Response of Human Mesenchymal Stem Cells to Patterned and Randomly Oriented Poly(Vinyl Alcohol) Nano-fibrous Scaffolds Surface-Modified with Arg-Gly-Asp (RGD) Ligand

The aim of this study was to obtain a better insight of how nano-fibrous scaffolds can affect human mesenchymal stem cells responses. Therefore, in this study, using electrospinning technique, poly(vinyl alcohol) (PVA) nano-fibers with two different patterns were prepared. In the first structure, PVA nano-fibers were oriented randomly and in the second structure, nano-fibers were electrospun in such a way that a special pattern was obtained. In order to enhance their stability, scaffolds were cross-linked using glutaraldehyde vapor. RGD immobilization was used to improve cell adhesion properties of the scaffolds. SEM micrographs demonstrated that the cell adhesion was effectively enhanced after RGD immobilization and higher cell densities were observed on RGD-modified scaffolds. Randomly oriented nano-fibers showed better cell adhesion compared to patterned structure. Patterned structure also revealed slightly lower cell viability compared to random nano-fibers. Finally, it was assumed that randomly oriented nano-fibers provide a more favorable surface for cells.     

Production and characterization of chitosan fibers and 3-D fiber mesh scaffolds for tissue engineering applications

This study reports on the production of chitosan fibers and 3-D fiber meshes for the use as tissue engineering scaffolds. Both structures were produced by means of a wet spinning technique. Maximum strain at break and tensile strength of the developed fibers were found to be 8.5% and 204.9 MPa, respectively. After 14 d of immersion in simulated body fluid (SBF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and inductively coupled plasma emission (ICP) spectroscopy analyses showed that a bioactive Ca-P layer was formed on the surface of the fibers, meaning that they exhibit a bioactive behavior. The samples showed around 120% max. swelling in physiological conditions. The pore sizes of 3-D chitosan fiber mesh scaffolds were observed to be in the range of 100-500 microm by SEM. The equilibrium-swelling ratio of the developed scaffolds was found to be around 170% (w/w) in NaCl solution at 37 degrees C. Besides that, the limit swelling strain was less than 30%, as obtained by mechanical spectroscopy measurements in the same conditions. The viscoelastic properties of the scaffolds were also evaluated by both creep and dynamic mechanical tests. By means of using short-term MEM extraction test, both types of structures (fibers and scaffolds) were found to be non-cytotoxic to fibroblasts. Furthermore, osteoblasts directly cultured over chitosan fiber mesh scaffolds presented good morphology and no inhibition of cell proliferation could be observed.Osteoblast-like cells proliferating over chitosan based fibers after 7 d of culture.     

In vitro and in vivo evaluation of silk fibroin-hardystonite-gentamicin nanofibrous scaffold for tissue engineering applications

Designing advanced biomaterials with regenerative and drug delivering functionalities remains a challenge in the field of tissue engineering. In this paper we present the design, development, and a use case of an electrospun nano-biocomposite scaffold composed of silk fibroin (SF), hardystonite (HT), and gentamicin (GEN). The fabricated SF nanofiber scaffolds provide mechanical support while HT acts as a bioactive and drug carrier, on which GEN is loaded as an antibacterial agent. Antibacterial zone of inhibition (ZOI) results indicate that the inclusion of 3–6 wt% GEN significantly improves the antibacterial performance of the scaffolds against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) bacteria, with an initial burst release of 10–20% and 72–85% total release over 7 days. The release rate of stimulatory silicon ions from SF-HT scaffolds reached 94.53±5 ppm after 7 days. Cell studies using osteoblasts show that the addition of HT significantly improved the cytocompatibility of the scaffolds. Angiogenesis, in vivo biocompatibility, tissue vascularization, and translatability of the scaffolds were studied via subcutaneous implantation in a rodent model over 4-weeks. When implanted subcutaneously, the GEN-loaded scaffold promoted angiogenesis and collagen formation, which suggests that the scaffold may be highly beneficial for further bone tissue engineering applications.     

Preparation and characterization of the biomineralized zinc oxide particles in spider silk peptides

In this work, hierarchical ZnO particles were prepared using a biomineralization strategy at room temperature in the presence of peptides acidified from spider silk proteins. A mechanism of the mineralization of the ZnO particles was that the affinity of original ZnO nanoparticles and zinc ions in the peptide chains played an important role in controlling the biocrystallizing formation of the pore ZnO particles. The intensity of their visible green luminescence was enhanced with increases of the mineralization time due to the porous surface defects. The hierarchical ZnO materials with biomolecules will facilitate their photoluminescence spectra applications as biosensors or optoelectronic nanodevices in the future, when covalently coupled with peptides or other biomolecules to achieve patterned growth over large areas of substrate.     

Fabrication of fibrous patterned architectures with controlled deposition and multidirectional alignment

In recent years, the ability to produce nanofibrous patterned architectures by electrospinning has exposed a wide range of potential applications in biomedical and industrial fields. Directional alignment, controlled deposition, and density variation into the patterns are desirable for many applications such as tissue engineering scaffolds and micro/nano‐electronic devices. In this study, we introduce a versatile method for fabrication of various kinds of nanofibrous deposition patterns with the help of microprocessor based control system for switching collector electrodes. By controlling the concurrent activation time of two adjacent electrodes, we demonstrated that amount of fibers going into the pattern can be adjusted and alignment in electrospun fibers can be obtained. We also revealed that the deposition density of electrospun fibers in different areas of patterned architectures can be varied. This advanced technique can have a significant impact in enhancing the technology of electrospinning and can help develop new applications in health sciences and industrial sectors. Copyright © 2015 John Wiley & Sons, Ltd.     

Fabrication of 2D photonic crystals using block copolymer patterns on as grown LEDs

Di-block copolymer polystyrene-block-polymethyl methacrylate (PS-b-PMMA) was used to make patterns over a large area of as grown LEDs. The polymer patterns on LEDs surface could be transferred to the underlying p-GaN, the topmost layer of as grown LEDs by both reactive ion etching (RIE) and photo-enhanced chemical (PEC) etching. Removal of remaining polymer chains results in patterned LEDs which shows higher light extraction efficiency. In our experiment, much higher intensity for patterned LEDs in both photoluminescence (PL) and electroluminescence (EL) data plot were found. Similar improvements were found in I-V and L-I curves for patterned LEDs.     

Biofabrication of Cell‐Loaded 3D Spider Silk Constructs

Biofabrication is an emerging and rapidly expanding field of research in which additive manufacturing techniques in combination with cell printing are exploited to generate hierarchical tissue‐like structures. Materials that combine printability with cytocompatibility, so called bioinks, are currently the biggest bottleneck. Since recombinant spider silk proteins are non‐immunogenic, cytocompatible, and exhibit physical crosslinking, their potential as a new bioink system was evaluated. Cell‐loaded spider silk constructs can be printed by robotic dispensing without the need for crosslinking additives or thickeners for mechanical stabilization. Cells are able to adhere and proliferate with good viability over at least one week in such spider silk scaffolds. Introduction of a cell‐binding motif to the spider silk protein further enables fine‐tuned control over cell–material interactions. Spider silk hydrogels are thus a highly attractive novel bioink for biofabrication.     

Silica–gelatin hybrids for tissue regeneration: inter-relationships between the process variables

Owing to their diverse range of highly tailorable material properties, inorganic/organic hybrids have the potential to meet the needs of biodegradable porous scaffolds across a range of tissue engineering applications. One such hybrid platform, the silica–gelatin sol–gel system, was examined and developed in this study. These hybrid scaffolds exhibit covalently linked interpenetrating networks of organic and inorganic components, which allows for independent control over their mechanical and degradation properties. A combination of the sol–gel foaming process and freeze drying was used to create an interconnected pore network. The synthesis and processing of the scaffolds has many variables that affect their structure and properties. The focus of this study was to develop a matrix tool that shows the inter-relationship between process variables by correlating the key hybrid material properties with the synthesis parameters that govern them. This was achieved by investigating the effect of the organic (gelatin) molecular weight and collating previously reported data. Control of molecular weight of the polymer is as an avenue that allows the modification of hybrid material properties without changing the surface chemistry of the material, which is a factor that governs the cell and tissue interaction with the scaffold. This presents a significant step forward in understanding the complete potential of the silica–gelatin hybrid system as a medical device.     

Light-Responsive Polyblend Films with Reconfigurable Surface Micropatterns as Rewritable Information Storage Media

Stimulus-sensitive surfaces with tunable morphologies exhibit a wide range of applications in the fields of surface science and engineering. Herein, a cost-effective yet practical strategy is proposed to fabricate photo-sensitive patterning surface on film/substrate wrinkle system based on an azo-containing polyblend. By manipulating the stress field of the bilayer system globally and/or locally upon the stress relaxation triggered by the reversible cis-trans isomerization of the azobenzene, heating/cooling triggered surface wrinkles on the polyblend films could be tailor-made with visible-light-irradiation. Notably, upon selective photo-irradiation, bespoke surface patterns may be cyclically generated or eliminated, allowing these reconfigurable patterned polyblend surfaces to be used as rewritable information storage media for non-ink printing. The as-prepared photo-printed information patterns with high-resolution are shown to be rewritable for multiple cycles and legible for over 90 d in dark ambient conditions. This study not only provides a versatile strategy for flourishing the stimulus-sensitive systems, but also sheds light on the stress relaxation-triggered morphological evolution of the wrinkling polyblend films.      

A facile approach to fabricate hierarchically structured poly(3‐hexylthiophene‐2,5‐diyl) films

Microstructured surfaces have great potentials to improve the performances and efficiency of optoelectronic devices. In this work, a simple robust approach based on surface instabilities was presented to fabricate poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) films with ridge‐like/wrinkled composite microstructures. Namely, the hierarchically patterned films were prepared by spin coating the P3HT/tetrahydrofuran (THF) solution on a polydimethylsiloxane (PDMS) substrate to form stable ridge‐like structures, followed by solvent vapor swelling to create surface wrinkles with the orientation guided by the ridge‐like structures. During spin coating of the P3HT/THF solution, the ridge‐like structures were generated by the in‐situ template of the THF swelling‐induced creasing structures on the PDMS substrate. To our knowledge, it is the first report that the creasing structures are used as a recoverable template for patterning films. The crease‐templated ridge‐like structures were well modulated by the THF swelling time, the modulus of the PDMS substrate, the P3HT/THF solution concentration and the selective/blanket exposure of the PDMS substrate to O₂ plasma. UV–vis and fluorescence spectrometry measurements indicated that the light absorption and fluorescent emission were improved on the hierarchically patterned P3HT films, which can be utilized to enhance the efficiencies of organic solar cells. Furthermore, this simple versatile method based on the solvent swelling‐induced crease as the in‐situ recoverable template has been extended to pattern other spin‐coated films with different compositions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 928–939     

Fabrication,chemical modification,and topographical patterning of reactive gels assembled from azlactone‐functionalized polymers and a diamine

The work reported here demonstrates an approach to the fabrication of chemically reactive and topographically patterned hydrogels using the azlactone‐functionalized polymer poly(2‐vinyl‐4,4'‐dimethylazlactone) (PVDMA) and the hydrophilic diamine Jeffamine®. Gels were initially assembled in DMSO but can be subsequently transferred into aqueous media to form hydrogels. Spectroscopic characterization of assembled gels demonstrated that variation in the stoichiometric ratio of azlactones to amines during gel synthesis permits control over the extent of crosslinking in the gels. Residual azlactones not consumed during crosslinking can be exploited to further functionalize these gels with hydrophobic, hydrophilic, and macromolecular amines that influence the physicochemical properties of these materials in aqueous solvents. The surface and bulk of these gels can be differentially functionalized (i.e., different functional groups on the gel surface relative to the bulk) by taking advantage of different rates of diffusion of macromolecular amines versus small molecule amines into assembled gels. Finally, these azlactone‐functionalized gels can be topographically patterned with microwell arrays using a replica molding technique and chemically modified postfabrication with amine nucleophiles. This reactive approach to the fabrication of topographically patterned and chemically functionalized hydrogels offers a straightforward method for the rapid synthesis of micropatterned scaffolds of interest in a broad range of applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3185–3194     

Polycaprolactone-polymethyl methacrylate electrospun blends for biomedical applications

Electrospinning is one of most versatile process to fabricate porous scaffolds in biomedical field. Synthetic polymers such as polycaprolactone (PCL) and polymethyl methacrylate (PMMA) provide excellent properties for biomedical applications due to their biocompatibility and tunable mechanical properties. PCL-PMMA electrospun blends combine compressive/tensile properties of individual polymers as well as biocompatibility/biodegradability. Together with porosity of scaffold, drug/nutrient supply is required in tissue regeneration and healing. High pressure CO₂ has been investigated to plasticize many biopolymers and impregnate drugs in scaffolds. This study explores several compositions of PCL-PMMA electrospun scaffolds for morphological and mechanical properties. These scaffolds are impregnated with hydrophilic (Rhodamine B) and hydrophobic (Fluorescein) dyes using high pressure CO₂ and air plasma treatment. Furthermore, release profiles of dyes have been studied from thin films and porous scaffolds to understand several controlling factors for controlled release applications. Results show dye-polymer interactions, CO₂ impregnation and stress relaxation of electrospun fibers are key factors in release profile from electrospun fibers. This study is a step forward in developing PCL-PMMA based electrospun scaffolds for drug delivery and tissue engineering.     

Formation of nematic ordered cellulose and chitin

We proposed in a previous paper a unique form of β-glucan association, nematic ordered cellulose (NOC) that is molecularly ordered, yet non-crystalline. NOC has unique characteristics; in particular, its surface properties provide with a function of tracks or scaffolds for regulated movements and fiber-production of Acetobacter xylinum [Kondo et al. 2002. Proc. Natl. Acad. Sci. USA 99: 14008–14013]. In order to extend the usage of this NOC film as a functional template, the present article attempts to clarify how β-glucan association is initiated and established by uniaxial stretching of water swollen cellulose gel films. Wide angle X-ray diffraction, high-resolution transmission electron microscopy and atomic force microscopy were employed to exhibit molecular behavior of the ordering at various scales. Then, the preparative method for NOC was applied to the other carbohydrate polymers such as α-chitin and cellulose/α-chitin blends, leading to nematic ordered states as well as cellulose. However, the method did not necessarily provide the typical structure like NOC at the molecular scale. Instead, it yielded a variety of hierarchical nematic ordered states at various scales, which allows development of new artificial ordered sheet structures.     

Combining horizontal and vertical substructure relationships in scaffold hierarchies for activity prediction

For a systematic exploration of structural relationships between molecular scaffolds, ～24,000 unique scaffolds were extracted from 458 different target sets. Substructure relationships between these scaffolds were systematically determined. The scaffold tree data structure was utilized to study structural relationships between original scaffolds and derivative scaffolds obtained by rule-based decomposition. Leaf-to-root substructure relationships that resulted from rule-based decomposition were compared to leaf-to-leaf relationships between original scaffolds most of which were not part of the scaffold tree hierarchy. Decomposed scaffolds not contained in active target set compounds were prioritized on the basis of hierarchical scaffold patterns and additional substructure relationships. For high-priority virtual scaffolds, activity predictions were carried out, and these scaffolds were often found in external test compounds having the predicted activity. Taken together, our results suggest that leaf-to-root substructure relationships in scaffold trees should best be complemented with additional substructure relationships to determine high-priority virtual scaffolds for activity prediction.     

Patterned hydrogel substrates for cell culture with electrohydrodynamic jet printing

Cells respond to and are directed by physiochemical cues in their microenvironment, including geometry and substrate stiffness. The development of substrates for cell culture with precisely controlled physiochemical characteristics has the potential to advance the understanding of cell biology considerably. In this communication, E-jet printing is introduced as a method for creating high-resolution protein patterns on substrates with controlled elasticity. It is the first application of E-jet printing on a soft surface. Protein spots as small as 5 μm in diameter on polyacrylamide are demonstrated. The patterned hydrogels are shown to support cell attachment and spreading. Polyacrylamide substrates patterned by E-jet printing may be applied to further the study of cellular mechanobiology.     

Effect of fluorosurfactant on capillary instabilities in nanoimprinted polymer patterns

Surface forces play a paramount role in most aspects of Nanoimprint Lithography. In particular, subjecting nanoimprinted patterns to moderate heating allows surface tension to smooth out undesirable roughness and defects in the patterns, but this “thermal reflow” treatment can induce structural decay or even collapse of the patterns by capillary instability if this process is not carefully controlled. Adhesion between the mold and polymer film can also cause the imprinted structure to tear or fracture. Fluorinated surfactants (FS) are attractive for reducing mold adhesion, yet the effects of these additives on nanostructure stability during thermal reflow are not well understood. Here we present thermal stability studies of line-space grating patterns created by Thermal Embossing Nanoimprint Lithography (TENIL) on model polystyrene (PS) films with FS additives. As expected by energy considerations, FS segregates to the air interface, where it seems to facilitate mold release. This also reduces the surface energy and thus reduces the driving force for pattern “slumping” (height decay). However, the beneficial effects of the surfactant are counterbalanced by the fact that the FS decreases the effective film viscosity, which accelerates nanopattern leveling. The net effect is that the pattern height decay is strongly a function of FS concentration. This enhanced film fluidity in the presence of FS also makes the pattern more susceptible to an undulatory capillary instability under thermal reflow conditions. Surface phase segregation of FS and PS is also observed in conjunction with both slumping and lateral capillary instabilities, which may be useful for producing chemically patterned surfaces. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2591–2600, 2009     

Nanoengineered multiscale hierarchical structures with tailored wetting properties

A simple method for fabricating micro/nanoscale hierarchical structures is presented using a two-step temperature-directed capillary molding technique. This lithographic method involves a sequential application of the molding process in which a uniform polymer-coated surface is molded with a patterned mold by means of capillary force above the glass transition temperature of the polymer. Various microstructures and nanostructures were fabricated with minimum resolution down to approximately 50 nm with good reproducibility. Also contact angle measurements of water indicated that two wetting states coexist on a multiscale hierarchical structure where heterogeneous wetting is dominant for the microstructure and homogeneous wetting for the nanostructure. A simple theoretical model combining these two wetting states was presented, which was in good agreement with the experimental data. Using this approach, multiscale hierarchical structures for biomimetic functional surfaces can be fabricated with precise control over geometrical parameters and the wettability of a solid surface can be tailored in a controllable manner.     

Multiple Hydrogen Bonding Enables the Self‐Healing of Sensors for Human–Machine Interactions

Despite its widespread use in signal collection, flexible sensors have been rarely used in human–machine interactions owing to its indistinguishable signal, poor reliability, and poor stability when inflicted with unavoidable scratches and/or mechanical cuts. A highly sensitive and self‐healing sensor enabled by multiple hydrogen bonding network and nanostructured conductive network is demonstrated. The nanostructured supramolecular sensor displays extremely fast (ca. 15 s) and repeatable self‐healing ability with high healing efficiency (93 % after the third healing process). It can precisely detect tiny human motions, demonstrating highly distinguishable and reliable signals even after cutting–healing and bending over 20 000 cycles. Furthermore, a human–machine interaction system is integrated to develop a facial expression control system and an electronic larynx, aiming to control the robot to assist the patient's daily life and help the mute to realize real‐time speaking.     

Preparation of AgCl-polyacrylamide composite microspheres via combination of a polymer microgel template method and a reverse micelle technique

A new route was created for the preparation of AgCl-polyacrylamide (AgCl-PAM) composite microspheres with patterned surface structures. The route is a combination of a polymer microgel template method and a reverse micelle technique. The size of the AgCl nanoparticles existing on the surfaces of the composite microspheres and the clearness of the surface patterns of the composite microspheres can be altered by simply adjusting the amount of precipitated AgCl and the rate of the deposition reaction. The route can be also used for the preparation of other water-insoluble salt-polymer composite microspheres, such as BaSO(4)-PAM. It is expected that the composite microspheres with patterned surface structures may not only combine the advantages of polymers and those of inorganic compounds, but also combine the advantages of microspheres in the micrometer size range and those in the nanometer size range.     

Fabrication and Evaluation of Alginate/Bacterial Cellulose Nanocrystals–Chitosan–Gelatin Composite Scaffolds

It is common knowledge that pure alginate hydrogel is more likely to have weak mechanical strength, a lack of cell recognition sites, extensive swelling and uncontrolled degradation, and thus be unable to satisfy the demands of the ideal scaffold. To address these problems, we attempted to fabricate alginate/bacterial cellulose nanocrystals-chitosan-gelatin (Alg/BCNs-CS-GT) composite scaffolds using the combined method involving the incorporation of BCNs in the alginate matrix, internal gelation through the hydroxyapatite-d-glucono-δ-lactone (HAP-GDL) complex, and layer-by-layer (LBL) electrostatic assembly of polyelectrolytes. Meanwhile, the effect of various contents of BCNs on the scaffold morphology, porosity, mechanical properties, and swelling and degradation behavior was investigated. The experimental results showed that the fabricated Alg/BCNs-CS-GT composite scaffolds exhibited regular 3D morphologies and well-developed pore structures. With the increase in BCNs content, the pore size of Alg/BCNs-CS-GT composite scaffolds was gradually reduced from 200 μm to 70 μm. Furthermore, BCNs were fully embedded in the alginate matrix through the intermolecular hydrogen bond with alginate. Moreover, the addition of BCNs could effectively control the swelling and biodegradation of the Alg/BCNs-CS-GT composite scaffolds. Furthermore, the in vitro cytotoxicity studies indicated that the porous fiber network of BCNs could fully mimic the extracellular matrix structure, which promoted the adhesion and spreading of MG63 cells and MC3T3-E1 cells on the Alg/BCNs-CS-GT composite scaffolds. In addition, these cells could grow in the 3D-porous structure of composite scaffolds, which exhibited good proliferative viability. Based on the effect of BCNs on the cytocompatibility of composite scaffolds, the optimum BCNs content for the Alg/BCNs-CS-GT composite scaffolds was 0.2% (w/v). On the basis of good merits, such as regular 3D morphology, well-developed pore structure, controlled swelling and biodegradation behavior, and good cytocompatibility, the Alg/BCNs-CS-GT composite scaffolds may exhibit great potential as the ideal scaffold in the bone tissue engineering field.