacteri...

Dominant Albumin–Surface Interactions under Independent Control of Surface Charge and Wettability

Abstract: Understanding protein adsorption behaviors on solid surfaces constitutes an important step toward development of efficacious and biocompatible medical devices. Both surface charge and wettability have been shown to influence protein adsorption attributes, including kinetics, quantities, deformation, and reversibility. However, determining the dominant interaction in these surface-induced phenomena is challenging because of the complexity of inter-related mechanisms at the liquid/solid interface. Herein, we reveal the dominant interfacial forces in these essential protein adsorption attributes under the influence of a combination of surface charge and wettability, using quartz crystal microbalance with dissipation monitoring and atomic force microscopy-based force spectroscopy on a series of model surfaces. These surfaces were fabricated via layer-by-layer assembly, which allowed two-dimensional control of surface charge and wettability with minimal cross-parameter dependency. We focused on a soft globular protein, bovine serum albumin (BSA), which is prone to conformational changes during adsorption. The information obtained from the two techniques shows that both surface charge and hydrophobicity can increase the protein-surface interaction forces and the adsorbed amount. However, surface hydrophobicity triggered a greater extent of deformation in the adsorbed BSA molecules, leading to more dehydration, spreading, and resistance to elution by ionic strength changes regardless of the surface charge. The role played by the surface charge in the adsorbed protein conformation and extent of desorption induced by changes in the ionic strength is secondary to that of surface hydrophobicity. These findings advance the understanding of how surface chemistry and properties can be tailored for directing protein-substrate interactions.

Recent Developments in Controlled Release of Antibiotics.

Abstract: Traditional use of antibiotics through injection or oral ingestion has many disadvantages, such as detrimental side effects in the host, less effectiveness, high and repeated doses, and development of drug resistance. For prevention and treatment of implant-associated infections, the continuous local delivery of antibiotics is required. Thus, there is a strong demand for the development of drug carrier systems to control the release of antibiotics in a moderate manner over an appropriate timescale. This review summarizes the carrier platforms used for the loading of antibiotics, and highlights their drug release behaviors as well as in vitro and in vivo antibacterial properties.