Lin Sang

Biodegradable radiopaque iodinated poly(ester urethane)s containing poly(ε-caprolactone) blocks: Synthesis, characterization, and biocompatibility

Biodegradable radiopaque iodinated poly(ester-urethane) (I-PU), consisting of poly(ε-caprolactone) (PCL) diol and iodinated bisphenol A (IBPA), has been successfully synthesized via a coupling reaction of PCL-diisocyanate and IBPA with varying compositions. The IBPA with four iodine atoms per molecule was applied as a chain extender to endow the I-PUs with intrinsic X-ray visibility. The chemical structure and molecular weights of I-PUs were characterized by Fourier transform infrared spectroscopy (FT-IR), proton-nuclear magnetic resonance, and gel permeation chromatography (GPC). The effects of IBPA on the physical properties of I-PUs were systematically studied by means of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and wide-angle X-ray diffraction (WAXD). The DSC results showed that the crystallization of PCL segments in I-PUs was restrained with increasing amount of IBPA, which was also confirmed by WAXD. In the X-radiography analysis, all the synthesized I-PUs exhibited high radiopacity compared with an aluminum wedge of equivalent thickness. Enzymatic degradation tests showed that the incorporation of IBPA prolonged the degradation of I-PUs and distinct mass loss and degradation happened in the third month. Basic cytocompatibility conducted using rat adipose-derived cells proved that all the I-PUs and their biodegradation products were nontoxic. The radiopaque I-PUs is expected to possess a significant advantage over the traditional polymer counterparts in some related biomedical fields.

Morphology, crystallization and mechanical properties of poly(ɛ-caprolactone)/graphene oxide nanocomposites

A series of nanocomposites based on poly(ɛ-caprolactone) (PCL) and graphene oxide (GO) were prepared by in situ polymerization. Scanning electron microscopy observation revealed not only a well dispersion of GO but also a strong interfacial interaction between GO and the PCL matrix, as evidenced by the presence of some GO nanosheets embedded in the matrix. Effects of GO nanofillers on the crystal structure, crystallization behavior and spherulitic morphology of the PCL matrix were investigated in detail. The results showed that the crystallization temperature of PCL enhanced significantly due to the presence of GO in the nanocomposites, however, the addition of GO did not affect the crystal structure greatly. Thermal stability of PCL remarkably increased with the addition of GO nanosheets, compared with that of pure PCL. Incorporation of GO greatly improved the tensile strength and Young’s modulus of PCL without a significant loss of the elongation at break.

A comparative study of the crystalline structure and mechanical properties of carbon fiber/polyamide 6 composites enhanced with/without silane treatment

Carbon fiber (CF) reinforced polyamide 6 (PA6) composites were manufactured by extrusion compounding and injection molding. The carbon fiber was considered in two forms including untreated and treated with silane coupling agent. The main focus of this study was to investigate the effects of the silane treatment on the mechanical properties and crystalline structure of the composites. Mechanical test results showed that the tensile, impact and flexural strength were significantly increased by incorporation of silane-treated carbon fiber. In particular, the specific tensile, impact and flexural strength of silane-treated CF composites with 20% fibre mass fraction are, respectively, 42%, 51.6% and 30% higher than those of untreated CF composites. Scanning electron microscopy examination showed that the tensile fracture surface of silane-treated CF composites failed in a fiber breakage pattern while the untreated CF composites fractured via a fiber pull-out pattern, suggesting an enhanced interfacial adhesion with the matrix. In addition, the incorporation of silane-treated CF increased the degree of crystallinity, promoted the formation of the thermodynamic crystalline form and induced the specific transcrystalline structure, as indicated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarizing optical microscopy (POM) analysis. Moreover, the mechanism of silane-treated CF reinforced PA6 composites with improved mechanical properties was discussed.

Mechanical properties and crystallization behavior of poly(butylene succinate) composites reinforced with basalt fiber

Biodegradable poly(butylene succinate) (PBS)/basalt fiber (BF) composites were prepared by melt blending method using twin-screw extruder followed by injection molding. Mechanical properties, crystallization and melting behavior, morphology, crystal structure and thermal stability of PBS/BF composites with various BF contents were investigated by different techniques. The tensile and impact properties of the composites were improved markedly with the addition of BF, due to the efficient interfacial adhesion between fibers and PBS matrix. Crystallization and melting behavior of PBS in its composites kept almost unchanged, indicating that the nucleation effect of BF was minimal and, meanwhile, it played a role in hindrance of chain motion. TG analysis showed that the thermal stability of PBS/BF composites was enhanced by the addition of BF. The crystal structure of PBS was not affected by the incorporation of BF, while the nucleation density increased gradually and the spherulite size reduced remarkably with the increase in BF. No transcrystallization phenomenon on the surface of BF was observed maybe as a result of without surface treatment.

Synthesis and characterization of poly(ɛ-caprolactone)/Fe3o4 nanocomposites by in situ polymerization

A series of magnetic nanocomposites based on poly(ɛ-caprolactone) (PCL) and Fe3O4 nanoparticles were prepared using a facile in situ polymerization method. The chemical structures of the PCL/Fe3O4 nanocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy. Results of wide-angle X-ray diffraction (WAXD) showed that the incorporation of the Fe3O4 nanoparticles did not affect the crystallization structure of the PCL. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology and dispersion of the Fe3O4 nanoparticles within the as-synthesized nanocomposites. Results of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM) showed that the crystallization temperature was raised and the spherulites size decreased by the presence of Fe3O4 nanoparticles in the nanocomposites due to the heterogeneous nucleation effect. The thermal stability of the PCL was depressed by incorporation of Fe3O4 nanoparticles from thermogravimetric analysis (TGA). The superparamagnetic behavior of the PCL/Fe3O4 nanocomposites was testified by the superconducting quantum interference device (SQUID) magnetometer analysis. The obtained biodegradable nanocomposites will have a great potential in magnetic resonance imaging contrast and targeted drug delivery.

Thermo-oxidative ageing effect on mechanical properties and morphology of short fibre reinforced polyamide composites – comparison of carbon and glass fibres

The present paper examined the thermo-oxidative ageing behavior of short carbon fibre reinforced polyamide 6 composites (CF/PA6), in comparison with commercial glass reinforced composites (Ultramid® B3WG7). The mechanical results revealed that the tensile strength of CF/PA6 composites (retention above 90%) was well maintained, while the notched Izod impact strength of both CF/PA6 and Ultramid® B3WG7 were continuously decreased during the ageing process. Annealing effects on PA6 and chain arrangement were found in the initial ageing stage, and a better thermal stability of CF/PA6 compared with the Ultramid® B3WG7 sample was observed from the TGA curves as the ageing time was prolonged. A noticeable color transition from white to black was observed in Ultramid® B3WG7 samples when the increasing ageing temperature. The ageing process also resulted in topography damage with matrix cracks and fibre/matrix interfacial debonding due to chain scission, oxidization and formation of chromophoric groups of polyamide molecules, which was illustrated by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Furthermore, metallographs of polished cross-sections of Ultramid® B3WG7 demonstrated the evolution of an oxidized layer of the composites at increased ageing temperatures for prolonged ageing time, which was ascribed to the contribution of mechanical changes that play an important role at high ageing temperatures.

Insight into the role of bound water of a nucleating agent in polymer nucleation: a comparative study of anhydrous and monohydrated orotic acid on crystallization of poly(L-lactic acid)

To gain an insight into the role of bound water of a nucleating agent in polymer nucleation, a biobased nucleating agent, orotic acid (OA), was selected as a model to investigate the effects on crystallization of poly(L-lactic acid) (PLLA). In such a context, two commercially available types of OA in anhydrous (OA-a) and monohydrated (OA-m) forms were melt mixed with PLLA, and their nucleation effectiveness on nonisothermal and isothermal melt crystallization of PLLA was comparatively studied. Results indicate that both forms of OA can significantly improve nonisothermal crystallization temperature and degree of crystallinity, overall isothermal crystallization rate, as well as nucleation density of PLLA. Interestingly, OA-a shows more prominent nucleation efficiency than OA-m. That is, the bound water of OA-m and its dehydration transition play a negative role in nucleation effects on PLLA crystallization. It is attributed to the deteriorated dispersion and the reduced active concentration of dehydration-transformed OA-a in PLLA/OA-m blends, as compared with pristine OA-a in PLLA/OA-a blends. Furthermore, an epitaxial mechanism is proposed to explain the nucleation phenomenon of PLLA/OA blends.

Fabrication and Characterization of P34HB Scaffolds with Oriented Microtubules

Sponge-like scaffold with a specific three-dimensional structure resembling the actual extracellular matrix of a particular tissue show significant potential for the regeneration and repair of damaged anisotropic tissues. In this research, an oriented microtubular P34HB scaffold was prepared successfully. The mechanical property showed that anisotropy of modulus is much greater than a typical non-oriented scaffold. Altering the P34HB concentration allowed P34HB scaffolds to be produced with complex pore orientations, and anisotropy in pore size and alignment.

Crystallization and mechanical properties of basalt fiber-reinforced polypropylene composites with different elastomers

In this study, composites based on polypropylene (PP), basalt fiber (BF), polypropylene-graft-maleic anhydride (MAPP) and different elastomers were manufactured by extrusion compounding and injection molding. The main focus of this study was to comparatively investigate the effect of three kinds of elastomers (ethylene–propylene–diene monomer (EPDM), polyethylene–octene (POE) and ethylene–vinyl–acetate (EVA)) on non-isothermal crystallization and mechanical properties of the composites with various BF contents. The tensile test results showed that BF had a reinforcing effect on PP resin, and the addition of MAPP further improved the tensile properties by the enhancement of PP/BF interfacial bonding. Among the elastomers, EPDM was more effective in improving the tensile strength and tensile modulus, while POE significantly toughened the impact strength. Micrographs of scanning electron microscope on the impact fracture surfaces indicated a good dispersion by the addition of POE and EPDM, while some agglomerations were observed in the presence of EVA. The non-isothermal crystallization kinetics were investigated based on Avrami and Mo equations at six different cooling rates by using differential scanning calorimetry. Micrographic images of polarized optical microscopy showed that the spherulite size of PP reduced in the presence of EPDM and EVA.

Proteomic analysis of chondromodulin-I-induced differentiation of mesenchymal stem cells into chondrocytes

To identify novel proteins that might help clarify the molecular mechanisms underlying chondromodulin-I (ChM-I) induction of mesenchymal stem cells (MSCs) differentiate into chondrocytes. MSCs are triggered to differentiate into chondrocytes, which are recognized as important factors in cartilage tissue engineering. ChM-I is a glycoprotein that stimulates the growth of chondrocytes and inhibits angiogenesis in vitro. In this study, the proteomic approach was used to evaluate protein changes between undifferentiated MSCs and ChM-I-transfected MSCs. The expression of the protein spots was analyzed using two-dimensional gel electrophoresis. Then, 14 protein spots were identified between MSCs and ChM-I-transfected MSCs. 309 proteins were identified using mass spectrometry (MS). The differentially regulated proteins were categorized and annotated using Protein Analysis Through Evolutionary Relationships (PANTHER) analysis with the aid of the Database for Annotation, Visualization and Integrated Discovery (DAVID) tool. These proteins are included in a variety of metabolic pathways and signal transduction pathways, such as focal adhesion, glycolysis, actin cytoskeleton regulation, and ribosome. These results demonstrate novel information about the molecular mechanism by which ChM-I induce MSCs to differentiate into chondrocytes. These results also provide a solid foundation for the development of tissue-engineered cartilage.