Papers by Author: Hyun Min Kim

Abstract: Titanium has limitations in its clinical performance in dental and orthopaedic applications. Over the last decade, numerous implant surface modifications have been developed and are currently used with the aim of enhancing bone integration. In the present study, we have experimented a bioactive titanium prepared by a simple chemical and moderate heat treatment that leads to the formation of a bone-like apatite layer on its surface in simulated body fluids. We haved used foetal rat calvaria cell cultures to investigate bone nodule formation on bioactive titanium. Scanning electron microscopy (SEM) showed that cells attached and spread on the bioactive surfaces. After 22 days of culture, bone nodules were detected on the material surface. Furthermore, the mineralized bone nodules remained attached to the bioactive titanium surface but not to untreated titanium. SEM observations and EDX microanalysis of sectioned squares showed that bone-like tissue directly bonded to bioactive titanium, but not pure titanium. These results indicated the importance of the implant surface composition in supporting differentiation of osteogenic cells and the subsequent apposition of bone matrix allowing a strong bond to bone. Furthermore, these findings may provide promising strategies for the development of biologically active implants.

Abstract: β-tricalcium phosphate (β-TCP) based cement features unique biodegradability and mild temperature rise as a material for bone reconstruction. However, the bone cement often raises a shelf life issue and therefore study was made focusing on the temperature and humidity during storage. With the increase of storing days, the density and compressive strength of hardened cement were found to drastically decrease for the cement powder stored in a mixed state. In addition, the setting property was finally lost at the same time. Such a degradation was more evident at higher temperature and was the result of the formation of dicalcium phosphate anhydrous (DCP) instead of dicalcium phosphate dehydrate (DCPD) during the storage. On the contrary, for the cement stored in an unmixed state, very slight changes were detected in density, compressive strength and setting time with the increase of storing days even if the powders were kept in a humid environment. In the unmixed ones, DCP was not precipitated regardless of the storing temperature. Discussion was made on the condition for precipitating either DCPD or DCP in terms of the amount of water supplied during setting. Practically the work suggested that the β-TCP based cement needs to be conserved at lower temperature and in dry environment as possible to effectively increase the shelf life.

Abstract: Demineralized bone matrix (DBM)-calcium phosphate cement (CPC) composites were subjected to cellular test of osteogenic potentials and implantation in animal model. The expression of osteogenic marker gene from mouse preosteoblast cell line MC3T3-E1 adhered to the DBM-CPC composite was much higher than plain CPC. In addition, the DBM-CPC composite implanted nude mice revealed osteoinduction between the implanted composite and adjacent tissues, whereas the plain CPC induced osteoconduction.

Abstract: In this study, we attempted preparation and assessments of composite pastes of demineralized bone matrix (DBM) and calcium phosphate cement (CPC). While the composite pastes presented self-setting behavior up to a certain DBM content without significant differences in setting time, temperature increase and phase transformation, compressive strength and injection capability decreased in general with the DBM content. The DBM particulates were observed to uniformly disperse in the composite cross-sections, suggesting a new model of bioactive paste with tissue regenerative function.

Abstract: Thick coatings of bone morphogenetic protein (BMP)-calcium phosphate nano-composite were prepared by a biomimetic process, in which substrates were immersed in modified simulated body fluid containing rh-BMP2 at room temperature and pressure. In vitro analyses showed that the calcium phosphate and BMP formed stable and uniform coating of composite on surface of substrate, and that the composite derive significant improvement in tissue formation, suggesting an osteoinductive bioactive surface.

Abstract: Ceramic-polymer bi-structured nano-hybrid, in which the bioactive silicate surface is nano-hybridized with flexible polymeric bulk, was synthesized in the tetraethoxysilane (TEOS)-polydimethylsiloxane (PDMS) sol-gel system. Different solutions for surface and bulk, whose compositions of TEOS: PDMS were respectively fixed 100: 0 and varied from 50: 50 to 20: 80 with various molecular weight (Mw) of PDMS, were subjected to lamination and controlled polymerization and condensation process, producing a large transparent crack-free monolithic bulk. Characterizations at near-surface cross-section of the bi-structured hybrids revealed that typical bioactive silicate was combined with all types of bulk hybrids regardless of their PDMS contents and Mw without distinct interface, indicating possibility of a novel bioactive nano-composite with enhanced physical and biological functions.

Abstract: Synthetic model of a large transparent crack-free monolithic ceramic-polymer hybrid, which was synthesized using triethoxysilane end-capped poly(tetramethylene oxide) (Si-PTMO) and tetraethoxysilane (TEOS), was examined in the CaO-SiO2-PTMO sol-gel system. Bulk precursor with nominal mass ratio of PTMO: TEOS = 80: 20 and surface precursor with nominal molar ratio of TEOS: Ca(NO3)2 = 1: 0.3 were subjected to hybridization through hydrolysis and condensation process, producing a bi-structured hybrid in which polymeric bulk was molecular hybridized with bioactive silicate surface. Spectroscopic and microscopic characterizations revealed that the surface of hybrid was typical bioactive silicate. In vitro study using a simulated body fluid (SBF) revealed that the hybrid formed an apatite on its surface within 6 hours in SBF, suggesting bioactive materials with high capability of tissue integration as well as polymeric physical properties.

Abstract: Preparation of bioactive glasses was attempted utilizing waste bovine as raw resource. Bioactive and biodegradable batch compositions in the Na2O-CaO-SiO2 system were included with calcined bovine, whose phase was high-purity oxy-hydroxyapatite. Bovine inclusion as large as 40 mass% was shown to present highly bioactive glasses; bovine in the bioactive and biodegradable compositions presented glasses with controlled bioactivity and biodegradability, respectively. These indicate not only a plenty biological resource of bio-interactive materials, but also an alternative strategy for bioactive glasses with multi-functional applications.

Abstract: Self-setting paste model in bioactive glass systems was investigated. Particulate glasses based on the systems CaO-SiO2-P2O5 and Na2O-CaO-SiO2 were combined with sodium phosphate solution to constitute paste models. Setting behavior of these pastes, i.e., workability and setting within 30 min were obtained by controlled composition-mass conditions. Specifically, it was found that the setting behavior could be controlled by glass compositions as well as mixing ratios of solids and solutions. These suggest new concept of bioactive cement for various biomedical applications.

Abstract: Sulfonic groups (-SO3H) were covalently attached on different polymeric surfaces enabling them to induce apatite nucleation, for developing bioactive apatite-polymer composites with a bonelike 3-dimensional structure. High molecular weight polyethylene (HMWPE) and ethylene-co-vinyl alcohol co-polymer (EVOH) were used. The polymers were soaked in two types of sulphate-containing solutions with different concentrations, sulphuric acid (H2SO4) and chlorosulfonic acid (ClSO3H). To incorporate calcium ions into to the sulfonated polymers, the samples were soaked in a saturated Ca(OH)2 solution for 24 hours. After soaking of the samples in a simulated body fluid (SBF), formation of an apatite layer on both surfaces was observed. The results obtained prove the validity of the proposed concept and show that the -SO3H groups are effective on inducing apatite nucleation on the surface of these polymers.