Zhu Xiong

Investigation of the heat resistance, wettability and hemocompatibility of a polylactide membrane via surface crosslinking induced crystallization

Polylactide (PLA) has attracted much attention as a sustainable and environmentally friendly material. However, the poor heat resistance restricts its potential application as a porous membrane. Herein, a PLA membrane with excellent heat resistance, hydrophilicity and hemocompatibility was developed via a surface crosslinking induced crystallization strategy, which involved two key reactions, namely, copolymerization of N-vinyl-2-pyrrolidone (NVP) and triethoxyvinylsilane (VTES) and the subsequent hydrolysis condensation on the surface of the PLA membrane. Attenuated total reflectance Fourier transform infrared spectra (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were applied to analyse the surface chemistry and crystallization evolution, which confirmed that the P(VP-VTES) copolymer was hydrothermally crosslinked and induced the crystallization of the PLA membrane. The surface crystallization significantly improved the heat resistance and preserved membrane morphology, which was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and the dimension shrinkage. The modified PLA membrane with χc ∼ 37% remained almost unchanged dimensions and morphology even after annealing at 100 °C for 5 min. The improved hemocompatibility was verified by the prolonged clotting time and recalcification time, which was consistent with the enhanced hydrophilicity. All results showed that surface crosslinking induced crystallization strategy simultaneously improved the heat resistance and hemocompatibility, indicating a promising method for preparing robust and compatible PLA membranes.

Enhanced catalytic degradation of 4-NP using a superhydrophilic PVDF membrane decorated with Au nanoparticles

Poly(vinylidene fluoride) (PVDF) membranes have been widely applied to treat wastewater, however, the removal of toxic aromatic phenolic compounds remains a technical challenge due to the serious adsorption fouling and difficult degradation. Herein, we aimed to design a superhydrophilic PVDF membrane decorated with Au nanoparticles, which enhanced the rapid degradation of p-nitrophenol (4-NP). The superhydrophilic PVDF membrane with a micro/nano structured surface was decorated with Au nanoparticles via poly(dopamine) (PDA) as a spacer. The influences of membrane affinity (e.g. Hydrophilic Membrane (HM), micro/nano structured superhydrophilic membrane (MSiM), and micro/nano structured superhydrophobic membrane (MSoM)) on PDA deposition and the subsequent Au decoration were comprehensively investigated. The synthesized Au nanoparticles were characterized using transmission electron microscopy (TEM) and UV-vis absorption spectra. The morphology and composition was evaluated using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Static catalytic experiments demonstrated that MSiM degraded over 90% of 4-NP in 5 minutes with a kinetic reaction rate constant of 47.84 × 10−2 min−1 and high stability over 6 cycles. A membrane catalytic reactor (MCR) was designed to realize the continuous catalytic degradation of 4-NP with a kinetic reaction rate constant of 7 × 10−2 min−1.

APTES assisted surface heparinization of polylactide porous membranes for improved hemocompatibility

Surface heparinization is considered an efficient strategy to improve the hemocompatibility of polymeric membranes. We aim to realize the feasible surface heparinization of polylactide (PLA) membranes by means of a colourless 3-aminopropyltriethoxysilane (APTES) functionalized platform. APTES conjugated heparin (Hep–APTES) was first synthesized through the amidation reaction and then anchored onto PLA membrane via surface attachment, condensation, multilayer formation. The surface chemistry was confirmed by Fourier Transform Infrared-Attenuated Total Reflectance (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS). The influences of heparinization time and micro-swelling agent (DMAc) on the heparin density, stability and sustained-release were investigated. The hydrophilicity, flux and morphology were also studied by contact angle, pure water flux and Scanning Electron Microscope (SEM). The hemocompatibility was evaluated by the activated partial thromboplastin time (APTT), prothrombin time (PT), the content of fibrinogen (FIB), platelet and Bovine Serum Albumin (BSA) adsorption respectively. All results demonstrated that APTES assisted surface heparinization provided a feasible and efficient strategy to improve the hemocompatibility of PLA membrane.

Robust poly(lactic acid) membranes improved by polysulfone-g-poly(lactic acid) copolymers for hemodialysis

Poly(lactic acid) (PLA) is a sustainable membrane candidate for liquid separation and purification. However, the inherent brittleness restrains its practical application, especially for a porous membrane with thin thickness and high porosity. We aim to prepare PLA membranes with controlled pore structure and dialysis performance with improved mechanical and thermal stability by incorporating polysulfone-graft-poly(lactic acid) (PSf-g-PLA) copolymer. Different from the common rubbery elastomer, the brush-like PSf-g-PLA copolymer with a rigid backbone chain and soft side chains was elaborately synthesized to toughen and modify PLA membranes via a phase inversion process. 1H NMR, FTIR and GPC were conducted to determine the structure and molecular weight of the PSf-g-PLA. The influences of chloromethylation substitution and the content of copolymer on the membrane microstructure, the mechanical and thermal stability, and the dialysis performance were investigated in detail. It was demonstrated that the modified PLA membrane exhibited a pure water flux of 54 L m−2 h−1, 95% rejection to BSA, and 65% and 18% clearance of urea and lysozyme, respectively. Besides, both mechanical and thermal stability of the modified PLA membrane were improved by incorporating brush-like PSf-g-PLA.

Surface PEGylation on PLA membranes via micro-swelling and crosslinking for improved biocompatibility/hemocompatibility

Poly(lactic acid) (PLA) has attracted growing attention as a sustainable and environmentally benign membrane material. The good biocompatibility/hemocompatibility is essential for hemodialysis membranes. To circumvent the inadequate hydrophilicity/biocompatibility/hemocompatibility, we have developed a feasible strategy that enables the persistent PEGylation on PLA membranes via micro-swelling and subsequent UV-initiated crosslinking of poly(ethylene glycol)diacrylate (PEGDA). The content of DMSO and PEGDA in the reaction solution was crucial to control the surface PEGylation kinetics. Besides, the influence of PEGylation on membrane chemistry, morphology, hydrophilicity, water flux and dynamic fouling resistance to BSA was investigated. It was demonstrated that the biocompatibility/hemocompatibility was significantly improved by the surface PEGylation in terms of reduced BSA adsorption, extended APTT and alleviative platelet adhesion.

Tunable adhesion of superoleophilic/superhydrophobic poly (lactic acid) membrane for controlled-release of oil soluble drugs

Superhydrophobic membranes with tunable adhesion have attracted intense interests for various engineering applications. In this work, superhydrophobic sustainable poly (lactic acid) (PLA) porous membrane with tunable adhesive force from 101μN to 29μN was successfully fabricated via one-step phase separation method. The incorporation of Perfluoro-1-decene (PFD) into the PLLA/PDLA membrane via the in situ polymerization can facilely tune the PLLA/PDLA stereocomplex crystallization during phase inversion, which consequently caused the unique morphology blooming evolution from bud to full-blown state. The resulted membrane showed tunable pore size, porosity, surface area, surface roughness and superhydrophobicity, which enabled the membrane with controlled-release of oil soluble drugs.

Investigation of abnormal thermoresponsive PVDF membranes on casting solution, membrane morphology and filtration performance

An interesting PVDF membrane with unusual thermoresponsive behavior was prepared by the incorporation of P(OEGMA-co-VTMOS). The P(OEGMA-co-VTMOS) copolymer was first in situ synthesized in a PVDF/triethyl phosphate (TEP) casting solution. A P(OEGMA-co-VTMOS) network was assembled in the PVDF membrane through hydrolysis and condensation during phase inversion. PVDF/P(OEGMA-co-VTMOS) in organic solvent demonstrated a typical LCST around 35 °C, reflecting the reversible transition of the coil-to-globule conformation. Microphase separation was responsible for the appearance of turbidity of the casting solution. FTIR, XPS, TGA and SEM confirmed the surface enrichment of the copolymer, especially in the membrane bottom. The hydrophilicity and protein anti adsorption were improved despite the temperature variation. In particular, AFM in aqueous media was conducted to determine the reversible morphology and water channel variation under heating and cooling. Different from common thermoresponsive membranes, the so-modified PVDF membranes exhibit a reversible abnormal change of pure water flux and BSA rejection with temperature. The intriguing thermoresponsive behavior and mechanism of the modified PVDF membrane was thoroughly investigated from the aspects of PVDF/TEP casting solution, membrane morphology in aqueous media and water/BSA filtration performance.