GeunHyung Kim

Electrospun PCL nanofibers with anisotropic mechanical properties as a biomedical scaffold

To design an ideal scaffold, various factors should be considered, such as pore size and morphology, mechanical properties versus porosity, surface properties and appropriate biodegradability. Of these factors, the importance of mechanical properties on cell growth is particularly obvious in tissues such as bone, cartilage, blood vessels, tendons and muscles. Although electrospun nanofibers provide easily applicable nano-sized structures which could be used as biomedical scaffolds, the mechanical properties are poor since an increased pore size and porosity are generally accompanied by a decrease in mechanical properties. In addition, the general electrospinning has been limited to the fabrication of a variety of anisotropic mechanical properties, which are extremely important parameters for designing a musculoskeletal system. In this study, scaffolds consisting of variously oriented nanofibers were produced using an electrospinning process modified with an auxiliary electrode and a two-axis robot collecting system. Using an auxiliary electrode, a stable Taylor cone and initial spun jets were obtained. The influence of the electrode was evaluated with electric field simulation. Using the modified electrospinning process, various directions of orientation of electrospun fibers could be acquired and the fabricated oriented nanofiber webs showed a mechanically anisotropic behavior and a higher hydrophilic property compared to randomly distributed fibrous mats.

Three-dimensional hierarchical composite scaffolds consisting of polycaprolactone, β-tricalcium phosphate, and collagen nanofibers: fabrication, physical properties, and in vitro cell activity for bone tissue regeneration.

β-Tricalcium phosphate (β-TCP) and collagen have been widely used to regenerate various hard tissues, but although Bioceramics and collagen have various biological advantages with respect to cellular activity, their usage has been limited due to β-TCPs inherent brittleness and low mechanical properties, along with the low shape-ability of the three-dimensional collagen. To overcome these material deficiencies, we fabricated a new hierarchical scaffold that consisted of a melt-plotted polycaprolactone (PCL)/β-TCP composite and embedded collagen nanofibers. The fabrication process was combined with general melt-plotting methods and electrospinning. To evaluate the capability of this hierarchical scaffold to act as a biomaterial for bone tissue regeneration, physical and biological assessments were performed. Scanning electron microscope (SEM) micrographs of the fabricated scaffolds indicated that the β-TCP particles were uniformly embedded in PCL struts and that electrospun collagen nanofibers (diameter = 160 nm) were well layered between the composite struts. By accommodating the β-TCP and collagen nanofibers, the hierarchical composite scaffolds showed dramatic water-absorption ability (100% increase), increased hydrophilic properties (20%), and good mechanical properties similar to PCL/β-TCP composite. MTT assay and SEM images of cell-seeded scaffolds showed that the initial attachment of osteoblast-like cells (MG63) in the hierarchical scaffold was 2.2 times higher than that on the PCL/β-TCP composite scaffold. Additionally, the proliferation rate of the cells was about two times higher than that of the composite scaffold after 7 days of cell culture. Based on these results, we conclude that the collagen nanofibers and β-TCP particles in the scaffold provide good synergistic effects for cell activity.

3D polycaprolactone scaffolds with controlled pore structure using a rapid prototyping system

Designing a three-dimensional (3-D) ideal scaffold has been one of the main goals in biomaterials and tissue engineering, and various mechanical techniques have been applied to fabricate biomedical scaffolds used for soft and hard tissue regeneration. Scaffolds should be biodegradable and biocompatible, provide temporary support for cell growth to allow cell adhesion, and consist of a defined structure that can be formed into customized shapes by a computer-aided design system. This versatility in preparing scaffolds gives us the opportunity to use rapid prototyping devices to fabricate polymeric scaffolds. In this study, we fabricated polycaprolactone scaffolds with interconnecting pores using a 3-D melt plotting system and compared the plotted scaffolds to those made by salt leaching. Scanning electron microscopy, a laser scanning microscope, micro-computed tomography, and dynamic mechanical analysis were used to characterize the geometry and mechanical properties of the resulting scaffolds and morphology of attached cells. The plotted scaffolds had the obvious advantage that their mechanical properties could be easily manipulated by adjusting the scaffold geometry. In addition, the plotted scaffolds provided more opportunity for cells to expand between the strands of the scaffold compared to the salt-leached scaffold.

Analysis of thermo-physical and optical properties of a diffuser using PET/PC/PBT copolymer in LCD backlight units

The effect of water absorption and thermo-physical properties on the warpage of a diffusing plate fabricated with poly(ethylene terephtalate)/polycarbonate/polybutylene terephtalate copolymer in a direct-lit backlight unit (BLU) of a liquid crystal display (LCD) has been investigated. The warpage of the new diffusing polymer was significantly reduced relative to that of a conventional PMMA diffusing plate. To improve the diffusivity of a diffuser, a new manufacturing technology, a stripe coating method, was suggested. By using this method, scattering characteristics of the new diffusing material was measured and compared to that of the diffuser which was not treated with stripe coating. Spatial profiles of the luminance are displayed for a BLU having cold cathode fluorescent lamps (CCFLs) array and a flat fluorescent lamp (FFL). As with the superior thermo-physical property that alleviates the warpage, the diffuser plate partially coated with diffusing agents is expected to achieve better uniformity and/or slimmer BLU.

Designed hybrid scaffolds consisting of polycaprolactone microstrands and electrospun collagen-nanofibers for bone tissue regeneration

Biomedical scaffolds used in bone tissue engineering should have various properties including appropriate bioactivity, mechanical strength, and morphologically optimized pore structures. Collagen has been well known as a good biomaterial for various types of tissue regeneration, but its usage has been limited due to its low mechanical property and rapid degradation. In this work, a new hybrid scaffold consisting of polycaprolactone (PCL) and collagen is proposed for bone tissue regeneration. The PCL enhances the mechanical properties of the hybrid scaffold and controls the pore structure. Layered collagen nanofibers were used to enhance the initial cell attachment and proliferation. The results showed that the hybrid scaffold yielded better mechanical properties of pure PCL scaffold as well as enhanced biological activity than the pure PCL scaffold did. The effect of pore size on bone regeneration was investigated using two hybrid scaffolds with pore sizes of 200 ± 20 and 300 ± 27 μm. After post-seeding for 7 days, the cell proliferation with pore size, 200 ± 20 μm, was greater than that with pore size, 300 ± 27 μm, due to the high surface area of the scaffold.

Formation of oriented nanofibers using electrospinning

This letter reports on a simple, easy method for generating suspended nanofibers on a dielectric substrate using various target electrodes. By controlling the electrostatic field between the target electrodes, the nanofibers can be oriented to the electric field direction at the electrodes. The alignment of nanofibers was dependent on the applied frequency, field strength, and shape of the electrode.

Cells (MC3T3-E1)-Laden Alginate Scaffolds Fabricated by a Modified Solid-Freeform Fabrication Process Supplemented with an Aerosol Spraying

In this study, we propose a new cell encapsulation method consisting of a dispensing method and an aerosol-spraying method. The aerosol spray using a cross-linking agent, calcium chloride (CaCl(2)), was used to control the surface gelation of dispensed alginate struts during dispensing. To show the feasibility of the method, we used preosteoblast (MC3T3-E1) cells. By changing the relationship between the various dispensing/aerosol-spraying conditions and cell viability, we could determine the optimal cell-dispensing process: a nozzle size (240 μm) and an aerosol spray flow rate (0.93 ± 0.12 mL min(-1)), 10 mm s(-1) nozzle moving speed, a 10 wt % concentration of CaCl(2) in the aerosol solution, and 2 wt % concentration of CaCl(2) in the second cross-linking process. Based on these optimized process conditions, we successfully fabricated a three-dimensional, pore-structured, cell-laden alginate scaffold of 20 × 20 × 4.6 mm(3) and 84% cell viability. During long cell culture periods (16, 25, 33, and 45 days), the preosteoblasts in the alginate scaffold survived and proliferated well.

Polymeric Composites Tailored by Electric Field

A solid composite of desirable microstructure can be produced by curing a liquid polymeric suspension in an electric field. Redistribution effect of the field-induced forces exceeds that of centrifugation, which is frequently employed to manufacture functionally graded materials. Moreover, unlike centrifugational sedimentation, the current approach can electrically rearrange the inclusions in targeted areas. The electric field can be employed to produce a composite having uniformly oriented structure or only modify the material in selected regions. Field-aided technology enables polymeric composites to be locally micro-tailored for a given application. Moreover, materials of literally any composition can be manipulated. In this article we present testing results for compositions of graphite and ceramic particles as well as glass fibers in epoxy. Electrical and rheological interactions of inclusions in a liquid epoxy are discussed. Measurements of tensile modulus and ultimate strength of epoxy composites having different microstructure of 10 vol% graphite, ceramic particles and glass fiber are presented.

Coaxial structured collagen–alginate scaffolds: fabrication, physical properties, and biomedical application for skin tissue regeneration

Collagen is the most promising natural biomaterial and has been used in various tissue engineering applications for skin, bone, and cartilage because it provides good biocompatibility and low antigenicity. Although collagen is an excellent candidate material for various biomedical applications, its difficult processability and mechanical properties have remained important limitations. To overcome the problems, several methods including indirect printing combined with a sacrificing mold and low-temperature printing were suggested. However, it is difficult to fabricate precisely controlled 3D pore structure using the methods. In a previous study, we introduced a three-dimensional (3D) pore-structure-controlled collagen scaffold fabricated by a 3D dispensing system supplemented with a cryogenic and freeze-drying system. The fabricated scaffold had remarkably good cellular behaviour (cell migration and differentiation) but poor mechanical stability due to the highly porous structure consisting of micro-sized strands and poor mechanical nature of collagen. To overcome this deficiency, we designed a hybrid (core/shell) scaffold composed of an outer collagen and an inner alginate. The collagen/alginate scaffolds exhibited good structural stability (core–shell structure), increased Youngs modulus about seven times compared to pure collagen scaffold under a similar pore-structure, and resulted in good cell viability, similar to a pure collagen scaffold. In an in vivo test, the hybrid scaffold was used as a dermal substitute and provided good granulation tissue formation and rapid vascularisation.

Designed Three-Dimensional Collagen Scaffolds for Skin Tissue Regeneration

One of the challenges in tissue engineering is the development of a reproducible three-dimensional (3D) scaffold to support cell migration and infiltration. As a dermal substitute, 3D collagen scaffolds with precisely controlled pore structures were fabricated using an innovative cryogenic dispenser system. The scaffolds were composed of perpendicular, highly porous collagen strands in successive layers. The fabricated scaffolds were evaluated in an in vitro keratinocyte/fibroblast coculture test. Fibroblasts were well dispersed within the scaffold, and keratinocytes had completely migrated through the well-designed pore structure and differentiated on top of the scaffold surface. The differentiated keratinocytes generated a stratum corneum in the 3D dispensed scaffolds, similar to that in normal skin tissue.