Compatibilization effect of poly(epsilon-caprolactone)-b-poly(ethylene glycol) block copolymers and phase morphology analysis in immiscible poly(lactide)/poly(epsilon-caprolactone) blends

Simultaneous enhancement in mechanical strength, electrical conductivity, and electromagnetic shielding properties in PVDF–ABS blends containing PMMA wrapped multiwall carbon nanotubes

A unique approach was adopted to drive the multiwall carbon nanotubes (MWNTs) to the interface of immiscible PVDF–ABS blends by wrapping the nanotubes with a mutually miscible homopolymer (PMMA).

Synergistic effect of PLA–PBAT–PLA tri-block copolymers with two molecular weights as compatibilizers on the mechanical and rheological properties of PLA/PBAT blends

Systematic study on the synergistic effects of different molecular-weight PLA–PBAT–PLA tri-block copolymers on the mechanical and rheological properties of PLA/PBAT blends.

Ionic liquids–lignin combination: an innovative way to improve mechanical behaviour and water vapour permeability of eco-designed biodegradable polymer blends

In this work, the potential use of lignin combined with ionic liquids (ILs) has been investigated on the final properties of biodegradable polymer blends.

Compatibilization strategies in poly(lactic acid)-based blends

Recent compatibilization strategies in poly(lactic acid)-based blends have been reviewed in this paper.

Heparinized PLLA/PLCL nanofibrous scaffold for potential engineering of small-diameter blood vessel: tunable elasticity and anticoagulation property

The success of tissue engineered vascular grafts depends greatly on the synthetic tubular scaffold, which can mimic the architecture, mechanical, and anticoagulation properties of native blood vessels. In this study, small-diameter tubular scaffolds were fabricated with different weight ratios of poly(l-lactic acid) (PLLA) and poly(l-lactide-co-ɛ-caprolactone) (PLCL) by means of thermally induced phase separation technique. To improve the anticoagulation property of materials, heparin was covalently linked to the tubular scaffolds by N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide coupling chemistry. The as-prepared PLLA/PLCL scaffolds retained microporous nanofibrous structure as observed in the neat PLLA scaffolds, and their structural and mechanical properties can be fine-tuned by changing the ratio of two components. The scaffold containing 60% PLCL content was found to be the most promising scaffold for engineering small-diameter blood vessel in terms of elastic properties and structural integrity. The heparinized scaffolds showed higher hydrophilicity, lower protein adsorption ability, and better in vitro anticoagulation property than their untreated counterparts. Pig iliac endothelial cells seeded on the heparinized scaffold showed good cellular attachment, spreading, proliferation, and phenotypic maintenance. Furthermore, the heparinized scaffolds exhibited neovascularization after subcutaneous implantation into the New Zealand white rabbits for 1 and 2 months. Taken together, the heparinized PLLA/PLCL nanofibrous scaffolds have the great potential for vascular tissue engineering application.

Thermotropic dynamic processes in multiphase polymer systems by (cryo-)AFM

The structural (volume and enthalpy) relaxation of polymers during physical aging has a great relevance in materials science and engineering as it significantly changes the long-term material performance. In this article, we propose a methodological approach of (cryo-)atomic force microscopy (AFM) monitoring of macromolecular rearrangements which accompany structural relaxation within bulk of the polymer during physical aging. In contrast to conventional spectroscopic, scattering and thermal analysis techniques, high resolution topographical/phase imaging of the bulk cross-section over a large period of time and within a wide range of temperatures (-120 °C to +20 °C) yields unique information about the evolution of the polymer ultrastructure as a function of time and temperature in situ.

The mechanical behavior and biocompatibility of polymer blends for Patent Ductus Arteriosus (PDA) occlusion device

Patent Ductus Arteriosus (PDA) is a cardiovascular defect that occurs in 1 out of every 2000 births, and if left untreated, may lead to severe cardiovascular problems. Current options for occluding utilize meta scaffolds with polymer fabric, and are permanent. The purpose of this study was to develop a fully degradable occluder for the closure of PDA, that can be deployed percutaneously without open-heart surgery. For percutaneous deployment, both elasticity and sufficient mechanical strength are required of the device components. As this combination of properties is not achievable with currently-available homo- or copolymers, blends of biodegradable poly(ε-caprolactone) (PCL) and poly(L-lactide-co-ε-caprolactone) (PLC) with various compositions were studied as the potential material for the PDA occlusion device. Microstructures of this blend were characterized by differential scanning calorimetry (DSC) and tensile tests. DSC results demonstrated the immiscibility between PCL and its copolymer PLC. Furthermore, the mechanical properties, i.e. elastic modulus and strain recovery, of the blends could be largely tailored by changing the continuous phase component. Based on the thermo-mechanical tests, suitable blends were selected to fabricate a prototype of PDA occluder and its in vitro performance, in term of device recovery (from its sheathed configuration), biodegradation rate and blood compatibility, was evaluated. The current results indicate that the device is able to recover elastically from a sheath within 2-3min for deployment; the device starts to disintegrate within 5-6 months, and the materials have no adverse effects on the platelet and leucocyte components of the blood. Biocompatibility implantation studies of the device showed acceptable tissue response. Finally, an artificial PDA conduit was created in a pig model, and the device deployment was tested from a sheath: the device recovered within 2-3min of unsheathing and fully sealed the conduit, the device remains stable and is completely covered by tissue at 1 month follow up. Thus, a novel prototype for PDA occlusion that is fully degradable has been developed to overcome the limitations of the currently used metal/fabric devices.

Modulating rheological and degradation properties of temperature-responsive gelling systems composed of blends of PCLA-PEG-PCLA triblock copolymers and their fully hexanoyl-capped derivatives

In this study, the ability to modulate rheological and degradation properties of temperature-responsive gelling systems composed of aqueous blends of poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-lactide) (PCLA-PEG-PCLA) triblock copolymers (i.e. uncapped) and their fully capped derivatives was investigated. Uncapped and capped PCLA-PEG-PCLA triblock copolymers, abbreviated as degree of modification 0 and 2 (DM0 and DM2, respectively), were composed of identical PCLA and PEG blocks but different end groups: namely hydroxyl and hexanoyl end groups. DM0 was synthesized by ring opening polymerization of l-lactide and ε-caprolactone in toluene using PEG as initiator and tin(II) 2-ethylhexanoate as the catalyst. A portion of DM0 was subsequently reacted with an excess of hexanoyl chloride in solution to yield DM2. The cloud point and phase behaviour of DM0 and DM2 in buffer as well as that of their blends were determined by light scattering in a diluted state and by vial tilting and rheological measurements in a concentrated state. Degradation/dissolution properties of temperature-responsive gelling systems were studied in vitro at pH 7.4 and 37°C. The cloud points of DM0/DM2 blends were ratio-dependent and could be tailored from 15 to 40°C for blends containing 15 to 100wt.% DM0. Vial tilting and rheological experiments showed that, with solid contents between 20 and 30wt.%, DM0/DM2 blends (15/85 to 25/75w/w) had a sol-to-gel transition temperature at 10-20°C, whereas blends with less than 15wt.% DM0 formed gels below 4°C and the ones with more than 25wt.% DM0 did not show a sol-to-gel transition up to 50°C. Complete degradation of temperature-responsive gelling systems took ∼100days, independent of the DM0 fraction and the initial solid content. Analysis of residual gels in time by GPC and (1)H-NMR showed no chemical polymer degradation, but indicated gel degradation by dissolution. Preferential dissolution of lactoyl-rich polymers induced enrichment of the residual gels in caproyl-rich polymers. To the best of our knowledge, degradation of temperature-responsive gelling systems by dissolution has not been reported or hypothesized as being the consequence of acylation of polymers. In conclusion, blending of PCLA-PEG-PCLA triblock polymers composed of identical backbones but different end groups provides for a straightforward preparation of temperature-responsive gelling systems with well-characterized rheological properties and potential in drug delivery. Furthermore, acylation of triblock copolymers may allow for the design of bioerodible systems with control over degradation by polymer dissolution.

Polyester-grafted cellulose nanowhiskers: a new approach for tuning the microstructure of immiscible polyester blends

Cellulose nanowhiskers (CNW), extracted from ramie fibers by sulfuric acid hydrolysis, were used as substrates to compatibilize binary polyester blends containing 50/50 (w/w) polycaprolactone (PCL) and polylactide (PLA). To tailor their interfacial energy and fine-tune their adhesion with the components of the blend, CNW were subjected to different surface polyester grafting by the means of ring-opening polymerization. PCL and PLA homopolyesters as well as P(CL-b-LA) diblock copolymers were successfully grafted on the surface of CNW and the resulting substrates were loaded into the PCL/PLA blend by melt-blending. Morphological and rheological analyses were conducted in order to evaluate the ability of these nanoparticles to enhance the compatibility of PCL/PLA blends. Our results showed that unmodified CNW as well as (co)polyester-grafted CNW improved, at different levels, the compatibility of PCL/PLA blends by preventing from coalescence the dispersed domains. (co)polyester-grafted CNW also enhance the mechanical properties of the blend, which can be explained by the formation of cocontinuous phase morphology at the interface. Our findings suggest that (co)polyester-grafted CNW, especially CNW-g-P(CL-b-LA) diblock copolymers, can serve as a suitable nanofiller to tune the compatibility of PCL/PLA blends and their related microstructures.

Polymersomes of asymmetric bilayer membrane formed by phase-guided assembly

Encapsulating delicate biomolecules into submicron-sized polymer particulate systems with preserved native conformation and sufficient loading efficiency is of great challenge. To address this issue, we developed a unique polymersome which differs from reported polymersome in that its bilayer membrane was formed of two different amphiphilic diblock copolymers in an "asymmetric" way. By adding two diblock copolymers, poly (ethylene glycol)-block-poly (ε-caprolactone) (PEG-PCL) and dextran-block-poly (ε-caprolactone) (DEX-PCL), into a so-called dextran-in-PEG aqueous two-phase system, DEX-PCL formed the inner leaflet around the dispersed dextran phase and PEG-PCL formed the outer leaflet with the PEG block facing the PEG continuous phase. We name this unique assembly process as "phase-guided assembly". Polymersomes of asymmetric bilayer membrane possess a series of advantages over "symmetric" polymer bilayer vesicles previously reported. The asymmetric bilayer created a different chemical environment of the interior to which proteins were encapsulated highly efficiently (up to 90%) by thermodynamically favored partition. Probably due to the thermodynamic preference, erythropoietin (EPO) encapsulated in this system showed a well-preserved bioactivity in cell proliferation assay. The core of the polymersomes may be cross-linked to enhance their mechanical strength. Phase-guided assembly system and asymmetric bilayer polymersomes demonstrated in this study may serve the high demands for delivering nucleotide and protein medicines and other biological applications.