Carbon dioxide impregnation of electrospun polycaprolactone fibers

Electrospun Antibacterial Nanomaterials for Wound Dressings Applications

Chronic wounds are caused by bacterial infections and create major healthcare discomforts; to overcome this issue, wound dressings with antibacterial properties are to be utilized. The requirements of antibacterial wound dressings cannot be fulfilled by traditional wound dressing materials. Hence, to improve and accelerate the process of wound healing, an antibacterial wound dressing is to be designed. Electrospun nanofibers offer a promising solution to the management of wound healing, and numerous options are available to load antibacterial compounds onto the nanofiber webs. This review gives us an overview of some recent advances of electrospun antibacterial nanomaterials used in wound dressings. First, we provide a brief overview of the electrospinning process of nanofibers in wound healing and later discuss electrospun fibers that have incorporated various antimicrobial agents to be used in wound dressings. In addition, we highlight the latest research and patents related to electrospun nanofibers in wound dressing. This review also aims to concentrate on the importance of nanofibers for wound dressing applications and discuss functionalized antibacterial nanofibers in wound dressing.

Modifying an Active Compound's Release Kinetic Using a Supercritical Impregnation Process to Incorporate an Active Agent into PLA Electrospun Mats

The main objective of this work was to study the release of cinnamaldehyde (CIN) from electrospun poly lactic acid (e-PLA) mats obtained through two techniques: (i) direct incorporation of active compound during the electrospinning process (e-PLA-CIN); and (ii) supercritical carbon dioxide (scCO₂) impregnation of CIN within electrospun PLA mats (e-PLA/CIN_imp). The development and characterization of both of these active electrospun mats were investigated with the main purpose of modifying the release kinetic of this active compound. Morphological, structural, and thermal properties of these materials were also studied, and control mats e-PLA and e-PLACO2 were developed in order to understand the effect of electrospinning and scCO₂ impregnation, respectively, on PLA properties. Both strategies of incorporation of this active compound into PLA matrix resulted in different morphologies that influenced chemical and physical properties of these composites and in different release kinetics of CIN. The electrospinning and scCO₂ impregnation processes and the presence of CIN altered PLA thermal and structural properties when compared to an extruded PLA material. The incorporation of CIN through scCO₂ impregnation resulted in higher release rate and lower diffusion coefficients when compared to active electrospun mats with CIN incorporated during the electrospinning process.

Recent advances in electrospun nanofibers for wound healing

Electrospun nanofibers represent a novel class of materials that show great potential in many biomedical applications including biosensing, regenerative medicine, tissue engineering, drug delivery and wound healing. In this work, we review recent advances in electrospun nanofibers for wound healing. This article begins with a brief introduction on the wound, and then discusses the unique features of electrospun nanofibers critical for wound healing. It further highlights recent studies that have used electrospun nanofibers for wound healing applications and devices, including sutures, multifunctional dressings, dermal substitutes, engineered epidermis and full-thickness skin regeneration. Finally, we finish with conclusions and future perspective in this field.

Understanding drug release from PCL/gelatin electrospun blends

Electrospinning is one of the efficient processes to fabricate polymeric fibrous scaffolds for several biomedical applications. Several studies have published to demonstrate drug release from electrospun scaffolds. Blends of natural and synthetic electrospun fibers provide excellent platform to combine mechanical and bioactive properties. Drug release from polymer blends is a complex process. Drug release from polymer can be dominated by one or more of following mechanisms: polymer erosion, relaxation, and degradation. In this study, electrospun polycaprolactone (PCL)–gelatin blends are investigated to understand release mechanism of Rhodamine B dye. Also, this article summarizes the effect of high-pressure carbon dioxide on drug loading and release from PCL–gelatin fibers. Results indicate that release media diffusion is a dominant mechanism for PCL–gelatin electrospun fibers. Thickness of electrospun mat becomes critical for blends with gelatin. As gelatin is highly soluble in water and has tendency of gelation, it affects diffusion of release media in and out of scaffold. This article is a key step forward in understanding release from electrospun blends.

Nanocomposite Electrospun Nanofiber Membranes for Environmental Remediation

Rapid worldwide industrialization and population growth is going to lead to an extensive environmental pollution. Therefore, so many people are currently suffering from the water shortage induced by the respective pollution, as well as poor air quality and a huge fund is wasted in the world each year due to the relevant problems. Environmental remediation necessitates implementation of novel materials and technologies, which are cost and energy efficient. Nanomaterials, with their unique chemical and physical properties, are an optimum solution. Accordingly, there is a strong motivation in seeking nano-based approaches for alleviation of environmental problems in an energy efficient, thereby, inexpensive manner. Thanks to a high porosity and surface area presenting an extraordinary permeability (thereby an energy efficiency) and selectivity, respectively, nanofibrous membranes are a desirable candidate. Their functionality and applicability is even promoted when adopting a nanocomposite strategy. In this case, specific nanofillers, such as metal oxides, carbon nanotubes, precious metals, and smart biological agents, are incorporated either during electrospinning or in the post-processing. Moreover, to meet operational requirements, e.g., to enhance mechanical stability, decrease of pressure drop, etc., nanofibrous membranes are backed by a microfibrous non-woven forming a hybrid membrane. The novel generation of nanocomposite/hybrid nanofibrous membranes can perform extraordinarily well in environmental remediation and control. This reality justifies authoring of this review paper.

The future of carbon dioxide for polymer processing in tissue engineering

The use of CO2 for scaffold fabrication in tissue engineering was popularized in the mid-1990 s as a tool for producing polymeric foam scaffolds, but had fallen out of favor to some extent, in part due to challenges with pore interconnectivity. Pore interconnectivity issues have since been resolved by numerous dedicated studies that have collectively outlined how to control the appropriate parameters to achieve a pore structure desirable for tissue regeneration. In addition to CO2 foaming, several groups have leveraged CO2 as a swelling agent to impregnate scaffolds with drugs and other bioactive additives, and for encapsulation of plasmids within scaffolds for gene delivery. Moreover, in contrast to CO2 foaming, which typically relies on supercritical CO2 at very high pressures, CO2 at much lower pressures has also been used to sinter polymeric microspheres together in the presence of cells to create cell-seeded scaffolds in a single step. CO2 has a number of advantages for polymer processing in tissue engineering, including its ease of use, low cost, and the opportunity to circumvent the use of organic solvents. Building on these advantages, and especially now with the tremendous precedent that has paved the way in defining operating parameters, and making the technology accessible for new groups to adapt, we invite and encourage our colleagues in the field to leverage CO2 as a new tool to enhance their own respective unique capabilities.

Producing Polymer Fibers by Electrospinning in Supercritical Fluids

Nanofibers have a wide range of applications, including filtration and biomedical engineering. Porous or hollow fibers with large surface-to-volume ratios are more popular in some fields than the common nanofibers. Porous nanofibers can be obtained through electrospinning with highly volatile solvents or through special treatment following electrospinning. A new process where electrospinning is conducted in supercritical or near-critical CO2to produce porous or hollow nanofibers has been summarized. In addition, a process entailing compressed N2-assisted electrospinning was attempted to produce PVP nanofibers in this work, but it was proved to be unsuccessful. Since the fiber morphologies are dependent on the phase behavior of organic solvents in supercritical fluids, ASPEN PLUS 2006 was used to simulate the phase equilibrium of the solvent-supercritical fluid system to explain why porous or hollow fibers can be obtained in compressed CO2, but not in compressed N2.

Design and fabrication of tubular scaffolds via direct writing in a melt electrospinning mode

Flexible tubular structures fabricated from solution electrospun fibers are finding increasing use in tissue engineering applications. However it is difficult to control the deposition of fibers due to the chaotic nature of the solution electrospinning jet. By using non-conductive polymer melts instead of polymer solutions the path and collection of the fiber becomes predictable. In this work we demonstrate the melt electrospinning of polycaprolactone in a direct writing mode onto a rotating cylinder. This allows the design and fabrication of tubes using 20 μm diameter fibers with controllable micropatterns and mechanical properties. A key design parameter is the fiber winding angle, where it allows control over scaffold pore morphology (e.g. size, shape, number and porosity). Furthermore, the establishment of a finite element model as a predictive design tool is validated against mechanical testing results of melt electrospun tubes to show that a lesser winding angle provides improved mechanical response to uniaxial tension and compression. In addition, we show that melt electrospun tubes support the growth of three different cell types in vitro and are therefore promising scaffolds for tissue engineering applications.

Next generation of electrosprayed fibers for tissue regeneration

Electrospinning is a widely established polymer-processing technology that allows generation of fibers (in nanometer to micrometer size) that can be collected to form nonwoven structures. By choosing suitable process parameters and appropriate solvent systems, fiber size can be controlled. Since the technology allows the possibility of tailoring the mechanical properties and biological properties, there has been a significant effort to adapt the technology in tissue regeneration and drug delivery. This review focuses on recent developments in adapting this technology for tissue regeneration applications. In particular, different configurations of nozzles and collector plates are summarized from the view of cell seeding and distribution. Further developments in obtaining thick layers of tissues and thin layered membranes are discussed. Recent advances in porous structure spatial architecture parameters such as pore size, fiber size, fiber stiffness, and matrix turnover are summarized. In addition, possibility of developing simple three-dimensional models using electrosprayed fibers that can be utilized in routine cell culture studies is described.

Perspectives on: Supercritical Fluid Technology for 3D Tissue Engineering Scaffold Applications

Supercritical fluid technology has proven to be useful for many pharmaceutical applications and is now emerging as an alternative to conventional processes for the preparation of 3D structures and injectable particles suitable to be used in regenerative medicine. A current overview of the basic principles underlying supercritical fluid technology, the state of the art and future potential of this technology are presented.

Improvement of cytocompatibility of electrospinning PLLA microfibers by blending PVP

In this study, microfiber films were used as scaffolds for the purpose of vascular tissue engineering. The microfiber films were prepared by electrospinning of poly (l-lactide) (PLLA) and polyvinyl pyrrolidone (PVP). PLLA and PVP with different ratios were blended with dichloromethane as a spinning solvent at room temperature. The properties of the composite microfiber films were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and contact angle measurement. The SEM images showed that the morphology of the microfiber films was mainly affected by the weight ratios of PLLA/PVP. The DSC results demonstrated that PLLA and PVP mixed uniformly. And the hydrophilicity of the films measured increased along with the decrease of the PLLA/PVP ratio. Vascular smooth muscle cells (VSMCs) were used to test the cytocompatibility. Cell morphology and cell proliferation were measured by SEM, laser scanning confocal microscopy (LSCM) and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay after 2, 4, 6 days of culture. The results indicated that the cell morphology and proliferation on the composite films were better than that on the pure PLLA film. Furthermore, morphology and proliferation of VSMCs became better with decreasing of the weight ratio of PLLA/PVP. In addition, adhesion of platelet on the films was observed by SEM. The SEM images showed that the number of adhered platelets decreased with increment of PVP content in the films. The electrospinning microfiber composite films of PLLA and PVP would have potential use as the scaffolds for vascular tissue engineering.

Fabrication of burst pressure competent vascular grafts via electrospinning: effects of microstructure

In this work, electrospun tubes of interest for vascular tissue engineering were fabricated and evaluated for burst pressure and suture retention strength (SRS) in the same context as tensile strength providing a direct, novel comparison. Tubes could be fabricated displaying average burst pressures up to 4000 mmHg--well above the standard of 2000 mmHg--and SRS values matching those of relevant natural tissues. Surprisingly, highly oriented fiber and maximal tensile properties are not absolutely necessary to attain clinically adequate burst pressures. The ability to resist bursting is clearly related to both initial solution solids loading and electrospinning deposition time. We make novel in situ observations of the relative microstructural characteristics of failure during bursting, and connect this to the conditions used to fabricate the graft. Processes typically thought to promote fiber alignment are, in fact, highly condition-dependent and do not always provide superior properties. In fact, electrospun structures displaying no discernable alignment could achieve burst pressures regarded clinically sufficient. The properties of individual electrospun fiber clearly do not fully dictate macroscale properties. Normal background levels of point bonding are enhanced by increased rotational speeds, and can have effects on properties more dominant than those of alignment.

Advancing tissue engineering by using electrospun nanofibers

Electrospinning is a versatile technique that enables the development of nanofiber-based scaffolds, from a variety of polymers that may have drug-release properties. Using nanofibers, it is now possible to produce biomimetic scaffolds that can mimic the extracellular matrix for tissue engineering. Interestingly, nanofibers can guide cell growth along their direction. Combining factors like fiber diameter, alignment and chemicals offers new ways to control tissue engineering. In vivo evaluation of nanomats included their degradation, tissue reactions and engineering of specific tissues. New advances made in electrospinning, especially in drug delivery, support the massive potential of these nanobiomaterials. Nevertheless, there is already at least one product based on electrospun nanofibers with drug-release properties in a Phase III clinical trial, for wound dressing. Hopefully, clinical applications in tissue engineering will follow to enhance the success of regenerative therapies.