Controlled heparin conjugation on electrospun poly(ε-caprolactone)/gelatin fibers for morphology-dependent protein delivery and enhanced cellular affinity

Electrospun fibrous scaffolds have now been shown to possess great potential for tissue engineering applications, owing to their unique mimicry of natural extracellular matrix structure. In this study, poly(ε-caprolactone) and gelatin were electrospun to fabricate tissue-engineered scaffolds with three different fiber morphologies (1.0 μm, 3.0 μm and co-electrospun containing both 1.0 and 3.0 μm diameter fibers). Subsequently, these scaffolds were conjugated with heparin to immobilize a bioactive molecule by electrostatic interactions. This study determined the quantity of heparin conjugation on the scaffolds and that the crosslinking time and the fiber morphologies govern the extent of heparin conjugation on the fibers. In order to evaluate the release capacity of the heparin-conjugated scaffolds, lysozyme was used as a model protein for conjugation. The heparin-conjugated scaffolds provided high loading efficiency and cumulative release of lysozyme with a relatively linear relationship. In addition, the release kinetics was significantly dependent on heparin conjugation and fiber morphology. This fundamental investigation into how fiber morphology and crosslinking protocols can affect the heparin binding ability of electrospun fibers is crucial for predicting the delivery of many different types of bioactive molecules from an electrospun scaffold for tissue engineering applications.     

Collagen–PCL Sheath–Core Bicomponent Electrospun Scaffolds Increase Osteogenic Differentiation and Calcium Accretion of Human Adipose-Derived Stem Cells

Human adipose-derived stem cells (hASCs) are an abundant cell source capable of osteogenic differentiation, and have been investigated as an autologous stem cell source for bone tissue engineering applications. The objective of this study was to determine if the addition of a type-I collagen sheath to the surface of poly(ε-caprolactone) (PCL) nanofibers would enhance viability, proliferation and osteogenesis of hASCs. This is the first study to examine the differentiation behavior of hASCs on collagen–PCL sheath–core bicomponent nanofiber scaffolds developed using a co-axial electrospinning technique. The use of a sheath–core configuration ensured a uniform coating of collagen on the PCL nanofibers. PCL nanofiber scaffolds prepared using a conventional electrospinning technique served as controls. hASCs were seeded at a density of 20 000 cells/cm² on 1 cm² electrospun nanofiber (pure PCL or collagen–PCL sheath–core) sheets. Confocal microscopy and hASC proliferation data confirmed the presence of viable cells after 2 weeks in culture on all scaffolds. Greater cell spreading occurred on bicomponent collagen–PCL scaffolds at earlier time points. hASCs were osteogenically differentiated by addition of soluble osteogenic inductive factors. Calcium quantification indicated cell-mediated calcium accretion was approx. 5-times higher on bicomponent collagen–PCL sheath–core scaffolds compared to PCL controls, indicating collagen–PCL bicomponent scaffolds promoted greater hASC osteogenesis after two weeks of culture in osteogenic medium. This is the first study to examine the effects of collagen–PCL sheath–core composite nanofibers on hASC viability, proliferation and osteogenesis. The sheath–core composite fibers significantly increased calcium accretion of hASCs, indicating that collagen–PCL sheath–core bicomponent structures have potential for bone tissue engineering applications using hASCs.     

The effect of controlled release of PDGF-BB from heparin-conjugated electrospun PCL/gelatin scaffolds on cellular bioactivity and infiltration

Heparin-conjugated electrospun poly(ε-caprolactone) (PCL)/gelatin scaffolds were developed to provide controlled release of platelet-derived growth factor-BB (PDGF-BB) and allow prolonged bioactivity of this molecule. A mixture of PCL and gelatin was electrospun into three different morphologies. Next, heparin molecules were conjugated to the reactive surface of the scaffolds. This heparin-conjugated scaffold allowed the immobilization of PDGF-BB via electrostatic interaction. In?vitro PDGF-BB release profiles indicated that passive physical adsorption of PDGF-BB to non-heparinized scaffolds resulted in an initial burst release of PDGF-BB within 5 days, which then leveled off. However, electrostatic interaction between PDGF-BB and the heparin-conjugated scaffolds gave rise to a sustained release of PDGF-BB over the course of 20 days without an initial burst. Moreover, PDGF-BB that was strongly bound to the heparin-conjugated scaffolds enhanced smooth muscle cell (SMC) proliferation. In addition, scaffolds composed of 3.0?μm diameter fibers that were immobilized with PDGF-BB accelerated SMC infiltration into the scaffold when compared to scaffolds composed of smaller diameter fibers or scaffolds that did not release PDGF-BB. We concluded that the combination of the large pore structure in the scaffolds and the heparin-mediated delivery of PDGF-BB provided the most effective cellular interactions through synergistic physical and chemical cues.     

Bicomponent electrospinning to fabricate three-dimensional hydrogel-hybrid nanofibrous scaffolds with spatial fiber tortuosity

Electrospun fibrous mats have emerged as powerful tissue engineering scaffolds capable of providing highly effective and versatile physical guidance, mimicking the extracellular environment. However, electrospinning typically produces a sheet-like structure, which is a major limitation associated with current electrospinning technologies. To address this challenge, highly porous, volumetric hydrogel-hybrid fibrous scaffolds were fabricated by one Taylor cone-based side-by-side dual electrospinning of poly (ε-caprolactone) (PCL) and poly (vinyl pyrrolidone) (PVP), which possess distinct properties (i.e., hydrophobic and hydrogel properties, respectively). Immersion of the resulting scaffolds in water induced spatial tortuosity of the hydrogel PVP fibers while maintaining their aligned fibrous structures in parallel with the PCL fibers. The resulting conformational changes in the entire bicomponent fibers upon immersion in water led to volumetric expansion of the fibrous scaffolds. The spatial fiber tortuosity significantly increased the pore volumes of electrospun fibrous mats and dramatically promoted cellular infiltration into the scaffold interior both in vitro and in vivo. Harmonizing the flexible PCL fibers with the soft PVP-hydrogel layers produced highly ductile fibrous structures that could mechanically resist cellular contractile forces upon in vivo implantation. This facile dual electrospinning followed by the spatial fiber tortuosity for fabricating three-dimensional hydrogel-hybrid fibrous scaffolds will extend the use of electrospun fibers toward various tissue engineering applications.     

Encapsulation and Controlled Release of Heparin from Electrospun Poly(L-Lactide-co-ε-Caprolactone) Nanofibers

Poly(L-lactide-co-ε-caprolactone) nanofibers with heparin incorporated were successfully fabricated by coaxial electrospinning. The morphologies of electrospun nanofibers were studied by scanning electron microscopy (SEM), and a significant decrease in fiber diameter was observed with increasing heparin concentration. The transmission electron microscopy (TEM) images indicated that coaxial electrospinning could generate core–shell structure nanofibers which have the potential to encapsulate drugs (heparin in this study) into the core part of nanofibers. Approximately 80% of the encapsulated heparin was sustainedly and stably released from the fibrous composite in 14 days by a diffusion/erosion coupled mechanism. The release behavior of heparin from blend electrospun nanofibers was also studied and showed an obvious burst release in the initial stage. An in vitro proliferation test was conducted to study the effect of heparin released from nanofibers, and the results suggest that the heparin maintains its bioactivity after encapsulating with and delivery through coaxially electrospun fibers.     

Fabrication and characterization of poly(γ-glutamic acid)-graft-chondroitin sulfate/polycaprolactone porous scaffolds for cartilage tissue engineering

The development of blended biomacromolecule and polyester scaffolds can potentially be used in many tissue engineering applications. This study was to develop a poly(γ-glutamic acid)-graft-chondroitin sulfate-blend-poly(ε-caprolactone) (γ-PGA-g-CS/PCL) composite biomaterial as a scaffold for cartilage tissue engineering. Chondroitin sulfate (CS) was grafted to γ-PGA, forming a γ-PGA-g-CS copolymer with 1-ethyl-3-(3-dimethyl-aminopropyl) carbodiimide (EDC) system. The γ-PGA-g-CS copolymers were then blended with PCL to yield a porous γ-PGA-g-CS/PCL scaffold by salt leaching. These blended scaffolds were characterized by ¹H NMR, ESCA, water-binding capacity, mechanical test, degradation rate and CS assay. The results showed that with γ-PGA-g-CS as a component, the water-binding capacity and the degradation rate of the scaffolds would substantially increase. During a 4 week period of culture, the mechanical stability of γ-PGA-g-CS/PCL scaffolds was raised gradually and chondrocytes were induced to function normally in vitro. Furthermore, a larger amount of secreted GAGs was present in the γ-PGA-g-CS/PCL matrices than in the control (PCL), as revealed by Alcian blue staining of the histochemical sections. Thus, γ-PGA-g-CS/PCL matrices exhibit excellent biodegradation and biocompatibility for chondrocytes and have potential in tissue engineering as temporary substitutes for articular cartilage regeneration.     

Cellular Behavior on Epidermal Growth Factor (EGF)-Immobilized PCL/Gelatin Nanofibrous Scaffolds

Nano-scaled poly(ε-caprolactone) (PCL) and PCL/gelatin fibrous scaffolds with immobilized epidermal growth factor (EGF) were prepared for the purpose of wound-healing treatments. The tissue scaffolds were fabricated by electrospinning and the parameters that affect the electrospinning process were optimized. While the fiber diameters were 488 ± 114 nm and 663 ± 107 nm for PCL and PCL/gelatin scaffolds, respectively, the porosities were calculated as 79% for PCL and 68% for PCL/gelatin scaffolds. Electrospun PCL and PCL/gelatin scaffolds were first modified with 1,6-diaminohexane to introduce amino groups on their surfaces, then EGF was chemically conjugated to the surface of nanofibers. The results obtained from Attenuated Total Reflectance Fourier Transform Infrared (ATR–FT-IR) spectroscopy and quantitative measurements showed that EGF was successfully immobilized on nanofibrous scaffolds. L929 mouse fibroblastic cells were cultivated on both neat and EGF-immobilized PCL and PCL/gelatin scaffolds in order to investigate the effect of EGF on cell spreading and proliferation. According to the results, especially EGF-immobilized PCL/gelatin scaffolds exerted early cell spreading and superior and rapid proliferation compared to EGF-immobilized PCL scaffolds and neat PCL, PCL/gelatin scaffolds. Consequently, EGF-immobilized PCL/gelatin scaffolds could potentially be employed as novel scaffolds for skin tissueengineering applications.     

Water/O2-Plasma-Assisted Treatment of PCL Membranes for Biosignal Immobilization

The main purpose of this study was to obtain COOH functionalities on the surface of poly-ε-caprolactone (PCL) membranes using low-pressure water/O₂-plasma-assisted treatment. PCL membranes were prepared using the solvent-casting technique. Then, low-pressure water/O₂ plasma treatments were performed in a cylindrical, capacitively coupled RF-plasma-reactor in three steps: H₂O/O₂-plasma treatment; in situ (oxalyl chloride vapors) gas/solid reaction to convert –OH functionalities into –COCl groups; and hydrolysis for final –COOH functionalities. Optimization of plasma modification processes was done using the DoE software program. COOH and OH functionalities on modified surfaces were detected quantitatively using the fluorescent labeling technique and an UVX 300G sensor. Chemical structural information of untreated, plasma treated and oxalyl chloride functionalized PCL membranes were acquired using pyrolysis GC/MS and ESCA analysis. High-resolution AFM images revealed that nanopatterns were more affected than micropatterns by plasma treatments. AFM images recorded with amino-functionalized tips presented increased size of the features on the surface that suggests higher density of the carboxyls on the nanotopographical elements. Low-pressure water/O₂-plasma-treated and oxalyl chloride functionalized samples were biologically activated with insulin and/or heparin biosignal molecules using a PEO (polyoxyethylene bis amine) spacer. The success of the immobilization process was checked qualitatively by ESCA analysis. In addition, fluorescent labeling techniques were used for the quantitative determination of immobilized biomolecules. Cell-culture experiments indicated that biomolecule immobilization onto PCL scaffolds was effective on L929 cell adhesion and proliferation, especially in the presence of heparin.     

Controlled biomineralization of electrospun poly(ε-caprolactone) fibers to enhance their mechanical properties

Electrospun polymeric fibers have been investigated as scaffolding materials for bone tissue engineering. However, their mechanical properties, and in particular stiffness and ultimate tensile strength, cannot match those of natural bones. The objective of the study was to develop novel composite nanofiber scaffolds by attaching minerals to polymeric fibers using an adhesive material – the mussel-inspired protein polydopamine – as a “superglue”. Herein, we report for the first time the use of dopamine to regulate mineralization of electrospun poly(ε-caprolactone) (PCL) fibers to enhance their mechanical properties. We examined the mineralization of the PCL fibers by adjusting the concentration of HCO₃^? and dopamine in the mineralized solution, the reaction time and the surface composition of the fibers. We also examined mineralization on the surface of polydopamine-coated PCL fibers. We demonstrated the control of morphology, grain size and thickness of minerals deposited on the surface of electrospun fibers. The obtained mineral coatings render electrospun fibers with much higher stiffness, ultimate tensile strength and toughness, which could be closer to the mechanical properties of natural bone. Such great enhancement of mechanical properties for electrospun fibers through mussel protein-mediated mineralization has not been seen previously. This study could also be extended to the fabrication of other composite materials to better bridge the interfaces between organic and inorganic phases.     

Coaxial electrospun poly(ε-caprolactone), multiwalled carbon nanotubes, and polyacrylic acid/polyvinyl alcohol scaffold for skeletal muscle tissue engineering

Skeletal muscle repair after injury usually results in scar tissue and decreased functionality. In this study, we coaxially electrospun poly(ε-caprolactone), multiwalled carbon nanotubes, and a hydrogel consisting of polyvinyl alcohol and polyacrylic acid (PCL-MWCNT-H) to create a self-contained nanoactuating scaffold for skeletal muscle tissue replacement. This was then compared to electrospun PCL and PCL-MWCNT scaffolds. All scaffolds displayed some conductivity; however, MWCNT incorporation increased the conductivity. Only the PCL-MWCNT-H actuated when stimulated with 15 and 20 V. The PCL, PCL-MWCNT, and hydrogel only scaffolds demonstrated no reaction when 5, 8, 10, 15, and 20 V were applied. Thus, all components of the PCL-MWCNT-H scaffold are essential for movement. All three PCL-containing scaffolds were biocompatible, but the PCL-MWCNT-H scaffolds displayed more multinucleated cells with actin interaction. After tensile testing, the MWCNT-containing scaffolds had higher strength than the rat and pig skeletal muscle. Although the mechanical properties were higher than muscle, the PCL-MWCNT-H scaffold shows promise as a potential bioartificial nanoactuator for skeletal muscle.     

Electrically conductive nanofibers with highly oriented structures and their potential application in skeletal muscle tissue engineering

Recent trends in scaffold design have focused on materials that can provide appropriate guidance cues for particular cell types to modulate cell behavior. In this study highly aligned and electrically conductive nanofibers that can simultaneously provide topographical and electrical cues for cells were developed. Thereafter their potential to serve as functional scaffolds for skeletal muscle tissue engineering was investigated. Well-ordered nanofibers, composed of polyaniline (PANi) and poly(ε-caprolactone) (PCL), were electrospun by introducing an external magnetic field in the collector region. Incorporation of PANi into PCL fibers significantly increased the electrical conductivity from a non-detectable level for the pure PCL fibers to 63.6 ± 6.6 mS cm^?1 for the fibers containing 3 wt.% PANi (PCL/PANi-3). To investigate the synergistic effects of topographical and electrical cues using the electrospun scaffolds on skeletal myoblast differentiation, mouse C2C12 myoblasts were cultured on random PCL (R-PCL), aligned PCL (A-PCL), random PCL/PANi-3 (R-PCL/PANi) and aligned PCL/PANi-3 (A-PCL/PANi) nanofibers. Our results showed that the aligned nanofibers (A-PCL and A-PCL/PANi) could guide myoblast orientation and promote myotube formation (i.e. approximately 40% and 80% increases in myotube numbers) compared with R-PCL scaffolds. In addition, electrically conductive A-PCL/PANi nanofibers further enhanced myotube maturation (i.e. approximately 30% and 23% or 15% and 18% increases in the fusion and maturation indices) compared with non-conductive A-PCL scaffolds or R-PCL/PANi. These results demonstrated that a combined effect of both guidance cues was more effective than an individual cue, suggesting a potential use of A-PCL/PANi nanofibers for skeletal muscle regeneration.     

Thermal behavior and spherulitic superstructures of SBC triblock copolymers based on polystyrene (S), polybutadiene (B) and a crystallizable poly(ε-caprolactone) (C) block

The dynamic crystallization and the melting behavior of polystyrene-block-poly(ε-caprolactone) (PS-b-PCL, short notation SC), polybutadiene-block-poly(ε-caprolactone) (PB-b-PCL, BC) and polystyrene-block-polybutadiene-block-poly(ε-caprolactone) (PS-b-PB-b-PCL, SBC) have been studied using differential scanning calorimetry. The copolymers with high molecular weight exhibit microphase separation into microphases consisting of polystyrene, polybutadiene and poly(ε-caprolactone) and partial crystallization of the corresponding PCL block. The crystallization occurs at temperatures below the PS glass transition. Depending on the block copolymer composition, crystallization takes place through a combination of heterogeneous and homogeneous nucleation. Isothermal crystallization was studied in order to determine the equilibrium melting point, T_m⁰, of the PCL block, which depends on the weight ratio w_PB: w_PCL. The crystallization kinetics was analyzed in terms of Avrami equation. A general decrease in the overall crystallization rate in the block copolymers relative to the equivalent PCL homopolymer was found. Additionally, the growth rate of the spherulites was followed using polarized optical microscopy. Depending on the composition and flexibility of the block connected to PCL, some copolymers showed ring-banded spherulites.     

Biocomposites Electrospun with Poly(ε-caprolactone) and Silk Fibroin Powder for Biomedical Applications

Biomedical synthetic polymers have been used in soft and hard tissue regeneration because of their good processability and biodegradability. However, biomaterials such as poly(ε-caprolactone) (PCL) have various shortcomings, including intrinsic hydrophobicity and lack of bioactive functional groups. The material must be reinforced with natural biomaterials to achieve good cellular and mechanical performance as biomedical material. We fabricated a biocomposite using PCL and silk fibroin (SF) powder, which has good biocompatibility and mechanical properties. The hydrophilicity, mechanical properties and cellular behavior of the PCL/SF fibers were analyzed. In addition, we obtained a highly oriented conduit of electrospun biocomposite fibers by modifying the rolling collector of the electrospinning system. As the alignment of micro/nanofibers increased, the orthotropic mechanical properties were improved. The biocompatibility of the biocomposite was evaluated in a culture of bone-marrow-derived rat mesenchymal stem cells. The cellular result demonstrated the potential usefulness of electrospun biocomposites for various biomedical conduit systems.     

Diaphragmatic muscle reconstruction with an aligned electrospun poly(ε-caprolactone)/collagen hybrid scaffold

Large diaphragmatic muscle defects in congenital diaphragmatic hernia (CDH) are reconstructed by prosthetic materials or autologous grafts, which are associated with high complications and reherniation. In this study we examined the feasibility of using aligned electrospun poly(ε-caprolactone) (PCL)/collagen hybrid scaffolds for diaphragmatic muscle reconstruction. The hybrid scaffolds were implanted into a central left hemi-diaphragmatic defect (approximately 70% of the diaphragmatic tissue on the left side) in rats. Radiographic and magnetic resonance imaging (MRI) analyses showed no evidence of herniation or retraction up to 6 months after implantation. Histological and immunohistochemical evaluations revealed ingrowth of muscle tissue into the scaffolds. The mechanical properties of the retrieved diaphragmatic scaffolds were similar to those of normal diaphragm at the designated time points. Our results show that the aligned electrospun hybrid scaffolds allowed muscle cell migration and tissue formation. The aligned scaffolds may provide implantable functional muscle tissues for patients with diaphragmatic muscle defects.     

In vivo biocompatibility and biodegradation of 3D-printed porous scaffolds based on a hydroxyl-functionalized poly(ε-caprolactone)

The aim of this study was to evaluate the in vivo biodegradation and biocompatibility of three-dimensional (3D) scaffolds based on a hydroxyl-functionalized polyester (poly(hydroxymethylglycolide-co-ε-caprolactone), PHMGCL), which has enhanced hydrophilicity, increased degradation rate, and improved cell-material interactions as compared to its counterpart poly(ε-caprolactone), PCL. In this study, 3D scaffolds based on this polymer (PHMGCL, HMG:CL 8:92) were prepared by means of fiber deposition (melt-plotting). The biodegradation and tissue biocompatibility of PHMGCL and PCL scaffolds after subcutaneous implantation in Balb/c mice were investigated. At 4 and 12 weeks post implantation, the scaffolds were retrieved and evaluated for extent of degradation by measuring the residual weight of the scaffolds, thermal properties (DSC), and morphology (SEM) whereas the polymer was analyzed for both its composition ((1)H NMR) and molecular weight (GPC). The scaffolds with infiltrated tissues were harvested, fixed, stained and histologically analyzed. The in vitro enzymatic degradation of these scaffolds was also investigated in lipase solutions. It was shown that PHMGCL 3D-scaffolds lost more than 60% of their weight within 3 months of implantation while PCL scaffolds showed no weight loss in this time frame. The molecular weight (M(w)) of PHMGCL decreased from 46.9 kDa before implantation to 23.2 kDa after 3 months of implantation, while the molecular weight of PCL was unchanged in this period. (1)H NMR analysis showed that the degradation of PHMGCL was characterized by a loss of HMG units. In vitro enzymatic degradation showed that PHMGCL scaffolds were degraded within 50 h, while the degradation time for PCL scaffolds of similar structure was 72 h. A normal foreign body response to both scaffold types characterized by the presence of macrophages, lymphocytes, and fibrosis was observed with a more rapid onset in PHMGCL scaffolds. The extent of tissue-scaffold interactions as well as vascularization was shown to be higher for PHMGCL scaffolds compared to PCL ones. Therefore, the fast degradable PHMGCL which showed good biocompatibility is a promising biomaterial for tissue engineering applications.     

Fiber angle and aspect ratio influence the shear mechanics of oriented electrospun nanofibrous scaffolds

Fibrocartilages, including the knee meniscus and the annulus fibrosus (AF) of the intervertebral disc, play critical mechanical roles in load transmission across joints and their function is dependent upon well-defined structural hierarchies, organization, and composition. All, however, are compromised in the pathologic transformations associated with tissue degeneration. Tissue engineering strategies that address these key features, for example, aligned nanofibrous scaffolds seeded with mesenchymal stem cells (MSCs), represent a promising approach for the regeneration of these fibrous structures. While such engineered constructs can replicate native tissue structure and uniaxial tensile properties, the multidirectional loading encountered by these tissues in vivo necessitates that they function adequately in other loading modalities as well, including shear. As previous findings have shown that native tissue tensile and shear properties are dependent on fiber angle and sample aspect ratio, respectively, the objective of the present study was to evaluate the effects of a changing fiber angle and sample aspect ratio on the shear properties of aligned electrospun poly(ε-caprolactone) (PCL) scaffolds, and to determine how extracellular matrix deposition by resident MSCs modulates the measured shear response. Results show that fiber orientation and sample aspect ratio significantly influence the response of scaffolds in shear, and that measured shear strains can be predicted by finite element models. Furthermore, acellular PCL scaffolds possessed a relatively high shear modulus, 2-4 fold greater than native tissue, independent of fiber angle and aspect ratio. It was further noted that under testing conditions that engendered significant fiber stretch, the aggregate resistance to shear was higher, indicating a role for fiber stretch in the overall shear response. Finally, with time in culture, the shear modulus of MSC laden constructs increased, suggesting that deposited ECM contributes to the construct shear properties. Collectively, these findings show that aligned electrospun PCL scaffolds are a promising tool for engineering fibrocartilage tissues, and that the shear properties of both acellular and cell-seeded formulations can match or exceed native tissue benchmarks.     

PCL–gelatin composite nanofibers electrospun using diluted acetic acid–ethyl acetate solvent system for stem cell-based bone tissue engineering

Composite nanofibrous scaffolds with various poly(ε-caprolactone) (PCL)/gelatin ratios (90:10, 80:20, 70:30, 60:40, 50:50 wt.%) were successfully electrospun using diluted acetic and ethyl acetate mixture. The effects of this solvent system on the solution properties of the composites and its electrospinning properties were investigated. Viscosity and conductivity of the solutions, with the addition of gelatin, allowed for the electrospinning of uniform nanofibers with increasing hydrophilicity and degradation. Composite nanofibers containing 30 and 40 wt.% gelatin showed an optimum combination of hydrophilicity and degradability and also maintained the structural integrity of the scaffold. Human mesenchymal stem cells (hMSCs) showed favorable interaction with and proliferation on, the composite scaffolds. hMSC proliferation was highest in the 30 and 40 wt.% gelatin containing composites. Our experimental data suggested that PCL–gelatin composite nanofibers containing 30–40 wt.% of gelatin and electrospun in diluted acetic acid–ethyl acetate mixture produced nanofiber scaffolds with optimum hydrophilicity, degradability, and bio-functionality for stem cell-based bone tissue engineering.     

Electrospun tubular scaffolds: On the effectiveness of blending poly(ε-caprolactone) with poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Tissue engineering can effectively contribute to the development of novel vascular prostheses aimed to overcome the well-known drawbacks of small-diameter grafts. To date, poly(ε-caprolactone) (PCL), a bioresorbable synthetic poly(α-hydroxyester), is considered one of the most promising materials for vascular tissue engineering. In this work, the potential advantage of intimate blending soft PCL and hard poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a polymer of microbial origin, has been evaluated. Nonwoven mats and small-diameter tubular scaffolds of PCL, PHBV, and PCL/PHBV were fabricated by means of electrospinning technique. Mechanical properties and suture retention strength were investigated according to the international standard for cardiovascular implants. Biological tests demonstrated that both PCL-based scaffolds supported survival and growth of rat cerebral endothelial cells in a short time. The fiber alignment of the electrospun tubular scaffolds contributed to a more rapid and homogeneous cell colonization of the luminal surface. ? 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012.     

Material-driven differentiation of induced pluripotent stem cells in neuron growth factor-grafted poly(ε-caprolactone)-poly(β-hydroxybutyrate) scaffolds

The potential of constructs comprising induced pluripotent stem (iPS) cells and biopolymers can be high for neurological surgery practice, if the systematic activity of neuronal regeneration is clarified. This study shows a guided differentiation of iPS cells toward neurons in neuron growth factor (NGF)-grafted poly(ε-caprolactone) (PCL)-poly(β-hydroxybutyrate) (PHB) scaffolds. The porosity of PCL-PHB scaffolds enhanced with increasing the concentration of salt particles (porogen) and the weight percentage of PCL. An increase in the graft concentration of NGF elevated the atomic ratios of N/C and O/C on the surface of NGF-grafted PCL-PHB scaffolds. In addition, incorporating heparin and NGF promoted the adhesion and viability of iPS cells in constructs. When the weight percentage of PCL increased, the viability of iPS cells reduced; however, more PCL in constructs benefited the adhesion of iPS cells. Under the influence of heparin and NGF, a high weight percentage of PCL and a long inductive period improved iPS cells to differentiate into neuron-like cells carrying βIII tubulin and inhibited other differentiation(s). The material-driven differentiation in NGF-grafted PCL-PHB constructs can be promising in guiding iPS cells to produce neurons for nerve tissue engineering.     

Synthesis and characterization of elastic PLGA/PCL/PLGA tri-block copolymers

Various ABA-type tri-block copolymers composed of poly(L-lactide) (PLA) or poly (lactide-co-glycolide) (PLGA) as the side A block and poly(ε-caprolactone) (PCL) as the middle B block were synthesized to produce rapidly degrading elastic matrices useful for tissue engineering scaffolds. The terminal di-hydroxyl groups in PCL-diol (MW 2000) were used as the initiator for the ring-opening polymerization of L-lactide or D,L-lactide and glycolide, employing stannous octoate as a catalyst. A series of copolymers were synthesized by varying the chain length and monomer composition of the PLA (PLGA) block, while the chain length of the PCL block was fixed. It was found that PLGA/PCL/PLGA copolymers with a MW of 10 000 and lactide/glycolide ratios of 50/50 and 75/25 demonstrated desirable mechanical properties of elasticity (Young's modulus 26.0 and 19.8 MPa) and showed controllable degradability over a 2-month period depending on the monomer composition.