Biomedical subjects

Hyun-Min Kim

Publications and source records attributed to Hyun-Min Kim.

At least 19 recordsLinked to original sources

PubMed2006

Surface modification of hydroxyapatite nanocrystals by grafting polymers containing phosphonic acid groups.

A novel approach for the surface modification of hydroxyapatite (HAp) nanocrystals is described by grafting polymerization of vinyl phosphonic acid (VPA) using a redox initiating system in an aqueous media. Fourier transform infrared (FT-IR) and XRD analyses confirmed the modification reaction on HAp surfaces. Inductively coupled plasma mass spectroscopy (ICP MS) showed that the Ca/P molar ratio decreased from 1.67 to 1.36 with increasing the feed VPA amount. Zeta potentials of unmodified HAp and modified HAp in phosphate-buffered saline (PBS) solutions (pH 7.4, ionic strength = 10 mM) were negative and decreased with increasing the amount of grafted PVPA. Transmission electron microscopy (TEM) measurements and time-dependent phase monitoring indicated that the colloidal stability of modified HAp over unmodified HAp in water dramatically increased and tended to exist as single nanocrystals without aggregation.

Adsorption↗

PubMed2006

The pattern of gene amplification is determined by the chromosomal location of hairpin-capped breaks.

DNA palindromes often colocalize in cancer cells with chromosomal regions that are predisposed to gene amplification. The molecular mechanisms by which palindromes can cause gene amplification are largely unknown. Using yeast as a model system, we found that hairpin-capped double-strand breaks (DSBs) occurring at the location of human Alu-quasipalindromes lead to the formation of intrachromosomal amplicons with large inverted repeats (equivalent to homogeneously staining regions in mammalian chromosomes) or extrachromosomal palindromic molecules (equivalent to double minutes [DM] in mammalian cells). We demonstrate that the specific outcomes of gene amplification depend on the applied selection, the nature of the break, and the chromosomal location of the amplified gene relative to the site of the hairpin-capped DSB. The rules for the palindrome-dependent pathway of gene amplification defined in yeast may operate during the formation of amplicons in human tumors.

Alu Elements↗

PubMed2005

Process and kinetics of bonelike apatite formation on sintered hydroxyapatite in a simulated body fluid.

The surfaces of two hydroxyapatites (HA), which have been sintered at different temperatures of 800 and 1200 degrees C, was investigated as a function of soaking time in simulated body fluid (SBF) using transmission electron microscopy (TEM) attached with energy-dispersive spectrometry (EDX) and laser electrophoresis spectroscopy. The TEM-EDX indicated that after soaking in SBF, both the HAs form bonelike apatite by undergoing the same surface structural change, i.e., formations of a Ca-rich amorphous or nano-crystalline calcium phosphate (ACP) and a Ca-poor ACP, which eventually crystallized into bonelike apatite. Zeta potential characterized by the electrophoresis indicated that during exposure to SBF, the HA surfaces reveal negative surface charge, thereby interacting with the positive calcium ions in the fluid to form the Ca-rich ACP, which gains positive surface charge. The Ca-rich ACP on the HAs then interacts with the negative phosphate ions in the fluid to form the Ca-poor ACP, which stabilizes by being crystallized into bonelike apatite with a low solubility in the SBF. The exposure times for formations of these phases of the Ca-rich ACP, the Ca-poor ACP as well as the apatite were, however, all late on HA sintered at 1200 degrees C, compared with the HA sintered at 800 degrees C. This phenomenon was attributed to a lower initial negative surface charge of the HA sintered at 800 degrees C than of that one sintered at 1200 degrees C, owing to poverty in surface hydroxyl and phosphate groups which are responsible for the surface negativity of the HA. These indicate that sintered temperature of HA might influence not in terms of the process but in terms of the rate of formation of biologically active bonelike apatite on its surface, through which the HA integrates with living bone.

Apatites↗

PubMed2004

Osteoinduction of porous bioactive titanium metal.

This is the first report of bone induction in a non-osseous site by titanium metal, which has long been recognized as a non-bioactive material. After undergoing specific chemical and thermal treatments, porous bioactive titanium induced bone formation without the need of additional osteogenic cells or osteoinductive agents. Four types of titanium implants were implanted in the dorsal muscles of mature beagle dogs, and were examined histologically after periods of 3 and 12 months. Chemically and thermally treated titanium, as well as pure titanium, was implanted either as porous blocks or as fibre mesh cylinders. Bone formation was found only in the chemically and thermally treated porous block implants removed after 12 months. The present study shows that even a non-soluble metal that contains no calcium or phosphorus can be an osteoinductive material when treated to form an appropriate macrostructure and microstructure. This finding may elucidate the nature of osteoinduction, and lead to the advent of epochal osteoinductive biomaterials for tissue regeneration.

Animals↗

PubMed2004

Preparation of bioactive titanium metal via anodic oxidation treatment.

Titania with specific structures of anatase and rutile was found to induce apatite formation in vitro. In this study, anodic oxidation in H(2)SO(4) solution, which could form anatase and rutile on titanium metal surface by conditioning the process, was employed to modify the structure and bioactivity of biomedical titanium. After the titanium metal was subjected to anodic oxidation treatment, thin film X-ray diffraction and scanning electron microscopy results showed the titanium metals surfaces were covered by porous titania of anatase and/or rutile. In simulated body fluid (SBF), the titanium anodically oxidized under the conditions with spark-discharge could induce apatite formation on its surface. The induction period of apatite formation was decreased with increasing amount of either anatase or rutile by conditioning the anodic oxidation. After the titanium metal, anodically oxidized under the conditions without spark-discharge, was subjected to heat treatment at 600 degrees C for 1 h, it could also induce apatite formation in SBF because the amount of anatase and/or rutile was increased by the heat treatment. Our results showed that induction of apatite-forming ability on titanium metal could be attained by anodic oxidation conjoined with heat treatment. So it was believed that anodic oxidation in H(2)SO(4) solution was an effective way to prepare bioactive titanium.

Apatites↗

PubMed2003

Surface potential change in bioactive titanium metal during the process of apatite formation in simulated body fluid.

Bioactive titanium metal can be prepared by NaOH and heat treatments that present the metal with a graded bioactive surface layer of amorphous sodium titanate. This study used laser electrophoresis together with transmission electron microscopy (TEM) and energy-dispersive X-ray microanalysis (EDX) to relate the surface potential change of the bioactive titanium metal with its surface structural change in simulated body fluid (SBF). The surface potential of the metal was highly negative immediately after immersion in SBF. With increasing soaking time, the surface potential increased, revealing a maximum positive value, and then decreased to a constant negative value. TEM-EDX showed that immediately after immersion in SBF, the metal surface formed Ti-OH groups by exchanging Na(+) ions in the surface sodium titanate with H3O(+) ions in the fluid. Thereafter, with increasing soaking time the metal surface formed an amorphous calcium titanate, then an amorphous calcium phosphate, and, finally, apatite with bone-like composition and structure. These results indicate that the process of apatite formation on bioactive titanium metal is initiated by the formation of Ti-OH groups with negative charges that interact with calcium ions with positive charges to form calcium titanate. The calcium titanate gains a positive charge and later interacts with phosphate ions with negative charges, forming amorphous calcium phosphate. The amorphous calcium phosphate eventually transforms and stabilizes into bone-like crystalline apatite with a negative charge.

Apatites↗

PubMed2003

Biology of alkali- and heat-treated titanium implants.

In cementless fixation systems, surface character is an important factor. Alkali and heat treatments of titanium metal have been shown to produce strong bonding to bone and a higher ongrowth rate. In this study we examined the effect of alkali and heat treatments on titanium rods in an intramedullary rabbit femur model, in regard to the cementless hip stem. The implant rods were 5 mm in diameter and 25 mm in length. Half of the implants were immersed in 5 mol/L sodium hydroxide solution and heated at 600 degrees C for 1 h (AH implants), and the other half were untreated (CL implants). The rods were implanted into the distal femur of the rabbits; AH implants into the left femur and CL implants into the right. The bone-implant interfaces were evaluated at 3, 6, and 12 weeks after implantation. Pull-out tests showed that the AH implants had a significantly higher bonding strength to bone than the CL implants at each time point. As postoperative time elapsed, histological examination revealed that new bone formed on the surface of both types of implants, but significantly more bone made direct contact with the surface of the AH implants. At 12 weeks, approximately 56% of the whole surface of the AH implants was covered with the bone. In conclusion, alkali- and heat-treated titanium offers strong bone bonding and a high affinity to bone as opposed to a conventional mechanical interlocking mechanism. Alkali and heat treatments of titanium may be suitable surface treatments for cementless joint replacement implants.

Animals↗

PubMed2003

Preparation of antibacterial silver-doped silica glass microspheres.

Various types of inorganic substances doped with silver ions have been developed as antibacterial materials, and some have already been commercialized. Colorless and chemically durable materials that slowly release silver ions are, however, still need to be developed. The present authors have previously shown that when a silica glass doped with silver and aluminium ions is prepared using the sol-gel method, the resultant product is colorless, chemically durable, and slowly releases silver ions into water over a long period. The doped silica glass takes a form of microspheres <1 microm in diameter, it is easily mixed with organic polymers, and the mixture can be formed into a thin film or fine fibers, etc. We report on the preparation of silver doped silica glass microspheres having a diameter =1 microm, using the sol-gel method. Initially, tetraethoxysilane was partially prehydrolyzed by water in ethanol, and then aluminium triisopropoxide was added to the solution to form Si-O-Al bonds. Finally, an ammonia solution containing silver nitrate was added to form silica microspheres doped with silver ion together with aluminium ions. The results show monodispersed microspheres 0.4-0.6 microm in diameter were obtained with nominal compositions of Si/Al/Ag = 1/0.01-0.03/0.003-0.03, with a molar ratio of Al/Ag = 1-3.3. The microspheres were colorless, showed a high chemical durability, and slowly released silver ions into water at 37 degrees C. Microspheres with the composition Si/Al/Ag = 1/0.01/0.01 showed excellent antibacterial activity against Escherichia coli. The minimum inhibitory concentration (MIC) of the microspheres was 400, which is less than the MIC value (800) of commercial antibacterial materials.

Anti-Bacterial Agents↗

PubMed2003

Thromboresistance of alkali- and heat-treated titanium metal formed with apatite.

Fibrin deposition and platelet adhesion onto alkali- and heat-treated titanium metal (AH-Ti), alkali- and water-treated titanium metal (Wa-Ti), and alkali- and heat-treated titanium metal formed with apatite (Ap-Ti) in simulated body fluid (SBF) were evaluated by exposure to anticoagulated blood or washed platelet suspension (WPS) under static conditions and subsequent observation with scanning electron microscopy (SEM). The results were compared with those for commercially pure titanium metal (cp-Ti). Thrombus formation on AH-Ti and Wa-Ti, which were exposed to heparinized whole blood for 1 h, was significantly less than that on cp-Ti, on which pronounced depositions of fibrin-erythrocytes and lymphocytes were observed. No thrombus was observed on Ap-Ti, possibly because of a high adsorption of heparin. Morphological change of platelets attached to surfaces via adsorbed plasma proteins was found to a significant extent on AH-Ti and Wa-Ti exposed to WPS. However, there was almost no difference between cp-Ti and Ap-Ti in round morphology of adherent platelets. These findings suggested that Ap-Ti exhibits stronger antithrombogenic characteristics than cp-Ti and other materials examined in heparinized blood.

Adsorption↗

PubMed2003

Preparation and assessment of revised simulated body fluids.

A simulated body fluid (SBF) with ion concentrations approximately equal to those of human blood plasma has been used widely for in vitro assessment of the bioactivity of artificial materials and for the formation of bone-like apatite on various substrates. The ion concentrations of a conventional SBF (c-SBF) are, however, not exactly equal to those of blood plasma. In the present study, a revision of c-SBF was made to prepare new SBFs (r-SBF, i-SBF, and m-SBF) with ion concentrations equal to or closer to those of blood plasma. The ion concentrations of the r-SBF and i-SBF were designed to be equal to those of blood plasma in total and dissociated amounts, respectively. The m-SBF was designed to have a total ion concentration equal to that of blood plasma, except for the concentration of HCO(-) (3), which was set to the saturated level with respect to calcite. The ion concentrations and pH of the as-prepared new SBFs were found to be equal to those of the nominal values. Upon sealed storage, the r-SBF and i-SBF showed no change in ion concentrations for up to 4 weeks at 5 degrees C, and up to 2 weeks at 36.5 degrees C, but thereafter they showed a decrease in HCO(-) (3) concentration and an increase in pH. Under the same storage conditions, the c-SBF and m-SBF showed no change in ion concentrations and pH values over a period of up to 8 weeks. These results indicate that the r-SBF and i-SBF are less stable than the c-SBF and m-SBF in terms of changes in ion concentrations relative to storage period. The m-SBF is optimal for in vitro bioactivity assessment of artificial materials and for biomimetic production of bone-like apatite.

Blood Chemical Analysis↗

PubMed2003

Formation and growth of clusters in conventional and new kinds of simulated body fluids.

Simulated body fluid (SBF) with ion concentrations approximately equal to those of human blood plasma has been widely used for the in vitro assessment of the bioactivity of artificial materials and for the formation of bonelike apatite on various substrates. Ion concentrations of conventional SBF (c-SBF) are, however, not exactly equal to those of blood plasma, and hence the apatite formed in c-SBF is not the same as bone apatite in its composition and structure. Recently, the present authors prepared new kinds of SBFs (r-SBF, i-SBF, and m-SBF) with ion concentrations nearer to those of blood plasma. The r-SBF and i-SBF have ion concentrations equal to those of blood plasma in total and dissociated amounts, respectively. The m-SBF has ion concentrations equal to those of blood plasma in total amount except for the HCO(-) (3) concentration, which was set to the saturated level with respect to calcite. In the present study, the stabilities of c-SBF, r-SBF, i-SBF and m-SBF were examined in terms of cluster formation in the fluids by means of dynamic light scattering photometry. The c-SBF and m-SBF were found to form only calcium phosphate clusters, whose initial hydrodynamic diameter was approximately 1 nm, and this did not change with storage time at 36.5 degrees C. Besides the calcium phosphate clusters, r-SBF and i-SBF formed calcium carbonate clusters, whose initial hydrodynamic diameters were 10-30 nm, and these increased significantly with storage time. The formation and growth of calcium carbonate clusters in r-SBF and i-SBF can be attributed to their supersaturation with respect to calcite. These indicate that r-SBF and i-SBF lack long-term stability. The m-SBF is recommended for the assessment of bioactivity of artificial materials as well as the formation of bonelike apatite on various substrates from the viewpoint of stability as well as similarity to blood plasma.

Apatites↗

PubMed2003

Structural dependence of apatite formation on titania gels in a simulated body fluid.

The apatite-forming ability of titania gels with different structures has been investigated in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma. Titania gels with an amorphous structure or with an anatase or rutile structure were prepared by the sol-gel process with a subsequent heat treatment at various temperatures. The titania gels with an amorphous structure did not induce apatite formation on their surfaces in the simulated body fluid, whereas gels with an anatase or rutile structure induced apatite formation on their surfaces. The deposition of apatite was more pronounced on the anatase gels than on the rutile gels. This indicates that a specific structure of titania is effective in inducing apatite formation in a body environment. Such a specific structure was assumed in this study to be the crystalline planar arrangement in the anatase structure, which facilitates epitaxy of the apatite crystal.

Apatites↗

PubMed2003

A comparative study between in vivo bone ingrowth and in vitro apatite formation on Na2O-CaO-SiO2 glasses.

This study compared in vivo bioactivity with the in vitro apatite-forming ability of biomaterials. Granules of five kinds of P(2)O(5)-free Na(2)O-CaO-SiO(2) glasses, showing different apatite-forming ability in simulated body fluid (SBF), were implanted into a defect on the femoral condyle of rabbits. Bone ingrowth was evaluated using scanning electron microscopy among five kinds of glasses at 1, 2, 3, 6, and 12 weeks. Quantitative analysis was performed measuring the depth of new bone ingrowth from the periphery. In addition, the total areas of newly formed bone among glass particles were examined at 3 and 6 weeks using confocal laser scanning microscopy (CLSM) after weekly administration of fluorescent calcein. The depth of bone ingrowth among glass particles increased in proportion to their apatite-forming ability in vitro. The CLSM study showed a correlation between the quantities of labeled newly formed bone and in vitro apatite-forming ability. In the P(2)O(5)-free Na(2)O-CaO-SiO(2) glasses, the periods within 3-6 days for inducing apatite in SBF considered a necessary condition to convey bioactivity in vivo, and in vivo evaluations at 2-3 weeks is important to determine this. The in vivo bioactivity was precisely reproduced by apatite-forming ability in SBF. Therefore, evaluating apatite formation in SBF is a good screening test for the in vivo bioactivity of materials, resulting in reduction of the need for animal sacrifices and savings in experimental time.

Animal Testing Alternatives↗

PubMed2003

Novel bioactive materials with different mechanical properties.

Some ceramics, such as Bioglass, sintered hydroxyapatite, and glass-ceramic A-W, spontaneously bond to living bone. They are called bioactive materials and are already clinically used as important bone substitutes. However, compared with human cortical bone, they have lower fracture toughness and higher elastic moduli. Therefore, it is desirable to develop bioactive materials with improved mechanical properties. All the bioactive materials mentioned above form a bone-like apatite layer on their surfaces in the living body, and bond to bone through this apatite layer. The formation of bone-like apatite on artificial material is induced by functional groups, such as Si-OH, Ti-OH, Zr-OH, Nb-OH, Ta-OH, -COOH, and PO(4)H(2). These groups have specific structures revealing negatively charge, and induce apatite formation via formations of an amorphous calcium compound, e.g., calcium silicate, calcium titanate, and amorphous calcium phosphate. These fundamental findings provide methods for preparing new bioactive materials with different mechanical properties. Tough bioactive materials can be prepared by the chemical treatment of metals and ceramics that have high fracture toughness, e.g., by the NaOH and heat treatments of titanium metal, titanium alloys, and tantalum metal, and by H(3)PO(4) treatment of tetragonal zirconia. Soft bioactive materials can be synthesized by the sol-gel process, in which the bioactive silica or titania is polymerized with a flexible polymer, such as polydimethylsiloxane or polytetramethyloxide, at the molecular level to form an inorganic-organic nano-hybrid. The biomimetic process has been used to deposit nano-sized bone-like apatite on fine polymer fibers, which were textured into a three-dimensional knit framework. This strategy is expected to ultimately lead to bioactive composites that have a bone-like structure and, hence, bone-like mechanical properties.

Animals↗

PubMed2003

Repair of segmental long bone defect in rabbit femur using bioactive titanium cylindrical mesh cage.

A segmental rabbit femur defect was repaired using an empty bioactive titanium (BAT) mesh cage. A 10mm long titanium mesh cage was positioned in the bony defect and reinforced by intramedullary fixation. The BAT surface was prepared by chemical and thermal treatment. Pure titanium cages were used as a control. Torsional stiffness of the BAT group at 4 weeks was approximately equal to, and at 8 weeks twice, that of the intact femur. Differences between the torsional stiffness of the control and BAT groups were significant at both time intervals. Histological examinations showed that woven bone appeared around the cage by 4 weeks and transformed to lamella bone by 8 weeks. New bone bonded to the BAT surface without an intervening layer. The BAT cage enhanced the bone repairing process and achieved faster repair of long bone segmental defects.

Animals↗

PubMed2003

Histological and mechanical investigation of the bone-bonding ability of anodically oxidized titanium in rabbits.

The purpose of this study was to histologically and mechanically investigate the in vivo bone-bonding ability of anodically oxidized titanium (AO Ti) with an anatase crystal layer on its surface. AO Ti plates, anodically oxidized at 155 V in 1 M H2SO4, were implanted into the proximal metaphyses of mature rabbit tibiae for 4, 8, 16, and 24 weeks and investigated by light microscopy, scanning electron microscopy and detaching test. High bone-bonding ability, comparable to our previous study data of the bioactive titanium produced by sodium-free alkali and heat treatment, was observed at the early stages of implantation. However, no substantial increase was demonstrated. AO Ti plates bonded to bone directly, with no intervening soft tissue layer, and no breakage of the AO Ti layer was observed. The AO Ti layer was porous through to the titanium substrate, while the porosity was low. Apatite-like deposition into the pores of the AO layer was observed only in the superficial zone. The lack of improvement of bone-bonding ability in the later stages of implantation may be attributed to the low porosity and to the superficial ingrowths of apatite-like deposits into the pores of the AO Ti layer.

Animals↗

PubMed2002

Apatite-forming ability of a zirconia/alumina nano-composite induced by chemical treatment.

Induction of an apatite-forming ability on a nano-composite of a ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP) and alumina (Al2O3) polycrystals via chemical treatment with aqueous solutions of H3PO4, H2SO4, HCl, or NaOH has been investigated. The Ce-TZP/Al2O3 composite is attractive as a load-bearing bone substitute because of its mechanical properties. The chemical treatments produced Zr-OH surface functional groups, which are known to be effective for apatite nucleation in a body environment. The composite, after chemical treatment, was shown to form a bonelike apatite layer when immersed in a simulated body fluid containing ion concentrations nearly equal to those in human blood plasma. This implies that it may form apatite in the living body and bond to living bone through the apatite layer. This type of bioactive Ce-TZP/Al2O3 composite is therefore expected to be useful as a bone substitute, even under load-bearing conditions.

Aluminum↗

PubMed2002

Effect of water treatment on the apatite-forming ability of NaOH-treated titanium metal.

NaOH and heat treatments of titanium metal induce an apatite-forming ability on the metal by producing a bioactive graded sodium titanate structure on its surface. An enhancement of the apatite-forming ability of titanium metal induced by the NaOH treatment was attempted by conjoining the water and heat treatments. These treatments are assumed to convert the sodium titanate into anatase, which is presumed to be more effective for apatite nucleation. The sodium titanate gel on the metal formed from the NaOH treatment was shown to transform into anatase by a simple immersion in pure water, with subsequent heat treatments. Forming anatase on the metal significantly improved the apatite-forming ability of the metal in a simulated body fluid (SBF). The apatite-forming ability correlated directly with the amount of anatase on the metal. It is therefore expected that bioactive titanium metal and its alloys with a higher bone-bonding ability can be obtained with the use of the water and subsequent heat treatments after the NaOH treatment.

Apatites↗