Biocompatible Crosslinked Nanofibers of Poly(Vinyl Alcohol)/Carboxymethyl‐Kappa‐Carrageenan Produced by a Green Process

This study presents a new type of biocompatible nanofiber based on poly(vinyl alcohol) (PVA) and carboxymethyl‐kappa‐carrageenan (CMKC) blends, produced with no generation of hazardous waste. The nanofibers are produced by electrospinning using PVA:CMKC blends with ratios of 1:0, 1:0.25, 1:0.4, 1:0.5, and 1:0.75 (w/w PVA:CMKC) in aqueous solution, followed by thermal crosslinking. The diameter of the fibers is in the nanometer scale and below 300 nm. Fourier transform infrared spectroscopy shows the presence of the carboxyl and sulfate groups in all the fibers with CMKC. The nanofibers from water‐soluble polymers are stabilized by thermal crosslinking. The incorporation of CMKC improves cytocompatibility, biodegradability, cell growth, and cell adhesion, compared to PVA nanofibers. Furthermore, the incorporation of CMKC modulates phenotype of human adipose‐derived stem cells (ADSCs). PVA/CMKC nanofibers enhance ADSC response to osteogenic differentiation signals and are therefore good candidates for application in tissue engineering to support stem cells.     

Fabrication and characterization of composites composed of a bioresorbable polyester matrix and surface modified calcium carbonate whisker for bone regeneration

This work aims to evaluate the potential of a bioresorbable composite as material for bone regeneration. Surface‐modified calcium carbonate whiskers (CCWs) were prepared by grafting of ethylene glycol (EG) using 1,6‐hexamethylene diisocyanate as coupling agent, followed by ring‐opening polymerization of l ‐lactide initiated by the hydroxyl group of EG. The resulting PLLA‐EG‐g‐CCW was used as filler to reinforce a bioresorbable terpolymer, poly(l ‐lactide‐co‐trimethylene carbonate‐co‐glycolide) (PLTG). The mechanical properties and thermal stability of the PLTG/PLLA‐EG‐g‐CCW composites were greatly improved. Compared with neat PLTG, a 39.3% increase in tensile strength and 26.7% increase in elongation at break were obtained for the composite with 2 wt% PLLA‐EG‐g‐CCW filler. This was assigned to the reinforcement effect of evenly dispersed PLLA‐EG‐g‐CCW in the polymeric matrix. In fact, entanglement of PLLA grafts at the surface of PLLA‐EG‐g‐CCW with PLTG chains results in a homogeneous distribution of the filler in the matrix. Thus, the composites are simultaneously strengthened and toughened. The cytocompatibility of the materials was evaluated from cell morphology and 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay using L929 mouse fibroblast cell line. The results indicate that the composite presents very low cytotoxicity. Copyright © 2017 John Wiley & Sons, Ltd.     

Improved antibacterial properties of an Mg‐Zn‐Ca alloy coated with chitosan nanofibers incorporating silver sulfadiazine multiwall carbon nanotubes for bone implants

Bacteria‐caused infection remains an issue in the treatment of bone defects by means of Mg‐Zn‐Ca alloy implants. This study aimed to improve the antibacterial properties of an Mg‐Zn‐Ca alloy by coating with chitosan‐based nanofibers with incorporated silver sulfadiazine (AgSD) and multiwall carbon nanotubes (MWCNTs). AgSD and MWCNTs were prepared at a weight ratio of 1:1 and then added to chitosan at varying concentrations (ie, 0, 0.25, 0.5, and 1.5 wt.%) to form composites. The obtained composites were ejected in nanofiber form using an electrospinning technique and coated on the surface of an Mg‐Zn‐Ca alloy to improve its antibacterial properties. A microstructural examination by scanning electron microscopy (SEM) revealed the diameter of chitosan nanofiber ejected increased with the concentration of AgSD‐MWCNTs. The incorporation of AgSD‐MWCNTs into the chitosan nanofibers was confirmed by Fourier transform infrared spectroscopy (FTIR). Examination of the antibacterial activity shows that chitosan nanofibers with AgSD‐MWCNTs can significantly inhibit the growth and infiltration of Escherichia coli and Staphylococcus aureus. Biocompatibility assay and cell morphology observations demonstrate that AgSD‐MWCNTs incorporated into nanofibers are cytocompatible. Taken together, the results of this study demonstrate the potential application of electrospun chitosan with AgSD‐MWCNTs as an antibacterial coating on Mg‐Zn‐Ca alloy implants for bone treatment.     

含骨脱细胞基质电纺纤维的成骨性能

通过脱细胞技术制备了猪骨脱细胞基质(DBM), 用胃蛋白酶消化DBM使其变为可溶形式, 采用静电纺丝技术制备了含有DBM的左旋聚乳酸(PLLA)电纺纤维(PLLA/DBM), 并对PLLA/DBM的形貌、 亲水性、 细胞相容性、 成骨性能和体外矿化能力进行评价. 研究结果表明, 脱细胞处理能够有效去除骨组织中的细胞成分, 使DNA含量显著下降. DBM经胃蛋白酶处理后溶于六氟异丙醇(HFIP), 可进行静电纺丝, 制备的PLLA/DBM[m(PLLA)∶m(DBM)=10∶0, 9∶1, 7∶3, 5∶5]电纺纤维具有良好的亲水性, 且无细胞毒性, 对骨髓间充质干细胞的黏附及成骨分化有明显的诱导促进作用, 体外生物矿化效果优良.     

Electrospinning of carboxymethyl starch/poly(L‐lactide acid) composite nanofiber

Carboxymethyl starch (CMS) is a natural polymer derived from sago starch that is obtained from sago palm (Metroxylon spp.). Herein, CMS was used as a polysaccharide source in preparations of composite nanofibers with poly(L‐lactide acid) (PLLA). The incorporation of CMS with PLLA in nanofiber form has great potential to be used in biomedical applications. The composite PLLA/CMS nanofibers were fabricated by electrospinning technique at various ratios of CMS, which were 5, 10, 15, and 20% vol/vol. The composite nanofibers were characterized according to their physical morphology, chemical interaction, wettability, water uptake, and thermal and mechanical behaviors. The result showed that uniform and bead‐free nanofibers were produced at the low ratio of CMS while fractal and discontinuing fiber was observed at a high ratio of CMS. A better mechanical strength was obtained at low CMS ratio as compared with higher one. Fourier transform infrared results showed that there was an interaction between CMS and PLLA after electrospinning. The surface hydrophilicity and water uptake increased with increasing ratio of CMS. The results from the differential scanning calorimeter analysis showed the decrease of the glass transition (T_g) and cold crystallization temperature (T_cc) of the nanofiber after addition of CMS in PLLA.     

Electrospun poly(l‐lactide) nanofibers coated with mineral trioxide aggregate enhance odontogenic differentiation of dental pulp stem cells

A combination of bioceramics and nanofibrous scaffolds holds promising potential for inducing of mineralization in connective tissues. The aim of the present study was to investigate the attachment, proliferation and odontogenic differentiation of dental pulp stem cells (DPSC) on poly(l ‐lactide) (PLLA) nanofibers coated with mineral trioxide aggregate (MTA). Polymeric scaffolds were fabricated via the electrospinning method and their surface was coated with MTA. DPSC were isolated from dental pulp and their biological behavior was evaluated on scaffolds and the control group using MTT assay. Alkaline phosphatase (ALP) activity, biomineralization and the expression of odontogenic genes were analyzed during odontogenic differentiation. Isolated DPSC showed spindle‐shaped morphology with multi‐lineage differentiation potential and were positive for CD73, CD90 and CD105. MTA‐coated PLLA (PLLA/MTA) exhibited nanofibrous structure with average fiber diameter of 756 ± 157 nm and interconnected pores and also suitable mechanical properties. Similar to MTA, these scaffolds were shown to be biocompatible and to support the attachment and proliferation of DPSC. ALP activity transiently peaked on day 14 and was significantly higher in PLLA/MTA scaffolds than in the control groups. In addition, increasing biomineralization was observed in all groups with a higher amount in PLLA/MTA. Odontogenic‐related genes, DSPP and collagen type I showed a higher expression in PLLA/MTA on days 21 and 14, respectively. Taken together, MTA/PLLA electrospun nanofibers enhanced the odontogenic differentiation of DPSC and showed the desired characteristics of a pulp capping material.     

Enhanced crystallization,thermal properties,and hydrolysis resistance of poly(l-lactic acid) and its stereocomplex by incorporation of graphene nanoplatelets

Poly(d-lactic acid) (PDLA) and graphene nanoplatelets were used as nucleating agents for poly(l-lactic acid) (PLLA). The graphene (1 wt%) shows a more pronounced effect than PDLA in facilitating PLLA crystallization. Graphene effect on crystallization of stereocomplex (SC) polylactide is also demonstrated. Although medium molecular weight PLLA was blended with a limited content (1 wt%) of low molecular weight PDLA in the presence of graphene (0.5 phr), SC melting temperature is slightly increased without the use of high molecular weight polylactide pair. Also, optimal graphene content (0.5 phr–1.5 phr) promotes crystallization of PLLA homocrystals in the three-component system (PLLA/PDLA/graphene). Graphene additionally enhances Young's modulus and barrier property to thermal degradation of both PLLA and SC systems. Furthermore, PLLA/graphene is more resistant to hydrolysis than PLLA. Likewise, PLLA/PDLA/graphene is more stable than PLLA/PDLA during hydrolysis.     

Toughening modification of PLLA with PCL in the presence of PCL‐b‐PLLA diblock copolymers as compatibilizer

To obtain an effective compatibilizer for the blends of poly(L‐lactide) (PLLA) and poly(ε‐caprolactone) (PCL), the diblock copolymers PCL‐b‐PLLA with different ratios of PCL/PLLA (CL/LA) and different molecular weights (M_n) were synthesized by ring‐opening polymerization (ROP) of L‐lactide with monohydric poly(ε‐caprolactone) (PCL‐OH) as a macro‐initiator. These copolymers were melt blended with PLLA/PCL (80/20) blend at contents between 3.0 and 20 phr (parts per hundred resin), and the effects of added PCL‐b‐PLLA on the mechanical, morphological, rheological, and thermodynamic properties of the PLLA/PCL/PCL‐b‐PLLA blends were investigated. The compatibility between PLLA matrix and PCL phase was enhanced with decreasing in CL/LA ratios or increasing in M_n for the added PCL‐b‐PLLA. Moreover, the crystallinity of PLLA matrix increased because of the added compatibilizers. The PCL‐b‐PLLA with the ratio of CL/LA (50/50) and M_n ≥ 39.0 kg/mol were effective compatibilizers for PLLA/PCL blends. When the content of PCL‐b‐PLLA is greater than or equal to 5 phr, the elongations at break of the PLLA/PCL/PCL‐b‐PLLA blends all reached approximately 180%, about 25 times more than the pristine PLLA/PCL(80/20) blend.     

S‐Nitrosoglutathione‐Based Nitric Oxide‐Releasing Nanofibers Exhibit Dual Antimicrobial and Antithrombotic Activity for Biomedical Applications

The novel use of nanofibers as a physical barrier between blood and medical devices has allowed for modifiable, innovative surface coatings on devices ordinarily plagued by thrombosis, delayed healing, and chronic infection. In this study, the nitric oxide (NO) donor S‐nitrosoglutathione (GSNO) is blended with the biodegradable polymers polyhydroxybutyrate (PHB) and polylactic acid (PLA) for the fabrication of hemocompatible, antibacterial nanofibers tailored for blood‐contacting applications. Stress/strain behavior of different concentrations of PHB and PLA is recorded to optimize the mechanical properties of the nanofibers. Nanofibers incorporated with different concentrations of GSNO (10, 15, 20 wt%) are evaluated based on their NO‐releasing kinetics. PLA/PHB + 20 wt% GSNO nanofibers display the greatest NO release over 72 h (0.4–1.5 × 10^?10 mol mg^?1 min^?1). NO‐releasing fibers successfully reduce viable adhered bacterial counts by ≈80% after 24 h of exposure to Staphylococcus aureus. NO‐releasing nanofibers exposed to porcine plasma reduce platelet adhesion by 64.6% compared to control nanofibers. The nanofibers are found noncytotoxic (>95% viability) toward NIH/3T3 mouse fibroblasts, and 4′,6‐diamidino‐2‐phenylindole and phalloidin staining shows that fibroblasts cultured on NO‐releasing fibers have improved cellular adhesion and functionality. Therefore, these novel NO‐releasing nanofibers provide a safe antimicrobial and hemocompatible coating for blood‐contacting medical devices.     

Controlling the Poly(ε‐caprolactone) Degradation to Maintain the Stemness and Function of Adipose‐Derived Mesenchymal Stem Cells in Vascular Regeneration Application

Biodegradable poly(ε‐caprolactone) (PCL) scaffolds with adipose‐derived mesenchymal stem cells (ADSCs) have been used in vascular regeneration studies. An evaluation method of the effect of PCL degradation products (DP) on the viability, stemness, and differentiation capacities of ADSCs is established. ADSCs are cultured in medium containing different concentrations of PCL DP before evaluating the effect of PCL DP on the cell apoptosis and proliferation, cell surface antigens, adipogenic and osteogenic differentiation capacities, and capacities to differentiate into endothelial cells and smooth muscle cells. The results demonstrate that PCL DP exceed 0.05 mg mL^?1 may change the stemness and differentiation capacities of ADSCs. Therefore, to control the proper concentration of PCL DP is essential for ADSCs in vascular regeneration application.     

Acceleration of osteogenic differentiation by sustained release of BMP2 in PLLA/graphene oxide nanofibrous scaffold

After about three decades of experience, tissue engineering has become one of the most important approaches in reconstructive medical research to treat non‐self‐healing bone injuries and lesions. Herein, nanofibrous composite scaffolds fabricated by electrospinning, which containing of poly(L‐lactic acid) (PLLA), graphene oxide (GO), and bone morphogenetic protein 2 (BMP2) for bone tissue engineering applications. After structural evaluations, adipose tissue derived mesenchymal stem cells (AT‐MSCs) were applied to monitor scaffold's biological behavior and osteoinductivity properties. All fabricated scaffolds had nanofibrous structure with interconnected pores, bead free, and well mechanical properties. But the best biological behavior including cell attachment, protein adsorption, and support cells proliferation was detected by PLLA‐GO‐BMP2 nanofibrous scaffold compared to the PLLA and PLLA‐GO. Moreover, detected ALP activity, calcium content and expression level of bone‐related gene markers in AT‐MSCs grown on PLLA‐GO‐BMP2 nanofibrous scaffold was also significantly promoted in compression with the cells grown on other scaffolds. In fact, the simultaneous presence of two factors, GO and BMP2, in the PLLA nanofibrous scaffold structure has a synergistic effect and therefore has a promising potential for tissue engineering applications in the repair of bone lesions.     

Osteogenic Effects of VEGF‐Overexpressed Human Adipose‐Derived Stem Cells with Whitlockite Reinforced Cryogel for Bone Regeneration

Bone is a vascularized tissue that is comprised of collagen fibers and calcium phosphate crystals such as hydroxyapatite (HAp) and whitlockite (WH). HAp and WH are known to elicit bone regeneration by stimulating osteoblast activities and osteogenic commitment of stem cells. In addition, vascular endothelial growth factor (VEGF) is shown to promote osteogenesis and angiogenesis which is considered as an essential process in bone repair by providing nutrients. In this study, VEGF‐secreting human adipose‐derived stem cells (VEGF‐ADSCs) are developed by transducing ADSCs with VEGF‐encoded lentivirus. Additionally, WH‐reinforced gelatin/heparin cryogels (WH‐C) are fabricated by loading WH into gelatin/heparin cryogels. VEGF‐ADSC secrete tenfold more VEGF than ADSC and show increased VEGF secretion with cell growth. Also, incorporation of WH into cryogels provides a mineralized environment with ions secreted from WH. When the VEGF‐ADSCs are seeded on WH‐C, sustained release of VEGF is observed due to the specific affinity of VEGF to heparin. Finally, the synergistic effect of VEGF‐ADSC and WH on osteogenesis is successfully confirmed by alkaline phosphatase and real‐time polymerase chain reaction analysis. In vivo bone formation is demonstrated via implantation of VEGF‐ADSC seeded WH‐C into mouse calvarial bone defect model, resulted in enhanced bone development with the highest bone volume/total volume.     

Antibacterial and wound healing properties of cellulose acetate electrospun nanofibers loaded with bioactive glass nanoparticles; in-vivo study

Bioactive glasses (BGs) have gained great attention owing to their versatile biological properties. Combining BG nanoparticles (BGNPs) with polymeric nanofibers produced nanocomposites of great performance in various biomedical applications especially in regenerative medicine. In this study, a novel nanocomposite nanofibrous system was developed and optimized from cellulose acetate (CA) electrospun nanofibers containing different concentrations of BGNPs. Morphology, IR and elemental analysis of the prepared electrospun nanofibers were determined using SEM, FT-IR and EDX respectively. Electrical conductivity and viscosity were also studied. Antibacterial properties were then investigated using agar well diffusion method. Moreover, biological wound healing capabilities for the prepared nanofiber dressing were assessed using in-vivo diabetic rat model with induced wounds. The fully characterized CA electrospun uniform nanofiber (100–200 nm) with incorporated BGNPs exhibited broad range of antimicrobial activity against gram negative and positive bacteria. The BGNP loaded CA nanofiber accelerated wound closure efficiently by the 10th day. The remaining wound areas for treated rats were 95.7?±?1.8, 36.4?±?3.2, 6.3?±?1.5 and 0.8?±?0.9 on 1st, 5th, 10th and 15th days respectively. Therefore, the newly prepared BGNP CA nanocomposite nanofiber could be used as a promising antibacterial and wound healing dressing for rapid and efficient recovery.

     

Application of polymeric nanofibers in soft tissues regeneration

Nanotechnology has wide applications in many fields, especially in the biological sciences and medicine. Nanomaterials are applied as potential materials for treatment and diagnosis. The development of nanofibers has greatly enhanced the scope for fabricating designs that can potentially be used in medical sciences. The application of polymeric nanofibers in biomaterials sciences and tissue engineering review in fields of skin and eye, neural and cardiovascular tissues, and urological tissues. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of graphene nanosheets on stereocomplex crystallization behaviors of star‐shaped poly (D(L)‐lactide) stereoblock copolymer

The nanocompsites of star‐shaped poly(D‐lactide)‐co‐poly(L‐lactide) stereoblock copolymers (s‐PDLA‐PLLA) with two‐dimensional graphene nanosheets (GNSs) were prepared by solution mixing method. Crystallization behaviors were investigated using differential scanning calorimetry, polarized optical microscopy, and wide angle X‐ray diffraction. The results of isothermal crystallization behaviors of the nanocompsites clearly indicated that the GNS could remarkably accelerate the overall crystallization rate of s‐PDLA‐PLLA copolymer. Unique stereocomplex crystallites with melting temperature about 207.0°C formed in isothermal crystallization for all samples. The crystallization temperatures of s‐PDLA‐PLLAs shifted to higher temperatures, and the crystallization peak shapes became sharper with increasing GNS contents. The maximum crystallization temperature of the sample with 3 wt% GNS was about 128.2°C, ie, 15°C higher than pure s‐PDLA‐PLLA. At isothermal crystallization processes, the halftime of crystallization (t_0.5) of the sample with 3 wt% GNS decreased to 6.4 minutes from 12.9 minutes of pure s‐PDLA‐PLLA at 160°C.The Avrami exponent n values for the nanocomposites samples were 2.6 to 3.0 indicating the crystallization mechanism with three‐dimensional heterogeneous nucleation and spherulites growth. The morphology and average diameter of spherulites of s‐PDLA‐PLLA with various GNS contents were observed in isothermal crystallization processes by polarized optical microscopy. Spherulite growth rates of samples were evaluated by using combined isothermal and nonisothermal procedures and analyzed by the secondary nucleation theory. The results evidenced that the GNS has acceleration effects on the crystallization of s‐PDLA‐PLLA with good nucleation ability in the s‐PDLA‐PLLA material.     

Composites of poly(L‐lactide‐trimethylene carbonate‐glycolide) and surface modified SBA‐15 as bone repair material

This work aims to develop novel composites from a poly(L ‐lactide‐co‐trimethylene carbonate‐co‐glycolide) (PLTG) terpolymer and mesoporous silica (SBA‐15) nanofillers surface modified by post‐synthetic functionalization. SBA‐15 first reacts with a silane coupling agent, γ‐aminopropyl‐trimethoxysilane to introduce ammonium group. PLLA chains were then grafted on the surface of SBA‐15 through ammonium initiated ring‐opening polymerization of L ‐lactide. Composites were prepared via solution mixing of PLTG terpolymer and surface modified SBA‐15. The structures and properties of pure SBA‐15, γ‐aminopropyl‐trimethoxysilane modified SBA‐15 (H₂N‐SBA‐15), PLLA modified SBA‐15 (PLLA‐NH‐SBA‐15), and PLTG/PLLA‐NH‐SBA‐15 composites were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, N₂ adsorption‐desorption, differential scanning calorimetry, contact angle measurement, and mechanical testing. The results demonstrated that PLLA chains were successfully grafted onto the surface of SBA‐15 with grafting amounts up to 16 wt.%. The PLTG/PLLA‐NH‐SBA‐15 composites exhibit good mechanical properties. The tensile strength, Young's modulus, and elongation at break of the composite containing 5 wt.% of PLLA‐NH‐SBA‐15 were 39.9 MPa, 1.3 GPa, and 273.6%, respectively, which were all higher than those of neat PLTG or of the composite containing 5 wt.% of pure SBA‐15. Cytocompatibility tests showed that the composites present very low cytotoxicity.     

An optimistic approach “from hydrophobic to super hydrophilic nanofibers” for enhanced absorption properties

Water holding capacity becomes essential for hygiene applications including baby diapers. Microfibers of hydrophilic polymers have been useful source for such applications. While, super hydrophilic and stable nanofibers incorporation with functional antibacterial agent are essential to get higher absorption of water along with antimicrobial activity against harmful bacteria. In current work, hydrophobic polymeric nanofibers are transformed to super hydrophilic nanofibers by addition of copper (II) oxide (CuO hereafter) nanoparticles. CuO nanoparticles provided two distinctive properties to existing nanofibers. Firstly, nanofibers surface area was significantly increased, and secondly copper (II) oxide itself is hydrophilic material which imparted hydrophilicity to base polymer. Polyacrylonitrile, crosslinked Polyvinyl Alcohol, and PICT were selected as super hydrophobic polymeric nanofibers. Copper II oxide nanoparticles (same concentration) were added in all polymer solution and electrospun. Surface, morphological, and hydrophilic properties were characterized and it was concluded that copper II oxide is suitable for transforming hydrophobic nanofibers to super hydrophilic nanofibers. Water holding capacity (WHC) was also improved for all prepared nanofiber mats. WHC for PVA/CuO, PAN/CuO, and PICT/CuO were recorded an average of 23 g/g, 21 g/g, and 18 g/g respectively. Combining all useful results from possible characterization of nanofiber mats, it is expected that CuO nanoparticles loaded nanofibers will have potential application as antibacterial, sustainable, and stable replacement of hygiene products.     

Chemomechanical and morphological properties with proliferation of keratinocyte cells of electrospun poyhydroxyalkanoate fibers incorporated with essential oil

Delivery systems based on electrospun polymeric nanofibers have shown potential for delivery of bioactive and plant extract formulations. This research focused on the fabrication of polyhydroxyalkanoate (PHA) copolymer nanofibers as a vehicle for loading of the Thai traditional herbal extract of Plai oil (Zingiber cassumunar Roxb). Nanofibers were formed by dissolving PHA and Plai oil together in dichloromethane solvent, with the PHA concentration being varied (5, 8, and 10%), followed by electrospinning for 4 hours. Based on the submicron diameters of the nanofibers, 8% PHA proved to be the optimal concentration. The concentration of Plai oil (10, 20, and 30%) was used, and hence, the solution viscosity influenced the nanofiber synthesis and physical properties of the nanofibers were obtained. Scanning electron microscope results indicated that the average diameters of cylindrical PHA nanofibers loaded with Plai oil (10%, 20%, and 30%) were 1.10, 1.01, and 1.11 μm, respectively, highlighting that fibers composed of 20% Plai oil were classifiable as nanofibers. Tensile testing of 20% Plai oil‐loaded nanofibers indicated that stiffness and elongation at break were within the acceptable range. Fourier transform infrared and differential scanning calorimetry measurements highlighted the presence of terpenen‐4‐ol, a component found in Plai oil, in the nanofiber film samples of PHA/Plai oil, confirming its inclusion in the systems. In addition, cell proliferation was set up to confirm the morphology and toxicity of skin keratinocyte cell line, and the results show that the HaCaT cells were attached on the PHA nanofibers which the nanofibers containing 20% Plai oil may affect cell behavior in spite the fact that it is not toxic to the cells.     

Improved efficacy of bio‐mineralization of human mesenchymal stem cells on modified PLLA nanofibers coated with bioactive materials via enhanced expression of integrin α2β1

Current therapeutic interventions in bone defects are mainly focused on finding the best bioactive materials for inducing bone regeneration via activating the related intracellular signaling pathways. Integrins are trans‐membrane receptors that facilitate cell‐extracellular matrix (ECM) interactions and activate signal transduction. To develop a suitable platform for supporting human bone marrow mesenchymal stem cells (hBM‐MSCs) differentiation into bone tissue, electrospun poly L‐lactide (PLLA) nanofiber scaffolds were coated with nano‐hydroxyapatite (PLLA/nHa group), gelatin nanoparticles (PLLA/Gel group), and nHa/Gel nanoparticles (PLLA/nHa/Gel group) and their impacts on cell proliferation, expression of osteoblastic biomarkers, and bone differentiation were examined and compared. MTT data showed that proliferation of hBM‐MSCs on PLLA/nHa/Gel scaffolds was significantly higher than other groups (P < .05). Alkaline phosphatase activity was also more increased in hBM‐MSCs cultured under osteogenic media on PLLA/nHa/Gel scaffolds compared to others. Gene expression evaluation confirmed up‐regulation of integrin α2β1 as well as the osteogenic genes BGLAP, COL1A1, and RUNX2. Following use of integrin α2β1 blocker antibody, the protein level of integrin α2β1 in cells seeded on PLLA/nHa/Gel scaffolds was decreased compared to control, which confirmed that most of the integrin receptors were bound to gelatin molecules on scaffolds and could activate the integrin α2β1/ERK axis. Collectively, PLLA/nHa/Gel scaffold is a suitable platform for hBM‐MSCs adhesion, proliferation, and osteogenic differentiation in less time via activating integrin α2β1/ERK axis, and thus it might be applicable in bone tissue engineering.     

Free poly(l‐lactic acid) spherulites grown from thermally induced phase separation and crystallization kinetics

Free poly(L‐lactic acid) (PLLA) sheaves and spherulites were prepared by thermally induced phase separation method from its tetrahydrofuran solution without the assistance of other additives. The effects of variables such as polymer concentration, quenching temperature and time on the morphology of PLLA spherulites were studied. The morphology, size, degree of crystallinity, and crystal structure of spherulites were characterized by SEM, DSC and XRD, and so forth. No obvious sheaves or spherulites were observed at quenching temperature of 8 and 0 °C, whereas sheaves composed of fluffy nanofibers with diameter of about 250 nm were formed at quenching temperature range of ?10 to ?40 °C. With increasing quenching time, the PLLA morphology changed from small sheaves to big sheaves (cauliflower‐like) to spherulites. Low concentration (3 and 5 wt %) solutions were favorable for the formation of sheaves, whereas high concentration (7 wt %) solution as good for the formation of spherulites. The mechanism for the formation of PLLA sheaves or spherulites was examined by the isothermal and nonisothermal crystallization of PLLA/tetrahydrofuran solutions using DSC. The Avrami equation was used to analyze the data and good linear double‐logarithmic plots were obtained. The Avrami exponent n and rate constant K indicated the crystal growth mechanism was intermediate between completely instantaneous and completely sporadic types of nucleation and growth, and the spherulites were there dimensional. Compared to the spherulites embedded in the bulky film obtained from the melt processing, this study provided a feasible technique for the fabrication of free PLLA spherulites. The PLLA spherulites composed of fluffy nanofibers with a high porosity (≥90%) may be potentially applied as functional materials such as catalyst support, adsorption and biomedical materials, and so forth. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1476–1489