An alternative solvent system for the steady state electrospinning of polycaprolactone

Polycaprolactone/gelatin-based scaffolds with tailored performance: in vitro and in vivo validation

Nanofibrous scaffolds composed of polycaprolactone (PCL) and gelatin (Ge) were obtained through a hydrolytic assisted electrospinning process. The PCL-to-Ge proportion (100/0 to 20/80), as well as the dissolution time (24, 48, 72, 96, 120 h) into a 1:1 formic/acetic acid solvent before electrospinning were modified to obtain the different samples. A strong influence of these factors on the physicochemical properties of the scaffolds was observed. Higher Ge percentage reduced crystallinity, allowed a uniform morphology and increased water contact angle. The increase in the dissolution time considerably reduced the molar mass and, subsequently, fibre diameter and crystallinity were affected. During in vitro biocompatibility tests, higher cell adhesion and proliferation were found for the 60/40, 50/50 and 40/60 PCL/Ge compositions that was corroborated by MTT assay, fluorescence and microscopy. A weakened structure, more labile to the in vitro degradation in physiologic conditions was found for these compositions with higher dissolution times (72 and 96 h). Particularly, the 40/60 PCL/Ge scaffolds revealed an interesting progressive degradation behaviour as a function of the dissolution time. Moreover, these scaffolds were non-inflammatory, as revealed by the pyrogen test and after the 15-day subcutaneous in vivo implantation in mice. Finally, a reduction of the scar tissue area after infarction was found for the 40/60 PCL/Ge scaffolds electrospun after 72 h implanted in rat hearts. These results are especially interesting and represent a feasible way to avoid undesired inflammatory reactions during the scaffold assimilation.

Morphology and Properties of Electrospun PCL and Its Composites for Medical Applications: A Mini Review

Polycaprolactone (PCL) is one of the most used synthetic polymers for medical applications due to its biocompatibility and slow biodegradation character. Combining the inherent properties of the PCL matrix with the characteristic of nanofibrous particles, result into promising materials that can be suitable for different applications, including the biomedical applications. The advantages of nanofibrous structures include large surface area, a small diameter of pores and a high porosity, which make them of great interest in different applications. Electrospinning, as technique, has been heavily used for the preparation of nano- and micro-sized fibers. This review discusses the different methods for the electrospinning of PCL and its composites for advanced applications. Furthermore, the steady state conditions as well as the effect of the electrospinning parameters on the resultant morphology of the electrospun fiber are also reported.

Pyridine as an additive to improve the deposition of continuous electrospun filaments

Electrospun filaments are leading to a new generation of medical yarns that have the ability to enhance tissue healing through their biophysical cues. We have recently developed a technology to fabricate continuous electrospun filaments by depositing the submicron fibres onto a thin wire. Here we investigate the influence of pyridine on the fibre deposition. We have added pyridine to polydioxanone solutions at concentrations ranging from 0 to 100 ppm, increasing the conductivity of the solutions almost linearly from 0.04 uS/cm to 7 uS/cm. Following electrospinning, this led to deposition length increasing from 1 cm to 14 cm. The samples containing pyridine easily underwent cold drawing. The strength of drawn filaments increased from 0.8 N to 1.5 N and this corresponded to a decrease in fibre diameter, with values dropping from 2.7 μm to 1 μm. Overall, these findings are useful to increase the reliability of the manufacturing process of continuous electrospun filaments and to vary their biophysical properties required for their application as medical yarns such as surgical sutures.

Electrospun patterned porous scaffolds for the support of ovarian follicles growth: a feasibility study

Recently, the interest of the scientific community is focused on the application of tissue engineering approach for the fertility restoration. In this paper innovative patterned electrospun fibrous scaffolds were fabricated and used as 3D system for porcine follicles culture. The obtained scaffolds demonstrated to be a suitable support which did not alter or interfere with the typical spherical follicles morphology. The fibrillar structure of the scaffolds mimics the morphology of the healthy native tissue. The use of porcine follicles implied many advantages respect to the use of mouse model. Relevant results showed that more than the scaffold pattern and struts dimension, the selection of proper biomaterials improve the follicles adhesion and development.

Application of ANN modeling techniques in the prediction of the diameter of PCL/gelatin nanofibers in environmental and medical studies

Prediction of the diameter of a nanofiber is very difficult, owing to complexity of the interactions of the parameters which have an impact on the diameter and the fact that there is no comprehensive method to predict the diameter of a nanofiber. Therefore, the aim of this study was to compare the multi-layer perceptron (MLP), radial basis function (RBF), and support vector machine (SVM) models to develop mathematical models for the diameter prediction of poly(ε-caprolactone) (PCL)/gelatin (Gt) nanofibers. Four parameters, namely, the weight ratio, applied voltage, injection rate, and distance, were considered as input data. Then, a prediction of the diameter for the nanofiber model (PDNFM) was developed using data mining techniques such as MLP, RBFNN, and SVM. The PDNFM_MLP is introduced as the most accurate model to predict the diameter of PCL/Gt nanofibers on the basis of costs and time-saving. According to the results of the sensitivity analysis, the value of the PCL/Gt weight ratio is the most significant input which influences PDNFM_MLP in PCL/Gt electrospinning. Therefore, the PDNFM model, using a decision support system (DSS) tool can easily predict the diameter of PCL/Gt nanofibers prior to electrospinning.

A new tool for prediction the diameter of nanofibers is presented: the use of adaptive modeling techniques to predict fiber diameter and study the impact of electrospinning process parameters on electrospinning fiber diameter.

Plasma Functionalization of Polycaprolactone Nanofibers Changes Protein Interactions with Cells, Resulting in Increased Cell Viability

The surface properties of electrospun scaffolds can greatly influence protein adsorption and, thus, strongly dictate cell-material interactions. In this study, we aim to investigate possible correlations between the surface properties of argon, nitrogen, and ammonia and helium plasma-functionalized polycaprolactone (PCL) nanofibers (NFs) and their cellular interactions by examining the protein corona patterns of the plasma-treated NFs as well as the cell membrane proteins involved in cell proliferation. As a result of the performed plasma treatments, PCL NFs morphology was preserved, while wettability was improved profoundly after all treatments because of the incorporation of polar surface groups. Depending on the discharge gas, different types of groups are incorporated, which influenced the resultant cell-material interactions. Argon plasma-functionalized PCL NFs, only enriched by oxygen-containing functional groups, were found to show the best cell-material interactions, followed by N₂ and He/NH₃ plasma-treated samples. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and liquid chromatography-mass spectrometry clearly indicated an increased protein retention compared with non-treated PCL NFs. The nine proteins retained best on plasma-treated NF are important mediators of extracellular matrix interaction, illustrating the importance thereof for cell proliferation and the viability of cells. Finally, 92 proteins that can be used to differentiate how the different plasma treatments are clustered and subjected to a gene ontology study, illustrating the importance of keratinization and extracellular matrix organization.

Novel poly(ε-caprolactone)/amino-functionalized tannin electrospun membranes as scaffolds for tissue engineering

Poly(ε-caprolactone) (PCL) is a hydrophobic and cytocompatible aliphatic polyester that has been used to produce PCL-based nanofibrous for both wound healing and tissue repair. However, the high hydrophobicity and low water adsorptive have been challenges for developing PCL-based materials for use in tissue engineering field. Here, we report a new polymer (a hydrophilic amino-functionalized tannin (TN)) that is associated with PCL for developing PCL-TN blends at different PCL:TN weight ratios (100:0, 95:5, 85:15 and 78:22). PCL:TN ratio may be tuned to modulate hydrophilicity and cytocompatibility of the nanofibers. The neutralization step and surface wettability played an important role in the attachment of human adipose-derived stem cells (ADSC cells) on PCL-TN membranes. Also, fluorescence images confirmed great proliferation of ADSC cells on the PCL-TN electrospun surfaces. Yet, neutralized PCL-TN nanofibers promoted bactericidal activity against Pseudomonas aeruginosa. These membranes have potential to be used as scaffolds for tissue engineering purposes.

The Effect of Polycaprolactone Nanofibers on the Dynamic and Impact Behavior of Glass Fibre Reinforced Polymer Composites

In this article, the effect of polycaprolactone nanofibers on the dynamic behavior of glass fiber reinforced polymer composites is investigated. The vibratory behavior of composite beams in their pristine state (without any nano modification) and the same beams modified with polycaprolactone fibers is considered experimentally. The experimental results show that the incorporation of polycaprolactone nanofibers increases the damping; however, it does not significantly affect the natural frequencies. Additionally, the paper analyses the effect of polycaprolactone nanofibers on the impact behavior of glass fiber/epoxy composites. This has already been analyzed experimentally in a previous study. In this work, we developed a finite element model to simulate the impact behavior of such composite laminates. Our results confirm the conclusions done experimentally and prove that composites reinforced with polycaprolactone nanofibers are more resistant to damage and experience less damage when subjected to the same impact as the pristine composites. This study contributes to the knowledge about the dynamic behavior and the impact resistance of glass fiber reinforced polymer composites reinforced with polycaprolactone nanofibers. The findings of this study show that interleaving with polycaprolactone nanofibers can be used to control the vibrations and improve the impact damage resistance of structures made of composite mats as aircrafts or wind turbines.

Nanostructured Hydrogels by Blend Electrospinning of Polycaprolactone/Gelatin Nanofibers

Nanofibrous membranes based on polycaprolactone (PCL) have a large potential for use in biomedical applications but are limited by the hydrophobicity of PCL. Blend electrospinning of PCL with other biomedical suited materials, such as gelatin (Gt) allows for the design of better and new materials. This study investigates the possibility of blend electrospinning PCL/Gt nanofibrous membranes which can be used to design a range of novel materials better suited for biomedical applications. The electrospinnability and stability of PCL/Gt blend nanofibers from a non-toxic acid solvent system are investigated. The solvent system developed in this work allows good electrospinnable emulsions for the whole PCL/Gt composition range. Uniform bead-free nanofibers can easily be produced, and the resulting fiber diameter can be tuned by altering the total polymer concentration. Addition of small amounts of water stabilizes the electrospinning emulsions, allowing the electrospinning of large and homogeneous nanofibrous structures over a prolonged period. The resulting blend nanofibrous membranes are analyzed for their composition, morphology, and homogeneity. Cold-gelling experiments on these novel membranes show the possibility of obtaining water-stable PCL/Gt nanofibrous membranes, as well as nanostructured hydrogels reinforced with nanofibers. Both material classes provide a high potential for designing new material applications.

Polycaprolactone-chitosan nanofibers influence cell morphology to induce early osteogenic differentiation

Osteogenic differentiation is highly correlated with cell morphology. Morphological changes are a stimulus as well as a consequence of the differentiation process. Besides, geometrical, biochemical and mechanical properties of a substrate can modulate cell adhesion and morphology. Therefore, in the current study, nanofibrous substrate properties were used to implement necessary changes in cell morphology which induced osteogenic differentiation without biological supplements. A polycaprolactone-chitosan nanofiber substrate had been fabricated with an average diameter of ∼75 nm and an appropriate ratio of polymers that balances surface biocompatibility as well as mechanical strength. DSC and wide-angle XRD analysis revealed miscibility between polymers; whereas a degradation study confirmed the structural integrity of nanofibers. Nanofibers did not cause any cytotoxicity to MC3T3-E1 cells as confirmed by Live/Dead® staining. Morphological studies by SEM and confocal microscopy showed significant changes in terms of cell shape, area, compactness, aspect ratio and nucleus area in cells grown on nanofibers which indicated the osteogenic differentiation inducing potential of nanofibers. This was further confirmed by enhanced mineral deposition and alkaline phosphatase activity up to three weeks. In summary, polycaprolactone-chitosan nanofibers could induce early osteogenic differentiation in MC3T3-E1 pre-osteoblasts without any biological supplements by modulating cell morphology. Moreover, cell morphological features can be used as a predictive and informative approach at the early stages of differentiation experiments.

Electrospinning of Polycaprolactone/Pluronic F127 dissolved in glacial acetic acid: fibrous scaffolds fabrication, characterization and in vitro evaluation

Abstracts The Polycaprolactone (PCL) fibrous scaffolds in nano to micro scale have been considered as excellent templates for cell culture and tissue growth. The hydrophobic nature of the PCL, however, yields low initial cell seeding density, heterogeneous cell spreading and slow cell growth rate. Therefore, in this study the surface hydrophilic fibrous scaffolds were directly fabricated by the electrospinning of PCL solutions with small quantities (0.5-5%) of Pluronic F127 (PEO₁₀₀-PPO₆₅-PEO₁₀₀) dissolved in benign solvent of glacial acetic acid. The clear and miscible solutions were achieved by controlling the proper F127 content in the blend solutions. The continuous and smooth fibers with average diameters from 0.71 to 1.43 μm made up the fibrous scaffolds in non-woven mode. Then the water wetting angle of the scaffolds could be adjusted from 126° to 0° by varying F127 content owing to its hydrophilic PEO chains presented on surface the blended fibers. Finally, it was demonstrated that the blended fibrous scaffolds with the F127 content less than 1% exhibited better cell attachment, proliferation and spreading performance than those of pure PCL scaffolds.

Nanobead-on-string composites for tendon tissue engineering

The bead-on-string topography of electrospun nanocomposite scaffolds improves fibroblast response in terms of cell spreading and proliferation.

Properties of Electrospun Nanofibers of Multi-Block Copolymers of [Poly-ε-caprolactone-b-poly(tetrahydrofuran-co-ε-caprolactone)]m Synthesized by Janus Polymerization

Novel biodegradable multiblock copolymers of [PCL-b-P(THF-co-CL)]_m with PCL fractions of 53.3 and 88.4 wt % were prepared by Janus polymerization of ε-caprolactone (CL) and tetrahydrofuran (THF). Their electrospun mats were obtained with optimized parameters containing bead-free nanofibers whose diameters were between 290 and 520 nm. The mechanical properties of the nanofiber scaffolds were measured showing the tensile strength and strain at break of 8–10 MPa and 123–161%, respectively. Annealing improved their mechanical properties and their tensile strength and strain at break of the samples increased to 10–13 MPa and 267–338%, respectively. Due to the porous structure and crystallization in nanoscale confinement, the mechanical properties of the nanofiber scaffolds appeared as plastics, rather than as the elastomers observed in bulk thermal-molded film.

Tailored release of triiodothyronine and retinoic acid from a spatio-temporally fabricated nanofiber composite instigating neuronal differentiation

Regeneration of the central and peripheral nervous system is challenging since the functional restoration of injured nerves is an incredible task. The fabrication of an ideal nerve guide that fulfills the requirement to regenerate nerve tissue is a herculean challenge requiring a combination of both biochemical and topographical cues. The present study explores the combinatorial effect of aligned nanofibers and the regulated delivery of triiodothyronine and retinoic acid on nerve regeneration. A sequential release mechanism is adopted in fabricating the nanofiber scaffold, with triiodothyronine incorporated into the nanofiber shell ensuring its prior release, followed by retinoic acid (entrapped within zein nanoparticles) from the core. The composite nanofibers thus fabricated possess excellent mechanical, physical and thermal properties and good topographical morphology and were highly biocompatible. The nanofibers were scrutinized for their efficacy in stimulating differentiation to a neuronal phenotype. The elongation factor (E-factor) of the neural cells had doubled in the bioactive incorporated composite compared to other scaffolds, as observed on phalloidin staining of their cytoskeleton, which endorsed enhanced neural differentiation on the fabricated nanofiber scaffold. There was a significant increase in the expression of neural-lineage specific markers on investigation of mRNA by real time PCR, showing a 10 fold increase in the gene expression of β-III-tubulin, a 5.5 fold increase for microtubule associated protein 2 gene and 3.5 fold for neurofilament M gene in the cells cultured over bioactive incorporated aligned nanofiber composites. Similarly protein expression was analyzed by immunofluorescence and flow cytometry studies, which showed an increase in the expression of β-III-tubulin in the composite nanofiber. This corroborates that neuronal differentiation is enhanced by the aligned nanotopography and spatio-temporal delivery of triiodothyronine and retinoic acid, opening avenues for nerve regenerative graft fabrication.

Incorporation of Calcium Containing Mesoporous (MCM-41-Type) Particles in Electrospun PCL Fibers by Using Benign Solvents

The electrospinning technique is a versatile method for the production of fibrous scaffolds able to resemble the morphology of the native extra cellular matrix. In the present paper, electrospinning is used to fabricate novel SiO₂ particles (type MCM-41) containing poly(epsilon-caprolactone) (PCL) fibers. The main aims of the present work are both the optimization of the particle synthesis and the fabrication of composite fibers, obtained using benign solvents, suitable as drug delivery systems and scaffolds for soft tissue engineering applications. The optimized synthesis and characterization of calcium-containing MCM-41 particles are reported. Homogeneous bead-free composite electrospun mats were obtained by using acetic acid and formic acid as solvents; neat PCL electrospun mats were used as control. Initially, an optimization of the electrospinning environmental parameters, like relative humidity, was performed. The obtained composite nanofibers were characterized from the morphological, chemical and mechanical points of view, the acellular bioactivity of the composite nanofibers was also investigated. Positive results were obtained in terms of mesoporous particle incorporation in the fibers and no significant differences in terms of average fiber diameter were detected between the neat and composite electrospun fibers. Even if the Ca-containing MCM-41 particles are bioactive, this property is not preserved in the composite fibers. In fact, during the bioactivity assessment, the particles were released confirming the potential application of the composite fibers as a drug delivery system. Preliminary in vitro tests with bone marrow stromal cells were performed to investigate cell adhesion on the fabricated composite mats, the positive obtained results confirmed the suitability of the composite fibers as scaffolds for soft tissue engineering.

Binding of indocyanine green in polycaprolactone fibers using blend electrospinning for in vivo laser-assisted vascular anastomosis

BACKGROUND AND OBJECTIVE

The clinical application of laser-assisted vascular anastomosis is afflicted by unreliable and low bonding strengths as well as tedious handling during microvascular surgery. The challenge to be met arises from the flow-off of the chromophore during soldering that changes the absorption and stains the surrounding tissue, leading to an uncontrollable thermal damage zone. In this study, we investigated the feasibility to produce an indocyanine green (ICG)-loaded patch by electrospinning and tested its applicability to both in vitro and in vivo microvascular laser soldering.

MATERIALS AND METHODS

A blend of polycaprolactone and ICG was electrospun to produce a pliable patch. Prior to soldering, the patch was soaked in 40% wt. bovine serum albumin solution. The solder patch was wrapped in vitro around blood vessel stumps of rabbit aortas. An intraluminal balloon catheter enabled an easy alignment and held the setup in place. The soldering energy was delivered via a diffusor fiber from the vessel lumen using a diode laser at 810 nm. During the procedure, the surface temperature was observed with an infrared camera. Afterward, samples were embedded in methylmethacrylate and epon to study thermal damage. The quality of the fusion was assessed by measuring the tensile strength. After in vitro tests with rabbit aortas, eight large white pigs were subjected to an acute in vivo experiment, and the artery of the latissimus dorsi flap was anastomosed to the distal femoral artery.

RESULTS

The ICG-loaded patch, produced by electrospinning, has a thickness of 279 ± 62 μm, a fiber diameter of 1.20 ± 0.19 μm, and an attenuation coefficient of 1,119 ± 183 cm^-1 at a wavelength of 790 nm. The patch was pliable and easy to handle during surgery. No leakage of the chromophore was observed. Thermal damage was restricted to the Tunica adventitia and Tunica media and the area of the vessel wall that was covered with the patch. Six pigs were successfully treated, without any bleeding and with a continuous blood flow. The in vivo flap model yielded a similar tensile strength compared to in vitro laser-assisted vascular anastomoses (138 ± 52 vs. 117 ± 30 mN/mm² ).

CONCLUSION

Our study demonstrated the applicability of the ICG-loaded patch for laser-assisted vascular anastomosis. By using electrospinning, ICG could be bound to polymer fibers, avoiding its flow-off and the staining of the surrounding tissue. This patch demonstrated several advantages over liquid solder as it was easier to apply, ensured a high and reliable bonding strength while maintaining a constant concentration of ICG concentration during the surgery. Lasers Surg. Med. 49:928-939, 2017. © 2017 Wiley Periodicals, Inc.

Microchip-based 3D-Cell Culture Using Polymer Nanofibers Generated by Solution Blow Spinning

Polymer nano/micro fibers have found many applications including 3D cell culture and the creation of wound dressings. The fibers can be produced by a variety of techniques that include electrospinning, the primary disadvantage of which include the requirement for a high voltage supply (which may cause issues such as polymer denaturation) and lack of portability. More recently, solution blow spinning, where a high velocity sheath gas is used instead of high voltage, has been used to generate polymer fibers. In this work, we used blow spinning to create nano/microfibers for microchip-based 3D cell culture. First, we thoroughly investigated fiber generation from a 3D printed gas sheath device using two polymers that are amenable to cell culture (polycaprolactone, PCL and polystyrene, PS) as well as the parameters that can affect PCL and PS fiber quality. Using the 3D printed sheath device, it was found that the pressure of the sheath N2 and the concentration of polymer solutions determine if fibers can be produced as well as the resulting fiber morphology. In addition, we showed how these fibers can be used for 3D cell culture by directly depositing PCL fibers in petri dishes and well plates. It is shown the fibers have good compatibility with RAW 264.7 macrophages and the PCL fiber scaffold can be as thick as 178 ± 14 μm. PCL fibers created from solution blow spinning (with the 3D printed sheath device) were then integrated with a microfluidic device for the first time to fabricate a 3D cell culture scaffold with a flow component. After culturing and stimulating macrophages on the fluidic device, it was found that the integrated 3D fibrous scaffold is a better mimic of the extracellular matrix (as opposed to a flat, 2D substrate), with enhanced nitrite accumulation (product of nitric oxide release) from macrophages stimulated with lipopolysaccharide. PS fibers were also made and integrated in a microfluidic device for 3D culture of endothelial cells, which stayed viable for at least 72 hours (48 hours under the flowing conditions). This approach will be useful for future studies involving more realistic microchip-based culture models for studying cell-to-cell communication.

Incorporation of bioactive glass nanoparticles in electrospun PCL/chitosan fibers by using benign solvents

The use of bioactive glass (BG) particles as a filler for the development of composite electrospun fibers has already been widely reported and investigated. The novelty of the present research work is represented by the use of benign solvents (like acetic acid and formic acid) for electrospinning of composite fibers containing BG particles, by using a blend of PCL and chitosan. In this work, different BG particle sizes were investigated, namely nanosized and micron-sized. A preliminary investigation about the possible alteration of BG particles in the electrospinning solvents was performed using SEM analysis. The obtained composite fibers were investigated in terms of morphological, chemical and mechanical properties. An in vitro mineralization assay in simulated body fluid (SBF) was performed to investigate the capability of the composite electrospun fibers to induce the formation of hydroxycarbonate apatite (HCA).

Steering surface topographies of electrospun fibers: understanding the mechanisms

A profound understanding of how to tailor surface topographies of electrospun fibers is of great importance for surface sensitive applications including optical sensing, catalysis, drug delivery and tissue engineering. Hereby, a novel approach to comprehend the driving forces for fiber surface topography formation is introduced through inclusion of the dynamic solvent-polymer interaction during fiber formation. Thus, the interplay between polymer solubility as well as computed fiber jet surface temperature changes in function of time during solvent evaporation and the resultant phase separation behavior are studied. The correlation of experimental and theoretical results shows that the temperature difference between the polymer solution jet surface temperature and the dew point of the controlled electrospinning environment are the main influencing factors with respect to water condensation and thus phase separation leading to the final fiber surface topography. As polymer matrices with enhanced surface area are particularly appealing for sensing applications, we further functionalized our nanoporous fibrous membranes with a phosphorescent oxygen-sensitive dye. The hybrid membranes possess high brightness, stability in aqueous medium, linear response to oxygen and hence represent a promising scaffold for cell growth, contactless monitoring of oxygen and live fluorescence imaging in 3-D cell models.

Effect of different solvent systems on PHBV/PEO electrospun fibers

The selection of non-hazardous solvent systems is an important factor that can significantly influence fiber formation during polymer electrospinning.

Biodegradable polymer scaffolds

Tissue engineering aims to repair the damaged tissue by transplantation of cells or introducing bioactive factors in a biocompatible scaffold. In recent years, biodegradable polymer scaffolds mimicking the extracellular matrix have been developed to promote the cell proliferation and extracellular matrix deposition. The biodegradable polymer scaffolds thus act as templates for tissue repair and regeneration. This article reviews the updated information regarding various types of natural and synthetic biodegradable polymers as well as their functions, physico-chemical properties, and degradation mechanisms in the development of biodegradable scaffolds for tissue engineering applications, including their combination with 3D printing.

Preparation and characterization of polycaprolactone microspheres by electrospraying

The ability to reproducibly produce and effectively collect electrosprayed polymeric microspheres with controlled morphology and size in bulk form is challenging. In this study, microparticles were produced by electrospraying polycaprolactone (PCL) of various molecular weights and solution concentrations in chloroform, and by collecting materials on different substrates. The resultant PCL microparticles were characterized by optical and electron microscopy to investigate the effect of molecular weight, solution concentration, applied voltage, working distance, and flow rate on their morphology and size. The work demonstrates the key role of a moderate molecular weight and/or solution concentration in the formation of spherical PCL particles via an electrospraying process. Increasing the applied voltage was found to produce smaller and more uniform PCL microparticles. There was a relatively low increase in the particle average size with an increase in the working distance and flow rate. Four types of substrates were adopted to collect electrosprayed PCL particles: a glass slide, aluminium foil, liquid bath, and copper wire. Unlike 2D bulk structures collected on the other substrates, a 3D tubular structure of microspheres was formed on the copper wire which could find application in the construction of 3D tumor mimics.

Nanofibers containing tetracycline/β-cyclodextrin: Physico-chemical characterization and antimicrobial evaluation

This study aimed to compare two nanofiber drug delivery systems that were prepared with an electrospun process and have the potential to serve as adjuvants for the treatment of periodontal disease. The first system was composed of polycaprolactone loaded with tetracycline (TCN) and the second was composed of polycaprolactone loaded with tetracycline/β-cyclodextrin (TCN:BCD). An antimicrobial diffusion test was performed for each of these sets of nanofibers with the microorganisms, Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis, both of which contribute to periodontal disease. In vitro release profiles were also obtained, and the nanofibers were characterized by thermal analysis, x-ray powder diffraction, infrared absorption spectroscopy, and scanning electron microscopy. Profiles of the TCN and TCN:BCD nanofibers showed that drug release occurred for up to 14days. However, the TCN:BCD nanofibers appeared to better protect and enhance the biological absorption of TCN due to the formation of a TCN:BCD inclusion complex.

Engineered electrospun poly(caprolactone)/polycaprolactone-g-hydroxyapatite nano-fibrous scaffold promotes human fibroblasts adhesion and proliferation

Polycaprolactone (PCL)/hydroxyapatite nano-composites are among the best candidates for tissue engineering. However, interactions between nHAp and PCL are difficult to control leading to inhomogeneous dispersion of the bio-ceramic particles. Grafting of polymer chains at high density/chain length while promotes the phase compatibility may result in reduced HAp exposed surface area and therefore, bioactivity is compromised. This issue is addressed here by grafting PCL chains onto HAp nano-particles through ring opening polymerization of ε-caprolactone (PCL-g-HAp). FTIR and TGA analysis showed that PCL (6.9wt%), was successfully grafted on the HAp. PCL/PCL-g-HAp nano-fibrous scaffold showed up to 10 and 33% enhancement in tensile strength and modulus, respectively, compared to those of PCL/HAp. The effects of HAp on the in vitro HAp formation were investigated for both the PCL/HAp and PCL/PCL-g-HAp scaffolds. Precipitation of HAp on the nano-composite scaffolds observed after 15days incubation in simulated body fluid (SBF), as confirmed by scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Human fibroblasts were seeded on PCL, PCL/HAp and PCL/PCL-g-HAp scaffolds. According to MTT assay, the highest cell proliferation was recorded for PCL/PCL-g-HAp nano-composite, at all time intervals (1-21days, P<0.001). Fluorescent microscopy (of DAPI stained samples) and electron microscopy images showed that all nano-fibrous scaffolds (PCL, PCL/HAp, and PCL/PCL-g-HAp), were non-toxic against cells, while more cell adhesion, and the most uniform cell distribution observed on the PCL/PCL-g-HAp. Overall, grafting of relatively short chains of PCL on the surface of HAp nano-particles stimulates fibroblasts adhesion and proliferation on the PCL/PCL-g-HAp nano-composite.

Damage-Resistant Composites Using Electrospun Nanofibers: A Multiscale Analysis of the Toughening Mechanisms

Today, fiber-reinforced polymer composites are a standard material in applications where a high stiffness and strength are required at minimal weight, such as aerospace structures, ultralight vehicles, or even flywheels for highly efficient power storage systems. Although fiber-reinforced polymer composites show many advantages compared to other materials, delamination between reinforcing plies remains a major problem limiting further breakthrough. Traditional solutions that have been proposed to toughen the interlaminar region between reinforcing plies have already reached their limit or have important disadvantages such as a high cost or the need for adapted production processes. Recently, electrospun nanofibers have been suggested as a more viable interlaminar toughening method. Although the expected benefits are numerous, the research on composite laminates enhanced with electrospun nanofibrous veils is still very limited. The work that has been done so far is almost exclusively focused on interlaminar fracture toughness tests with different kinds of nanofibers, where typically a trial and error approach has been used. A thorough understanding of the micromechanical fracture mechanisms and the parameters to obtain toughened composites has not been reported as of yet, but it is crucial to advance the research and design highly damage-resistant composites. This article provides such insight by analyzing the nanofiber toughening effect on three different levels for several nanofiber types. Only by combining the results from different levels, a thorough understanding can be obtained. These levels correspond to the hierarchical nature of a composite: the laminate, the interlaminar region, and the matrix resin. It is found that each level corresponds to certain mechanisms that result in a toughening effect. The bridging of microcracks by electrospun nanofibers is the main toughening mechanism resulting in damage resistance. Nevertheless, the way in which the nanofiber bridging mechanism expresses itself is different for each scale and dependent on parameters linked to a certain scale. The multiscale analysis of the toughening mechanisms reported in this paper is therefore crucial for understanding the behavior of nanofiber toughened composites, and as such allows for designing novel, damage-resistant, nanofiber-toughened materials.

Versatile Production of Poly(Epsilon-Caprolactone) Fibers by Electrospinning Using Benign Solvents

The electrospinning technique is widely used for the fabrication of micro- and nanofibrous structures. Recent studies have focused on the use of less toxic and harmful solvents (benign solvents) for electrospinning, even if those solvents usually require an accurate and longer process of optimization. The aim of the present work is to demonstrate the versatility of the use of benign solvents, like acetic acid and formic acid, for the fabrication of microfibrous and nanofibrous electrospun poly(epsilon-caprolactone) mats. The solvent systems were also shown to be suitable for the fabrication of electrospun structures with macroporosity, as well as for the fabrication of composite electrospun mats, fabricated by the addition of bioactive glass (45S5 composition) particles in the polymeric solution.

An Investigation of the Behavior of Solvent based Polycaprolactone ink for Material Jetting

An initial study of processing bioresorbable polycaprolactone (PCL) through material jetting was conducted using a Fujifilm Dimatix DMP-2830 material printer. The aim of this work was to investigate a potential solvent based method of jetting polycaprolactone. Several solvents were used to prepare a PCL solvent based ink and 1, 4-dioxane was chosen with the consideration of both solubility and safety. The morphology of PCL formed under different substrate temperatures, droplet spacings were investigated. Multi-layer PCL structures were printed and characterized. This work shows that biodegradable polycaprolactone can be processed through material jetting.

Acellular Bioactivity of Sol-Gel Derived Borate Glass-Polycaprolactone Electrospun Scaffolds

Recently, sol-gel derived borate glasses (BGs) have shown unprecedented conversion rates to bone-like mineral (hydroxycarbonated apatite). In an effort to explore their potential applications in bone tissue engineering, this study reports on the fabrication and characterization of BG particle incorporated electrospun "- polycaprolactone (PCL) fibrous composites. The electrospinning technique successfully incorporated PCL fibres with BG particles at 2.5 and 5 w/v%, with the higher BG loading creating a three-dimensional cotton-wool like morphology. Dynamic vapour sorption showed greater extents of mass change with BG content attributable to water sorption, and indicating greater reactivity in the composite systems. In vitro bioactivity was investigated in simulated body fluid for up to 7 days. Scanning electron microscopy, Fourier-transform infrared spectroscopy and xray diffraction indicated apatite formation in the 5 w/v% incorporated composite scaffold, which initiated as early as day 3. In summary, sol-gel derived BGs incorporatedfibrous electrospun PCL composites indicate rapid reactivity and bioactivity with potential applications in mineralized tissue engineering.

Blend electrospinning of dye-functionalized chitosan and poly(ε-caprolactone): towards biocompatible pH-sensors

Covalent dye-modification provides a valuable solution for a versatile dye-functionalization with proper dye-immobilization, showing major potential for natural (bio)polymers.

In vivo drug release behavior and osseointegration of a doxorubicin-loaded tissue-engineered scaffold

This pre-clinical study presented a dual function of a doxorubicin-loaded scaffold for both chemotherapeutic agent delivery and bone formation.

Long-Term Sustained Ciprofloxacin Release from PMMA and Hydrophilic Polymer Blended Nanofibers

Nanofibers represent an attractive novel drug delivery system for prolonged and controlled release. However, sustained release of hydrophilic drugs, like ciprofloxacin hydrochloride (CIP), from polymeric nanofibers is not an easy task. The present study investigates the effect of different hydrophobic polymers (PCL and PMMA) alone in monolithic nanofibers or with hydrophilic polymers (PVA, PEO, and chitosan) in blended nanofibers aiming to achieve sustained CIP release. CIP release from PCL nanofibers was 46% and from PMMA just 1.5% over 40 day period. Thus, PMMA holds great promise for modification of CIP release from blended nanofibers. PMMA blends with 10% PEO, PVA, or chitosan were used to electrospin nanofibers from solution in the mixture of acetic and formic acid. These nanofibers exhibited different drug-release profiles: PEO containing nanofiber mats demonstrated high burst effect, chitosan containing mats revealed very slow gradual release, and PVA containing mats yielded smaller burst effect with favorable sustained release. We have also shown that gradual sustain release of antibiotic like CIP can be additionally tuned over 18 days with various blend ratios of PMMA with PVA or chitosan reaching almost 100%. A mathematical model in agreement with the experimental observation revealed that the sustained CIP release from the blended nanofibers corresponded to the two-stage desorption process.