Structure,morphology and cell affinity of poly(l-lactide) films surface-functionalized with chitosan nanofibers via a solid–liquid phase separation technique

Poly(l-lactide) films with a nano-structured surface by immobilizing chitosan nanofibers (CSNFs) for improving the cell affinity were fabricated via a solid-liquid phase separation technique. The successful grafting of CSNFs on the surface of poly(l-lactide) films was confirmed by the binding energy of N1s at 398.0 eV in the X-ray photoelectron spectroscopy and the amide I and II bands of chitosan at 1650 and 1568 cm^? 1 in the Fourier transform infrared spectroscopy. Compared with the poly(l-lactide) film, the hydrophilicity was improved with a lower water contact angle of 83.3 ± 1.9° and 75.3 ± 2.5° for the CSNFs-grafted and CSNFs-grafted/anchored poly(l-lactide) films respectively. The scanning electron microscopy and atomic force microscopy analyses showed that the grafted CSNFs with 50–500 nm in diameter were randomly arranged on the film surface and entangled with the anchored CSNFs on the outermost layer. The 3T3 fibroblasts culture indicated cells tended to attach and stretch along the CSNFs on the film surface. The cell viability measurement revealed that among all the samples, the film with both grafted and anchored CSNFs exhibited the highest cell proliferation rate that was twice as much of the poly(l-lactide) film at 7 d. Herein, engineering a nano-structured surface by solid–liquid phase separation will be a promising tool for surface modification of biomaterials.     

Fabrication and in vivo osteogenesis of biomimetic poly(propylene carbonate) scaffold with nanofibrous chitosan network in macropores for bone tissue engineering

A biomimetic poly(propylene carbonate) (PPC) porous scaffold with nanofibrous chitosan network within macropores (PPC/CSNFs) for bone tissue engineering was fabricated by a dual solid–liquid phase separation technique. PPC scaffold with interconnected solid pore wall structure was prepared by the first phase separation, which showed a high porosity of 91.9% and a good compressive modulus of 14.2 ± 0.56 MPa, respectively. By the second phase separation, nanofibrous chitosan of 50–500 nm in diameter was formed in the macropores with little influence on the pore structure and the mechanical properties of PPC scaffold. The nanofibrous chitosan content was calculated to be 9.78% by elemental analysis. After incubation in SBF for 14 days, more apatite crystals were deposited on the pore surface as well as the nanofibrous chitosan surface of PPC/CSNFs scaffold compared with PPC scaffold. The in vitro culture of bone mesenchymal stem cells showed that PPC/CSNFs scaffold exhibited a better cell viability than PPC scaffold. After implantation in rabbits for 16 weeks, the defect was entirely repaired by PPC/CSNFs scaffold, as opposed to the incomplete healing for PPC scaffold. It indicated that PPC/CSNFs scaffold showed a faster in vivo osteogenesis rate than PPC scaffold. Hereby, PPC/CSNFs scaffold will be a potential candidate for bone tissue engineering.     

Xylan polysaccharides fabricated into nanofibrous substrate for myocardial infarction

Myocardial infarction, a main cause of heart failure, leads to loss of cardiac tissue impairment of left ventricular function. Repair of diseased myocardium with in vitro engineered cardiac muscle patch/injectable biopolymers with cells may become a viable option for myocardial infarction. We attempted to solve these problems by in vitro study by selecting a plant based polysaccharides beech wood Xylan for the normal functioning of infarcted myocardium. The present study fabricated Xylan based nanofibrous scaffolds cross-linked with glutaraldehyde (Glu) vapors for 24 h, 48 h and 1% Glu blended fibers for the culture of neonatal rat cardiac cells for myocardial infarction. These nanofibers were characterized by SEM, FT-IR, tensile testing and cell culture studies for the normal expression of cardiac proteins. The observed results showed that the Xylan/polyvinyl alcohol (PVA) 24 h Glu vapor cross-linked nanofibers (427 nm) having mechanical strength of 2.43 MPa and Young modulus of 3.74 MPa are suitable for the culture of cardiac cells. Cardiac cells proliferation increased only by 11% in Xylan/PVA 24 h Glu cross-linked nanofibers compared to control tissue culture plate (TCP). The normal cardiac cell morphology was observed in 24 h cross-linked Xylan/PVA nanofibers but 48 h cross-linked fibers cell morphology was changed to flattened and elongated on the fibrous surfaces. Confocal analysis for cardiac expression proteins actinin, connexin 43 was observed normally in 24 h Glu cross-linked nanofibers compared to all other nanofibrous scaffolds. The fabricated Xylan/PVA nanofibrous scaffold may have good potential for the normal functioning of infarcted myocardium.     

Preparation of zeolite-A/chitosan hybrid composites and their bioactivities and antimicrobial activities

Zeolite-A/chitosan hybrid composites with zeolite contents of 20–55 wt.% were prepared by in situ transformation of silica/chitosan mixtures in a sodium aluminate alkaline solution through impregnation–gelation–hydrothermal synthesis. The products were characterized by X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy, thermogravimetric analysis, and mercury penetration porosimetry. Their in vitro bioactivities were examined using as-synthesized and Ca^2 +-exchanged hybrid composites in simulated body fluid (SBF) for hydroxyapatite (HAP) growth. Their antimicrobial activities for Escherichia coli (E. coli) in trypticase soy broth (TSB) were evaluated using Ag⁺-exchanged hybrid composites. The zeolite-A/chitosan hybrid composites could be prepared as various shapes, including cylinders, plates and thin films. They possessed macropores with pore sizes ranging from 100 to 300 μm and showed compressive mechanical strength as high as 3.2 MPa when the zeolite content was 35 wt.%. Fast growth on the Ca^2 +-exchanged hybrid composites was observed with the highest weight gain of 51.4% in 30 days. The 35 wt.% Ag⁺-exchanged hybrid composite showed the highest antimicrobial activity, which could reduce the 9 × 10⁶ CFU mL^? 1 E. coli concentration to zero within 4 h of incubation time with the Ag⁺-exchanged hybrid composite amount of 0.4 g L^? 1. The bioactivity and antimicrobial activity could be combined by ion-exchanging the composites first with Ca^2 + and then with Ag⁺. These zeolite-A/chitosan hybrid composites have potential applications on tissue engineering and antimicrobial food packaging.     

Electrospun chitosan/PEDOT nanofibers

Plasma-modified chitosan and poly(3,4-ethylenedioxythiophene) were blended to obtain conducting nanofibers with polyvinyl alcohol as a supporting polymer at various volumetric ratios by electrospinning method. Chemical compositions and molecular interactions among nanofiber blend components were determined using Fourier transform infrared spectroscopy (FTIR). The conducting blends containing plasma-modified chitosan resulted in a superior antibacterial activity and thinner fiber formation than those containing chitosan without plasma-modification. The obtained nanofiber diameters of plasma-modified chitosan were in the range of 170 to 200 nm and those obtained from unmodified chitosan were in the range of 190 to 246 nm. The electrical and electrochemical properties of nanofibers were also investigated by four-point probe conductivity and cyclic voltammetry measurements.     

Effect of carbonization temperature on properties of aligned electrospun polyacrylonitrile carbon nanofibers

Aligned electrospun nanofibrous bundle was used as the raw material for pretreatment, preoxidation and carbonization processes to prepare carbon nanofibers in a procedure temperature-controlled sintering furnace. Effect of carbonization temperature on the morphology and structural performance of nanofibers was investigated in present study. Results showed that R_I (the relative intensity radio between Disordered peak and Graphite peak) of nanofibers carbonized at 1000 °C is 0.90, carbon content is up to 85.67%, conductivity is 105.44 S·cm^− 1, Young's modulus is 68.8 ± 0.42 GPa, and fiber strength is 306.0 ± 9.0 MPa, all of which endow the fibers with a superior comprehensive property.     

Functional shape memory composite nanofibers with graphene oxide filler

In the present study, we prepared a series of graphene oxide (GO) filled shape memory polyurethane (SMPU) nanofibers and systematically investigated the morphological, thermal and mechanical properties, surface wettability, and the shape memory effect (SME) followed by the proposed programming model. The results show that GO can be well dispersed within the SMPU matrix, and the introduction of GO significantly improves the mechanical strength, surface wettability, and thermal stability of the SMPU. Compared with pristine SMPU nanofibrous mats, the prepared SMPU/GO nanofibrous mats have better SME and lower thermal shrinkage. When the loading amount of GO increased to 4.0 wt%, the thermal shrinkage ratio (R_ts) of composite nanofibrous mats could be as low as 4.7 ± 0.3%, while the average fixation ratio (R_f) and recovery ratio (R_r) could be as high as 92.1% and 96.5%, respectively. The study indicates that GO is a desirable reinforcing filler for preparing shape memory nanofibers with improved properties.     

Gold nanoparticle/polymer nanofibrous composites by laser ablation and electrospinning

Poly(vinylpyrolidone) (PVP) nanofibers incorporating gold nanoparticles (Au-NPs) were produced in combination with laser ablation and electrospinning techniques. The Au-NPs were directly synthesized in PVP solution by laser ablation and then, the electrospinning of PVP/Au-NPs solution was carried out for obtaining nanofibrous composites. The presence of Au-NPs in the PVP nanofibers was confirmed by SEM, TEM and EDX analyses. The SEM imaging elucidated that the electrospun PVP/Au-NPs nanofibers were bead-free having average fiber diameter of 810 ± 480 nm. The TEM imaging indicated that the Au-NPs were in spherical shape having diameters in the range of 5 to 20 nm and the Au-NPs were more or less dispersed homogeneously in the PVP nanofiber matrix. The FTIR study suggested the presence of molecular interactions between PVP matrix and the Au-NPs in the nanofibrous composites. The UV–Vis measurement confirmed the enhancement of the optical properties of the PVP/Au-NPs nanofibers in the solid state due to the surface plasma resonance effect of Au-NPs.     

Physico-chemical/biological properties of tripolyphosphate cross-linked chitosan based nanofibers

In this study, chitosan-PEO blend, prepared in a 15 M acetic acid, was electrospun into nanofibers (~ 78 nm diameter) with bead free morphology. While investigating physico-chemical parameters of blend solutions, effect of yield stress on chitosan based nanofiber fabrication was clearly evidenced. Architectural stability of nanofiber mat in aqueous medium was achieved by ionotropic cross-linking of chitosan by tripolyphosphate (TPP) ions. The TPP cross-linked nanofiber mat showed swelling up to ~ 300% in 1 h and ~ 40% degradation during 30 day study period. 3T3 fibroblast cells showed good attachment, proliferation and viability on TPP treated chitosan based nanofiber mats. The results indicate non-toxic nature of TPP cross-linked chitosan based nanofibers and their potential to be explored as a tissue engineering matrix.     

Electrospun nanofibers composed of poly(ε-caprolactone) and polyethylenimine for tissue engineering applications

Poly(ε-caprolactone) (PCL) electrospun nanofibers have been reported as a scaffold for tissue engineering application. However, high hydrophobicity of PCL limits use of functional scaffold. In this study, PCL/polyethylenimine (PEI) blend electrospun nanofibers were prepared to overcome the limitation of PCL ones because the PEI as a cationic polymer can increase cell adhesion and can improve the electrospinnability of PCL. The structure, mechanical properties and biological activity of the PCL/PEI electrospun nanofibers were studied. The diameters of the PCL/PEI nanofibers ranged from 150.4 ± 33 to 220.4 ± 32 nm. The PCL/PEI nanofibers showed suitable mechanical properties with adequate porosity and increased hydrophilic behavior. The cell adhesion and cell proliferation of PCL nanofibers were increased by blending with PEI due to the hydrophilic properties of PEI.     

Macroporous and nanofibrous poly(lactide-co-glycolide)(50/50) scaffolds via phase separation combined with particle-leaching

Poly(lactide-co-glycolide) (PLGA) copolymers are the most prevalent materials for tissue engineering applications. To mimic the real microenvironment of extracellular matrix (ECM) for cell growth, nanofibrous PLGA scaffolds are preferred. PLGA5050 (in which the molar ratio of lactidyl to glycolidyl units is 50:50), which is an utterly amorphous polymer, was first reported to be made into nanofibrous networks (fiber diameter around 500 nm) using phase separation from PLGA5050/THF solutions in this study. The concentration of polymeric solution had significant effects on fiber diameter and unit length. Nonsolvent (e.g. H₂O) was unnecessary to form the PLGA5050 gel, which was critical to nanofibrosis, as if the environmental temperature for gelation occurrence was low enough (? 70 °C). The physical crosslinks to stabilize the PLGA5050/THF gel were believed to be GA segments along the backbone owing to their inferior solubility in THF. The addition of H₂O would cause adverse effects of liquid–liquid phase separation and nanofibrosis failure owing to the hydrophilicity of glycolidyl units. Associating with the phase separation method, particle-leaching technique was applied to fabricate three-dimensional scaffolds with macroporous and nanofibrous structures. To ensure the occurrence of nanofibrosis on macropore walls, the temperature of salt particles should be best lowed to ? 70 °C beforehand. Accordingly, scaffolds prepared under varied parameters exhibited different nanofiber and pore morphologies, which affected the pore size, porosity, specific surface area, water contact angle and protein adsorption ability etc. The preliminary cell (MC3T3-E1) culture confirmed the cell ingrowth into the macroporous and nanofibrous PLGA5050 scaffolds in comparison with the solely nanofibrous matrixes. This kind of bi-scaled three dimensional matrixes can be superior candidate scaffolds for tissue engineering applications.     

Fabrication and characterization of three-dimensional nanofiber membrance of PCL–MWCNTs by electrospinning

The uniform and highly smooth nanofibers of poly(ε-caprolactone) (PCL) composited with different multi-walled carbon nanotubes (MWCNTs) content (ranging from 0.1 wt.% to 5 wt.%) were successfully prepared by electrospinning method without the occurrence of bead defects in this study. The PCL–0.5 wt.%MWCNTs nanofiber membrane exhibited the maximum tensile strength (about 1.42 MPa), which was increased by 46% compared with that of electrospun pure PCL nanofiber membrane. Moreover, the PCL–MWCNTs nanofiber membrane exhibited three-dimensional porous structure with a high porosity over 90%. The average diameter of PCL–MWCNTs nanofibers decreased with the addition of MWCNTs and there was a narrow diameter distribution in the range of 52–244 nm when the amount of MWCNTs was 0.5 wt.%. Compared with pure PCL nanofibers, PCL–MWCNTs nanofibers showed accelerating degradation behavior. In addition, the cytotoxicity results revealed that the electrospun PCL–MWCNTs nanofiber membranes possessed good in vitro biocompatibility, and hemolysis and kinetic clotting tests indicated that the PCL nanofiber membranes did not enhance blood coagulation after the addition of MWCNTs. It can be concluded that such kind of electrospun PCL–MWCNTs nanofibers may be promising candidate for tissue engineering scaffold application.     

Thermally induced porous carbon nanofibers for electrochemical capacitor electrodes from phenylsilane and polyacrylonitrile blend solutions

This work focuses on preparations of porous carbon composite nanofibers (CCNFs) with silicon-containing compounds and the introduction of a high specific surface area through the creation of pores by a simple thermal treatment. Blends of phenylsilane (PS) solutions at various concentrations and polyacrylonitrile (PAN) were electrospun into nanofibers. This process was followed by carbonization at 800 °C to create CCNFs with diameters of 60–200 nm and a high specific surface area of over 800 m²/g. The specific capacitance of the electrode in 6 M KOH solution was extraordinarily high (180 F/g).     

Development,characterization, and in vitro bioactivity studies of sol–gel bioactive glass/poly(l-lactide) nanocomposite scaffolds

Developing materials combining the advantages of synthetic polymers and bioactive glass nanoparticles can provide an efficient bone engineering scaffold. In this study, sol–gel bioactive glass (SG) nanoparticles were synthesized by quick alkali-mediation; sol–gel derived bioactive glass/poly(l-lactide) nanocomposite scaffolds were then developed. The influence of the glass content on the porosity of nanocomposite scaffolds was evaluated by SEM. The results showed that the neat polymer scaffold (PLA) has a highly interconnected porous structure with a maximum pore size of about 250 μm. For the composite scaffold containing 25 wt.% glass (SGP25), the decrease in the maximum pore size, (to about 200 μm) was not significant while for the SGP50 composite scaffold containing 50 wt.% glass it was a significant decrease (to about 100 μm). The apparent porosity of the scaffolds was 56.56% ± 7.15, 54.14% ± 3.84, and 53.11% ± 3.99 for PLA, SGP25, and, SGP50 respectively. FT-IR, TGA, and XRD results revealed some interaction of the glass filler with the polymeric matrix in the scaffolds. The degradation study showed that, by increasing the glass content in the scaffolds, the water absorption decreased, the weight loss increased, and the cumulative ion concentrations released from them also increased. This indicates the possibility of modulating the degradation rate by varying the glass/polymer ratio. At the end of the incubation period, the weight losses were around 5.44% ± 0.96, 32.50% ± 2.73, and 41.47% ± 3.02 for the PLA, SGP25, and SGP50, respectively. Moreover, the water uptake reached 119.65% ± 18.88 and 93.39% ± 13.01 for SGP25 and SGP50, respectively. The addition of the SG to the scaffolds was found to enhance their in vitro bioactivity. Therefore, these nanocomposite scaffolds have a potential to be applied in bone engineering. All data are expressed as mean ± standard deviation (n = 3).     

Formation of nano-hydroxyapatite crystal in situ in chitosan–pectin polyelectrolyte complex network

Hydroxyapatite (HA)/polysaccharide composites have been widely used in bone tissue engineering due to their chemical similarity to natural bone. Polymer matrix-mediated synthesis of nano-hydroxyapatite is one of the simplest models for biomimetic. In this article, the nano-hydroxyapatite/chitosan–pectin (nHCP) composites were prepared through in situ mineralization of hydroxyapatite in chitosan–pectin polyelectrolyte complex (PEC) network. The formation processes of nHCP were investigated by X-ray diffraction (XRD) analysis. The interactions between nHA crystal and chitosan–pectin PEC networks were studied using Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). The morphology and structure of nHA crystal were characterized by XRD and Transmission Electron Microscope (TEM). Results suggested that the interfacial interactions between nano-hydroxyapatite crystal and chitosan–pectin PEC network assist the site specific nucleation and growth of nHA nanoparticles. The nHA crystals grow along the c-axis. In this process, pH value is the main factor to control the nucleation and growth of nHA crystal in chitosan–pectin PEC networks, because both the interactions' strength between nHA crystal and chitosan–pectin and diffusion rate of inorganic ions depend on the pH value of the reaction system. Apart from the pH value, the chitosan/pectin ratio and [Ca²⁺] also take important effects on the formation of nHA crystal. An effective way to control the size of nHA crystal is to adjust the content of pectin and [Ca²⁺]. It is interesting that the Zeta potential of nHCP composites is about ? 30 mV when the chitosan/pectin ratio ≦ 1:1, and the dispersion solution of nHCP composites has higher stability, which provides the possibility to prepare 3D porous scaffolds with nHCP for bone tissue engineering.     

Trabecular scaffolds created using micro CT guided fused deposition modeling

Free form fabrication and high resolution imaging techniques enable the creation of biomimetic tissue engineering scaffolds. A 3D CAD model of canine trabecular bone was produced via micro CT and exported to a fused deposition modeler, to produce polybutylene terephthalate (PBT) trabeculated scaffolds and four other scaffold groups of varying pore structures. The five scaffold groups were divided into subgroups (n = 6) and compression tested at two load rates (49 N/s and 294 N/s). Two groups were soaked in a 25 °C saline solution for 7 days before compression testing. Micro CT was used to compare porosity, connectivity density, and trabecular separation of each scaffold type to a canine trabecular bone sample. At 49 N/s the dry trabecular scaffolds had a compressive stiffness of 4.94 ± 1.19 MPa, similar to the simple linear small pore scaffolds and significantly more stiff (p < 0.05) than either of the complex interconnected pore scaffolds. At 294 N/s, the compressive stiffness values for all five groups roughly doubled. Soaking in saline had an insignificant effect on stiffness. The trabecular scaffolds matched bone samples in porosity; however, achieving physiologic connectivity density and trabecular separation will require further refining of scaffold processing.     

Microstructure,mechanical property and corrosion behaviors of interpenetrating C/Mg-Zn-Mn composite fabricated by suction casting

A novel interpenetrating C/Mg-Zn-Mn composite was fabricated by infiltrating Mg-Zn-Mn alloy into porous carbon using suction casting technique. The microstructure, mechanical properties and corrosion behaviors of the composite have been evaluated by means of SEM, XRD, mechanical testing and immersion test. It was shown that the composite had a compact structure and the interfacial bonding between Mg-Zn-Mn alloy and carbon scaffold was very well. The composite had an ultimate compressive strength of (195 ± 15) MPa, which is near with the natural bone (2–180 MPa) and about 150-fold higher than that of the original porous carbon scaffold, and it still retained half of the strength of the bulk Mg-Zn-Mn alloy. The corrosion test indicated that the mass loss percentage of the composite was 52.9% after 30 days′ immersion in simulated body fluid (SBF) at 37 ± 0.5 °C, and the corrosion rates were 0.043 mg/cm²h and 0.028 mg/cm²h after 3 and 7 days′ immersion, respectively. The corrosion products on the composite surface were mainly Mg(OH)₂ and hydroxyapatite (HA).     

Biomimetic mineralisation of apatites on Ca2+ activated cellulose templates

We investigated the activation of regenerated cellulose 2D model thin films and 3D fabric templates with calcium dihydroxide. The Langmuir–Blodgett (LB) film technique was applied for manufacturing of the model thin films using a trimethylsilyl derivative of cellulose (TMS-cellulose). Regenerated cellulose films were obtained by treating the TMS-cellulose LB-films with hydrochloric acid vapours. For 3D templates, regenerated cellulose fabrics (Lyocell®) were used. The regenerated cellulose templates were activated with a Ca(OH)₂-suspension and subsequently exposed to 1.5 × SBF to induce the in situ formation of biomimetic calcium phosphate phases. FTIR and Raman spectroscopy showed that the Ca(OH)₂ and calcite present from reaction with HCO₃⁻ on the template surface were dissolved in the initial stage of exposure to the 1.5 × SBF. After 1 day, the formation of apatitic phases in 1.5 × SBF was observed. According to detailed calculations, high supersaturation levels S in close vicinity to the template surface (S > 16) resulting from the Ca²⁺ diffusion induced the formation of biomimetic calcium phosphate. The biomimetic calcium phosphates were identified by FTIR and Raman spectroscopy as highly carbonated apatites (HCA) lacking hydroxyl ions. 3D fabric templates of regenerated cellulose covered with a biomimetic coating of apatite might be of particular interest for novel scaffold architectures in bone repair and tissue engineering.     

Preparation of monolithic aluminium titanate with well-defined macropores via a sol–gel process accompanied by phase separation

Monolithic aluminium titanate with well-defined macropores has been prepared through a sol–gel process accompanied by phase separation, using poly(ethylene oxide) (PEO) to induce the phase separation and formamide (FA) to control the gelation of Al₂O₃–TiO₂ system. Appropriate amounts of PEO and formamide allow the formation of aluminium titanate xerogel with cocontinuous macroporous structure and a monolithic shape. The pore size of the resultant dried gels is in the range of 2–3 μm and the porosity is above 60%. The as-dried gel is amorphous and completely transforms into a single phase Al₂TiO₅ after heat-treated at 1300 °C. The macroporous structure is well maintained while the skeleton becomes smooth after heat-treatment.     

Transparent and flexible cellulose nanofibers/silver nanowires/acrylic resin composite electrode

In this study, we report a novel, eco-friendly and simple method to fabricate cellulose nanofibers (CNFs)/silver nanowires (AgNWs)/acrylic resin (AR) composite electrode. CNFs with average diameter of 15 nm were disintegrated only by one time-pass grinding. Aqueous dispersion of AgNWs was embedded onto the surface of CNFs film by simple vacuum filtration. The final composite electrode was obtained by impregnating CNFs/AgNWs film to AR with the assist of adhesive tape. This electrode with AgNWs density of 134 mg/m² showed low sheet resistance (4 Ω/sq), and high light transmittance (85%) which was 6% lower than that of neat AR. The coefficient of thermal expansion of the composite electrode was as low as 25.32 ppm K⁻¹. The tensile strength and Young’s modulus of CNFs/AgNWs/AR composite film were 35.71 MPa and 1.63 GPa, which were about 8 and 5.8 times larger than neat AR film, respectively.