Sukyoung Kim

Development of a novel bone grafting material using autogenous teeth

We developed a novel bone grafting material that incorporates autogenous teeth (AutoBT), and provided the basis for its clinical application. AutoBT contains organic and inorganic mineral components and is prepared from autogenous grafting material, thus eliminating the risk of an immune reaction that may lead to rejection. AutoBT was used at the time of implant placement, simultaneously with osteoinduction surgery, and excellent bony healing by osteoinduction and osteoconduction was confirmed.

Tissue-engineered growth of bone by marrow cell transplantation using porous calcium metaphosphate matrices

In this study we investigated not only osteoblastic cell proliferation and differentiation on the surface of calcium metaphosphate (CMP) matrices in vitro but also bone formation by ectopic implantation of these cell-matrix constructs in athymic mice in vivo. Interconnected porous CMP matrices with pores 200 microm in size were prepared to use as scaffolds for rat-marrow stromal-cell attachment. Cell-matrix constructs were cultured in vitro, and cell proliferation and ALPase activities were monitored for 56 days. In addition to their being cultured in vitro, cell-matrix constructs were implanted into subcutaneous sites of athymic mice. In vitro these porous CMP matrices supported the proliferation of osteoblastic cells as well as their differentiation, as indicated by high ALPase activity. In vivo the transplanted marrow cells gave rise to bone tissues in the pores of the CMP matrices. A small amount of woven bone formation was detected first at 4 weeks; osteogenesis progressed vigorously with time, and thick lamellar bones that had been remodeled were observed at 12 weeks. These findings demonstrate the potential for using a porous CMP matrix as a biodegradable scaffold ex vivo along with attached marrow-derived mesenchymal cells for transplantation into a site for bone regeneration in vivo.

Three-dimensional matrices of calcium polyphosphates support bone growth in vitro and in vivo

Novel macroporous calcium polyphosphate (CPP) scaffolds, with three-dimensional interconnected structure, were fabricated using a polyurethane sponge method. They were then employed in both in vitro and in vivo assays to examine their suitability as bone tissue engineering scaffolds. In the former, subcultured rat marrow cells were seeded on the scaffolds at 7.0×105 cells/sample and cultured for 2 wk. Cell-free controls were employed to monitor changes in the scaffold itself. In the in vivo assay, CPP rods were implanted in rat distal femur and recovered after 2 wk. Samples were examined by scanning electron microscopy following freeze-fracturing. Both in vitro and in vivo assays demonstrated the growth of bone within the scaffolds. In vitro, the bone/CPP interface was occupied by a morphologically distinguishable cement line, while in vivo non-mineralized fibrous tissue was seen at the interface together with bone ingrowth into the scaffold microporosity. The morphology of the individual surface grains of the CPP scaffolds employed in vivo changed to a more rounded form, while no change in geometry was observed in the in vitro cell-free group. These preliminary studies indicate that three-dimensional CPPs can be successfully used as scaffolds for bone tissue engineering.

Studies on calcium phosphate coatings

Hydroxyapatite, one form of calcium phosphate, is preferred for its ability to interact with living bone, resulting in improvements of implant fixation and faster bone healing. The interlayer of nitrides or oxides formed by DC magnetron sputtering improved the bonding strength of plasma-sprayed hydroxyapatite coating to a maximum of 10 times for iridium oxide, due to the increases in chemical bonding at interfaces of interlayer/hydroxyapatite coating. The thin and defects-free layer of calcium phosphate was formed by e-beam evaporation. The Ca/P ratio of film was successfully controlled with the evaporants having the different ratio of Ca/P with addition of CaO. The Ca/P ratio of film had great effects on the structure formation after heat treatment and the dissolution behavior. The film with the Ca/P ratio of 1.5 showed an extremely low dissolution rate even in the amorphous state. Calcium phosphate films had the average adhesion strength of 64.8 MPa.

Composite nanofiber mats consisting of hydroxyapatite and titania for biomedical applications

Composite nanofiber mats (HA/TiO2) consisting of hydroxyapatite (HA) and titania (TiO2) were fabricated via an electrospinning technique and then collagen (type I) was immobilized on the surface of the HA/TiO2 composite nanofiber mat to improve tissue compatibility. The structure and morphology of the collagen-immobilized composite nanofiber mat (HA/TiO2-col) was investigated using an X-ray diffractometer, electron spectroscopy for chemical analysis, and scanning electron microscope. The potential of the HA/TiO2-col composite nanofiber mat for use as a bone scaffold was assessed by an experiment with osteoblastic cells (MC3T3-E1) in terms of cell adhesion, proliferation, and differentiation. The results showed that the HA/TiO2-col composite nanofiber mats possess better cell adhesion and significantly higher proliferation and differentiation than untreated HA/TiO2 composite nanofiber mats. This result suggests that the HA/TiO2-col composite nanofiber mat has a high-potential for use in the field of bone regeneration and tissue engineering.

Influences of Heating Condition and Substrate-Surface Roughness on the Characteristics of Sol-Gel-Derived Hydroxyapatite Coatings

A prepared transparent HA solution was coated on Ti6Al4V substrates by a spin-coating technique. The crystallization of the sol-gel-derived HA coated on the metallic substrates could be done at relatively low firing temperatures (as low as 600°C). The characteristics of the HA-coated layer were dependent on the surface roughness of substrates and heating conditions such as firing temperature, holding time, heating rate, and atmosphere. The heat treatment at a slow heating rate (<2°C/min.) and a long heating time (>10 hrs) at 600°C in air produced the uniform surface and improved the crystallinity. The HA layer coated on 20 μm grit-blasted substates was more uniform and had fever cracks after firing, compared with that coated on 100 μm grit-blasted rougher substrates.

Comparative Characteristics of Porous Bioceramics for an Osteogenic Response In Vitro and In Vivo

Porous calcium phosphate ceramics are used in orthopedic and craniofacial applications to treat bone loss, or in dental applications to replace missing teeth. The implantation of these materials, however, does not induce stem cell differentiation, so suitable additional materials such as porous calcium phosphate discs are needed to influence physicochemical responses or structural changes. Rabbit adipose-derived stem cells (ADSC) and mouse osteoblastic cells (MC3T3-E1) were evaluated in vitro by the MTT assay, semi-quantitative RT-PCR, and immunoblotting using cells cultured in medium supplemented with extracts from bioceramics, including calcium metaphosphate (CMP), hydroxyapatite (HA) and collagen-grafted HA (HA-col). In vivo evaluation of the bone forming capacity of these bioceramics in rat models using femur defects and intramuscular implants for 12 weeks was performed. Histological analysis showed that newly formed stromal-rich tissues were observed in all the implanted regions and that the implants showed positive immunoreaction against type I collagen and alkaline phosphatase (ALP). The intramuscular implant region, in particular, showed strong positive immunoreactivity for both type I collagen and ALP, which was further confirmed by mRNA expression and immunoblotting results, indicating that each bioceramic material enhanced osteogenesis stimulation. These results support our hypothesis that smart bioceramics can induce osteoconduction and osteoinduction in vivo, although mature bone formation, including lacunae, osteocytes, and mineralization, was not prominent until 12 weeks after implantation.

Characterisation of transparent hydroxyapatite nanoceramics prepared by spark plasma sintering

Abstract Hydroxyapatites (HA) have good biocompatibility and are used as bioceramics for artificial bones. The application areas can be extended further if transparent and dense HA ceramics can be prepared. The preparation of dense and transparent HA ceramics were attempted using a spark plasma sintering technique at relatively low temperatures (900–1000°C) under a pressure of 80 MPa for a short time of 10 min. The sintered body was almost fully dense (>99%) and transparent with a transmittance >70%. The microstructure was examined by SEM, TEM, STEM and EDX. The HA ceramics exhibited a microstructure with grains, approximately 100 nm size. A number of intragranular voids, 5–10 nm in size, with flat boundaries were also observed. The voids were believed to have been generated by evaporation during spark plasma sintering and were stabilised during cooling. The grain boundaries were clean without a glassy phase.

BMP-2 Grafted nHA/PLGA Hybrid Nanofiber Scaffold Stimulates Osteoblastic Cells Growth.

Biomaterials play a pivotal role in regenerative medicine, which aims to regenerate and replace lost/degenerated tissues or organs. Natural bone is a hierarchical structure, comprised of various cells having specific functions that are regulated by sophisticated mechanisms. However, the regulation of the normal functions in damaged or injured cells is disrupted. In order to address this problem, we attempted to artificially generate a scaffold for mimicking the characteristics of the extracellular matrix at the nanoscale level to trigger osteoblastic cell growth. For this purpose, we have chemically grafted bone morphogenetic protein (BMP-2) onto the surface of L-glutamic acid modified hydroxyapatite incorporated into the PLGA nanofiber matrix. After extensive characterization using various spectroscopic techniques, the BMP-g-nHA/PLGA hybrid nanofiber scaffolds were subjected to various in vitro cytocompatibility tests. The results indicated that BMP-2 on BMP-g-nHA/PLGA hybrid nanofiber scaffolds greatly stimulated osteoblastic cells growth, contrary to the nHA/PLGA and pristine PLGA nanofiber scaffold, which are used as control. These results suggest that BMP-g-nHA/PLGA hybrid nanofiber scaffold can be used as a nanodrug carrier for the controlled and targeted delivery of BMP-2, which will open new possibilities for enhancing bone tissue regeneration and will help in the treatment of various bone-related diseases in the future.

Comparison study of porous calcium phosphate blocks prepared by piston and screw type extruders for bone scaffold

Piston and screw type extruders were used to prepare calcium phosphate blocks comprising macro-pores interconnected with micro-pores for bone substitutes and scaffolds. First, dicalcium phosphate dehydrate (DCPD, CaHPO4·2H2O), calcium nitrate tetrahydrate (CN, Ca(NO3)2·4H2O), hydroxyapatite (HAp, Ca10(PO4)6(OH)2), and polymer (poly-methyl methactrylate PMMA, (C5O2H8)n) beads were mixed with lubricants and a plasticizer to make a paste using a table mixer. The paste prepared for the screw extruder was thicker than that prepared for the piston extruder. The pastes were kneaded more than three times and then extruded. The extruded rods were dried at 100°C for 24hrs and sintered at 1250°C for 5hrs in the air. The porosity increased with increasing amount of DCPD and CN in both systems. The porosity of the piston extruded rod was higher than that of the screw extruder rod for the same raw material composition, except for the pure HAp porous bodies. In contrast to the porosity, the compressive strength was decreased upon the addition of DCPD and CN. The screw extruded specimens showed higher compressive strength than piston extruded ones. The macro-pores generated from the PMMA polymer beads were interconnected by micro-pores generated by the reaction of DCPD and CN, which existed in the strut. The SEM images clearly showed that the piston extruder generated more micro-pores than the screw extruder. The reaction of DCPD and CN affects the porosity, compressive strength and pore structure of the porous blocks. Also, the extruding method affects the pore characteristics.