Construction of fully biodegradable poly(L-lactic acid)/poly(D-lactic acid)-poly(lactide-co-caprolactone) block polymer films: Viscoelasticity, processability and flexibility.

Development of biodegradable polymer films is essential for sustainable energy conservation and ecological protection. In this work, to improve the processability and toughness of poly(lactic acid) (PLA) films, poly(lactide-co-caprolactone) (PLCL) segments were introduced into poly(L-lactic acid) (PLLA)/poly(D-lactic acid) (PDLA) chains via chain branching reactions during reactive processing, and fully biodegradable/flexible PLLA/D-PLCL block polymer with long-chain branches and stereocomplex (SC) crystalline structure was prepared. Compared with neat PLLA, PLLA/D-PLCL exhibited much higher complex viscosity/storage modulus, lower tanδ values in terminal region and obvious strain-hardening behavior. Through biaxial drawing, PLLA/D-PLCL films were prepared, which showed improved uniformity and non-preferred orientation. With increasing draw ratio, the total crystallinity (Xc) and Xc for SC crystal both increased. By introduction of PDLA, the two phases of PLLA and PLCL penetrated and entangled with each other, and the phase structure transformed from "sea-island" structure to "co-continuous network" structure, which was beneficial for exerting the toughening effect of flexible PLCL molecules on PLA matrix. The tensile strength and elongation at break of PLLA/D-PLCL films increased from 51.87 MPa and 28.22 % of neat PLLA film to 70.82 MPa and 148.28 %. This work provided a new strategy for developing fully biodegradable polymer films with high performance.

Investigation of Cell Adhesion and Cell Viability of the Endothelial and Fibroblast Cells on Electrospun PCL, PLGA and Coaxial Scaffolds for Production of Tissue Engineered Blood Vessel.

Endothelialization of artificial scaffolds is considered an effective strategy for increasing the efficiency of vascular transplantation. This study aimed to compare the biophysical/biocompatible properties of three different biodegradable fibrous scaffolds: Poly (ɛ-caprolactone) (PCL) alone, Poly Lactic-co-Glycolic Acid (PLGA) alone (both processed using Spraybase® electrospinning machine), and Coaxial scaffold where the fiber core and sheath was made of PCL and PLGA, respectively. Scaffold structural morphology was assessed by scanning electron microscope and tensile testing was used to investigate the scaffold tension resistance over time. Biocompatibility studies were carried out with human umbilical vein endothelial cells (HUVEC) and human vascular fibroblasts (HVF) for which cell viability (and cell proliferation over a 4-day period) and cell adhesion to the scaffolds were assessed by cytotoxicity assays and confocal microscopy, respectively. Our results showed that all biodegradable polymeric scaffolds are a reliable host to adhere and promote proliferation in HUVEC and HVF cells. In particular, PLGA membranes performed much better adhesion and enhanced cell proliferation compared to control in the absence of polymers. In addition, we demonstrate here that these biodegradable membranes present improved mechanical properties to construct potential tissue-engineered vascular graft.

Biocompatibility improvement and controlled in vitro degradation of poly (lactic acid)-b-poly(lactide-co-caprolactone) by formation of highly oriented structure for orthopedic application.

Poly (lactic acid) (PLA) has been proposed as a promising orthopedic implant material, whereas insufficient mechanical strength, unsatisfied biocompatibility and inappropriate degradation rate restrict its further application. In this work, self-reinforced poly (lactic acid)-b-poly(lactide-co-caprolactone) (PLA-b-PLCL) block copolymer with long-chain branches was fabricated through two-stage orientation. Compared with smooth and hydrophobic PLA surface, the surface of PLA-b-PLCL presented micro-phase separated structure with improved hydrophilicity, and cells seeded on it showed improved adhesion/proliferation and high alkaline phosphatase (ALP) activity. After the 1st stage orientation at temperature higher than Tg1 (glass transition temperature of PLA phase), the amount of CH3 and CO groups on surface of PLA-b-PLCL increased, while "groove-ridge" structure formed, resulting in enhancement of surface hydrophobicity. After the 2nd stage orientation at Tg1 ~ Tg2 (glass transition temperature of PLCL phase), surface hydrophobicity/amount of CO groups further increased and "groove-ridge" structure became more significant. Due to suitable wettability and enhanced material-cell mechanical interlocking, cell proliferation/ALP activity were improved and a continuous cell layer formed on sample surface. During in vitro degradation in phosphate buffered saline solution, by introduction of PLCL segments, the crystallinity decreased and solution absorption increased, resulting in a rapid deterioration of mechanical properties. After the 1st stage orientation, a dense microfibrillar structure with high crystallinity formed, which hindered diffusion of solution and delay hydrolytic degradation. After the 2nd stage orientation, PLCL segments were arranged more closely, resulting in a further inhibition of degradation, which was helpful for controlling the strength decay rate of PLA as bone fixation materials.

Fabrication and Characterization of PCL/PLGA Coaxial and Bilayer Fibrous Scaffolds for Tissue Engineering.

Electrospinning is an innovative new fibre technology that aims to design and fabricate membranes suitable for a wide range of tissue engineering (TE) applications including vascular grafts, which is the main objective of this research work. This study dealt with fabricating and characterising bilayer structures comprised of an electrospun sheet made of polycaprolactone (PCL, inner layer) and an outer layer made of poly lactic-co-glycolic acid (PLGA) and a coaxial porous scaffold with a micrometre fibre structure was successfully produced. The membranes' propriety for intended biomedical applications was assessed by evaluating their morphological structure/physical properties and structural integrity when they underwent the degradation process. A scanning electron microscope (SEM) was used to assess changes in the electrospun scaffolds' structural morphology such as in their fibre diameter, pore size (µm) and the porosity of the scaffold surface which was measured with Image J software. During the 12-week degradation process at room temperature, most of the scaffolds showed a similar trend in their degradation rate except the 60 min scaffolds. The coaxial scaffold had significantly less mass loss than the bilayer PCL/PLGA scaffold with 1.348% and 18.3%, respectively. The mechanical properties of the fibrous membranes were measured and the coaxial scaffolds showed greater tensile strength and elongation at break (%) compared to the bilayer scaffolds. According to the results obtained in this study, it can be concluded that a scaffold made with a coaxial needle is more suitable for tissue engineering applications due to the improved quality and functionality of the resulting polymeric membrane compared to the basic electrospinning process. However, whilst fabricating a vascular graft is the main aim of this research work, the biological data will not present in this paper.

Degradation and Characterisation of Electrospun Polycaprolactone (PCL) and Poly(lactic-co-glycolic acid) (PLGA) Scaffolds for Vascular Tissue Engineering.

The current study aimed to evaluate the characteristics and the effects of degradation on the structural properties of Poly(lactic-co-glycolic acid) (PLGA)- and polycaprolactone (PCL)-based nanofibrous scaffolds. Six scaffolds were prepared by electrospinning, three with PCL 15% (w/v) and three with PLGA 10% (w/v), with electrospinning processing times of 30, 60 and 90 min. Both types of scaffolds displayed more robust mechanical properties with increased spinning times. The tensile strength of both scaffolds with 90-min electrospun membranes did not show a significant difference in their strengths, as the PCL and PLGA scaffolds measured at 1.492 MPa ± 0.378 SD and 1.764 MPa ± 0.7982 SD, respectively. All membranes were shown to be hydrophobic under a wettability test. A degradation behaviour study was performed by immersing all scaffolds in phosphate-buffered saline (PBS) solution at room temperature for 12 weeks and for 4 weeks at 37 °C. The effects of degradation were monitored by taking each sample out of the PBS solution every week, and the structural changes were investigated under a scanning electron microscope (SEM). The PCL and PLGA scaffolds showed excellent fibre structure with adequate degradation, and the fibre diameter, measured over time, showed slight increase in size. Therefore, as an example of fibre water intake and progressive degradation, the scaffold's percentage weight loss increased each week, further supporting the porous membrane's degradability. The pore size and the porosity percentage of all scaffolds decreased substantially over the degradation period. The conclusion drawn from this experiment is that PCL and PLGA hold great promise for tissue engineering and regenerative medicine applications.

Constitutive Modelling of Polylactic Acid at Large Deformation Using Multiaxial Strains.

Sheet specimens of a PLLA-based polymer have been extended at a temperature near to the glass transition in both uniaxial and planar tension, with stress relaxation observed for some time after reaching the final strain. Both axial and transverse stresses were recorded in the planar experiments. In all cases during loading, yielding at small strain was followed by a drop in true stress and then strain hardening. This was followed by stress relaxation at constant strain, during which stress dropped to reach an effectively constant level. Stresses were modelled as steady state and transient components. Steady-state components were identified with the long-term stress in stress relaxation and associated with an elastic component of the model. Transient stresses were modelled using Eyring mechanisms. The greater part of the stress during strain hardening was associated with dissipative Eyring processes. The model was successful in predicting stresses in both uniaxial and planar extension over a limited range of strain rate.

Modelling the Mechanical and Strain Recovery Behaviour of Partially Crystalline PLA.

This is a study of the modelling and prediction of strain recovery in a polylactide. Strain recovery near the glass transition temperature is the underlying mechanism for the shape memory in an amorphous polymer. The investigation is aimed at modelling such shape memory behaviour. A PLA-based copolymer is subjected to stress-strain, stress relaxation and strain recovery experiments at large strain at 60 °C just below its glass transition temperature. The material is 13% crystalline. Using published data on the mechanical properties of the crystals, finite element modelling was used to determine the effect of the crystal phase on the overall mechanical behaviour of the material, which was found to be significant. The finite element models were also used to relate the stress-strain results to the yield stress of the amorphous phase. This yield stress was found to possess strain rate dependence consistent with an Eyring process. Stress relaxation experiments were also interpreted in terms of the Eyring process, and a two-process Eyring-based model was defined that was capable of modelling strain recovery behaviour. This was essentially a model of the amorphous phase. It was shown to be capable of useful predictions of strain recovery.

Self-assembly and structural manipulation of diblock-copolymer grafted nanoparticles in a homopolymer matrix.

Detailed coarse-grained molecular dynamics simulations are performed to investigate the structural and mechanical properties of nanoparticles (NPs) grafted with an amphiphilic AB diblock copolymer, with the A-block being compatible with NPs and the B-block being miscible with a homopolymer matrix. We systematically investigate the effects of the grafting density (Ng), the component ratio (α) and the flexibility of the grafted diblock copolymer on the structural and mechanical properties of polymer nanocomposites (PNCs). Interestingly, we observe that the grafted NPs can form a core-shell like structure attributed to the adsorption of the A-blocks onto the NPs, validated by the radial distribution function of the A and B blocks away from the surface of the NPs. The integrity of the core-shell structure is influenced by the grafting density and the component ratio of the grafted chains. The core-shell structure of the NPs becomes more perfect with greater Ng. The morphology of the NPs is shifted from a network structure to an isolated or well dispersed state upon increasing the grafting density. Meanwhile, we analyze the evolution of the morphology of the NPs during the uniaxial tensile process by calculating the number of neighboring NPs as a function of strain, thus finding that the NP network is broken-up at low grafting density, while only a little change is observed at high grafting density. Upon increasing the component ratio of the B-block to the A-block, the dispersion of the NPs becomes better, characterized by the radial distribution function of NPs-NPs, NPs-A-blocks, NPs-B-blocks, NPs-matrix, the number of neighboring NPs and the snapshots. Lastly, by changing the B-block from being flexible to stiff, the core-shell structure of the NPs disappears after the formation of a typical capsule morphology. This capsule-ordered structure becomes more prominent with the increase in Ng. Remarkably, compared to the effect of the core-shell morphology on the mechanical properties, the capsule morphology reinforces the mechanical properties more obviously. In general, this simulation work provides a deep insight into the structural and mechanical properties of NPs grafted with diblock copolymer chains, in the hope of providing some guidance on the design and preparation of high-performance PNCs.

Aligned electrospun cellulose scaffolds coated with rhBMP-2 for both in vitro and in vivo bone tissue engineering.

Physical properties of scaffolds such as nanofibers and aligned structures have been reported to exert profound effects on the growth and differentiation of stem cells due to their homing-effect features and contact guidance. However, the biological function of aligned nanofibers utilized as bone-scaffold has not been rigorously characterized. In the present study, aligned electrospun cellulose/CNCs nanocomposite nanofibers (ECCNNs) loaded with bone morphogenic protein-2 (BMP-2) were used for the first time to investigate (1) in vitro osteogenic differentiation of human mesenchymal stem cells (BMSCs) and (2) in vivo collagen assembly direction and cortical bone regeneration. Aligned ECCNNs scaffolds loaded with BMP-2 possess good biological compatibility. The growth orientation of BMSCs followed the underlying aligned nanofiber morphology, accompanied with increased alizarin red stain, alkaline phosphatase (ALP) activity and calcium content in vitro while, a rabbit calvaria bone defect model was used in an in vivo study with micro CT and histology analyses.

Controlled in vitro degradation behavior of highly oriented long-chain-branched poly(lactic acid) produced by solid-phase die drawing.

Highly oriented long-chain-branched poly(lactic acid) (LCB-PLA) was fabricated through solid-phase die drawing technology, and the in vitro degradation behavior of the oriented samples in phosphate-buffered saline (PBS) was studied. During degradation, the weight retention and molecular weight for both PLA and LCB-PLA increased with the increase of draw ratio. Moreover, the degradation autocatalytic effect was delayed, and the deterioration of mechanical strength was reduced by orientation, which was beneficial for controlling the degradation degree and decay rate of strength for PLA as bone fixation materials. The influence mechanism of orientation on the in vitro degradation of PLA was explored. The degradation of PLA in PBS was ascribed to the hydrolytic degradation of ester bonds on the molecular chain. By orientation, a dense microfibrillar crystalline structure formed both on the surface and inside of PLA samples, limiting the diffusion and absorption of PBS molecules into the PLA matrix effectively, inhibiting the hydrolytic degradation of ester bonds, and thus delaying the deterioration of mechanical properties of PLA. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

Multiple shape memory behavior of highly oriented long-chain-branched poly(lactic acid) and its recovery mechanism.

The shape memory effect of highly oriented long-chain-branched poly(lactic acid) (LCB-PLA) prepared through solid-phase die drawing technology was studied by comparison with PLA. When the recovery temperature increased from 60°C to 120°C, for PLA, only one-step recovery at about 80°C can be observed and the recovery ratio was below 21.5%, while, for LCB-PLA, multiple recovery behavior with high recovery ratio of 78.8% can be achieved. For oriented PLA, the recovery curve of the final sample showed the same trend with that of sample suffering just free drawing; while for oriented LCB-PLA, the recovery curve of the final sample showed the same trend with that of sample suffering just die drawing. After shape recovery, the mechanical properties of LCB-PLA showed a linear downward trend with the recovery temperature. Together with amorphous phase, the oriented mesomorphic phase, which formed during solid die drawing, can act as switching domains. And thus, upon heating, the chain segment of amorphous phase relaxed at first and triggered the first macroscopical shape recovery, leading to the decrease of long period (Lac) and the thickness of the amorphous layer (La ). Then, with further increasing temperature, the oriented mesomorphic phase gradually relaxed resulting subsequently multi-shape recovery, and the Lac and the La further decreased. Therefore, by regulating the recovery temperature of oriented LCB-PLA, the shape recovery ratio and mechanical strength can be controlled effectively, and thus the self-reinforced and self-fastening effect can be achieved simultaneously for PLA as bone fixation material. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 872-883, 2019.

Orientation direction dependency of cavitation in pre-oriented isotactic polypropylene at large strains.

Orientation direction dependency of whitening activated at large strains was studied using four pre-oriented isotactic polypropylene (iPP) samples with different molecular weights stretched along different directions with respect to the pre-orientation (0°, 45°, and 90°) by means of in situ wide-, small-, and ultra-small-angle X-ray scattering techniques. A macroscopic fracture of iPP materials was also observed following the stress whitening at large strains. These two associated processes in pre-oriented iPP samples at elevated temperatures were found to be governed by not only the molecular weight of iPP but also the pre-orientation direction. For a certain pre-orientation direction of iPP, both the critical stress of cavitation induced-whitening and failure stress increased with increasing molecular weight. For one given molecular weight, the pre-oriented iPP showed the smallest critical stress for whitening and failure stress along the pre-orientation direction (0°) while the samples displayed larger values for the same behaviors when stretched at 45° or 90° with respect to the pre-orientation direction. Such behavior suggested that oriented amorphous networks, with different mechanical strengths, can be generated during the second deformation processes in these pre-oriented iPP samples. The evolution of inter-fibrillar tie chains in highly oriented amorphous networks was considered as the main factor controlling the response of the inner network to the external stress since the cavitation-induced whitening activated at large strains was caused by the failure of load bearing inter-fibrillar tie chains in the oriented amorphous network.

Crystallization Temperature Dependence of Cavitation and Plastic Flow in the Tensile Deformation of Poly(ε-caprolactone).

In situ small-, ultrasmall-, and wide-angle X-ray scattering measurements were performed to investigate the structural evolution of crystalline lamellae and cavities as a function of deformation ratio during tensile deformation of isothermally crystallized poly(ε-caprolactone). The cavities were modeled as cylinder-shaped objects which are oriented along the stretching direction and randomly distributed in the samples, and their dimensions were evaluated by direct model fitting of scattering patterns. At small deformations, the orientation of these cavities at the onset of cavity formation was related to the isothermal crystallization temperature. Upon further stretching, the cavities were found to cluster in the interfibrillar regions at moderate strains where the long spacing of the newly developed lamellae along the stretching direction remained essentially constant. At large orientations, the cooperative deformational behavior mediated via slippage of fibrils was evidenced, the extent of which depended on the cavity number, which could be traced back to the significantly different coupling forces imposed by chains connecting adjacent fibrils. Furthermore, wide-angle X-ray scattering results revealed that a fraction of the polymer chains with their orientation perpendicular to the stretching direction were still preserved even at large macroscopic strains.

Mechanism of Hydrogen-Bonded Complex Formation between Ibuprofen and Nanocrystalline Hydroxyapatite.

Nanocrystalline hydroxyapatite (nanoHA) is the main hard component of bone and has the potential to be used to promote osseointegration of implants and to treat bone defects. Here, using active pharmaceutical ingredients (APIs) such as ibuprofen, we report on the prospects of combining nanoHA with biologically active compounds to improve the clinical performance of these treatments. In this study, we designed and investigated the possibility of API attachment to the surface of nanoHA crystals via the formation of a hydrogen-bonded complex. The mechanistic studies of an ibuprofen/nanoHA complex formation have been performed using a holistic approach encompassing spectroscopic (Fourier transform infrared (FTIR) and Raman) and X-ray diffraction techniques, as well as quantum chemistry calculations, while comparing the behavior of the ibuprofen/nanoHA complex with that of a physical mixture of the two components. Whereas ibuprofen exists in dimeric form both in solid and liquid state, our study showed that the formation of the ibuprofen/nanoHA complex most likely occurs via the dissociation of the ibuprofen dimer into monomeric species promoted by ethanol, with subsequent attachment of a monomer to the HA surface. An adsorption mode for this process is proposed; this includes hydrogen bonding of the hydroxyl group of ibuprofen to the hydroxyl group of the apatite, together with the interaction of the ibuprofen carbonyl group to an HA Ca center. Overall, this mechanistic study provides new insights into the molecular interactions between APIs and the surfaces of bioactive inorganic solids and sheds light on the relationship between the noncovalent bonding and drug release properties.

High orientation of long chain branched poly (lactic acid) with enhanced blood compatibility and bionic structure.

Highly oriented poly (lactic acid) (PLA) with bionic microgrooves was fabricated through solid hot drawing technology for further improving the mechanical properties and blood biocompatibility of PLA. In order to enhance the melt strength and thus obtain high orientation degree, long chain branched PLA was prepared at first through a two-step ring-opening reaction during processing. Linear viscoelasticity combined with branch-on-branch model was used to predict probable compositions and chain topologies of the products, and it was found that the molecular weight of PLA increased and topological structures with star like chain with three arms and tree-like chain with two generations formed during reactive processing, and consequently draw ratio as high as1200% can be achieved during the subsequent hot stretching. With the increase of draw ratio, the tensile strength and orientation degree of PLA increased dramatically. Long chain branching and orientation could significantly enhance the blood compatibility of PLA by prolonging clotting time and decreasing platelet activation. Microgrooves can be observed on the surface of the oriented PLA which were similar to the intimal layer of blood vessel, and such bionic structure resulted from the formation of the oriented shish kebab-like crystals along the draw direction.

Fabrication of drug-loaded anti-infective guided tissue regeneration membrane with adjustable biodegradation property.

For guided tissue regeneration (GTR) membrane, synchronization of the membrane biodegradation rate and tissue regeneration rate is important. Besides, the major reason for GTR membrane failure in clinical application is infection which can be prevented by loading anti-bacterial drug. To realize the consistency in membrane degradation rate and tissue regeneration rate of the anti-infective membrane, we developed metronidazole-loaded electrospun poly(ɛ-caprolactone)-gelatin nanofiber membranes with different poly(ɛ-caprolactone)/gelatin ratios (95:5, 90:10, 80:20, 70:30, 60:40, and 50:50). Homogeneous nanofibers were successfully fabricated. The mechanical strength of the membranes increased with the poly(ɛ-caprolactone) content, while the hydrophilicity decreased. The controlled and sustained release of metronidazole from all the membranes prevented the colonization of anaerobic bacteria. At all poly(ɛ-caprolactone)/gelatin ratios, all the membranes presented good biocompatibility while the increase of gelatin content resulted in enhanced cell adhesion and proliferation. Subcutaneous implantation in rabbits for 8 months demonstrated that all the membranes showed good biocompatibility without infection. Both in vitro and in vivo results showed that the biodegradation rate of the membranes was accelerated with the increase of gelatin content. The biodegradation rate and biocompatibility of the membranes can be adjusted by changing the PCL/gelatin ratio. The optimal membrane can be chosen based on the patient and tissue type to realize the synchronization of membrane degradation with tissue regeneration for the best treatment effect.

Near Infrared Investigation of Polypropylene-Clay Nanocomposites for Further Quality Control Purposes-Opportunities and Limitations.

Polymer nanocomposites are usually characterized using various methods, such as small angle X-ray diffraction (XRD) or transmission electron microscopy, to gain insights into the morphology of the material. The disadvantages of these common characterization methods are that they are expensive and time consuming in terms of sample preparation and testing. In this work, near infrared spectroscopy (NIR) spectroscopy is used to characterize nanocomposites produced using a unique twin-screw mini-mixer, which is able to replicate, at ~25 g scale, the same mixing quality as in larger scale twin screw extruders. We correlated the results of X-ray diffraction, transmission electron microscopy, G' and G″ from rotational rheology, Young's modulus, and tensile strength with those of NIR spectroscopy. Our work has demonstrated that NIR-technology is suitable for quantitative characterization of such properties. Furthermore, the results are very promising regarding the fact that the NIR probe can be installed in a nanocomposite-processing twin screw extruder to measure inline and in real time, and could be used to help optimize the compounding process for increased quality, consistency, and enhanced product properties.

Preparation and in vivo efficient anti-infection property of GTR/GBR implant made by metronidazole loaded electrospun polycaprolactone nanofiber membrane.

Infection is the major reason of GTR/GBR membrane failure in clinical application. In this work, we developed GTR/GBR nanofiber membranes with localized drug delivery function to prevent infection. Metronidazole (MNA), an antibiotic, was successfully incorporated into electrospun polycaprolactone (PCL) nanofibers at different concentrations (0, 1, 5, 10, 20, 30, and 40 wt% polymer). To obtain the optimum anti-infection membrane, we systematically investigated the physical-chemical and mechanical properties of the nanofiber membranes with different drug contents. The interaction between PCL and MNA was identified by molecular dynamics simulation. MNA released in a controlled, sustained manner over 2 weeks and the antibacterial activity of the released MNA remained. The incorporation of MNA improved the hydrophilicity and in vitro biodegradation rate of PCL nanofibers. The nanofiber membranes allowed cells to adhere to and proliferate on them and showed excellent barrier function. The membrane loaded with 30% MNA had the best comprehensive properties. Analysis of subcutaneous implants demonstrated that MNA-loaded nanofibers evoked a less severe inflammatory response than pure PCL nanofibers. These results demonstrate the potential of MNA-loaded nanofiber membranes as GTR/GBR membrane with antibacterial and anti-inflammatory function for extensive biomedical applications.

Drug loaded homogeneous electrospun PCL/gelatin hybrid nanofiber structures for anti-infective tissue regeneration membranes.

Infection is the major reason for guided tissue regeneration/guided bone regeneration (GTR/GBR) membrane failure in clinical application. In this work, we developed GTR/GBR membranes with localized drug delivery function to prevent infection by electrospinning of poly(ε-caprolactone) (PCL) and gelatin blended with metronidazole (MNA). Acetic acid (HAc) was introduced to improve the miscibility of PCL and gelatin to fabricate homogeneous hybrid nanofiber membranes. The effects of the addition of HAc and the MNA content (0, 1, 5, 10, 20, 30, and 40 wt.% of polymer) on the properties of the membranes were investigated. The membranes showed good mechanical properties, appropriate biodegradation rate and barrier function. The controlled and sustained release of MNA from the membranes significantly prevented the colonization of anaerobic bacteria. Cells could adhere to and proliferate on the membranes without cytotoxicity until the MNA content reached 30%. Subcutaneous implantation in rabbits for 8 months demonstrated that MNA-loaded membranes evoked a less severe inflammatory response depending on the dose of MNA than bare membranes. The biodegradation time of the membranes was appropriate for tissue regeneration. These results indicated the potential for using MNA-loaded PCL/gelatin electrospun membranes as anti-infective GTR/GBR membranes to optimize clinical application of GTR/GBR strategies.

Structure and blood compatibility of highly oriented PLA/MWNTs composites produced by solid hot drawing.

Highly oriented poly(lactic acid) (PLA)/multi-walled carbon nanotubes (MWNTs) composites were fabricated through solid hot drawing technology in an effort to improve the mechanical properties and blood biocompatibility of PLA as blood-contacting medical devices. It was found that proper MWNTs content and drawing orientation can improve the tensile strength and modulus of PLA dramatically. With the increase in draw ratio, the cold crystallization peak became smaller, and the glass transition and the melting peak of PLA moved to high temperature, while the crystallinity increased, and the grain size decreased, indicating the stress-induced crystallization of PLA during drawing. MWNTs showed a nucleation effect on PLA, leading to the rise in the melting temperature, increase in crystallinity and reduction of spherulite size for the composites. Moreover, the intensity of (002) diffraction of MWNTs increased with draw ratio, indicating that MWNTs were preferentially aligned and oriented during drawing. Microstructure observation demonstrated that PLA matrix had an ordered fibrillar bundle structure, and MWNTs in the composite tended to align parallel to the drawing direction. In addition, the dispersion of MWNTs in PLA was also improved by orientation. Introduction of MWNTs and drawing orientation could significantly enhance the blood compatibility of PLA by prolonging kinetic clotting time, reducing hemolysis ratio and platelet activation.