Hyeon Yoon

A cryogenic direct-plotting system for fabrication of 3D collagen scaffolds for tissue engineering

The goal of tissue engineering is to repair or regenerate damaged tissue using a combination of cellular biology and materials engineering techniques. One of the challenging problems in tissue engineering is the development of a reproducible three-dimensional (3D) scaffold to support cell migration and infiltration. Although natural polymers, such as dissolved collagen or alginate, are considered ideal for this purpose, their hydrophilic properties have hindered the fabrication of designed 3D scaffold structures. To overcome this problem, we developed a novel system for the cryogenic plotting of 3D scaffolds. Using this technique, we created various 3D collagen scaffolds with designed pore structures that exhibited desired properties. The diameter of the individual collagen strands, which varied from 250 µm to 500 µm, was reproducibly dependent on processing parameters, and the final collagen scaffold showed little shrinkage (less than 12%) relative to the initial design. To evaluate the fabricated scaffold, we adapted the scaffold to regenerate skin tissue. Immunohistochemical analysis demonstrated that co-cultured keratinocytes and fibroblasts completely migrated throughout the 3D collagen scaffold and keratinocytes were well differentiated on the surface of scaffold like a human skin.

A Three-Dimensional Polycaprolactone Scaffold Combined with a Drug Delivery System Consisting of Electrospun Nanofibers

A new three-dimensional (3D) scaffold containing a functional drug delivery system (DDS) consisting of electrospun micro/nanofibers is proposed. In the DDS scaffold, a core-shell laminated, structured, electrospun mat of hydrophobic polycaprolactone (PCL) and hydrophilic poly(ethylene oxide) (PEO)/rhodamine-B fibers was embedded in the normal 3D PCL scaffold, which was fabricated by a melt-plotting system. Rhodamine release from the scaffold was controlled physically by the thickness change of the PCL layer, and initial burst in drug release was eliminated by an appropriate thickness of the PCL layer. This simple technique may be useful in fabricating DDS-functional scaffolds for the clinical areas not only of bone and skin regeneration, but also of other tissue regeneration areas, regardless of the degradation rate of the structural scaffold.

Three-Dimensional Polycaprolactone Hierarchical Scaffolds Supplemented with Natural Biomaterials to Enhance Mesenchymal Stem Cell Proliferation

A hybrid technology that combines a three-dimensional (3-D) dispensing system with an electrospinning process was used to produce a hierarchical 3-D scaffold consisting of micro-sized polycaprolactone (PCL) strands and micro/nano-sized fibres. The micro/nanofibre biocomposites electrospun with PCL/small intestine submucosa (SIS) and PCL/Silk fibroin were layered between melt-plotted micro-strands. The scaffold containing SIS exhibited a stronger hydrophilic property than other scaffolds due to the various hydrophilic components in SIS. The 3-D hierarchical scaffold having biocomposites exhibited an incredibly enhanced initial cell attachment and proliferation of bone marrow-derived mesenchymal stem cells relative to the normally designed 3-D scaffold.

A superhydrophobic surface fabricated by an electrostatic process.

We describe the fabrication of a biomimically designed superhydrophobic poly(ε-caprolactone) surface, which was obtained using a modified electrostatic process. The fabricated surface exhibits a micron-sized pyramid structure consisting of accumulated droplets and nanofibres. By using this simple one-step process, we can achieve a superhydrophobic surface having both a high water contact angle and low threshold sliding angle, similar to that of the superhydrophobic plant leaf.

Micro/Nanofibrous Scaffolds Electrospun from PCL and Small Intestinal Submucosa

Small intestinal submucosa (SIS) has the potential for use as a natural scaffold material because of the presence of type-I and -III collagen and various cytokines. However, although the presence of growth factors in SIS leads to superior initial cell attachment and proliferation compared to synthetic polymeric scaffolds, the lack of reliable and reproducible shape controllability is a drawback. To overcome this problem, SIS was electrospun with a biodegradable and biocompatible polymer, polycaprolactone (PCL). PCL/SIS fibrous webs were fabricated with an electrospinning process using an auxiliary conical electrode to create stable micro/nanofibrous scaffolds. The hydrophilicity, mechanical properties and cellular behavior of the PCL/SIS fibrous scaffold were analyzed. In addition, aligned PCL/SIS fibrous webs were fabricated using various collector rotation speeds. As the alignment of micro/nanofibers increased, the hydrophilicity, orthotropic mechanical properties, and cellular behavior of PC-12 cells improved. These results show the potential for using PCL/SIS fibrous scaffolds as a good natural biomaterial.

Electric Field-Aided Formation Combined with a Nanoimprinting Technique for Replicating a Plant Leaf

The surface of the taro plant leaf was replicated using a nanoimprinting technique (NIT) supplemented with an electric field. This field-aided nanoimprinting method (FA-NIT) consists of two steps: applying an electric field to a liquid polymer under the plant leaves and the curing process of the polymer with the applied electric field. An appropriate electric field was needed to induce the electrokinetic phenomena of a liquid polymer to obtain a good replicated surface. The roughness fabricated by the FA-NIT was about 45% higher than the one prepared by NIT. The FA-NIT method is a good supplementary technique to improve the quality of NIT.

A micro-scale surface-structured PCL scaffold fabricated by a 3D plotter and a chemical blowing agent.

To study cell responses, polymeric scaffolds with a controllable pore size and porosity have been fabricated using rapid-prototyping methods. However, the scaffolds fabricated by rapid prototyping have very smooth surfaces, which tend to discourage initial cell attachment. Initial cell attachment, migration, differentiation and proliferation are strongly dependent on the chemical and physical characteristics of the scaffold surface. In this study, we propose a three-dimensional (3D) plotting method supplemented with a chemical blowing agent to produce a surface-modified 3D scaffold in which the surface is inscribed with nano- and micro-sized pores. The chemically-blown 3D polymeric scaffold exhibited positive qualities, including the compressive modulus, hydrophilicity and initial cell adhesion. Cell cultures on the scaffolds demonstrated that chondrocytes interacted better with the surface-modified scaffold than with a normal 3D scaffold.

Layer-by-layered electrospun micro/nanofibrous mats for drug delivery system

AbstractLayer-by-layered micro/nanofibrous mats consisted of poly(ɛ-caprolactone) (PCL) and poly(ethylene oxide) (PEO)/Rhodamine-B (RM), which is used as an indicator of drug release, were fabricated by using a modified electrospinning process to observe the release of RM from the layered mats. In this study, we focused on the edge-effect of the layer-by-layered electrospun mats, because the initial burst release from the layered mats occurred in the edge area of the mats. To overcome this deficiency, we proposed a new electrospun layer-by-layered mat, where the edge of the PEO/RM layer was completely covered with the PCL layer controlling the releasing drug. From the cumulative releasing behavior of the drug, we could observe that the drug release was well controlled regardless of the length of edge, and the initial burst was readily adjustable.

Polycarprolactone Ultrafine Fiber Membrane Fabricated Using a Charge-reduced Electrohydrodynamic Process

This paper introduces a modified electrospinning system for biomedical wound-healing applications. The conventional electrospinning process requires a grounded electrode on which highly charged electrospun ultrafine fibers are deposited. Biomedical wound-healing membranes, however, require a very low charge and a low level of remnant solvent on the electrospun membrane, which the conventional process cannot provide. An electrohydrodynamic process complemented with field-controllable electrodes (an auxiliary electrode and guiding electrodes) and an air blowing system was used to produce a membrane, with a considerably reduced charge and low remnant solvent concentration compared to one fabricated using the conventional method. The membrane had a small average pore size (102 nm) and high porosity (85.1%) for prevention of bacterial contamination.In vivo tests on rats showed that these directly electrospun fibrous membranes produced using the modified electrospinning process supported the good healing of skin burns.