Electrospun nanofibers-mediated on-demand drug release

pH-Responsive Degradable Electro-Spun Nanofibers Crosslinked via Boronic Ester Chemistry for Smart Wound Dressings

Recent advances in the treatment of chronic wounds have focused on the development of effective strategies for cutting-edge wound dressings based on nanostructured materials, particularly biocompatible poly(vinyl alcohol) (PVA)-based electro-spun (e-spun) nanofibers. However, PVA nanofibers need to be chemically crosslinked to ensure their dimensional stability in aqueous environment and their capability to encapsulate bioactive molecules. Herein, a robust approach for the fabrication of pH-degradable e-spun PVA nanofibers crosslinked with dynamic boronic ester (BE) linkages through a coupling reaction of PVA hydroxyl groups with the boronic acid groups of a phenyl diboronic acid crosslinker is reported. This comprehensive analysis reveals the importance of the mole ratio of boronic acid to hydroxyl group for the fabrication of well-defined BE-crosslinked fibrous mats with not only dimensional stability but also the ability to retain uniform fibrous form in aqueous solutions. These nanofibers degrade in both acidic and basic conditions that mimic wound environments, leading to controlled/enhanced release of encapsulated antimicrobial drug molecules. More importantly, drug-loaded BE-crosslinked fibers show excellent antimicrobial activities against both Gram-positive and Gram-negative bacteria, suggesting that this approach of exploring dynamic BE chemistry is amenable to the development of smart wound dressings with controlled/enhanced drug release.

Stimuli-responsive electrospun nanofibers for drug delivery, cancer therapy, wound dressing, and tissue engineering

The stimuli-responsive nanofibers prepared by electrospinning have become an ideal stimuli-responsive material due to their large specific surface area and porosity, which can respond extremely quickly to external environmental incitement. As an intelligent drug delivery platform, stimuli-responsive nanofibers can efficiently load drugs and then be stimulated by specific conditions (light, temperature, magnetic field, ultrasound, pH or ROS, etc.) to achieve slow, on-demand or targeted release, showing great potential in areas such as drug delivery, tumor therapy, wound dressing, and tissue engineering. Therefore, this paper reviews the recent trends of stimuli-responsive electrospun nanofibers as intelligent drug delivery platforms in the field of biomedicine.

Multifunctional Scaffolds Based on Emulsion and Coaxial Electrospinning Incorporation of Hydroxyapatite for Bone Tissue Regeneration

Tissue engineering is nowadays a powerful tool to restore damaged tissues and recover their normal functionality. Advantages over other current methods are well established, although a continuous evolution is still necessary to improve the final performance and the range of applications. Trends are nowadays focused on the development of multifunctional scaffolds with hierarchical structures and the capability to render a sustained delivery of bioactive molecules under an appropriate stimulus. Nanocomposites incorporating hydroxyapatite nanoparticles (HAp NPs) have a predominant role in bone tissue regeneration due to their high capacity to enhance osteoinduction, osteoconduction, and osteointegration, as well as their encapsulation efficiency and protection capability of bioactive agents. Selection of appropriated polymeric matrices is fundamental and consequently great efforts have been invested to increase the range of properties of available materials through copolymerization, blending, or combining structures constituted by different materials. Scaffolds can be obtained from different processes that differ in characteristics, such as texture or porosity. Probably, electrospinning has the greater relevance, since the obtained nanofiber membranes have a great similarity with the extracellular matrix and, in addition, they can easily incorporate functional and bioactive compounds. Coaxial and emulsion electrospinning processes appear ideal to generate complex systems able to incorporate highly different agents. The present review is mainly focused on the recent works performed with Hap-loaded scaffolds having at least one structural layer composed of core/shell nanofibers.

Codelivery of 1α,25-Dihydroxyvitamin D3 and CYP24A1 Inhibitor VID400 by Nanofiber Dressings Promotes Endogenous Antimicrobial Peptide LL-37 Induction

Surgical site infections represent a significant clinical problem. Herein, we report a nanofiber dressing for topical codelivery of immunomodulating compounds including 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) and VID400, a CYP24A1 inhibitor in a sustained manner, for inducing the expression of the endogenous cathelicidin antimicrobial peptide (CAMP) gene encoding the hCAP18 protein, which is processed into the LL-37 peptide. Nanofiber wound dressings with coencapsulation of 1,25(OH)₂D₃ and VID400 were generated by electrospinning. Both 1,25(OH)₂D₃ and VID400 were coencapsulated into nanofibers with loading efficiencies higher than 90% and exhibited a prolonged release from nanofiber membranes longer than 28 days. Incubation with 1,25(OH)₂D₃/VID400-coencapsulated poly(ϵ-caprolactone) nanofiber membranes greatly induced the hCAP18/LL-37 gene expression in monocytes, neutrophils, and keratinocytes in vitro. Moreover, the administration of 1,25(OH)₂D₃/VID400-coencapsulated nanofiber membranes dramatically promoted the hCAP18/LL-37 expression in dermal wounds created in both human CAMP transgenic mice and human skin tissues. The 1,25(OH)₂D₃- and VID400-coencapsulated nanofiber dressings enhanced innate immunity via the more effective induction of antimicrobial peptide than the free drug alone or 1,25(OH)₂D₃-loaded nanofibers. Together, 1,25(OH)₂D₃/VID400-embedded nanofiber dressings presented in this study show potential in preventing surgical site infections.

Electrospun Nanofibers for Bone Regeneration: From Biomimetic Composition, Structure to Function

In recent years, a variety of novel materials and processing technologies have been developed to prepare tissue engineering scaffolds for bone defect repair. Among them, nanofibers fabricated via electrospinning technology...

On-Demand Drug Delivery Systems Using Nanofibers

On-demand drug-delivery systems using nanofibers are extensively applicable for customized drug release based on target location and timing to achieve the desired therapeutic effects. A nanofiber formulation is typically created for a certain medication and changing the drug may have a significant impact on the release kinetics from the same delivery system. Nanofibers have several distinguishing features and properties, including the ease with which they may be manufactured, the variety of materials appropriate for processing into fibers, a large surface area, and a complex pore structure. Nanofibers with effective drug-loading capabilities, controllable release, and high stability have gained the interest of researchers owing to their potential applications in on-demand drug delivery systems. Based on their composition and drug-release characteristics, we review the numerous types of nanofibers from the most recent accessible studies. Nanofibers are classified based on their mechanism of drug release, as well as their structure and content. To achieve controlled drug release, a suitable polymer, large surface-to-volume ratio, and high porosity of the nanofiber mesh are necessary. The properties of nanofibers for modified drug release are categorized here as protracted, stimulus-activated, and biphasic. Swellable or degradable polymers are commonly utilized to alter drug release. In addition to the polymer used, the process and ambient conditions can have considerable impacts on the release characteristics of the nanofibers. The formulation of nanofibers is highly complicated and depends on many variables; nevertheless, numerous options are available to accomplish the desired nanofiber drug-release characteristics.

Implantable magnetic nanofibers with ON-OFF switchable release of curcumin for possible local hyperthermic chemotherapy of melanoma

Implantable thermo-responsive drug-loaded magnetic nanofibers (NFs) have attracted great interest for localized thermo-chemotherapy of cancer tissue/cells. From this perspective, smart polymeric electrospun NFs co-loaded with magnetic nanoparticles (MNPs) and a natural polyphenol anticancer agent, curcumin (CUR), were developed to enhance the local hyperthermic chemotherapy against melanoma, the most serious type of skin cancer. CUR/MNPs-loaded thermo-sensitive electrospun NFs exhibited alternating magnetic field (AMF)-responsive heat generation and "ON-OFF" switchable heating capability. Besides, corresponding to the reversible alterations in the swelling ratio, the "ON-OFF" switchable discharge of CUR from the magnetic NFs was detected in response to the "ON-OFF" switching of AMF application. Due to the combinatorial effect of hyperthermia and release of CUR after applying an AMF ("ON" state) for 600 s on the second and third days of incubation time, the viability of the B16F10 melanoma cancer cells exposed to the CUR/MNPs-NFs was reduced by 40% and 17%, respectively. Taken together, the macroscopic and nanoscale features of the smart NFs led to the creation of a reversibly adjustable structure that enabled hyperthermia and facile switchable release of CUR for eradication of melanoma cancer cells.

Electrospun Fibrous Membrane Containing a Cyclodextrin Covalent Organic Framework with Antibacterial Properties for Accelerating Wound Healing

Skin wounds are usually accompanied by bacterial infections and inflammations, leading to delayed wound healing, which remain a great challenge in clinical treatment. Therefore, it is of great significance to develop wound dressings that inhibit bacterial infections to accelerate wound healing. Herein, we reported the fabrication of inclusion complex (a β-cyclodextrin covalent organic framework loaded with enrofloxacin and flunixin meglumine)-incorporated electrospun thermoplastic polyurethane fibers (named ENR-FM-COF-TPU) via electrospinning. The obtained ENR-FM-COF-TPU fibrous membrane exhibited excellent physicochemical and biological properties such as uniform and stable morphology, proper hydrophobicity, good water uptake capacity, and admirable biocompatibility, which showed perfect behavior as a wound dressing. In addition, the ENR-FM-COF-TPU membrane achieved a sustained drug release of enrofloxacin and flunixin meglumine and displayed powerful antibacterial activity against Staphylococcus aureus and Escherichia coli with 99% inhibitory efficiency for 50 h. More importantly, the wound healing therapy effect was investigated using a full-thickness skin defect model of mice. It suggested that the ENR-FM-COF-TPU membrane could significantly accelerate and enhance wound healing through downregulating inflammatory cytokines (IL-1β and TNF-α) and increasing the expression of growth factors (VEGF and EGF). Due to its excellent properties, the ENR-FM-COF-TPU membrane may have promising potential in wound healing applications.

Electrospinning/Electrospray of Ferrocene Containing Copolymers to Fabricate ROS-Responsive Particles and Fibers

We demonstrate an electrospray/electrospinning process to fabricate stimuli-responsive nanofibers or particles that can be utilized as stimuli-responsive drug-loaded materials. A series of random copolymers consisting of hydrophobic ferrocene monomers and hydrophilic carboxyl groups, namely poly(ferrocenylmethyl methacrylate-r-methacrylic acid) [poly(FMMA-r-MA)] with varied composition, was synthesized with free radical copolymerization. The morphologies of the resulting objects created by electrospray/electrospinning of the poly(FMMA-r-MA) solutions were effectively varied from particulate to fibrous structures by control of the composition, suggesting that the morphology of electrosprayed/electrospun copolymer objects was governed by its composition and hence, interaction with the solvent, highlighting the significance of the balance of hydrophilicity/hydrophobicity of the copolymer chain to the assembled structure. Resulting particles and nanofibers exhibited largely preserved responsiveness to reactive oxygen species (ROS) during the deposition process, opening up the potential to fabricate ROS-sensitive material with various desirable structures toward different applications.

Advances in Functional Polymer Nanofibers: From Spinning Fabrication Techniques to Recent Biomedical Applications

Functional polymeric micro-/nanofibers have emerged as promising materials for the construction of structures potentially useful in biomedical fields. Among all kinds of technologies to produce polymer fibers, spinning methods have gained considerable attention. Herein, we provide a recent review on advances in the design of micro- and nanofibrous platforms via spinning techniques for biomedical applications. Specifically, we emphasize electrospinning, solution blow spinning, centrifugal spinning, and microfluidic spinning approaches. We first introduce the fundamentals of these spinning methods and then highlight the potential biomedical applications of such micro- and nanostructured fibers for drug delivery, tissue engineering, regenerative medicine, disease modeling, and sensing/biosensing. Finally, we outline the current challenges and future perspectives of spinning techniques for the practical applications of polymer fibers in the biomedical field.

Spatiotemporally Controlling the Release of Biological Effectors Enhances Their Effects on Cell Migration and Neurite Outgrowth

It is a major challenge to coordinate topographic cues from scaffolds with the on-demand, sustained release of biological effectors to maximize their performance in tissue regeneration. Here, a system involving masked, photo-triggered release of biological effectors from a temperature-sensitive scaffold for augmented cell migration and neurite outgrowth is reported. The scaffold contains microparticles of a phase-change material (PCM) sandwiched between two layers of electrospun fibers. The biological effectors are co-loaded with a photothermal dye in the PCM microparticles. Under irradiation with a near-infrared laser, the PCM will be melted to swiftly release the biological effectors. By imposing a photomask between the scaffold and the laser, only those microparticles in the irradiated region are melted, enabling a spatial control over the release. By adjusting the photomask, different regions of the scaffold can be sequentially irradiated at designated times, realizing on-demand and sustained release of the biological effectors with spatiotemporal controls. In one demonstration, this method is used to accelerate the directional migration of NIH-3T3 fibroblasts along the uniaxial or radial direction of fiber alignment by controlling the release of epidermal growth factor. In another demonstration, the release of nerve growth factor is managed to significantly promote neurite outgrowth from PC12 cells.

Electrospun nanofibers in cancer research: from engineering of in vitro 3D cancer models to therapy

Electrospinning is historically related to tissue engineering due to its ability to produce nano-/microscale fibrous materials with mechanical and functional properties that are extremely similar to those of the extracellular matrix of living tissues. The general interest in electrospun fibrous matrices has recently expanded to cancer research both as scaffolds for in vitro cancer modelling and as patches for in vivo therapeutic delivery. In this review, we examine electrospinning by providing a brief description of the process and overview of most materials used in this process, discussing the effect of changing the process parameters on fiber conformations and assemblies. Then, we describe two different applications of electrospinning in service of cancer research: firstly, as three-dimensional (3D) fibrous materials for generating in vitro pre-clinical cancer models; and secondly, as patches encapsulating anticancer agents for in vivo delivery.

Electrospun nanofibers: A nanotechnological approach for drug delivery and dissolution optimization in poorly water-soluble drugs

Electrospinning is a novel and sophisticated technique for the production of nanofibers with high surface area, extreme porous structure, small pore size, and surface morphologies that make them suitable for biomedical and bioengineering applications, which can provide solutions to current drug delivery issues of poorly water-soluble drugs. Electrospun nanofibers can be obtained through different methods asides from the conventional one, such as coaxial, multi-jet, side by side, emulsion, and melt electrospinning. In general, the application of an electric potential to a polymer solution causes a charged liquid jet that moves downfield to an oppositely charged collector, where the nanofibers are deposited. Plenty of polymers that differ in their origin, degradation character and water affinity are used during the process. Physicochemical properties of the drug, polymer(s), and solvent systems need to be addressed to guarantee successful manufacturing. Therefore, this review summarizes the recent progress in electrospun nanofibers for their use as a nanotechnological tool for dissolution optimization and drug delivery systems for poorly water-soluble drugs.

Porous Silicon Nanoparticles Embedded in Poly(lactic-co-glycolic acid) Nanofiber Scaffolds Deliver Neurotrophic Payloads to Enhance Neuronal Growth

Scaffolds made from biocompatible polymers provide physical cues to direct the extension of neurites and to encourage repair of damaged nerves. The inclusion of neurotrophic payloads in these scaffolds can substantially enhance regrowth and repair processes. However, many promising neurotrophic candidates are excluded from this approach due to incompatibilities with the polymer or with the polymer processing conditions. This work provides one solution to this problem by incorporating porous silicon nanoparticles (pSiNPs) that are pre-loaded with the therapeutic into a polymer scaffold during fabrication. The nanoparticle-drug-polymer hybrids are prepared in the form of oriented poly(lactic-co-glycolic acid) nanofiber scaffolds. We test three different therapeutic payloads: bpV(HOpic), a small molecule inhibitor of phosphatase and tensin homolog (PTEN); an RNA aptamer specific to tropomyosin-related kinase receptor type B (TrkB); and the protein nerve growth factor (NGF). Each therapeutic is loaded using a loading chemistry that is optimized to slow the rate of release of these water-soluble payloads. The drug-loaded pSiNP-nanofiber hybrids release approximately half of their TrkB aptamer, bpV(HOpic), or NGF payload in 2, 10, and >40 days, respectively. The nanofiber hybrids increase neurite extension relative to drug-free control nanofibers in a dorsal root ganglion explant assay.

Tough hydrogel module towards an implantable remote and controlled release device

On-demand controllable drug delivery systems enable the administration of precise dosages and thus have the potential to improve overall healthcare.

Aqueous-based electrospun P(NIPAAm-co-AAc)/RSF medicated fibrous mats for dual temperature- and pH-responsive drug controlled release

This paper presents a green method for fabricating dual temperature- and pH-responsive electrospun fibrous mats from an aqueous-based blend poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAAm-co-AAc)) and regenerated silk fibroin (RSF) by employing electrospinning technique. P(NIPAAm-co-AAc) was synthesized by free radical solution polymerization and its low critical solution temperature (LCST) was in the physiological range (38.8 °C). The P(NIPAAm-co-AAc)/RSF fibers were prepared by electrospinning technology in the presence of the crosslinking agents (EDC·HCl and NHS) with water as solvent. After in situ crosslinking and water-annealing process, the water-stable composite fibrous mats were obtained. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the crosslinking process. Temperature and pH dual stimuli-responsive swelling-shrinking behavior of the fibrous mats were observed when the temperature was below and above the LCST of the copolymer at different pHs. In addition, rhodamine B-loaded the fibrous mats also showed dual temperature and pH controlled release behavior, demonstrating the potential use of the fibrous mats for "smart" controlled drug delivery applications.

Poly(ε-caprolactone) (PCL) Hollow Nanoparticles with Surface Sealability and On-Demand Pore Generability for Easy Loading and NIR Light-Triggered Release of Drug

A new system for the easy loading and NIR light-triggered release of drugs is introduced. It consists of poly(ε-caprolactone) (PCL) hollow nanoparticles with surface openings containing a biodegradable fatty acid with phase-change ability and a biocompatible photothermal agent. These openings, which can enhance the connectivity between the interior and the exterior, enable the easy loading of drug molecules into the interior voids, and their successive sealing ensures a stable encapsulation of the drug. Upon exposure to an external NIR light irradiation, the photothermal agent generates heat that raises the local temperature of the hollow particles above the melting point of the fatty acid, leading to the formation of nanopores on their shells, and consequently, the instant release of the encapsulated drug molecules through the pores. The synergistic activity of the hyperthermia effect from the photothermal agent and the NIR-triggered release of the drug molecules results in noticeable anticancer efficacy.

Photothermal transforming agent and chemotherapeutic co-loaded electrospun nanofibers for tumor treatment

Background: Photothermal and chemotherapy treatment has been frequently studied for cancer therapy; however, chemotherapy is equally toxic to both normal and cancer cells. The clinical application value of most kinds of photothermal transforming agents remains limited, due to their poor degradation and minimal accumulation in tumors. Materials and methods: We reported the synthesis of photothermal transforming agents (MoS2) and chemotherapeutic (doxorubicin, DOX) co-loaded electrospun nanofibers using blend electrospinning for the treatment of postoperative tumor recurrence. Results: Under the irradiation of an 808 nm laser, the as-prepared chitosan/polyvinyl alcohol/MoS2/DOX nanofibers showed an admirable photothermal conversion capability with a photothermal conversion efficiency of 23.2%. These composite nanofibers are in vitro and in vivo biocompatible. In addition, they could control the sustained release of DOX and the generated heat can sensitize the chemotherapeutic efficacy of DOX via enhancing its release rate. Their chemo-/photothermal combined therapy efficiency was systematically studied in vitro and in vivo. Instead of circulating with the body fluid, MoS2 was trapped by the nanofibrous matrix in the tumor and so its tumor-killing ability was not compromised, thus rendering this composite nanofiber a promising alternative for future clinical translation within biomedical application fields. Conclusion: Chitosan/polyvinyl alcohol/MoS2/DOX nanofibers showed an excellent photothermal conversion capability with a photothermal conversion efficiency of 23.2% and can completely inhibit the postoperative tumor reoccurrence.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Fortifying Angiogenesis in Ischemic Muscle with FGF9-Loaded Electrospun Poly(Ester Amide) Fibers

Delivery of angiogenic growth factors lessens ischemia in preclinical models but has demonstrated little benefit in patients with peripheral vascular disease. Augmenting the wrapping of nascent microvessels by mural cells constitutes an alternative strategy to regenerating a functional microvasculature, particularly if integrated with a sustained delivery platform. Herein, electrospun poly(ester amide) (PEA) nanofiber mats are fabricated for delivering a mural cell-targeting factor, fibroblast growth factor 9 (FGF9). Proof-of-principle is established by placing FGF9/FGF2-loaded PEA fiber mats on the chick chorioallantoic membrane and identifying enhanced angiogenesis by 3D power Doppler micro-ultrasound imaging. To assess the delivery system in ischemic muscle, FGF9-loaded PEA fiber mats are implanted onto the surface of the tibialis anterior muscle of mice with hindlimb ischemia. The system supplies FGF9 into the tibialis anterior muscle and yields a neo-microvascular network with enhanced mural cell coverage up to 28 days after injury. The regenerating muscle that receives FGF9 display near-normal sized myofibers and reduced interstitial fibrosis. Moreover, the mice demonstrate improved locomotion. These findings of locally released FGF9 from PEA nanofibers raise prospects for a microvascular remodeling approach to improve muscle health in peripheral vascular disease.

Infection-responsive electrospun nanofiber mat for antibacterial guided tissue regeneration membrane

The release of anti-infection drugs in a targeted and efficient manner in response to the attack time and degree of severity of infection is a requirement of new generation implants. Herein, we design an infection-responsive guided tissue regeneration (GTR)/guided bone regeneration (GBR) membrane based on electrospun nanofibers. Polycaprolactone (PCL) nanofiber mats are coated with polydopamine to endow hydroxyl groups on the surface and then functionalized with siloxane to introduce amino groups. Metronidazole (MNA), an antibiotic drug, is esterified and then grafted onto the surface of the modified PCL nanofiber mats via ester linkages. The ester bonds can be selectively hydrolyzed by cholesterol esterase (CE), an enzyme secreted by macrophagocytes accumulated at the site of infection, whose concentration is positively related to the severity of the infection. The drug can be triggered to release from the nanofiber membranes in responsive to the CE. With the increase of the CE concentration, a higher amount of MNA is released from the nanofiber mat, resulting in the enhancement of the antibacterial capability of the MNA-grafted nanofiber mat. The nanofiber mat has good cytocompatibility. This CE-responsive drug delivery system based on the electrospun nanofiber mat is promising as an optimal choice for antibacterial GTR/GBR membrane.

Gold Nanocage-Incorporated Poly(ε-Caprolactone) (PCL) Fibers for Chemophotothermal Synergistic Cancer Therapy

This paper introduces a new fibrous system for synergistic cancer therapy, which consists of gold nanocage (AuNC)-loaded poly(ε-caprolactone) (PCL) fibers with encapsulation of a chemotherapeutic anticancer drug in their core and loading of a phase-changeable fatty acid in their sheath. Under on–off switching of near-infrared (NIR) light irradiation, the excellent photothermal ability and photostability of AuNCs allows repeated, significant heating of the fibers to a temperature available to hyperthermia. Simultaneously, the NIR light-induced heat generation enables the melting out of the loaded fatty acid, leading to a rapid release of the drug molecules from the fibers. The combination of this NIR light-triggered drug release with the repeated hyperthermia treatment exhibits excellent anticancer efficacy.

Poly(d,l-lactic-co-glycolic acid) (PLGA) hollow fiber with segmental switchability of its chains sensitive to NIR light for synergistic cancer therapy

This work introduces a new fibrous system for synergistic cancer therapy. The system consists of poly(d,l-lactic-co-glycolic acid) (PLGA) fibers with a core encapsulating an anticancer drug and a shell entrapping gold nanorods (AuNRs) as a photothermal agent. On exposure to NIR light, the photothermal agent generates heat to raise the local temperature of the fibers. If the temperature is above a glass transition (T_g) of the polymer, the polymer chains will be mobile, increasing free volume in size within the shell. As a result, a rapid release of the drug can be achieved. When NIR light is turned off, the release will stop with inactivity of the photothermal agent, followed by freezing the segmental motion of the polymer chains. The on-off switching of NIR light in a time-controllable manner allows a repeated and accurate release of the drug, leading to the significant enhancement of anticancer activity in combination with the hyperthermia effect arising from the photothermal agent.

Electrospinning: An enabling nanotechnology platform for drug delivery and regenerative medicine

Electrospinning provides an enabling nanotechnology platform for generating a rich variety of novel structured materials in many biomedical applications including drug delivery, biosensing, tissue engineering, and regenerative medicine. In this review article, we begin with a thorough discussion on the method of producing 1D, 2D, and 3D electrospun nanofiber materials. In particular, we emphasize on how the 3D printing technology can contribute to the improvement of traditional electrospinning technology for the fabrication of 3D electrospun nanofiber materials as drug delivery devices/implants, scaffolds or living tissue constructs. We then highlight several notable examples of electrospun nanofiber materials in specific biomedical applications including cancer therapy, guiding cellular responses, engineering in vitro 3D tissue models, and tissue regeneration. Finally, we finish with conclusions and future perspectives of electrospun nanofiber materials for drug delivery and regenerative medicine.

Multifunctional Electrospun Nanofibers for Enhancing Localized Cancer Treatment

Localized cancer treatment is one of the most effective strategies in clinical destruction of solid tumors at early stages as it can minimize the side effects of cancer therapeutics. Electrospun nanofibers have been demonstrated as a promising implantable platform in localized cancer treatment, enabling the on-site delivery of therapeutic components and minimizing side effects to normal tissues. This Review discusses the recent cutting-edge research with regard to electrospun nanofibers used for various therapeutic approaches, including gene therapy, chemotherapy, photodynamic therapy, thermal therapy, and combination therapy, in enhancing localized cancer treatment. Furthermore, it extensively analyzes the current challenges and potential breakthroughs in utilizing this novel platform for clinical transition in localized cancer treatment.

Endogenous pH-responsive nanoparticles with programmable size changes for targeted tumor therapy and imaging applications

Nanotechnology-based antitumor drug delivery systems, known as nanocarriers, have demonstrated their efficacy in recent years. Typically, the size of the nanocarriers is around 100 nm. It is imperative to achieve an optimum size of these nanocarriers which must be designed uniquely for each type of delivery process. For pH-responsive nanocarriers with programmable size, changes in pH (~6.5 for tumor tissue, ~5.5 for endosomes, and ~5.0 for lysosomes) may serve as an endogenous stimulus improving the safety and therapeutic efficacy of antitumor drugs. This review focuses on current advanced pH-responsive nanocarriers with programmable size changes for anticancer drug delivery. In particular, pH-responsive mechanisms for nanocarrier retention at tumor sites, size reduction for penetrating into tumor parenchyma, escaping from endo/lysosomes, and swelling or disassembly for drug release will be highlighted. Additional trends and challenges of employing these nanocarriers in future clinical applications are also addressed.

Multilineage Constructs for Scaffold-Based Tissue Engineering: A Review of Tissue-Specific Challenges

There is a growing interest in the regeneration of tissue in interfacial regions, where biological, physical, and chemical attributes vary across tissue type. The simultaneous use of distinct cell lineages can help in developing in vitro structures, analogous to native composite tissues. This literature review gathers the recent reports that have investigated multiple cell types of various sources and lineages in a coculture system for tissue-engineered constructs. Such studies aim at mimicking the native organization of tissues and their interfaces, and/or to improve the development of complex tissue substitutes. This paper thus distinguishes itself from those focusing on technical aspects of coculturing for a single specific tissue. The first part of this review is dedicated to variables of cocultured tissue engineering such as scaffold, cells, and in vitro culture environment. Next, tissue-specific coculture methods and approaches are covered for the most studied tissues. Finally, cross-analysis is performed to highlight emerging trends in coculture principles and to discuss how tissue-specific challenges can inspire new approaches for regeneration of different interfaces to improve the outcomes of various tissue engineering strategies.

Near-infrared light-responsive, diselenide containing core-cross-linked micelles prepared by the Diels–Alder click reaction for photocontrollable drug release application

We report a facile and efficient preparation of a NIR-triggered micelle system for a drug vehicle.

Early stage release control of an anticancer drug by drug-polymer miscibility in a hydrophobic fiber-based drug delivery system

The drug release profiles of doxorubicin-loaded electrospun fiber mats were investigated with regard to drug-polymer miscibility, fiber wettability and degradability. Doxorubicin in hydrophilic form (Dox-HCl) and hydrophobic free base form (Dox-base) was employed as model drugs, and an aliphatic polyester, poly(lactic acid) (PLA), was used as a drug-carrier matrix. When hydrophilic Dox-HCl was directly mixed with PLA solution, drug molecules formed large aggregates on the fiber surface or in the fiber core, due to poor drug-polymer compatibility. Drug aggregates on the fiber surface contributed to the rapid initial release. The hydrophobic form of Dox-base was dispersed better with PLA matrix compared to Dox-HCl. When dimethyl sulfoxide (DMSO) was used as the solvent for Dox-HCl, the miscibility of drug in the polymer matrix was significantly improved, forming a quasi-monolithic solution scheme. The drug release from this monolithic matrix was slowest, and this slow release led to a lower toxicity to hepatocellular carcinoma. When an enzyme was used to promote PLA degradation, the release rates were closely correlated with degradation rates, demonstrating degradation was the dominant release mechanism. The possible drug release mechanisms were speculated based on the release kinetics. The results suggest that manipulation of drug-polymer miscibility and polymer degradability can be an effective means of designing drug release profiles.

The drug release profiles of doxorubicin-loaded electrospun fiber mats were investigated with regard to drug-polymer miscibility, fiber wettability and degradability.

Optimization of electrospun poly(N-isopropyl acrylamide) mats for the rapid reversible adhesion of mammalian cells

Poly(N-isopropyl acrylamide) (pNIPAM) is a "smart" polymer that responds to changes in altering temperature near physiologically relevant temperatures, changing its relative hydrophobicity. Mammalian cells attach to pNIPAM at 37 °C and detach spontaneously as a confluent sheet when the temperature is shifted below the lower critical solution temperature (∼32 °C). A variety of methods have been used to create pNIPAM films, including plasma polymerization, self-assembled monolayers, and electron beam ionization. However, detachment of confluent cell sheets from these pNIPAM films can take well over an hour to achieve potentially impacting cellular behavior. In this work, pNIPAM mats were prepared via electrospinning (i.e., espNIPAM) by a previously described technique that the authors optimized for cell attachment and rapid cell detachment. Several electrospinning parameters were varied (needle gauge, collection time, and molecular weight of the polymer) to determine the optimum parameters. The espNIPAM mats were then characterized using Fourier-transform infrared, x-ray photoelectron spectroscopy, and scanning electron microscopy. The espNIPAM mats showing the most promise were seeded with mammalian cells from standard cell lines (MC3T3-E1) as well as cancerous tumor (EMT6) cells. Once confluent, the temperature of the cells and mats was changed to ∼25 °C, resulting in the extremely rapid swelling of the mats. The authors find that espNIPAM mats fabricated using small, dense fibers made of high molecular weight pNIPAM are extremely well-suited as a rapid release method for cell sheet harvesting.

Fabrication and Characterization of Three-Dimensional (3D) Core-Shell Structure Nanofibers Designed for 3D Dynamic Cell Culture

Three-dimensional elastic nanofibers (3D eNFs) can offer a suitable 3D dynamic microenvironment and sufficient flexibility to regulate cellular behavior and functional protein expression. In this study, we report a novel approach to prepare 3D nanofibers with excellent mechanical properties by solution-assisted electrospinning technology and in situ polymerization. The obtained 3D eNFs demonstrated excellent biocompatible properties to meet cell culture requirements under a dynamic environment in vitro. Moreover, these 3D eNFs also promoted human bone marrow mesenchymal stem cells (hMSCs) adhesion and collagen expression under biomechanical stimulation. The results demonstrated that this dynamic cell culture system could positively impact cellular collagen but has no significant effect on the proliferation of hMSCs grown in the 3D eNFs. This work may give rise to a new approach for constructing a 3D cell culture for tissue engineering.

Novel strategies for the formulation and processing of poorly water-soluble drugs

Low aqueous solubility of active pharmaceutical ingredients presents a serious challenge in the development process of new drug products. This article provides an overview on some of the current approaches for the formulation of poorly water-soluble drugs with a special focus on strategies pursued at the Center of Pharmaceutical Engineering of the TU Braunschweig. These comprise formulation in lipid-based colloidal drug delivery systems and experimental as well as computational approaches towards the efficient identification of the most suitable carrier systems. For less lipophilic substances the preparation of drug nanoparticles by milling and precipitation is investigated for instance by means of microsystem-based manufacturing techniques and with special regard to the preparation of individualized dosage forms. Another option to overcome issues with poor drug solubility is the incorporation into nanospun fibers.

Progress and perspectives in bioactive agent delivery via electrospun vascular grafts

The review discusses the progress in the design and synthesis of bioactive agents incorporated into vascular grafts obtained by the electrospinning process.

PHB-Based Gels as Delivery Agents of Chemotherapeutics for the Effective Shrinkage of Tumors

Injectable thermogel to deliver chemotherapeutics in a minimally invasive manner and to achieve their long term sustained release at tumor sites to minimize side effects is attractive for chemotherapy and precision medicine, but its rational design remains a challenge. In this work, a copolymer with natural biodegradable poly[(R)-3-hydroxybutyrate] (PHB), hydrophilic poly(ethylene glycol), and temperature sensitive poly(propylene glycol) blocks linked by urethane linkages is designed to show thermogelling characteristics which are beneficial for minimally invasive injection and safe degradation. This thermogelling polymer possesses in vitro biocompatibility with very low cyto-toxicity in HEK293 cells. Furthermore, it is able to form the gel to achieve the controllable release of paclitaxel (PTX) and doxorubicin (DOX) by adjusting polymer concentrations. A rodent model of hepatocarcinoma has been performed to demonstrate the in vivo applications of this PHB-based thermogel. The drug-loaded thermogel has been intratumorally injected and both PTX-loaded and DOX-loaded thermogel have significantly slowed down tumor growth. This work represents the first time that injectable PHB thermogels have possessed good controllable release effect of chemotherapeutics against the in vivo model of tumors and will benefit various applications, including on-demand drug delivery and personalized medicine.

Light responsive hybrid nanofibres for on-demand therapeutic drug and cell delivery

Smart materials for on-demand delivery of therapeutically active agents are challenging in pharmaceutical and biomaterials science. In the present study, we report hybrid nanofibres capable of being reversibly controlled to pulsatile deliver both therapeutic drugs and cells on-demand of near-infrared (NIR) light. The nanofibres, fabricated by co-electrospinning of poly (N-isopropylacrylamide), silica-coated gold nanorods and polyhedral oligomeric silsesquinoxanes have, for the first time, demonstrated rapid, reversible large-volume changes of 83% on-demand with NIR stimulation, with retained nanofibrous morphology. Combining with the extracellular matrix-mimicking fibrillary properties, the nanofibres achieved accelerated release of model drug or cells on demand with NIR triggering. The release of the model drug doxorubicin demonstrated normal anti-cancer efficacy by reducing the viability of human cervical cancer HeLa cells by 97% in 48 h. In parallel, the fibres allowed model cell NIH3T3 fibroblast entrapment, adhesion, proliferation, differentiation and, upon NIR irradiation, cell release with undisturbed cellular function. Copyright © 2016 John Wiley & Sons, Ltd.

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.