Aligned core-shell nanofibers delivering bioactive proteins

Delivery of TGFβ3 from Magnetically Responsive Coaxial Fibers Reduces Spinal Cord Astrocyte Reactivity In Vitro

A spinal cord injury (SCI) compresses the spinal cord, killing neurons and glia at the injury site and resulting in prolonged inflammation and scarring that prevents regeneration. Astrocytes, the main glia in the spinal cord, become reactive following SCI and contribute to adverse outcomes. The anti-inflammatory cytokine transforming growth factor beta 3 (TGFβ3) has been shown to mitigate astrocyte reactivity; however, the effects of prolonged TGFβ3 exposure on reactive astrocyte phenotype have not yet been explored. This study investigates whether magnetic core-shell electrospun fibers can be used to alter the release rate of TGFβ3 using externally applied magnetic fields, with the eventual application of tailored drug delivery based on SCI severity. Magnetic core-shell fibers are fabricated by incorporating superparamagnetic iron oxide nanoparticles (SPIONs) into the shell and TGFβ3 into the core solution for coaxial electrospinning. Magnetic field stimulation increased the release rate of TGFβ3 from the fibers by 25% over 7 days and released TGFβ3 reduced gene expression of key astrocyte reactivity markers by at least twofold. This is the first study to magnetically deliver bioactive proteins from magnetic fibers and to assess the effect of sustained release of TGFβ3 on reactive astrocyte phenotype.

Coaxial electrospun Ag-NPs-loaded endograft membrane with long-term antibacterial function treating mycotic aortic aneurysm

The use of endovascular stent-graft has become an important option in the treatment of aortic pathologies. However, the currently used endograft membranes have limited ability to prevent bacterial colonization. This makes them unsuitable for the treatment of mycotic aneurysms, as the infection is prone to progress after endograft implantation. Moreover, even in non-mycotic aortic pathologies, endograft infections can occur in the short or long term, especially for patients with diabetes mellitus or in immune insufficiency conditions. So, this study aimed to develop a kind of Ag-NPs-loaded endograft membrane by coaxial electrospinning technique, and a series of physical and chemical properties and biological properties of the Ag-NPs-loaded membrane were characterized. Animal experiments conducted in pigs confirmed that the Ag-NPs-loaded membrane was basically non-toxic, exhibited good biocompatibility, and effectively prevented bacterial growth in a mycotic aortic aneurysm model. In conclusion, the Ag-NPs-loaded membrane exhibited good biocompatibility, good anti-infection function and slow-release of Ag-NPs for long-term bacteriostasis. Thus, the Ag-NPs-loaded membrane might hold potential for preventing infection progression and treating mycotic aortic aneurysms in an endovascular way.

Therapeutic Agent-Loaded Fibrous Scaffolds for Biomedical Applications

Tissue engineering is a sophisticated field that involves the integration of various disciplines, such as clinical medicine, material science, and life science, to repair or regenerate damaged tissues and organs. To achieve the successful regeneration of damaged or diseased tissues, it is necessary to fabricate biomimetic scaffolds that provide structural support to the surrounding cells and tissues. Fibrous scaffolds loaded with therapeutic agents have shown considerable potential in tissue engineering. In this comprehensive review, we examine various methods for fabricating bioactive molecule-loaded fibrous scaffolds, including preparation methods for fibrous scaffolds and drug-loading techniques. Additionally, we delved into the recent biomedical applications of these scaffolds, such as tissue regeneration, inhibition of tumor recurrence, and immunomodulation. The aim of this review is to discuss the latest research trends in fibrous scaffold manufacturing methods, materials, drug-loading methods with parameter information, and therapeutic applications with the goal of contributing to the development of new technologies or improvements to existing ones.

Tunable Spun Fiber Constructs in Biomedicine: Influence of Processing Parameters in the Fibers' Architecture

Electrospinning and wet-spinning have been recognized as two of the most efficient and promising techniques for producing polymeric fibrous constructs for a wide range of applications, including optics, electronics, food industry and biomedical applications. They have gained considerable attention in the past few decades because of their unique features and tunable architectures that can mimic desirable biological features, responding more effectively to local demands. In this review, various fiber architectures and configurations, varying from monolayer and core-shell fibers to tri-axial, porous, multilayer, side-by-side and helical fibers, are discussed, highlighting the influence of processing parameters in the final constructs. Additionally, the envisaged biomedical purposes for the examined fiber architectures, mainly focused on drug delivery and tissue engineering applications, are explored at great length.

Multidrug-loaded electrospun micro/nanofibrous membranes: Fabrication strategies, release behaviors and applications in regenerative medicine

Electrospun micro/nanofibrous membranes (EFMs) have been widely investigated as local drug delivery systems. Multiple drugs can be simultaneously incorporated into one EFM to create synergistic effects, reduce side effects, and play their respective roles in the complex physiological processes of tissue regeneration and postoperative adhesion prevention. Due to the versatile electrospinning techniques, sustained and programmed release behaviors of multiple drugs could be achieved by modulating the structure of the EFMs and the location of the drugs. In this review, various multidrug incorporation approaches based on electrospinning are overviewed. In particular, the advantages and limitations of each drug incorporation technique, the methods to control drug release and the effect of one drug release on another are discussed. Then the applications of multidrug-loaded EFMs in regenerative medicine, including wound healing, bone regeneration, vascular tissue engineering, nerve regeneration, periodontal regeneration and adhesion prevention are comprehensively reviewed. Finally, the future perspectives and challenges in the research of multidrug-loaded EFMs are discussed.

Electrospun Biomaterials’ Applications and Processing

One of the largest fields of application of electrospun materials is the biomedical field, including development of scaffolds for tissue engineering, drug delivery and wound healing. Electrospinning appears as a promising technique in terms of scaffolds composition and architecture, which is the main aspect of this review paper, with a special attention to natural polymers including collagen, fibrinogen, silk fibroin, chitosan, chitin etc. Thanks to the adaptability of the electrospinning process, versatile hybrid, custom tailored structure scaffolds have been reported. The same is achieved due to the vast biomaterials’ processability as well as modifications of the basic electrospinning set-up and its combination with other techniques, simultaneously or by post-processing.

Beyond the Single-Nozzle: Coaxial Electrospinning Enables Innovative Nanofiber Chemistries, Geometries, and Applications

With an ever increasing scientific, technological, and industrial interest in high surface area, porous nanofiber mats, electrospinning has emerged as a popular method to produce fibrous assemblies for use across biomedical, energy, and environmental applications. However, not all precursor solutions nor complex geometries can be easily fabricated using the traditional single-nozzle apparatus. Therefore, coaxial electrospinning, a modified version of electrospinning that features a concentrically aligned dual nozzle, has been developed. This review will first describe the mechanism of electrospinning two precursor solutions simultaneously and the operational parameters that need to be optimized to fabricate continuous fibers. Modifications that can be made to the coaxial electrospinning process, which enable the fabrication of uniform fibers with improved properties, as well as the fabrication of fibers that are hollow, functionalized, and from "nonspinnable precursors" will be discussed as a means of promoting the advantages of using a coaxial setup. Examples of how coaxially electrospun nanofibers are employed in diverse applications will be provided throughout this review. We conclude with a timely discussion about the current limitations and challenges of coaxial electrospinning.

Electrospun Fiber Scaffolds for Engineering Glial Cell Behavior to Promote Neural Regeneration

Electrospinning is a fabrication technique used to produce nano- or micro- diameter fibers to generate biocompatible, biodegradable scaffolds for tissue engineering applications. Electrospun fiber scaffolds are advantageous for neural regeneration because they mimic the structure of the nervous system extracellular matrix and provide contact guidance for regenerating axons. Glia are non-neuronal regulatory cells that maintain homeostasis in the healthy nervous system and regulate regeneration in the injured nervous system. Electrospun fiber scaffolds offer a wide range of characteristics, such as fiber alignment, diameter, surface nanotopography, and surface chemistry that can be engineered to achieve a desired glial cell response to injury. Further, electrospun fibers can be loaded with drugs, nucleic acids, or proteins to provide the local, sustained release of such therapeutics to alter glial cell phenotype to better support regeneration. This review provides the first comprehensive overview of how electrospun fiber alignment, diameter, surface nanotopography, surface functionalization, and therapeutic delivery affect Schwann cells in the peripheral nervous system and astrocytes, oligodendrocytes, and microglia in the central nervous system both in vitro and in vivo. The information presented can be used to design and optimize electrospun fiber scaffolds to target glial cell response to mitigate nervous system injury and improve regeneration.

Highly Elastic and Water Stable Zein Microfibers as a Potential Drug Delivery System for Wound Healing

The development of biomaterials for wound healing applications requires providing a number of properties, such as antimicrobial action, facilitation of cell proliferation, biocompatibility and biodegradability. The aim of the present study was to investigate morphological and mechanical properties of zein-based microfibers, ultimately aimed at creating an environment suitable for wound healing. This was achieved through co-axial electrospinning of core-shell microfibers, with zein protein in the core and polyethylene oxide (PEO) in the shell. Small amounts of PEO or stearic acid were additionally incorporated into the fiber core to modify the morphology and mechanical properties of zein fibers. The presence of PEO in the core was found to be essential for the formation of tubular fibers, whereas PEO in the shell enhanced the stability of the microfibers in water and ensured high elasticity of the microfiber mats. Tetracycline hydrochloride was present in an amorphous form within the fibers, and displayed a burst release as a result of pore-formation in the fibers. The developed systems exhibited antimicrobial activity against Staphylococcus aureus and Escherichia coli, and showed no cytotoxic effect on fibroblasts. Biocompatibility, antimicrobial activity and favorable morphological and mechanical properties make the developed zein-based microfibers a potential biomaterial for wound healing purposes.

Fabrication and Plasma Modification of Nanofibrous Tissue Engineering Scaffolds

This paper provides a comprehensive overview of nanofibrous structures for tissue engineering purposes and the role of non-thermal plasma technology (NTP) within this field. Special attention is first given to nanofiber fabrication strategies, including thermally-induced phase separation, molecular self-assembly, and electrospinning, highlighting their strengths, weaknesses, and potentials. The review then continues to discuss the biodegradable polyesters typically employed for nanofiber fabrication, while the primary focus lies on their applicability and limitations. From thereon, the reader is introduced to the concept of NTP and its application in plasma-assisted surface modification of nanofibrous scaffolds. The final part of the review discusses the available literature on NTP-modified nanofibers looking at the impact of plasma activation and polymerization treatments on nanofiber wettability, surface chemistry, cell adhesion/proliferation and protein grafting. As such, this review provides a complete introduction into NTP-modified nanofibers, while aiming to address the current unexplored potentials left within the field.

Recent Developments in Nanofiber Fabrication and Modification for Bone Tissue Engineering

Bone tissue engineering is an alternative therapeutic intervention to repair or regenerate lost bone. This technique requires three essential components: stem cells that can differentiate into bone cells, growth factors that stimulate cell behavior for bone formation, and scaffolds that mimic the extracellular matrix. Among the various kinds of scaffolds, highly porous nanofibrous scaffolds are a potential candidate for supporting cell functions, such as adhesion, delivering growth factors, and forming new tissue. Various fabricating techniques for nanofibrous scaffolds have been investigated, including electrospinning, multi-axial electrospinning, and melt writing electrospinning. Although electrospun fiber fabrication has been possible for a decade, these fibers have gained attention in tissue regeneration owing to the possibility of further modifications of their chemical, biological, and mechanical properties. Recent reports suggest that post-modification after spinning make it possible to modify a nanofiber's chemical and physical characteristics for regenerating specific target tissues. The objectives of this review are to describe the details of recently developed fabrication and post-modification techniques and discuss the advanced applications and impact of the integrated system of nanofiber-based scaffolds in the field of bone tissue engineering. This review highlights the importance of nanofibrous scaffolds for bone tissue engineering.

Impact of UV sterilization and short term storage on the in vitro release kinetics and bioactivity of biomolecules from electrospun scaffolds

To effectively translate bioactive scaffolds into a preclinical setting, proper sterilization techniques and storage conditions need to be carefully considered, as the chosen sterilization technique and storage condition might affect the structural and mechanical properties of the scaffolds, as well as the bioactivity and release kinetics of the incorporated biomolecules. Since rarely tested or quantified, we show here in a proof-of-concept study how these parameters are affected by UV sterilization and one week storage at different temperatures using bioactive electrospun DegraPol scaffolds that were specifically designed for application in the field of tendon rupture repair. Even though UV sterilization and the different storage conditions did not impact the morphology or the physicochemical properties of the bioactive scaffolds, UV sterilization caused significant attenuation of the growth factor release kinetics, here platelet derived growth factor (PDGF-BB) release (by approx. 85%) and slight decrease in ascorbic acid release (by approx. 20%). In contrast, 4 °C and −20 °C storage did not have a major effect on the release kinetics of PDGF-BB, while storage at room temperature caused increase in PDGF-BB released. All storage conditions had little effect on ascorbic acid release. Equally important, neither UV sterilization nor storage affected the bioactivity of the released PDGF-BB, suggesting stability of the bioactive scaffolds for at least one week and showing potential for bioactive DegraPol scaffolds to be translated into an off-the-shelf available product. These parameters are expected to be scaffold and protein-dependent.

Emerging frontiers in drug release control by core-shell nanofibers: a review

In recent years, core-shell (CS) nanofiber has widely been used as a carrier for controlled drug release. This outstanding attention toward CS nanofiber is mainly due to its tremendous significance in controllable drug release in specific locations. The major advantage of CS nanofibers is forming a highly porous mesh, boosting its performance for many applications, due to its large surface-to-volume ratio. This inherently high ratio has prompted electrospun fibers to be considered one of the best drug-delivery-systems available, with the capacity to enhance properties such as cell attachment, drug loading, and mass transfer. Using electrospun fibers as CS nanofibers to incorporate different cargos such as antibiotics, anticancer agents, proteins, DNA, RNA, living cells, and diverse growth factors would considerably satisfy the need for a universal carrier in the field of nanotechnology. In addition to their high surface area, other benefit included in these nanofibers is the ability to trap drugs, easily controlled morphology, and their biomimetic characteristics. In this review, by taking the best advantages of the preparation and uses of CS nanofibers, a novel work in the domain of the controlled drug delivery by nanofiber-based scaffolds is presented.

Drug Delivery Applications of Core-Sheath Nanofibers Prepared by Coaxial Electrospinning: A Review

Electrospinning has emerged as one of the potential techniques for producing nanofibers. The use of electrospun nanofibers in drug delivery has increased rapidly over recent years due to their valuable properties, which include a large surface area, high porosity, small pore size, superior mechanical properties, and ease of surface modification. A drug loaded nanofiber membrane can be prepared via electrospinning using a model drug and polymer solution; however, the release of the drug from the nanofiber membrane in a safe and controlled way is challenging as a result of the initial burst release. Employing a core-sheath design provides a promising solution for controlling the initial burst release. Numerous studies have reported on the preparation of core-sheath nanofibers by coaxial electrospinning for drug delivery applications. This paper summarizes the physical phenomena, the effects of various parameters in coaxial electrospinning, and the usefulness of core-sheath nanofibers in drug delivery. Furthermore, this report also highlights the future challenges involved in utilizing core-sheath nanofibers for drug delivery applications.

Fabrication, mechanical property and in vitro evaluation of poly (L-lactic acid-co-ε-caprolactone) core-shell nanofiber scaffold for tissue engineering

Coaxial electrospinning, in which Poly (L-lactic acid-co-ε-caprolactone) (PLC) with different Lactic acid (LA) to caprolactone (CL) ratio (75:25 and 50:50) were employed to electrospin core-shell nanofibers which could mimic the native extracellular matrix for tissue engineering applications. Core-shell nanofibrous scaffolds of PLC (50:50)/BSA (426 ± 157 nm) and PLC (75:25)/BSA (427 ± 197 nm) were fabricated and model drug bovine serum albumin (BSA) was entrapped in the core layer. The morphology, core-shell structure and sustained release behaviors were evaluated by Scanning electron microscopy (SEM), transmission electron microscopy (TEM), inverted fluorescence microscopy, water contact angle test and in vitro release test, respectively. The effect of core-shell structure and shell layer materials on the variation tendency of mechanical characterization in dry and wet situation were also investigated by tensile testing. The in vitro biocompatibility of scaffolds were investigated by growing human mesenchymal stem cells (hMSCs) on scaffolds surface and the proliferation of cells were evaluated with Alamar Blue tests. In vitro cultivations of hMSCs showed that PLC (50:50)/BSA scaffolds supported a significantly higher proliferation rate of seeded cells than scaffolds prepared by polymer PLC (75:25)/BSA. Overall, the PLC core-shell nanofibers possessed potentially regulable mechanical properties useful for tissue engineering as well as sustained release potential for medical applications.

Core-shell nanofibers as drug delivery systems

Core-shell nanofibers have grown in popularity over the last decade owing to their special features and their many applications in biomedicine. They can be produced by electrospinning of immiscible polymer blends or emulsions through a single nozzle or by electrospinning using a coaxial nozzle. Several of the electrospinning parameters allow great versatility for the compositions and diameters of core-shell nanofibers to be produced. Morphology of core-shell nanofibers can be investigated using transmission electron microscopy and, in some cases, scanning electron microscopy. Several studies have shown that core-shell nanofibers have some advantages over monolithic nanofibers, such as better drug, protein, gene or probiotic incorporation into the nanofibers, greater control over drug release, and maintenance of protein structure and activity during electrospinning. We herein review the production and characterization of core-shell nanofibers, the critical parameters that affect their development, and their advantages as delivery systems.

Electrospinning Nanofibers for Therapeutics Delivery

The limitations of conventional therapeutic drugs necessitate the importance of developing novel therapeutics to treat diverse diseases. Conventional drugs have poor blood circulation time and are not stable or compatible with the biological system. Nanomaterials, with their exceptional structural properties, have gained significance as promising materials for the development of novel therapeutics. Nanofibers with unique physiochemical and biological properties have gained significant attention in the field of health care and biomedical research. The choice of a wide variety of materials for nanofiber fabrication, along with the release of therapeutic payload in sustained and controlled release patterns, make nanofibers an ideal material for drug delivery research. Electrospinning is the conventional method for fabricating nanofibers with different morphologies and is often used for the mass production of nanofibers. This review highlights the recent advancements in the use of nanofibers for the delivery of therapeutic drugs, nucleic acids and growth factors. A detailed mechanism for fabricating different types of nanofiber produced from electrospinning, and factors influencing nanofiber generation, are discussed. The insights from this review can provide a thorough understanding of the precise selection of materials used for fabricating nanofibers for specific therapeutic applications and also the importance of nanofibers for drug delivery applications.

Matrix Mediated Viral Gene Delivery: A Review

Polymeric matrices inherently protect viral vectors from pre-existing immune conditions, limit dissemination to off-target sites, and can sustain vector release. Advancing methodologies in development of particulate based vehicles have led to improved encapsulation of viral vectors. Polymeric delivery systems have contributed to increasing cellular transduction, responsive release mechanisms, cellular infiltration, and cellular signaling. Synthetic polymers are easily customizable, and are capable of balancing matrix retention with cellular infiltration. Natural polymers contain inherent biorecognizable motifs adding therapeutic efficacy to the incorporated viral vector. Recombinant polymers use highly conserved motifs to carefully engineer matrices, allowing for precise design including elements of vector retention and responsive release mechanisms. Composite polymer systems provide opportunities to create matrices with unique properties. Carefully designed matrices can control spatiotemporal release patterns that synergize with approaches in regenerative medicine and antitumor therapies.

Biomedical Applications of Electrospun Nanofibers: Drug and Nanoparticle Delivery

The electrospinning process has gained popularity due to its ease of use, simplicity and diverse applications. The properties of electrospun fibers can be controlled by modifying either process variables (e.g., applied voltage, solution flow rate, and distance between charged capillary and collector) or polymeric solution properties (e.g., concentration, molecular weight, viscosity, surface tension, solvent volatility, conductivity, and surface charge density). However, many variables affecting electrospinning are interdependent. An optimized electrospinning process is one in which these parameters remain constant and continuously produce nanofibers consistent in physicochemical properties. In addition, nozzle configurations, such as single nozzle, coaxial, multi-jet electrospinning, have an impact on the fiber characteristics. The polymeric solution could be aqueous, a polymeric melt or an emulsion, which in turn leads to different types of nanofiber formation. Nanofiber properties can also be modified by polarity inversion and by varying the collector design. The active moiety is incorporated into polymeric fibers by blending, surface modification or emulsion formation. The nanofibers can be further modified to deliver multiple drugs, and multilayer polymer coating allows sustained release of the incorporated active moiety. Electrospun nanofibers prepared from polymers are used to deliver antibiotic and anticancer agents, DNA, RNA, proteins and growth factors. This review provides a compilation of studies involving the use of electrospun fibers in biomedical applications with emphasis on nanoparticle-impregnated nanofibers.

Functionalized core/shell nanofibers for the differentiation of mesenchymal stem cells for vascular tissue engineering

AIM

Atherosclerosis is a common cardiovascular disease causing medical problems globally leading to coronary artery bypass surgery. The present study is to fabricate core/shell nanofibers to encapsulate VEGF for the differentiation of mesenchymal stem cells (MSCs) into smooth muscle cells to develop vascular grafts.

MATERIALS & METHODS

The fabricated core/shell nanofibers contained polycaprolactone/gelatin as the shell, and silk fibroin/VEGF as the core materials.

RESULTS

The results observed that the core/shell nanofibers interact to differentiate MSCs into smooth muscle cells by the expression of vascular smooth muscle cell (VSMC) contractile proteins α-actinin, myosin and F-actin.

CONCLUSION

The functionalized polycaprolactone/gelatin/silk fibroin/VEGF (250 ng) core/shell nanofibers were fabricated for the controlled release of VEGF in a persistent manner for the differentiation of MSCs into smooth muscle cells for vascular tissue engineering.

Electrospun amorphous solid dispersions of poorly water-soluble drugs: A review

The development of oral dosage forms for poorly water-soluble active pharmaceutical ingredients (APIs) is a persistent challenge. A range of methods has been explored to address this issue, and amorphous solid dispersions (ASDs) have received increasing attention. ASDs are typically prepared by starting with a liquid precursor (a solution or melt) and applying energy for solidification. Many techniques can be used, with the emergence of electrospinning as a potent option in recent years. This method uses electrical energy to induce changes from liquid to solid. Through the direct applications of electrical energy, electrospinning can generate nanofiber-based ASDs from drug-loaded solutions, melts and melt-solutions. The technique can also be combined with other approaches using the application of mechanical, thermal or other energy sources. Electrospinning has numerous advantages over other approaches to produce ASDs. These advantages include extremely rapid drying speeds, ease of implentation, compatibility with a wide range of active ingredients (including those which are thermally labile), and the generation of products with large surface areas and high porosity. Furthermore, this technique exhibits the potential to create so-called 'fifth-generation' ASDs with nanostructured architectures, such as core/shell or Janus systems and their combinations. These advanced systems can improve dissolution behaviour and provide programmable drug release profiles. Additionally, the fiber components and their spatial distributions can be precisely controlled. Electrospun fiber-based ASDs can maintain an incorporated active ingredient in the amorphous physical form for prolonged periods of time because of their homogeneous drug distribution within the polymer matrix (typically they comprise solid solutions), and ability to inhibit molecular motion. These ASDs can be utilised to generate oral dosage forms for poorly water-soluble drugs, resulting in linear or multiple-phase release of one or more APIs. Electrospun ASDs can also be exploited as templates for manipulating molecular self-assembly, offering a bridge between ASDs and other types of dosage forms. This review addresses the development, advantages and pharmaceutical applications of electrospinning for producing polymeric ASDs. Material preparation and analysis procedures are considered. The mechanisms through which performance has been improved are also discussed.

Electrospun polymeric nanofibres as wound dressings: A review

Skin wounds have significant morbidity and mortality rates associated. This is explained by the limited effectiveness of the currently available treatments, which in some cases do not allow the reestablishment of the structure and functions of the damaged skin, leading to wound infection and dehydration. These drawbacks may have an impact on the healing process and ultimately prompt patients' death. For this reason, researchers are currently developing new wound dressings that enhance skin regeneration. Among them, electrospun polymeric nanofibres have been regarded as promising tools for improving skin regeneration due to their structural similarity with the extracellular matrix of normal skin, capacity to promote cell growth and proliferation and bactericidal activity as well as suitability to deliver bioactive molecules to the wound site. In this review, an overview of the recent studies concerning the production and evaluation of electrospun polymeric nanofibrous membranes for skin regenerative purposes is provided. Moreover, the current challenges and future perspectives of electrospun nanofibrous membranes suitable for this biomedical application are highlighted.

Aligned laminin core-polydioxanone/collagen shell fiber matrices effective for neuritogenesis

Neural tissue regeneration is a significant challenge, because severe nerve injury is quite difficult to regenerate spontaneously. Although, many studies have been devoted to promote nerve regeneration, there are still many technical challenges to achieve satisfactory results. In this study, we designed biomimetic matrices composed of aligned laminin core-polydioxanone/collagen shell (Lam-PDO/Col) fibers, which can provide both topographical and biochemical cues for promoting neuritogenesis. The aligned Lam-PDO/Col core-shell fiber matrices were fabricated by magnetic field-assisted electrospinning with the coaxial system, and their potential as biofunctional scaffolds for promoting neuritogenesis was explored. It was demonstrated that the aligned Lam-PDO/Col core-shell fibers were successfully fabricated, and the laminin in the core of fibers was steadily and continuously released from fibers. In addition, the cellular behaviors of hippocampal neuronal cells on the matrices were significantly enhanced. Moreover, the aligned Lam-PDO/Col fiber matrices effectively improved and guided neurite outgrowth as well as the neurogenic differentiation by providing both topographical and biochemical cues through aligned fiber structure and sustained release of laminin. Collectively, it is suggested that the aligned Lam-PDO/Col core-shell fiber matrices are one of the most promising approaches for promoting neuritogenesis and neural tissue regeneration.

Advancements and Challenges in Multidomain Multicargo Delivery Vehicles

Reparative and regenerative processes are well-orchestrated temporal and spatial events that are governed by multiple cells, molecules, signaling pathways, and interactions thereof. Yet again, currently available implantable devices fail largely to recapitulate nature's complexity and sophistication in this regard. Herein, success stories and challenges in the field of layer-by-layer, composite, self-assembly, and core-shell technologies are discussed for the development of multidomain/multicargo delivery vehicles.

Preparation of poly(lactic acid)/graphene oxide nanofiber membranes with different structures by electrospinning for drug delivery

Nanofiber membranes display promising potential in biomedical fields, especially as scaffolds for drug delivery and tissue engineering. The structures and components of nanofibers play crucial roles in improving the mechanical properties and drug-releasing performance of nanofiber membranes. In this work, poly(lactic acid) (PLA)/graphene oxide (GO) nanofiber membranes with different structures (single-axial and co-axial structure) were prepared by electrospinning. The morphologies, structures, and mechanical properties of the as-prepared nanofiber membranes were characterized and compared. Furthermore, the drug-releasing performance of the as-prepared nanofiber membranes with different structures was evaluated by using an organic dye (Rhodamine B, RhB) as a drug model. Results show that the addition of GO not only significantly improved the thermal stability and mechanical properties of the PLA nanofiber membranes, but also promoted the cumulative release and release rate of RhB from nanofiber membranes. At the same GO concentration, the nanofiber membrane with the co-axial structure displayed a higher tensile strength and Young's modulus, but exhibited a lower cumulative release and release rate. The formation of the co-axial structure is beneficial in suppressing the initial burst release of RhB from nanofiber membranes.

PLA/GO nanofiber membrane with the co-axial structure exhibited the improved mechanical properties, which is also beneficial to separately loading different drugs in core-/sheath-structure and suppressing the initial burst release of drugs.

Multicompartment Drug Release System for Dynamic Modulation of Tissue Responses

Pharmacological modulation of responses to injury is complicated by the need to deliver multiple drugs with spatiotemporal resolution. Here, a novel controlled delivery system containing three separate compartments with each releasing its contents over different timescales is fabricated. Core-shell electrospun fibers create two of the compartments in the system, while electrosprayed spheres create the third. Utility is demonstrated by targeting the foreign body response to implants because it is a dynamic process resulting in implant failure. Sequential delivery of a drug targeting nuclear factor-κB (NF-κB) and an antifibrotic is characterized in in vitro experiments. Specifically, macrophage fusion and p65 nuclear translocation in the presence of releasate or with macrophages cultured on the surfaces of the constructs are evaluated. In addition, releasate from pirfenidone scaffolds is shown to reduce transforming growth factor-β (TGF-β)-induced pSMAD3 nuclear localization in fibroblasts. In vivo, drug eluting constructs successfully mitigate macrophage fusion at one week and fibrotic encapsulation in a dose-dependent manner at four weeks, demonstrating effective release of both drugs over different timescales. Future studies can employ this system to improve and prolong implant lifetimes, or load it with other drugs to modulate other dynamic processes.

Delivery of Therapeutic Proteins Using Electrospun Fibers-Recent Developments and Current Challenges

Proteins play a vital role within the human body by regulating various functions and even serving as structural constituent of many body parts. In this context, protein-based therapeutics have attracted a lot of attention in the last few decades as potential treatment of different diseases. Due to the steadily increasing interest in protein-based therapeutics, different dosage forms were investigated for delivering such complex macromolecules to the human body. Here, electrospun fibers hold a great potential for embedding proteins without structural damage and for controlled release of the protein for therapeutic applications. This review provides a comprehensive overview of the current state of protein-based carrier systems using electrospun fibers, with special emphasis on discussing their potential and key challenges in developing such therapeutic strategies, along with a prospective view of anticipated future directions.

Cardiac tissue engineering: from matrix design to the engineering of bionic hearts

The field of cardiac tissue engineering aims at replacing the scar tissue created after a patient has suffered from a myocardial infarction. Various technologies have been developed toward fabricating a functional engineered tissue that closely resembles that of the native heart. While the field continues to grow and techniques for better tissue fabrication continue to emerge, several hurdles still remain to be overcome. In this review we will focus on several key advances and recent technologies developed in the field, including biomimicking the natural extracellular matrix structure and enhancing the transfer of the electrical signal. We will also discuss recent developments in the engineering of bionic cardiac tissues which integrate the fields of tissue engineering and electronics to monitor and control tissue performance.

Differentiation of Bone Marrow Stem Cells into Schwann Cells for the Promotion of Neurite Outgrowth on Electrospun Fibers

Seeding nerve guidance conduits with Schwann cells can improve the outcome of peripheral nerve injury repair. Bone marrow stem cells (BMSCs) represent a good choice of cell source as they can differentiate into Schwann cells under appropriate conditions. In this work, we systematically investigated the differentiation of BMSCs into Schwann cells on scaffolds comprising electrospun fibers. We changed the alignment, diameter, and surface properties of the fibers to optimize the differentiation efficiency. The uniaxial alignment of fibers not only promoted the differentiation of BMSCs into Schwann cells but also dictated the morphology and alignment of the derived cells. Coating the surface of aligned fibers with laminin further enhanced the differentiation and thus increased the secretion of neurotrophins. When co-cultured with PC12 cells or chick dorsal root ganglion, the as-derived Schwann cells were able to promote the outgrowth of neurites from cell bodies and direct their extension along the fibers, demonstrating the positive impacts of both the neurotrophic effect and the morphological contact guidance. This work offers a promising strategy for integrating fiber guidance with stem cell therapy to augment peripheral nerve injury repair.

Heparin/collagen encapsulating nerve growth factor multilayers coated aligned PLLA nanofibrous scaffolds for nerve tissue engineering

Biomimicing topological structure of natural nerve tissue to direct axon growth and controlling sustained release of moderate neurotrophic factors are extremely propitious to the functional recovery of damaged nervous systems. In this study, the heparin/collagen encapsulating nerve growth factor (NGF) multilayers were coated onto the aligned poly-L-lactide (PLLA) nanofibrous scaffolds via a layer-by-layer (LbL) self-assembly technique to combine biomolecular signals, and physical guidance cues for peripheral nerve regeneration. Scanning electronic microscopy (SEM) revealed that the surface of aligned PLLA nanofibrous scaffolds coated with heparin/collagen multilayers became rougher and appeared some net-like filaments and protuberances in comparison with PLLA nanofibrous scaffolds. The heparin/collagen multilayers did not destroy the alignment of nanofibers. X-ray photoelectron spectroscopy and water contact angles displayed that heparin and collagen were successfully coated onto the aligned PLLA nanofibrous scaffolds and improved its hydrophilicity. Three-dimensional (3 D) confocal microscopy images further demonstrated that collagen, heparin, and NGF were not only coated onto the surface of aligned PLLA nanofibrous scaffolds but also permeated into the inner of scaffolds. Moreover, NGF presented a sustained release for 2 weeks from aligned nanofibrous scaffolds coated with 5.5 bilayers or above and remained good bioactivity. The heparin/collagen encapsulating NGF multilayers coated aligned nanofibrous scaffolds, in particular 5.5 bilayers or above, was more beneficial to Schwann cells (SCs) proliferation and PC12 cells differentiation as well as the SC cytoskeleton and neurite growth along the direction of nanofibrous alignment compared to the aligned PLLA nanofibrous scaffolds. This novel scaffolds combining sustained release of bioactive NGF and aligned nanofibrous topography presented an excellent potential in peripheral nerve regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1900-1910, 2017.

Three-dimensional aligned nanofibers-hydrogel scaffold for controlled non-viral drug/gene delivery to direct axon regeneration in spinal cord injury treatment

Spinal cord injuries (SCI) often lead to persistent neurological dysfunction due to failure in axon regeneration. Unfortunately, currently established treatments, such as direct drug administration, do not effectively treat SCI due to rapid drug clearance from our bodies. Here, we introduce a three-dimensional aligned nanofibers-hydrogel scaffold as a bio-functionalized platform to provide sustained non-viral delivery of proteins and nucleic acid therapeutics (small non-coding RNAs), along with synergistic contact guidance for nerve injury treatment. A hemi-incision model at cervical level 5 in the rat spinal cord was chosen to evaluate the efficacy of this scaffold design. Specifically, aligned axon regeneration was observed as early as one week post-injury. In addition, no excessive inflammatory response and scar tissue formation was triggered. Taken together, our results demonstrate the potential of our scaffold for neural tissue engineering applications.

Application of nanotechnology for the development of microbicides

The vaginal route is increasingly being considered for both local and systemic delivery of drugs, especially those unsuitable for oral administration. One of the opportunities offered by this route but yet to be fully utilised is the administration of microbicides. Microbicides have an unprecedented potential for mitigating the global burden from HIV infection as heterosexual contact accounts for most of the new infections occurring in sub-Saharan Africa, the region with the highest prevalent rates. Decades of efforts and massive investment of resources into developing an ideal microbicide have resulted in disappointing outcomes, as attested by several clinical trials assessing the suitability of those formulated so far. The highly complex and multi-level biochemical interactions that must occur among the virus, host cells and the drug for transmission to be halted means that a less sophisticated approach to formulating a microbicide e.g. conventional gels, etc may have to give way for a different formulation approach. Nanotechnology has been identified to offer prospects for fabricating structures with high capability of disrupting HIV transmission. In this review, predominant challenges seen in microbicide development have been highlighted and possible ways of surmounting them suggested. Furthermore, formulations utilising some of these highly promising nanostructures such as liposomes, nanofibres and nanoparticles have been discussed. A perspective on how a tripartite collaboration among governments and their agencies, the pharmaceutical industry and academic scientists to facilitate the development of an ideal microbicide in a timely manner has also been briefly deliberated.

Recent advances in multiaxial electrospinning for drug delivery

Electrospun fibers have seen an insurgence in biomedical applications due to their unique characteristics. Coaxial and triaxial electrospinning techniques have added new impetus via fabrication of multilayered nano and micro-size fibers. These techniques offer the possibility of forming fibers with features such as blending, reinforced core, porous and hollow structure. The unique fabrication process can be used to tailor the mechanical properties, biological properties and release of various factors, which can potentially be useful in various controlled drug delivery applications. Harvesting these advantages, various polymers and their combinations have been explored in a number of drug delivery and tissue regeneration applications. New advances have shown the requirement of drug-polymer compatibility in addition to drug-solvent compatibility. We summarize recent findings using both hydrophilic and hydrophobic (or lipophilic) drugs in hydrophobic or hydrophilic polymers on release behavior. We also describe the fundamental forces involved during the electrospinning process providing insight to the factors to be considered to form fibers. Also, various modeling efforts on the drug release profiles are summarized. In addition new developments in the immune response to the electrospun fibers, and advances in scale-up issues needed for industrial size manufacturing.

Modulation of human multipotent and pluripotent stem cells using surface nanotopographies and surface-immobilised bioactive signals: A review

The ability to control the interactions of stem cells with synthetic surfaces is proving to be effective and essential for the quality of passaged stem cells and ultimately the success of regenerative medicine. The stem cell niche is crucial for stem cell self-renewal and differentiation. Thus, mimicking the stem cell niche, and here in particular the extracellular matrix (ECM), in vitro is an important goal for the expansion of stem cells and their applications. Here, surface nanotopographies and surface-immobilised biosignals have been identified as major factors that control stem cell responses. The development of tailored surfaces having an optimum nanotopography and displaying suitable biosignals is proposed to be essential for future stem cell culture, cell therapy and regenerative medicine applications. While early research in the field has been restricted by the limited availability of micro- and nanofabrication techniques, new approaches involving the use of advanced fabrication and surface immobilisation methods are starting to emerge. In addition, new cell types such as induced pluripotent stem cells (iPSCs) have become available in the last decade, but have not been fully understood. This review summarises significant advances in the area and focuses on the approaches that are aimed at controlling the behavior of human stem cells including maintenance of their self-renewal ability and improvement of their lineage commitment using nanotopographies and biosignals. More specifically, we discuss developments in biointerface science that are an important driving force for new biomedical materials and advances in bioengineering aiming at improving stem cell culture protocols and 3D scaffolds for clinical applications. Cellular responses revolve around the interplay between the surface properties of the cell culture substrate and the biomolecular composition of the cell culture medium. Determination of the precise role played by each factor, as well as the synergistic effects amongst the factors, all of which influence stem cell responses is essential for future developments. This review provides an overview of the current state-of-the-art in the design of complex material surfaces aimed at being the next generation of tools tailored for applications in cell culture and regenerative medicine.

STATEMENT OF SIGNIFICANCE

This review focuses on the effect of surface nanotopographies and surface-bound biosignals on human stem cells. Recently, stem cell research attracts much attention especially the induced pluripotent stem cells (iPSCs) and direct lineage reprogramming. The fast advance of stem cell research benefits disease treatment and cell therapy. On the other hand, surface property of cell adhered materials has been demonstrated very important for in vitro cell culture and regenerative medicine. Modulation of cell behavior using surfaces is costeffective and more defined. Thus, we summarise the recent progress of modulation of human stem cells using surface science. We believe that this review will capture a broad audience interested in topographical and chemical patterning aimed at understanding complex cellular responses to biomaterials.

A vascular tissue engineering scaffold with core-shell structured nano-fibers formed by coaxial electrospinning and its biocompatibility evaluation

In this article, a tubular vascular tissue engineering scaffold with core-shell structured fibers was produced by coaxial electrospinning at an appropriate flow rate ratio between the inner and outer solution. PCL was selected as the core to provide the mechanical property and integrity to the scaffold while collagen was used as the shell to improve the attachment and proliferation of vascular cells due to its excellent biocompatibility. The fine core-shell structured fibers were demonstrated by scanning electron microscope and transmission electron microscope observations. Subsequently, the collagen shell was crosslinked by genipin and further bound with heparin. The crosslinking process was confirmed by the increasing of tensile strength, swelling ratio and thermogravimetric analysis measurements while the surface heparin content was characterized by means of a UV-spectrophotometer and activated partial thromboplastin time tests. Furthermore, the mechanical properties such as stitch strength and bursting pressure of the as-prepared scaffold were measured. Moreover, the biocompatibility of the scaffold was evaluated by cytotoxicity investigation with L929 cells via MTT assay. Endothelial cell adhesion assessments were conducted to reveal the possibility of the formation of an endothelial cell layer on the scaffold surface, while the ability of smooth muscle cell penetration into the scaffold wall was also assessed by confocal laser scanning microscopy. The as-prepared core-shell structured scaffold showed promising potential for use in vascular tissue engineering.

Advantages and challenges offered by biofunctional core-shell fiber systems for tissue engineering and drug delivery

Whereas highly porous scaffolds composed of electrospun nanofibers can mimick major features of the extracellular matrix in tissue engineering, they lack the ability to incorporate and release biocompounds (drugs, growth factors) safely in a controlled way. Here, electrospun core-shell fibers (core made from water and aqueous solutions of hydrophilic polymers and the shell from materials with well-defined release mechanisms) offer unique advantages in comparison with those that have helped make porous nanofibrillar scaffolds highly successful in tissue engineering. This review considers the preparation and biofunctionalization of such core-shell fibers as well as applications in various areas, including neural, vascular, cardiac, cartilage and bone tissue engineering, and touches on the topic of clinical trials.

Nanofibers used for the delivery of analgesics

Nanofibers are extremely advantageous for drug delivery because of their high surface area-to-volume ratios, high porosities and 3D open porous structures. Local delivery of analgesics by using nanofibers allows site-specificity and requires a lower overall drug dosage with lower adverse side effects. Different analgesics have been loaded onto various nanofibers, including those that are natural, synthetic and copolymer, for various medical applications. Analgesics can also be singly or coaxially loaded onto nanofibers to enhance clinical applications. In particular, analgesic-eluting nanofibers provide additional benefits to preventing wound adhesion and scar formation. This paper reviews current research and breakthrough discoveries on the innovative application of analgesic-loaded nanofibers that will alter the clinical therapy of pain.