Salt-Induced Electrospun Patterned Bundled Fibers for Spatially Regulating Cellular Responses

Neuronal cell response on aligned fibroporous electrospun mat generated from silver ion complexed ethylene vinyl alcohol copolymer

Generating electrospun mats with aligned fibers and obtaining neurite extension in the aligned fiber direction could provide hope for fabricating nerve guidance conduits or wraps through an easy method. The growing interest in generating electrospun mats with aligned fibers for tissue engineering is looking for simple methods to generate the same. Here, in this study, ethylene vinyl alcohol copolymer (EVAL) chains were complexed with silver ions (Ag⁺ ) to generate aligned fibers during the electrospinning process. The fibers thus produced were subjected to physico-chemical characterization and biological studies to ensure their properties and to examine whether suitable for neuronal cell attachment and neurite extension that may be useful in making nerve guidance conduits or wraps. The presence of silver ions and its complex formation with -OH of EVAL has been confirmed with EDX and XPS analysis respectively. The alignment of fibers was visualized from SEM analysis and confirmed using directionality analysis using Fiji-ImageJ software. Mechanical properties done with dumbbells punched out in longitudinal and transverse directions also substantiated the alignment of fibers. The results obtained from direct contact, MTT, and live/dead assay showed the cells are viable on the material. From the actin staining and immunostaining assays, it was evident that the PC12 cells could attach and extend their neurites in an aligned manner on the fibers. The maximum neurite extension was up to 200 μm in length. These properties of electrospun EVAL-Ag mat with aligned fibers indicated that it could be developed as a biocompatible nerve guidance conduit or wrap.

Cholate Conjugated Cationic Polymers for Regulation of Actin Dynamics

Cytoskeletal movement is a compulsory necessity for proper cell functioning and is largely controlled by actin filament dynamics. The actin dynamics can be finetuned by various natural and artificial materials...

Pastable, Adhesive, Injectable, Nanofibrous, and Tunable (PAINT) Biphasic Hybrid Matrices as Versatile Therapeutic Carriers

A critical challenge in many pharmaceutical fields is developing versatile adjuvant devices that can reduce the off-target delivery of therapeutic materials to target lesions. Herein, a biphasic hybrid fibrous system that can manipulate the spatial and temporal delivery of various therapeutic agents to target lesions by integrating multiple distinct systems and technologies such as fluffy coaxial electrospun polycaprolactone (PCL)/polystyrene (PS) fibers, cyclohexane-mediated leaching to remove PS layers selectively, amine display on PCL fibers, conjugation of naturally occurring adhesive gallol molecules onto hyaluronic acid (HA-g), and electrostatically complexing the aminated PCL fibers with the gallol-conjugated HA. In the context of "paintable" systems on target lesions, the resulting system is called a PAINT matrix (abbreviated according to the initial letter of its features: pastable, adhesive, injectable, nanofibrous, and tunable). Its viscoelastic property, which was attributed by coalescing aminated PCL fibers with viscous HA-g, enabled it to be noninvasively injected and fit into any cavity in the body with various morphologies, manually pasted on tissue surfaces, and adhered onto moisture-rich surfaces to ensure the secure delivery of therapeutics toward the target lesions. The PAINT matrix efficiently supplied immunomodulatory human neural stem cells (hNSCs) at rat hemisectioned spinal cord injury (SCI) sites and promoted both locomotive and sensory recovery in SCI models, presumably by protecting hNSCs against host immunosurveillance. The PAINT matrix will be broadly utilized for efficiently delivering therapeutics to difficult-to-reach target lesions by direct infusion or conventional biomaterial-mediated approaches due to their locations, wet surfaces, or complicated ambient environments.

Conductive Composite Fiber with Optimized Alignment Guides Neural Regeneration under Electrical Stimulation

Conductivity and alignment of scaffolds are two primary factors influencing the efficacy of nerve repair. Herein, conductive composite fibers composed of poly(ɛ-caprolactone) (PCL) and carbon nanotubes (CNTs) with different orientation degrees are prepared by electrospinning at various rotational speeds (0, 500, 1000, and 2000 rpm), and meanwhile the synergistic promotion mechanism of aligned topography and electrical stimulation on neural regeneration is fully demonstrated. Under an optimized rotational speed of 1000 rpm, the electrospun PCL fiber exhibits orientated structure at macroscopic (mean deviation angle = 2.78°) or microscopic crystal scale (orientation degree = 0.73), decreased contact angle of 99.2° ± 4.9°, and sufficient tensile strength in both perpendicular and parallel directions to fiber axis (1.13 ± 0.15 and 5.06 ± 0.98 MPa). CNTs are introduced into the aligned fiber for further improving conductivity (15.69-178.63 S m^-1 ), which is beneficial to the oriented growth of neural cells in vitro as well as the regeneration of injured sciatic nerves in vivo. On the basis of robust cell induction behavior, optimum sciatic nerve function index, and enhanced remyelination/axonal regeneration, such conductive PCL/CNTs composite fiber with optimized fiber alignment may serve as instructive candidates for promoting the scaffold- and cell-based strategies for neural repair.

AAVR-Displaying Interfaces: Serotype-Independent Adeno-Associated Virus Capture and Local Delivery Systems

Interfacing gene delivery vehicles with biomaterials has the potential to play a key role in diversifying gene transfer capabilities, including localized, patterned, and controlled delivery. However, strategies for modifying biomaterials to interact with delivery vectors must be redesigned whenever new delivery vehicles and applications are explored. We have developed a vector-independent biomaterial platform capable of interacting with various adeno-associated viral (AAV) serotypes. A water-soluble, cysteine-tagged, recombinant protein version of the recently discovered multi-AAV serotype receptor (AAVR), referred to as cys-AAVR, was conjugated to maleimide-displaying polycaprolactone (PCL) materials using click chemistry. The resulting cys-AAVR-PCL system bound to a broad range of therapeutically relevant AAV serotypes, thereby providing a platform capable of modulating the delivery of all AAV serotypes. Intramuscular injection of cys-AAVR-PCL microspheres with bound AAV vectors resulted in localized and sustained gene delivery as well as reduced spread to off-target organs compared to a vector solution. This cys-AAVR-PCL system is thus an effective approach for biomaterial-based AAV gene delivery for a broad range of therapeutic applications.

Cellular Response to Surface Morphology: Electrospinning and Computational Modeling

Surface properties of biomaterials, such as chemistry and morphology, have a major role in modulating cellular behavior and therefore impact on the development of high-performance devices for biomedical applications, such as scaffolds for tissue engineering and systems for drug delivery. Opportunely-designed micro- and nanostructures provides a unique way of controlling cell-biomaterial interaction. This mini-review discusses the current research on the use of electrospinning (extrusion of polymer nanofibers upon the application of an electric field) as effective technique to fabricate patterns of micro- and nano-scale resolution, and the corresponding biological studies. The focus is on the effect of morphological cues, including fiber alignment, porosity and surface roughness of electrospun mats, to direct cell migration and to influence cell adhesion, differentiation and proliferation. Experimental studies are combined with computational models that predict and correlate the surface composition of a biomaterial with the response of cells in contact with it. The use of predictive models can facilitate the rational design of new bio-interfaces.

Nanopatterned Scaffolds for Neural Tissue Engineering and Regenerative Medicine

Biologically inspired approaches employing nanoengineering techniques have been influential in the progress of neural tissue repair and regeneration. Neural tissues are exposed to complex nanoscale environments such as nanofibrils. In this chapter, we summarize representative nanotechniques, such as electrospinning, lithography, and 3D bioprinting, and their use in the design and fabrication of nanopatterned scaffolds for neural tissue engineering and regenerative medicine. Nanotopographical cues in combination with other cues (e.g., chemical cues) are crucial to neural tissue repair and regeneration using cells, including various types of stem cells. Production of biologically inspired nanopatterned scaffolds may encourage the next revolution for studies aiming to advance neural tissue engineering and regenerative medicine.

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.

Fabrication of biodegradable textile scaffold based on hydrophobized hyaluronic acid

In this work, we report on the preparation of a novel biodegradable textile scaffold made of palmitoyl-hyaluronan (palHA). Monofilament fibres of palHA with a diameter of 120μm were prepared by wet spinning. The wet-spun fibres were subsequently processed into a warp-knitted textile. To find a compromise between swelling in water and degradability of the final textile scaffold, a series of palHA derivatives with different degrees of substitution of the palmitoyl chain was synthesized. Freeze-drying not only provided shape fixation, but also speeded up scaffold degradation in vitro. Fibronectin, fibrinogen, laminin and collagen IV were physically adsorbed on the textile surface to enhance cell adhesion on the material. The highest amount of adsorbed cell-adhesive proteins was achieved with fibronectin (89%), followed by fibrinogen (81%). Finally, textiles modified with fibronectin or fibrinogen both supported the adhesion and proliferation of normal human fibroblasts in vitro, proving to be a useful cellular scaffold for tissue engineering.

Tubing-Electrospinning: A One-Step Process for Fabricating Fibrous Matrices with Spatial, Chemical, and Mechanical Gradients

Guiding newly generated tissues in a gradient pattern, thereby precisely mimicking inherent tissue morphology and subsequently arranging the intimate networks between adjacent tissues, is essential to raise the technical levels of tissue engineering and facilitate its transition into the clinic. In this study, a straightforward electrospinning method (the tubing-electrospinning technique) was developed to create fibrous matrices readily with diverse gradient patterns and to induce patterned cellular responses. Gradient fibrous matrices can be produced simply by installing a series of polymer-containing lengths of tubing into an electrospinning circuit and sequentially processing polymers without a time lag. The loading of polymer samples with different characteristics, including concentration, wettability, and mechanical properties, into the tubing system enabled unique features in fibrous matrices, such as longitudinal gradients in fiber density, surface properties, and mechanical stiffness. The resulting fibrous gradients were shown to arrange cellular migration and residence in a gradient manner, thereby offering efficient cues to mediate patterned tissue formation. The one-step process using tubing-electrospinning apparatus can be used without significant modifications regardless of the type of fibrous gradient. Hence, the tubing-electrospinning system can serve as a platform that can be readily used by a wide-range of users to induce patterned tissue formation in a gradient manner, which will ultimately improve the functionality of tissue engineering scaffolds.

Improved cellular infiltration in electrospun fiber via engineered porosity

Small pore sizes inherent to electrospun matrices can hinder efficient cellular ingrowth. To facilitate infiltration while retaining its extracellular matrix-like character, electrospinning was combined with salt leaching to produce a scaffold having deliberate, engineered delaminations. We made elegant use of a specific randomizing component of the electrospinning process, the Taylor Cone and the falling fiber beneath it, to produce a uniform, well-spread distribution of salt particles. After 3 weeks of culture, up to 4 mm of cellular infiltration was observed, along with cellular coverage of up to 70% within the delaminations. To our knowledge, this represents the first observation of extensive cellular infiltration of electrospun matrices. Infiltration appears to be driven primarily by localized proliferation rather than coordinated cellular locomotion. Cells also moved from the salt-generated porosity into the surrounding electrospun fiber matrix. Given that the details of salt deposition (amount, size, and number density) are far from optimized, the result provides a convincing illustration of the ability of mammalian cells to interact with appropriately tailored electrospun matrices. These layered structures can be precisely fabricated by varying the deposition interval and particle size conceivably to produce in vivo-like gradients in porosity such that the resulting scaffolds better resemble the desired final structure.