Fabrication and characterization of heparin-grafted poly-L-lactic acid-chitosan core-shell nanofibers scaffold for vascular gasket

Progress and challenges in macroencapsulation approaches for type 1 diabetes (T1D) treatment: Cells, biomaterials, and devices

Macroencapsulation technology has been an attractive topic in the field of treatment for Type 1 diabetes due to mechanical stability, versatility, and retrievability of the macro-capsule design. Macro-capsules can be categorized into extravascular and intravascular devices, in which solute transport relies either on diffusion or convection, respectively. Failure of macroencapsulation strategies can be due to limited regenerative capacity of the encased insulin-producing cells, sub-optimal performance of encapsulation biomaterials, insufficient immunoisolation, excessive blood thrombosis for vascular perfusion devices, and inadequate modes of mass transfer to support cell viability and function. However, significant technical advancements have been achieved in macroencapsulation technology, namely reducing diffusion distance for oxygen and nutrients, using pro-angiogenic factors to increase vascularization for islet engraftment, and optimizing membrane permeability and selectivity to prevent immune attacks from host's body. This review presents an overview of existing macroencapsulation devices and discusses the advances based on tissue-engineering approaches that will stimulate future research and development of macroencapsulation technology. Biotechnol. Bioeng. 2016;113: 1381-1402. © 2015 Wiley Periodicals, Inc.

Highly Compliant Vascular Grafts with Gelatin-Sheathed Coaxially Structured Nanofibers

We have developed three types of materials composed of polyurethane-gelatin, polycaprolactone-gelatin, or polylactic acid-gelatin nanofibers by coaxially electrospinning the hydrophobic core and gelatin sheath with a ratio of 1:5 at fixed concentrations. Results from attenuated total reflection-Fourier transformed infrared spectroscopy demonstrated the gelatin coating around nanofibers in all of the materials. Transmission electron microscopy images further displayed the core-sheath structures showing the core-to-sheath thickness ratio varied greatly with the highest ratio found in polyurethane-gelatin nanofibers. Scanning electron microscopy images revealed similar, uniform fibrous structures in all of the materials, which changed with genipin cross-linking due to interfiber interactions. Thermal analyses revealed varied interactions between the hydrophilic sheath and hydrophobic core among the three materials, which likely caused different core-sheath structures, and thus physicomechanical properties. The addition of gelatin around the hydrophobic polymer and their interactions led to the formation of graft scaffolds with tissue-like viscoelasticity, high compliance, excellent swelling capability, and absence of water permeability while maintaining competent tensile modulus, burst pressure, and suture retention. The hydrogel-like characteristics are advantageous for vascular grafting use, because of the capability of bypassing preclotting prior to implantation, retaining vascular fluid volume, and facilitating molecular transport across the graft wall, as shown by coculturing vascular cells sandwiched over a thick-wall scaffold. Varied core-sheath interactions within scaffolding nanofibers led to differences in graft functional properties such as water swelling ratio, compliance, and supporting growth of cocultured vascular cells. The PCL-gelatin scaffold with thick gelatin-sheathed nanofibers demonstrated a more compliant structure, elastic mechanics, and high water swelling property. Our results demonstrate a feasible approach to produce new hybrid, biodegradable nanofibrous scaffold biomaterials with interactive core-sheath structure, good biocompatibility, and tissue-like viscoelasticity, which may reduce potential problems with the use of individual polymers for vascular grafts.

Medicated Janus fibers fabricated using a Teflon-coated side-by-side spinneret

A family of medicated Janus fibers that provides highly tunable biphasic drug release was fabricated using a side-by-side electrospinning process employing a Teflon-coated parallel spinneret. The coated spinneret facilitated the formation of a Janus Taylor cone and in turn high quality integrated Janus structures, which could not be reliably obtained without the Teflon coating. The fibers prepared had one side consisting of polyvinylpyrrolidone (PVP) K60 and ketoprofen, and the other of ethyl cellulose (EC) and ketoprofen. To modulate and tune drug release, PVP K10 was doped into the EC side in some cases. The fibers were linear and had flat morphologies with an indent in the center. They provide biphasic drug release, with the PVP K60 side dissolving very rapidly to deliver a loading dose of the active ingredient, and the EC side resulting in sustained release of the remaining ketoprofen. The addition of PVP K10 to the EC side was able to accelerate the second stage of release; variation in the dopant amount permitted the release rate and extent this phase to be precisely tuned. These results offer the potential to rationally design systems with highly controllable drug release profiles, which can complement natural biological rhythms and deliver maximum therapeutic effects.

Electrosprayed nanoparticles and electrospun nanofibers based on natural materials: applications in tissue regeneration, drug delivery and pharmaceuticals

Nanotechnology refers to the fabrication, characterization, and application of substances in nanometer scale dimensions for various ends. The influence of nanotechnology on the healthcare industry is substantial, particularly in the areas of disease diagnosis and treatment. Recent investigations in nanotechnology for drug delivery and tissue engineering have delivered high-impact contributions in translational research, with associated pharmaceutical products and applications. Over the past decade, the synthesis of nanofibers or nanoparticles via electrostatic spinning or spraying, respectively, has emerged as an important nanostructuring methodology. This is due to both the versatility of the electrospinning/electrospraying process and the ensuing control of nanofiber/nanoparticle surface parameters. Electrosprayed nanoparticles and electrospun nanofibers are both employed as natural or synthetic carriers for the delivery of entrapped drugs, growth factors, health supplements, vitamins, and so on. The role of nanofiber/nanoparticle carriers is substantiated by the programmed, tailored, or targeted release of their contents in the guise of tissue engineering scaffolds or medical devices for drug delivery. This review focuses on the nanoformulation of natural materials via the electrospraying or electrospinning of nanoparticles or nanofibers for tissue engineering or drug delivery/pharmaceutical purposes. Here, we classify the natural materials with respect to their animal/plant origin and macrocyclic, small molecule or herbal active constituents, and further categorize the materials according to their proteinaceous or saccharide nature.

Nanofibers Fabricated Using Triaxial Electrospinning as Zero Order Drug Delivery Systems

A new strategy for creating functional trilayer nanofibers through triaxial electrospinning is demonstrated. Ethyl cellulose (EC) was used as the filament-forming matrix in the outer, middle, and inner working solutions and was combined with varied contents of the model active ingredient ketoprofen (KET) in the three fluids. Triaxial electrospinning was successfully carried out to generate medicated nanofibers. The resultant nanofibers had diameters of 0.74 ± 0.06 μm, linear morphologies, smooth surfaces, and clear trilayer nanostructures. The KET concentration in each layer gradually increased from the outer to the inner layer. In vitro dissolution tests demonstrated that the nanofibers could provide linear release of KET over 20 h. The protocol reported in this study thus provides a facile approach to creating functional nanofibers with sophisticated structural features.

Surface grafting of chitosan shell, polycaprolactone core fiber meshes to confer bioactivity

Electrospinning of polyesters (e.g. polycaprolactone) is an attractive approach for fabricating meshes with mechanical properties suitable for orthopedic tissue engineering applications. However, the resultant fused-fiber meshes are biologically inert, necessitating surface grafting of bioactive factors to stimulate cell adhesion. In this study, hydrophilic meshes displaying primary amine groups were prepared by coaxially electrospinning fibers with a chitosan/poly(ethylene oxide) shell and a polycaprolactone core. These chitosan–polycaprolactone fiber meshes were mechanically robust (Young’s modulus of 10.1 ± 1.6 MPa under aqueous conditions) with tensile properties comparable to polycaprolactone fiber meshes. Next, the integrin adhesion peptide arginine–glycine–aspartic acid was grafted to chitosan–polycaprolactone fiber meshes. Cell culture studies using bone marrow stromal cells indicated significantly better initial attachment and spreading on arginine–glycine–aspartic acid–conjugated fiber meshes. Specifically, metabolic activity, projected cell area, and cell aspect ratio were all elevated relative to cells seeded on polycaprolactone and unmodified chitosan–polycaprolactone meshes. These results demonstrate a flexible two-step process for creating bioactive electrospun fiber meshes.

Electrospun nanofibers incorporating self-decomposable silica nanoparticles as carriers for controlled delivery of anticancer drug

A decomposable silica nanoparticle-incorporated electrospun mat as a carrier for anticancer drugs.

Genipin cross-linked nanocomposite films for the immobilization of antimicrobial agent

Cellulose nanocrystal (CNC) reinforced chitosan based antimicrobial films were prepared by immobilizing nisin on the surface of the films. Nanocomposite films containing 18.65 μg/cm(2) of nisin reduced the count of L. monocytogenes by 6.73 log CFU/g, compared to the control meat samples (8.54 log CFU/g) during storage at 4 °C in a Ready-To-Eat (RTE) meat system. Film formulations containing 9.33 μg/cm(2) of nisin increased the lag phase of L. monocytogenes on meat by more than 21 days, whereas formulations with 18.65 μg/cm(2) completely inhibited the growth of L. monocytogenes during storage. Genipin was used to cross-link and protect the activity of nisin during storage. Nanocomposite films cross-linked with 0.05% w/v genipin exhibited the highest bioactivity (10.89 μg/cm(2)) during the storage experiment, as compared to that of the un-cross-linked films (7.23 μg/cm(2)). Genipin cross-linked films were able to reduce the growth rate of L. monocytogenes on ham samples by 21% as compared to the un-cross-linked films. Spectroscopic analysis confirmed the formation of genipin-nisin-chitosan heterocyclic cross-linked network. Genipin cross-linked films also improved the swelling, water solubility, and mechanical properties of the nanocomposite films.

Emerging chitin and chitosan nanofibrous materials for biomedical applications

Over the past several decades, we have witnessed significant progress in chitosan and chitin based nanostructured materials. The nanofibers from chitin and chitosan with appealing physical and biological features have attracted intense attention due to their excellent biological properties related to biodegradability, biocompatibility, antibacterial activity, low immunogenicity and wound healing capacity. Various methods, such as electrospinning, self-assembly, phase separation, mechanical treatment, printing, ultrasonication and chemical treatment were employed to prepare chitin and chitosan nanofibers. These nanofibrous materials have tremendous potential to be used as drug delivery systems, tissue engineering scaffolds, wound dressing materials, antimicrobial agents, and biosensors. This review article discusses the most recent progress in the preparation and application of chitin and chitosan based nanofibrous materials in biomedical fields.