Jin-Oh Jeong

Characterization of hydroxyapatite-coated bacterial cellulose scaffold for bone tissue engineering

The goal of this study was to develop a novel hydroxyapatite (HA) coated bacterial cellulose (BC) scaffold for bone tissue regeneration. HA-coated BC was prepared by immersing in 30 mL of 5× simulated body fluid at 37°C for 12 h. The resulting HA-coated BC scaffolds were characterized by scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared (ATRFTIR) spectroscopy, and thermal gravimetric analysis (TGA). HA spherical globules were newly formed on the surface of the BC, and a fibrous network of BC scaffolds still maintained their dimensions for cell adhesion and proliferation. ATR-FTIR spectroscopy analysis showed bands assigned to specific signals for phosphate and carbonate ions from HA. HA-coated BC scaffolds of thermal gravimetric analysis presented residue of around 25%. The ability for bone regeneration of HA-coated BC scaffolds was evaluated using a rat calvarial defect model for 4 and 8 weeks. After implantation, both BC and HAcoated BC scaffolds showed new bone formation derived from existing bone, and found new bone even inside the scaffold. Furthermore, a new bone area was signigicantly increased in the HA-coated BC scaffolds compared with those from BC scaffolds, and bone-like materials were frequently found in HA-coated BC scaffolds. Therefore, the HA-coated BC scaffolds can be used as an effective tool for bone tissue regeneration.

Development and characterization of heparin-immobilized polycaprolactone nanofibrous scaffolds for tissue engineering using gamma-irradiation

Polycaprolactone (PCL) has been considered a useful material for orthopedic devices and osseous implants because of its biocompatibility and bone-forming activity. However, PCL-based scaffolds have hydrophobic surfaces that reduce initial cell viability. In this study, we fabricated surface-modified PCL nanofibers for tissue engineering using radiation technology. We supplemented the hydrophilicity of the PCL nanofibers by introducing 2-aminoethyl methacrylate (AEMA) through gamma-irradiation and subsequently immobilized heparin onto the nanofibers using the EDC/NHS reaction. The SEM images show that there is almost no change in the morphology of nanofibers after radiation grafting of AEMA and heparin-immobilization onto PCL nanofibers. The surface properties of the scaffolds were characterized by ATR-FTIR, XPS, and fluorescamine staining in order to confirm the successful grafting of AEMA onto the PCL nanofibers. Immobilization of heparin was also confirmed by the amide I (1650 cm−1) and amide II group (1550 cm−1) from ATR-FTIR. The amounts of heparin were drastically increased on the AEMA–PCL nanofibers as revealed by TBO assay. The initial cell viability of hMSCs was significantly increased on the AEMA grafted nanofibers but grew slowly on heparin-immobilized nanofibers. The cumulative release of bone morphogenetic protein-2 (BMP-2) was slow and continuous onto the heparin-immobilized nanofibers (18.13 ± 3.87 μg mL−1) compared to PCL nanofibers (20.25 ± 1.45 μg mL−1). Therefore, heparin-immobilized nanofibers may be a good tool for tissue engineering applications using radiation technology.

Physicochemical characterization of gelatin-immobilized, acrylic acid-bacterial cellulose nanofibers as cell scaffolds using gamma-irradiation

Bacterial cellulose (BC) has been shown to have a high-burst pressure, high-water contact, and ultrafine highly nanofibrous structure similar with that in a natural extracellular matrix (ECM). In the present study, we developed a BC-based functional scaffold for tissue engineering using radiation technology. BC was generated by Gluconacetobacter hansenii TL-2C. Acrylic acid (AAc) was grafted onto BC surfaces under aqueous conditions using gamma-ray irradiation. The characterization of the scaffold was performed by scanning electron microscopy, ATR-FTIR spectroscopy, a toluidine blue O assay, and 2,4,6,-trinitro-benzensulfonic acid assay. AAc was grafted on the BC under gamma-ray irradiation. Gelatin was chemically conjugated on the AAc-BC scaffolds through EDC chemistry. The morphology of the modified BC nanofibers did not change, while representative features of AAc and gelatin were maintained. The adhesion and spreading of human mesenchymal stem cells was improved on the gelatin-AAc-BC nanofibers compared to unmodified BC and AAc-BC nanofibers. Our results suggest that gelatin-immobilized BC nanofiber scaffolds can be a promising way to fabricate three-dimentional, nanofibrous scaffolds that accelerate cell behavior for biomedical applications.

Effective gamma-ray sterilization and characterization of conductive polypyrrole biomaterials

Conductive polymers, including polypyrrole (PPy), have been extensively explored to fabricate electrically conductive biomaterials for bioelectrodes and tissue engineering scaffolds. For their in vivo uses, a sterilization method without severe impairment of original material properties and performance is necessary. Gamma-ray radiation has been commonly applied for sterilization of medical products because of its simple and uniform sterilization without heat generation. Herein we describe the first study on gamma-ray sterilization of PPy bioelectrodes and its effects on their characteristics. We irradiated PPy bioelectrodes with different doses (0–75 kGy) of gamma-rays. Gamma-ray irradiation of the PPy (γ-PPy) increased the oxygenation and hydrophilicity of the surfaces. Interestingly, gamma-ray irradiation did not alter the electrical impedances and conductivities of the PPy substrates. Additionally, γ-PPy prepared with various dopants (e.g., para-toluene sulfonate, polystyrene sulfonate, and chlorine) showed the electrochemical properties similar to the non-irradiated control. Gamma-ray irradiation at doses of ≥15 kGy was required for effective sterilization as evidenced by complete eradication of gram positive and negative bacteria. γ-PPy substrates also showed cytocompatibility similar to untreated control PPy, indicating no substantial alteration of cytocompatibility. In conclusion, gamma ray sterilization is a viable method of sterilization of conducting polymer-based biomaterials for biomedical applications.

방사선 이용 상처치료용 β-Glucan 하이드로젤 제조 및 특성 분석

Hydrogels consisted of β-glucan, poly(vinyl alcohol) (PVA), poly(vinyl pyrrolidone) (PVP), κ-carrageenan (κC) and glycerin were prepared by gamma-ray irradiation for damaged tissue regeneration. Irradiation doses of 25, 50, and 75 kGy were exposed, respectively, to the β-glucan hydrogel to evaluate the effect of irradiation dose on physical properties. The physical properties were examined such as gel fraction, absorption ratio, and compressive strength. It was found that the gel fraction and the compressive strength increased with increasing the irradiation dose. This is due to the fact that the crosslinking density increases with increasing the irradiation dose, whereas the absorption ratio decreased with increasing the irradiation dose. On observing the wound healing of rat skin, the resulting hydrogels accelerated the wound repair, which can be attributed to the release of β-glucan from the hydrogel. Therefore, radiation fabricated β-glucan/PVA/PVP/κC/glycerin blended hydrogel was suitable for wound healing and could be considered as good tissue regeneration biomaterials without chemical toxicity.

Development of Styrene-Grafted Polyurethane by Radiation-Based Techniques

Polyurethane (PU) is the fifth most common polymer in the general consumer market, following Polypropylene (PP), Polyethylene (PE), Polyvinyl chloride (PVC), and Polystyrene (PS), and the most common polymer for thermosetting resins. In particular, polyurethane has excellent hardness and heat resistance, is a widely used material for electronic products and automotive parts, and can be used to create products of various physical properties, including rigid and flexible foams, films, and fibers. However, the use of polar polymer polyurethane as an impact modifier of non-polar polymers is limited due to poor combustion resistance and impact resistance. In this study, we used gamma irradiation at 25 and 50 kGy to introduce the styrene of hydrophobic monomer on the polyurethane as an impact modifier of the non-polar polymer. To verify grafted styrene, we confirmed the phenyl group of styrene at 690 cm−1 by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) and at 6.4–6.8 ppm by 1H-Nuclear Magnetic Resonance (1H-NMR). Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), Thermogravimetric Analysis (TGA) and contact angle analysis were also used to confirm styrene introduction. This study has confirmed the possibility of applying high-functional composite through radiation-based techniques.

Preparation and evaluation of β -glucan hydrogel prepared by the radiation technique for drug carrier applications

β-Glucan can provide excellent environment to apply to drug carrier due to its immunological and anti-inflammatory effect. Minocycline hydrochloride (MH) has excellent oral bioavailability pharmacological properties. Specifically, MH is effectively absorbed into the gingiva for periodontal disease treatment. In this study, we attempt to develop MH loaded β-glucan hydrogel for periodontal disease treatment through radiation-crosslinking technique. In addition, MH loaded β-glucan hydrogels were tested for their cytotoxicity and antibacterial activity. Finally, we conducted an in vivo study to demonstrate the potential to prevent the invasion of bacteria to treat periodontal disease. The gel content and compressive strength of the β-glucan hydrogels increased as the β-glucan content and the absorbed dose (up to 7 kGy) increased. For a radiation dose of 7 kGy, the gelation and the compressive strength of a 6 wt% β-glucan hydrogel were approximately 92% and 270 kPa, respectively. As a drug, MH was consistently released from β-glucan hydrogels, reaching 80% at approximately 90 min. Furthermore, the MH loaded β-glucan hydrogels showed no cytotoxicity. The MH loaded β-glucan hydrogels exhibited good antibacterial activity against Porphyromonas gingivalis. In addition, MH loaded β-glucan hydrogel demonstrated the potential of a good capability to prevent the invasion of bacteria and to treat wounds.