PEGylated poly(ester amide) elastomer scaffolds for soft tissue engineering

Biodegradable synthetic elastomers with tunable mechanical and physicochemical properties remain attractive materials for soft tissue engineering. We have recently synthesized novel poly(1,3‐diamino‐2‐hydroxypropane‐co‐glycerol sebacate)‐co‐poly(ethylene glycol) (APS‐co‐PEG) biodegradable elastomers. This class of PEGylated elastomers has widely tunable mechanical and degradation properties compared wtih currently available biodegradable elastomers. To further investigate the biological application of this class of elastomers, we fabricated hybrid APS‐co‐PEG/polycaprolactone (PCL) porous scaffolds by electrospinning. The fiber morphology, chemical composition, mechanical properties, degradability, and cytocompatibility of hybrid APS‐co‐PEG/PCL electrospun scaffolds were characterized. These scaffolds exhibited a wide range of mechanical properties and similar cytocompatibility to PCL scaffolds. Importantly, PEGylation inhibited platelet adhesion on all APS‐co‐PEG/PCL electrospun scaffolds when compared with PCL and APS/PCL scaffolds, suggesting a potential role in mitigating thrombogenicity in vivo. Additionally, APS‐25PEG/PCL scaffolds were found to be mechanically analogous to human heart valve leaflet and supported attachment of human aortic valve cells. These results reveal that hybrid APS‐co‐PEG/PCL scaffolds may serve as promising constructs for soft tissue engineering, especially heart valve tissue engineering. Copyright © 2017 John Wiley & Sons, Ltd.     

Mechanically Robust Electrospun Hydrogel Scaffolds Crosslinked via Supramolecular Interactions

One of the major challenges in the processing of hydrogels based on poly(ethylene glycol) (PEG) is to create mechanically robust electrospun hydrogel scaffolds without chemical crosslinking postprocessing. In this study, this is achieved by the introduction of physical crosslinks in the form of supramolecular hydrogen bonding ureido‐pyrimidinone (UPy) moieties, resulting in chain‐extended UPy‐PEG polymers (CE‐UPy‐PEG) that can be electrospun from organic solvent. The resultant fibrous meshes are swollen in contact with water and form mechanically stable, elastic hydrogels, while the fibrous morphology remains intact. Mixing up to 30 wt% gelatin with these CE‐UPy‐PEG polymers introduce bioactivity into these scaffolds, without affecting the mechanical properties. Manipulating the electrospinning parameters results in meshes with either small or large fiber diameters, i.e., 0.63 ± 0.36 and 2.14 ± 0.63 µm, respectively. In that order, these meshes provide support for renal epithelial monolayer formation or a niche for the culture of cardiac progenitor cells.     

Dual Electrospun Supramolecular Polymer Systems for Selective Cell Migration

Dual electrospinning can be used to make multifunctional scaffolds for regenerative medicine applications. Here, two supramolecular polymers with different material properties are electrospun simultaneously to create a multifibrous mesh. Bisurea (BU)‐based polycaprolactone, an elastomer providing strength to the mesh, and ureido‐pyrimidinone (UPy) modified poly(ethylene glycol) (PEG), a hydrogelator, introducing the capacity to deliver compounds upon swelling. The dual spun scaffolds are modularly tuned by mixing UPyPEG hydrogelators with different polymer lengths, to control swelling of the hydrogel fiber, while maintaining the mechanical properties of the scaffold. Stromal cell derived factor 1 alpha (SDF1α) peptides are embedded in the UPyPEG fibers. The swelling and erosion of UPyPEG increase void spaces and released the SDF1α peptide. The functionalized scaffolds demonstrate preferential lymphocyte recruitment proposed to be created by a gradient formed by the released SDF1α peptide. This delivery approach offers the potential to develop multifibrous scaffolds with various functions.     

Incorporation of nanohydroxyapatite and vitamin D3 into electrospun PCL/Gelatin scaffolds: The influence on the physical and chemical properties and cell behavior for bone tissue engineering

Scaffold, an essential element of tissue engineering, should provide proper physical and chemical properties and evolve suitable cell behavior for tissue regeneration. Polycaprolactone/Gelatin (PCL/Gel)‐based nanocomposite scaffolds containing hydroxyapatite nanoparticles (nHA) and vitamin D3 (Vit D3) were fabricated using the electrospinning method. Structural and mechanical properties of the scaffold were determined by scanning electron microscopy (SEM) and tensile measurement. In this study, smooth and bead‐free morphology with a uniform fiber diameter and optimal porosity level with appropriate pore size was observed for PCL/Gel/nHA nanocomposite scaffold. The results indicated that adding nHA to PCL/Gel caused an increase of the mechanical properties of scaffold. In addition, chemical interactions between PCL, gelatin, and nHA molecules were shown with XRD and FT‐IR in the composite scaffolds. MG‐63 cell line has been cultured on the fabricated composite scaffolds; the results of viability and adhesion of cells on the scaffolds have been confirmed using MTT and SEM analysis methods. Here in this study, the culture of the osteoblast cells on the scaffolds showed that the addition of Vit D3 to PCL/Gel/nHA scaffold caused further attachment and proliferation of the cells. Moreover, DAPI staining results showed that the presence and viability of the cells were greater in PCL/Gel/nHA/Vit D3 scaffold than in PCL/Gel/nHA and PCL/Gel scaffolds. The results also approved increasing cell proliferation and alkaline phosphatase (ALP) activity for MG‐63 cells cultured on PCL/Gel/nHA/Vit D3 scaffold. The results indicated superior properties of hydroxyapatite nanoparticles and vitamin D3 incorporated in PCL/Gel scaffold for use in bone tissue engineering.     

Recent advances on electrospun scaffolds as matrices for tissue-engineered heart valves

Valvular heart diseases (VHDs) are a major health problem increasing morbidity and mortality worldwide. Currently, treatment of VHDs relies on valve replacement with mechanical or biological valves, which have major drawbacks in terms of durability and the ability to grow, repair and remodel. To this end, tissue-engineered heart valves (TEHVs) have emerged as ideal substitutes. TEHVs are composed of biodegradable, biocompatible and mechanically stable scaffolds that resemble the native valves. These scaffolds are seeded with autologous cells and conditioned in a bioreactor prior to implantation. Scaffolds that have been utilized so far for such application are (i) biological, (ii) synthetic and (iii) cell entrapment in polymerized extra-cellular matrix based scaffolds. Synthetic scaffolds are considered superior over the other two types in terms of controlled mechanical properties and degradation rate. They can be subdivided into porous, hydrogel and fibrous scaffolds. Among the three subcategories, fibrous scaffolds are preferred because they resemble the natural extra-cellular matrix for the native valve. Such scaffolds can be fabricated using phase separation, self-assembly and electrospinning. Electrospinning is a versatile technique for fabricating scaffolds for tissue engineering applications that possess many advantages. Electrospun scaffolds processed using a wide range of synthetic and natural polymers were proven to be promising in terms of mechanical properties comparable to the native valves, fiber diameter within the range of the natural extracellular matrix and good cellular response. However, further investigation in fabricating fibrous scaffolds for tissue-engineered heart valves is still needed. In this review, we discussed electrospun scaffolds as TEHVs matrices, how far they succeeded in meeting the criteria of ideal scaffolds for such application and what the shortage aspects and possible solutions are.     

Synthesis of PCL‐branched P(MMA‐co‐HEMA) to toughen electrospun PLLA fiber membrane

Electrospun biodegradable fiber mesh is a promising alternative scaffold for delivering progenitor cells for repairing damaged or diseased tissue, but its cripple mechanical stability has not met the requirement of tissue engineering yet. In this work, the well‐defined poly(ε‐caprolactone)‐branched poly(methyl methacrylate‐co‐hydroxyethylmethacrylate) (PCL‐PMH) has been successfully synthesized to toughen electrospun poly(l ‐lactide) (PLLA) fiber membrane. Characterization of the obtained nanofibrous meshes indicates that PCL‐PMH and PLLA can be well blended to make smooth fibers, and fibrous diameter vary little with blending PCL‐PMH. The aggregation state of two macromolecules is closely correlated with blend ratio, molecular structure, and molecular weight of PCL‐PMH, and only when PCL‐PMH and PLLA form good interfacial adhesion can PMH give full play to its potential for toughening the fiber membrane. The tensile strength and elongation at break of the blend are 6.20 MPa and 63.40% under the optimal conditions, respectively, and it also exhibits the representative feature of toughness materials. The blending fiber membrane is as no cytotoxic as original PLLA. This work will provide a new way for toughness of electrospun fiber membrane in practice.     

Mechanical investigation of bilayer vascular grafts electrospun from aliphatic polyesters

Electrospun biodegradable vascular grafts provide a wide range of design components from the selection of materials to the modification of fiber structure. In this study, both single layer and bilayer tubular scaffolds with inner diameter of 6 mm were electrospun from polycaprolactone with different molecular weights and poly(l ‐lactide) caprolactone polymers. Bilayer scaffolds were designed by using different combinations of the polymer types in each layer and obtaining fiber orientation in outer layers. Scaffolds were analyzed morphologically and mechanically. Obtained results of mechanical performance were discussed according to the used polymer‐type composition, fiber orientation, and composite effect of both layer in the final graft. Smooth muscle cells were seeded on the scaffolds to test biocompatibility of presented scaffolds. Results indicate that the use of different biodegradable polymers in different combinations in each layer causes notable differences in fiber morphology and mechanical performance of the scaffolds. Moreover, fiber orientation in outer layer improves tensile strength and burst pressures in radial directions while creating a suitable fibrous layer for smooth muscle cells by mimicking the extracellular matrix of tunica media in native vessels. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation and Characterization of Aligned PLLA/PCL/HA Composite Fibrous Membranes

Aligned poly(L-lactide) (PLLA)/poly(?-caprolactone) (PCL)/hydroxyapaite (HA) composite fibrous membranes were fabricated by electrospinning. Their morphology, thermal stability, mechanical properties, hydrophilic properties and biocompatibility were investigated. The electrospun fibers are highly aligned and the HA are oriented along the fiber axis. When HA are incorporated, the PLLA/PCL/HA composite fibers become thinner due to the increased conductivity. In addition, the aligned HA reinforce the electrospun fibrous membranes. The larger porosity and higher hydrophilic properties induced by HA in the electrospun fibers have improved the degradation of the PLLA/PCL/HA fibrous membranes which have no toxic effect on proliferation of adipose-derived stem cells.     

Nanofiber Configuration of Electrospun Scaffolds Dictating Cell Behaviors and Cell-scaffold Interactions

Electrospun nanofibers are of the same length scale as the native extracellular matrix and have been extensively reported to facilitate adhesion and proliferation of cells and to promote tissue repair and regeneration. With a primary focus on tissue repair and regeneration using electrospun scaffolds, only a few studies involved electrospun nanofiber scaffolds directing cell behaviors have been reported. In this study, we prepared electrospun nanofiber scaffolds with distinct fiber configurations, namely, random and aligned orientations of nanofibers, as well as oriented yarns, and investigated their effects on cell behaviors. Our results showed that these scaffolds supported good proliferation and viability of murine fibroblasts. Fiber configuration profoundly influenced cell morpho-logy and orientation but showed no effects on cell proliferation rate. The yarn scaffold had comparable total protein accumulation with the random and aligned scaffolds, but it supported a greater pro-liferation rate of fibroblasts with significantly elevated collagen de-position due to its porous fibrous configuration. Cell-seeded yarn scaffolds showed a greater Young's modulus compared with cell-free controls as early as 1 week. Together with its unique fiber configuration similar to the native extracellular matrix of the myocardium, the yarn scaffold might be a suitable matrix material for modeling cardiac fibrotic disorders.     

Improved survival of cardiac cells on surface modified electrospun nanofibers

Polycaprolactone (PCL) is a popular synthetic polymer used in the field of cardiac tissue engineering (CTE) due to its non-toxic degraded by products and low cost manufacturing method. However, hydrophobic nature of this material limits its wide spread application in different cell interaction processes. Therefore, current study aims to chemically modify PCL made random and aligned nanofibers with collagen coating mimicking the oriented matrix of the cardiac cells. Morphological and chemical properties of the electrospun PCL nanofibers were evaluated by SEM, FTIR, XRD and water contact angle measurement. Results indicated that the anisotropic characteristics of aligned nanofibers promoted cell attachment and alignment, which closely match the requirements of native cardiac cells. Thus, aligned nanofibers could be preferred for cardiac tissue regeneration and defects over random nanofibers.     

Polycaprolactone-polymethyl methacrylate electrospun blends for biomedical applications

Electrospinning is one of most versatile process to fabricate porous scaffolds in biomedical field. Synthetic polymers such as polycaprolactone (PCL) and polymethyl methacrylate (PMMA) provide excellent properties for biomedical applications due to their biocompatibility and tunable mechanical properties. PCL-PMMA electrospun blends combine compressive/tensile properties of individual polymers as well as biocompatibility/biodegradability. Together with porosity of scaffold, drug/nutrient supply is required in tissue regeneration and healing. High pressure CO₂ has been investigated to plasticize many biopolymers and impregnate drugs in scaffolds. This study explores several compositions of PCL-PMMA electrospun scaffolds for morphological and mechanical properties. These scaffolds are impregnated with hydrophilic (Rhodamine B) and hydrophobic (Fluorescein) dyes using high pressure CO₂ and air plasma treatment. Furthermore, release profiles of dyes have been studied from thin films and porous scaffolds to understand several controlling factors for controlled release applications. Results show dye-polymer interactions, CO₂ impregnation and stress relaxation of electrospun fibers are key factors in release profile from electrospun fibers. This study is a step forward in developing PCL-PMMA based electrospun scaffolds for drug delivery and tissue engineering.     

Enhancement of biocompatibility on aligned electrospun poly(3‐hydroxybutyrate) scaffold immobilized with laminin towards murine neuroblastoma Neuro2a cell line and rat brain‐derived neural stem cells (mNSCs)

Electrospinning has been extensively used to construct tissue‐engineered scaffolds because of its ability to provide the fibrous scaffold with structurally analogous to the naturally occurring protein in the extracellular matrix of native tissues. In addition, the modification of scaffolds with bioactive molecules is beneficial as this can create an environment that consists of biochemical cues to further promote cell adhesion, proliferation, and differentiation. In the present contribution, we prepared and investigated the potential used of aligned electrospun poly(3‐hydroxybutyrate) (PHB) scaffold immobilized with bioactive molecule to serve as nervous scaffold. Laminin was successfully immobilized on the surface using covalent binding between functional groups of modified scaffolds and protein. The ability to use for neural regeneration was evaluated in vitro towards murine neuroblastoma Neuro2a cell line and mouse brain‐derived neural stem cells. The surface modification with laminin immobilized on the PHB fibrous scaffolds supported the attachment and promoted the proliferation of Neuro2a very wells. Despite the good attachment and proliferation of Neuro2a and mouse brain‐derived neural stem cells were not able to proliferate on the neat PHB, hydrolyzed PHB and laminin immobilized on hydrolyzed PHB fibrous scaffold.     

Synergistic Effects of Beta Tri‐Calcium Phosphate and Porcine‐Derived Decellularized Bone Extracellular Matrix in 3D‐Printed Polycaprolactone Scaffold on Bone Regeneration

Bone‐derived extracellular matrix (ECM) is widely used in studies on bone regeneration because of its ability to provide a microenvironment of native bone tissue. However, a hydrogel, which is a main type of ECM application, is limited to use for bone graft substitutes due to relative lack of mechanical properties. The present study aims to fabricate a scaffold for guiding effective bone regeneration. A polycaprolactone (PCL)/beta‐tricalcium phosphate (β‐TCP)/bone decellularized extracellular matrix (dECM) scaffold capable of providing physical and physiological environment are fabricated using 3D printing technology and decoration method. PCL/β‐TCP/bone dECM scaffolds exhibit excellent cell seeding efficiency, proliferation, and early and late osteogenic differentiation capacity in vitro. In addition, outstanding results of bone regeneration are observed in PCL/β‐TCP/bone dECM scaffold group in the rabbit calvarial defect model in vivo. These results indicate that PCL/β‐TCP/bone dECM scaffolds have an outstanding potential as bone graft substitutes for effective bone regeneration.     

Polycaprolactone Electrospun Fiber Mats Prepared Using Benign Solvents: Blending with Copper(II)‐Chitosan Increases the Secretion of Vascular Endothelial Growth Factor in a Bone Marrow Stromal Cell Line

Inducing the formation of new blood vessels (angiogenesis) is an essential requirement for successful tissue engineering. Approaches have been proposed to enhance angiogenesis using growth factors and other biomolecules; however, this approaches present drawbacks in terms of high cost and patient safety. Copper is known to effectively regulate angiogenesis and can offer a more cost‐effective alternative than the direct use of growth factors. With this study, a strategy to incorporate copper in electrospun fibrous scaffolds with pro‐angiogenic properties is presented. Polycaprolactone (PCL) and copper(II)‐chitosan are electrospun using benign solvents. The morphological and physicochemical properties of the fiber mats are investigated through scanning electron microscopy (SEM), static contact angle measurements, energy dispersive X‐ray, and Fourier‐transform infrared spectroscopies. Scaffold stability in phosphate buffered saline at 37 °C is monitored over 1 week. A bone marrow stromal cell line (ST‐2) is cultured for 7 days and its behavior is evaluated using SEM, fluorescence microscopy and a tetrazolium salt‐based colorimetric assay. Results confirm that PCL/copper(II)‐chitosan is suitable for electrospinning. The fiber mats are biocompatible and favor cell colonization and infiltration. Most notably, the angiogenic potential of PCL/copper(II)‐chitosan blends is confirmed by a three‐fold increase in VEGF secretion by ST‐2 cells in the presence of copper(II)‐chitosan.     

The electrospun poly(ε‐caprolactone)/fluoridated hydroxyapatite nanocomposite for bone tissue engineering

Biodegradable cell‐incorporated scaffolds can guide the regeneration process of bone defects such as physiological resorption, tooth loss, and trauma which medically, socially, and economically hurt patients. Here, 0, 5, 10, and 15 wt% fluoridated hydroxyapatite (FHA) nanoparticles containing 25 wt% F^? and 75 wt% OH^? were incorporated into poly(ε‐caprolactone) (PCL) matrix to produce PCL/FHA nanocomposite scaffolds using electrospinning method. Then, scanning electron microscopy (SEM), X‐ray diffraction (XRD) pattern, and Fourier transform infrared spectroscopy (FTIR) were used to evaluate the morphology, phase structure, and functional groups of prepared electrospun scaffolds, respectively. Furthermore, the tensile strength and elastic modulus of electrospun scaffolds were investigated using the tensile test. Moreover, the biodegradation behavior of electrospun PCL/FHA scaffolds was studied by the evaluation of weight loss of mats and the alternation of pH in phosphate buffer saline (PBS) up to 30 days of incubation. Then, the biocompatibility of prepared mats was investigated by culturing MG‐63 osteoblast cell line and performing MTT assay. In addition, the adhesion of osteoblast cells on prepared electrospun scaffolds was studied using their SEM images. Results revealed that the fiber diameter of prepared electrospun PCL/FHA scaffolds alters between 700 and 900 nm. The mechanical assay illustrated the mat with 10 wt% FHA nanoparticles revealed the highest tensile strength and elastic modulus. The weight loss alternation of mats determined around 1% to 8% after 30 days of incubation. The biocompatibility and cell adhesion of mats improved by increasing the amounts of FHA nanoparticles.     

Synthesis and Characterization of Biodegradable Poly(ϵ-caprolactone)-b-Poly(L-lactide) and Study on Their Electrospun Scaffolds

A series of multi-block copolymers, poly(L-lactide)-b-poly (?-caprolactone) (PLLA-b-PCL) were synthesized. The first step of the synthesis consisted of the transesterification between the PLLA and 1,4-Butanediol, followed by the copolymerization of PLLA-diols and PCL, using isophorone diisocyanate (IPDI) as a coupling agent. The synthesized polymers were characterized by Fourier transform infrared (FTIR) spectra, differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). PLLA/PCL block copolymers were electrospun into ultrafine fibers. The morphology of the electrospun fibrous scaffolds were investigated by Scanning Electron Microscopy (SEM). Results showed that the morphology and diameter of the fibers were affected by the electrospinning solution concentrationan and different weight ratio of PLLA/PCL. These electrospun PLLA-b-PCL fibrous membranes exhibited good flexibility and deformability. In comparison with the electrospun PLLA membrane, the electrospun fibrous membranes of PLLA-b-PCL demonstrated an enhanced elongation with still high tensile strength and Young's modulus to be beneficial for tissue engineering scaffolds.     

Aligned and molecularly oriented semihollow ultrafine polymer fiber yarns by a facile method

In this work, aligned and molecularly oriented bone‐like PLLA semihollow fiber yarns were manufactured continuously from an optimized homogeneous polymer‐solvent‐nonsolvent system [PLLA, CH₂Cl₂, and dimethyl formamide (DMF)] by a single capillary electrospinning via self‐bundling technique. Here, it should be emphasized that the self‐bundling electrospinning technique, a very facile electrospinning technique with a grounded needle (which is to induce the self‐bundling of polymer nanofibers at the beginning of electrospinning process), is used for the alignment and molecular orientation of the polymer fiber, and the take‐up speed of the rotating drum for the electrospun fiber yarn collection is very low (0.5 m/s). PLLA can be dissolved in DMF and CH₂Cl₂ mixed solvent with different ratios. By varying the ratios of mixed solvent system, PLLA electrospun semihollow fiber with the porous inner structure and compact shell wall could be formed, the thickness of the shell and the size of inner pores could be adjusted. The results of polarized FTIR and wide angle X‐ray diffraction investigations verified that as‐prepared PLLA semihollow fiber yarns were well‐aligned and molecularly oriented. Both the formation mechanism of semihollow fibers with core‐shell structure and the orientation mechanism of polymer chains within the polymer fibers were all discussed. The as‐prepared self‐bundling electrospun PLLA fiber yarns possessed enhanced mechanical performance compared with the corresponding conventional electrospun PLLA fibrous nonwoven membranes. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1118–1125, 2010     

The effect of 3D printing on the morphological and mechanical properties of polycaprolactone filament and scaffold

Three‐dimensional (3D) printing becomes an attractive technique to fabricate tissue engineering scaffolds through its high control on fabrication and repeatability using the printing parameters. This technique can be combined by the finite element method (FEM), and tissue‐specific scaffolds with desirable morphological and mechanical properties can be designed and manufactured. In this study, the influential 3D printing parameters on the morphological and mechanical properties of polycaprolactone (PCL) filament and scaffold were studied experimentally and numerically. First, the effects of printing parameters and process on the properties of extruded PCL filament were investigated. Then, using FEM, the effects of filament specifications on the overall characteristics of the scaffold were evaluated. Results showed that both the printing process in terms of resting time and remaining time and the printing parameters like pressure, printing speed, and printing path length have influenced the filament properties. In addition, both the filament diameter and elastic modulus had significant effects on the properties of scaffold especially, a 20% increase in the filament diameter caused the scaffold compressive elastic modulus to rise by around 72%. It is concluded that the printing parameters and process must be tuned very well in fabricating scaffolds with the desired morphology and mechanical property.     

Electrospun Aligned Poly(L-lactide)/Poly(ϵ-caprolactone) /Poly(ethylene glycol) Blend Fibrous Membranes

Aligned poly(L-lactide) (PLLA)/poly(?-caprolactone) (PCL)/poly(ethylene glycol)(PEG) fibrous membranes were fabricated by electrospinning. Their morphology, thermal stability, mechanical properties, hydrophilic properties and in vitro degradation behaviors were investigated. With increasing the content of PEG, the PLLA/PCL/PEG blend fibers become thinner due to the increment in solution conductivity and decrease in solution viscosity. The thermal stability, hydrophilic properties, the tensile strength and elongation-at-break of PLLA/PCL/PEG blend fibrous membranes were improved, but porosity were decreased with the content of PEG changing from 10 wt% to 30 wt%. Furthermore, the incorporation of PEG enhanced the degradation of the PLLA/PCL/PEG fibrous membranes due to the better hydrophilic properties. In addition, the PLLA/PCL/PEG fibrous membranes have no toxic effect on proliferation of adipose-derived stem cells.