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Biomedical subjects

S Park

Publications and source records attributed to S Park.

At least 55 records · Page 3Linked to original sources
PubMed2005

Effects of dissolved calcium and phosphorous on osteoblast responses.

The dissolution behavior of hydroxyapatite (HA) and its effect on the initial cellular response is of both fundamental and clinical importance. In this study, plasma-sprayed HA coatings were characterized by X-ray diffraction and Fourier transform infrared spectroscopy (FTIR). Calcium (Ca) and inorganic phosphorous (Pi) ions released from plasma-sprayed HA coatings within 3 weeks were measured by flame atomic absorption and colorimetrically molybdenum blue complex, respectively. To investigate the effect of dissolution of HA coatings on osteoblast response, additional Ca and Pi were added into the cell culture media to simulate the dissolution concentrations. Human embryonic palatal mesenchyme cells, an osteoblast precursor cell line, were used to evaluate the biological responses to enhanced Ca and Pi media over 2 weeks. Osteoblast differentiation and mineralization were measured by alkaline phosphatase-specific assay and 1,25 (OH)2 vitamin D3 stimulated osteocalcin production. The coatings exhibited an HA-type structure. FTIR indicated the possible presence of carbonates on the coatings. A dissolution study indicated a continual increase in Ca and Pi over time. In the cell culture study, enhanced osteoblast differentiation occurred in the presence of additional Ca concentration in the cell culture media. However, additional Pi concentration in the cell culture media was suggested to slow down osteoblast differentiation and mineralization.

Calcium↗
PubMed2004

Competing magnetic phases on a kagomé staircase.

We present thermodynamic and neutron data on Ni3V2O8, a spin-1 system on a kagomé staircase. The extreme degeneracy of the kagomé antiferromagnet is lifted to produce two incommensurate phases at finite T--one amplitude modulated, the other helical--plus a commensurate canted antiferromagnet for T-->0. The H-T phase diagram is described by a model of competing first and second neighbor interactions with smaller anisotropic terms. Ni3V2O8 thus provides an elegant example of order from subleading interactions in a highly frustrated system.

Journal Article↗
PubMed2004

Thermal conductivity of geometrically frustrated, ferroelectric YMnO3: extraordinary spin-phonon interactions.

The thermal conductivity of the magnetically frustrated, ferroelectric YMnO3 exhibits an isotropic suppression in the cooperative paramagnetic state, followed by a sudden increase upon magnetic ordering. This unprecedented behavior without an associated static structural distortion probably originates from the strong dynamic coupling between acoustic phonons and low-energy spin fluctuations in geometrically frustrated magnets. The replacement of magnetic Ho for Y at the ferroelectrically active site results in an even larger effect, suggestive of the strong influence of multiferroicity.

Journal Article↗
PubMed2004

Structural anomalies and multiferroic behavior in magnetically frustrated TbMn2O5.

We have studied the magnetostructural phase diagram of multiferroic TbMn2O5 as a function of temperature and magnetic field by neutron diffraction. Dielectric and magnetic anomalies are found to be associated with steps in the magnetic propagation vector, including a rare example of a commensurate-incommensurate transition on cooling below 24 K, and in the structural parameters. The geometrically frustrated magnetic structure is stabilized by "canted antiferroelectric" displacements of the Mn3+ ions, an example of the magnetic Jahn-Teller effect. The Tb moments order ferromagnetically at low temperatures in an applied field, while the Mn magnetic structure is largely unchanged.

Journal Article↗
PubMed2004

Orbital and Spin Chains in ZnV2O4.

Our powder inelastic neutron scattering data indicate that ZnV2O4 is a system of spin chains that are three-dimensionally tangled in the cubic phase above 50 K due to randomly occupied t(2g) orbitals of V3+ (3d(2)) ions. Below 50 K in the tetragonal phase, the chains become straight due to antiferro-orbital ordering. This is evidenced by the characteristic wave vector dependence of the magnetic structure factor that changes from symmetric to asymmetric at the cubic-to-tetragonal transition.

Journal Article↗
PubMed2004

Adaptive control for insect leg position: controller properties depend on substrate compliance.

This paper concentrates on the system that controls the femur-tibia joint in the legs of the stick insect, Carausius morosus. Earlier investigations have shown that this joint is subject to a mixture of proportional and differential control whereby the differential part plays a prominent role. Experiments presented here suggest another interpretation: single legs of a stick insect were systematically perturbed using devices of different compliance and compensatory forces and movements monitored. When the compliance is high (soft spring), forces are generated that return the leg close to its original position. When the compliance is low (stiff spring), larger forces are generated but sustained changes in position occur that are proportional to the force that is applied. Selective ablation of leg sense organs showed that the leg did not maintain its position after elimination of afferents of the femoral chordotonal organ. Ablation of leg campaniform sensilla had no effect. These data support the idea that different control strategies are used, depending upon substrate compliance. In particular, what we and other authors have called a differential controller, is now considered as an integral controller that "intelligently gives up" when the correlation between motor output and movement of the leg is low.

Animals↗
PubMed2004

Colossal magnetodielectric effects in DyMn2O5.

We have investigated the detailed magnetic field dependence of the electric polarization and dielectric constant in (Tb,Dy,Ho)Mn2O5 where magnetic and ferroelectric transitions are intimately coupled. Our fundamental discovery is the unprecedented large change of the dielectric constant with magnetic field, particularly in DyMn2O5, associated with an unusual commensurate-incommensurate magnetic transition. This extraordinary effect appears to originate from the high sensitivity of the incommensurate state to external perturbation.

Journal Article↗
PubMed2004

Neurovascular protection reduces early brain injury after subarachnoid hemorrhage.

BACKGROUND AND PURPOSE: Cell death, especially apoptosis, occurred in brain tissues after subarachnoid hemorrhage (SAH). We examined the relationships between apoptosis and the disruption of blood-brain barrier (BBB), brain edema, and mortality in an established endovascular perforation model in male Sprague-Dawley rats. METHODS: A pan-caspase inhibitor (z-VAD-FMK) was administered intraperitoneally at 1 hour before and 6 hours after SAH. Expression of caspase-3 and positive TUNEL was examined as markers for apoptosis. RESULTS: Apoptosis occurred mostly in cerebral endothelial cells, partially in neurons in the hippocampus, and to a lesser degree in the cerebral cortex. Accordingly, increased BBB permeability and brain water content were observed, accompanied by neurological deficit and a high mortality at 24 hours after SAH. z-VAD-FMK suppressed TUNEL and caspase-3 staining in endothelial cells, decreased caspase-3 activation, reduced BBB permeability, relieved vasospasm, abolished brain edema, and improved neurological outcome. CONCLUSIONS: The major effect of z-VAD-FMK on early brain injury after SAH was probably neurovascular protection of cerebral endothelial cells, which results in less damage on BBB.

Amino Acid Chloromethyl Ketones↗
PubMed2004

Dynamics and scaling in a quantum spin chain material with bond randomness.

Single crystal inelastic neutron scattering is used to study dynamic spin correlations in the quasi-one-dimensional quantum antiferromagnet BaCu2(Si0.5Ge0.5)2O7, where the exchange constant fluctuates due to a random distribution of Si and Ge atoms. The measured low-energy spectrum is dominated by localized excitations and can be understood in the framework of the random singlet model. The observed scaling relations for the frequency dependencies of the correlation length and structure factor are in excellent agreement with recent theoretical predictions for the renormalization group fixed point.

Journal Article↗
PubMed2004

Cooperative ordering of gapped and gapless spin networks in Cu2Fe2Ge4O13.

The unusual magnetic properties of a novel low-dimensional quantum ferrimagnet Cu2Fe2Ge4O13 are studied using bulk methods, neutron diffraction, and inelastic neutron scattering. It is shown that this material can be described in terms of two low-dimensional quantum spin subsystems, one gapped and the other gapless, characterized by two distinct energy scales. Long-range magnetic ordering observed at low temperatures is a cooperative phenomenon caused by weak coupling of these two spin networks.

Journal Article↗
PubMed2004

Pink (P), a new locus responsible for a pink trait in onions (Allium cepa) resulting from natural mutations of anthocyanidin synthase.

A new locus conditioning a pink trait in onions was identified. Unusual pink onions were found in haploid populations induced from an F(1) hybrid between yellow and dark red parents and in F(3) populations originating from the same cross. Segregation ratios of red to pink in F(2), backcross, and F(3) populations indicated that this pink trait is determined by a single recessive locus. RT-PCR was carried out to look for any differential expression of anthocyanin synthesis genes between dark red and pink F(3) lines. The transcript level of anthocyanidin synthase (ANS) was significantly reduced in the pink line. To determine whether this reduced transcription is caused by other regulatory factors or by mutations in the ANS gene itself, ANS gene sequences from both dark red and pink F(3) lines were compared to detect any polymorphisms. Polymorphisms were identified, and subsequently utilized as molecular markers for the selection of ANS alleles. Absolute co-segregation of the pink allele and the ANS allele from the pink line was observed in parents, F(1) and F(3) populations. These results indicate that reduced transcription of the ANS gene caused by mutations in a cis -acting element is likely to result in the pink trait in onions.

Anthocyanins↗
PubMed2004

Electric polarization reversal and memory in a multiferroic material induced by magnetic fields.

Ferroelectric and magnetic materials are a time-honoured subject of study and have led to some of the most important technological advances to date. Magnetism and ferroelectricity are involved with local spins and off-centre structural distortions, respectively. These two seemingly unrelated phenomena can coexist in certain unusual materials, termed multiferroics. Despite the possible coexistence of ferroelectricity and magnetism, a pronounced interplay between these properties has rarely been observed. This has prevented the realization of multiferroic devices offering such functionality. Here, we report a striking interplay between ferroelectricity and magnetism in the multiferroic TbMn2O5, demonstrated by a highly reproducible electric polarization reversal and permanent polarization imprint that are both actuated by an applied magnetic field. Our results point to new device applications such as magnetically recorded ferroelectric memory.

Journal Article↗
PubMed2004

Percolative conduction in the half-metallic-ferromagnetic and ferroelectric mixture of (La, Lu, Sr)MnO3.

The immiscibility between rhombohedral La(5/8)Sr(3/8)MnO3 and hexagonal LuMnO3 leads to a microm-scale heterogeneous mixture of half-metallic-ferromagnetic and insulating-ferroelectric phases. Electronic conduction of the mixture exhibits nearly ideal percolation behavior in the paramagnetic state with a threshold of 0.224(5) metal volume fraction and a resistivity scaling exponent t=2.1+/-0.1, consistent with the predicted universal behavior of classical percolation. However, far below T(C), t increases to 2.4+/-0.1, probably resulting from intergrain tunneling. Therefore, this system represents a unique example of the temperature-induced crossover from universal to nonuniversal behavior of t.

Journal Article↗
PubMed2004

Mechanical response of bovine articular cartilage under dynamic unconfined compression loading at physiological stress levels.

OBJECTIVE: The objective of this study was to characterize the dynamic modulus and compressive strain magnitudes of bovine articular cartilage at physiological compressive stress levels and loading frequencies. DESIGN: Twelve distal femoral cartilage plugs (3mm in diameter) were loaded in a custom apparatus under load control, with a load amplitude up to 40 N and loading frequencies of 0.1, 1, 10 and 40 Hz, resulting in peak Cauchy stress amplitudes of 4.8 MPa (engineering stress 5.7 MPa). RESULTS: The equilibrium Young's modulus under a tare load of 0.4N was 0.49+/-0.10 MPa. In the limit of zero applied stress, the incremental dynamic modulus derived from the slope of the stress-strain curve increased from 14.6+/-6.9 MPa at 0.1 Hz to 28.7+/-7.8 MPa at 40 Hz. At 4 MPa of applied stress, the corresponding increase was from 48.2+/-13.5 MPa at 0.1 Hz to 64.8+/-13.0 MPa at 40 Hz. Peak compressive strain amplitudes varied from 15.8+/-3.4% at 0.1 Hz to 8.7+/-1.8% at 40 Hz. The phase angle decreased from 28.8 degrees +/-6.7 degrees at 0.1 Hz to-0.5 degrees +/-3.8 degrees at 40 Hz. DISCUSSION: These results are representative of the functional properties of articular cartilage under physiological load magnitudes and frequencies. The viscoelasticity and nonlinearity of the tissue helps to maintain the compressive strains below 20% under the physiological compressive stresses achieved in this study. These findings have implications for our understanding of cartilage metabolism and chondrocyte viability under various loading regimes. They also help establish guidelines for cartilage functional tissue engineering studies.

Animals↗
PubMed2004

Quantitative analysis of the viscoelastic properties of thin regions of fibroblasts using atomic force microscopy.

Viscoelasticity of the leading edge, i.e., the lamellipodium, of a cell is the key property for a deeper understanding of the active extension of a cell's leading edge. The fact that the lamellipodium of a cell is very thin (<1000 nm) imparts special challenges for accurate measurements of its viscoelastic behavior. It requires addressing strong substrate effects and comparatively high stresses (>1 kPa) on thin samples. We present the method for an atomic force microscopy-based microrheology that allows us to fully quantify the viscoelastic constants (elastic storage modulus, viscous loss modulus, and the Poisson ratio) of thin areas of a cell (<1000 nm) as well as those of thick areas. We account for substrate effects by applying two different models-a model for well-adhered regions (Chen model) and a model for nonadhered regions (Tu model). This method also provides detailed information about the adhered regions of a cell. The very thin regions relatively near the edge of NIH 3T3 fibroblasts can be identified by the Chen model as strongly adherent with an elastic strength of approximately 1.6 +/- 0.2 kPa and with an experimentally determined Poisson ratio of approximately 0.4 to 0.5. Further from the edge of these cells, the adherence decreases, and the Tu model is effective in evaluating its elastic strength ( approximately 0.6 +/- 0.1 kPa). Thus, our AFM-based microrheology allows us to correlate two key parameters of cell motility by relating elastic strength and the Poisson ratio to the adhesive state of a cell. This frequency-dependent measurement allows for the decomposition of the elastic modulus into loss and storage modulus. Applying this decomposition and Tu's and Chen's finite depth models allow us to obtain viscoelastic signatures in a frequency range from 50 to 300 Hz, showing a rubber plateau-like behavior.

Animals↗
PubMed2004

Lymphocyte recovery as a positive predictor of prolonged survival after autologous peripheral blood stem cell transplantation in T-cell non-Hodgkin's lymphoma.

We performed a retrospective study on recovery and survival of patients with T-cell NHL after autologous peripheral blood stem cell transplantation (APBSCT). Of a total of 39 patients with high-risk T-cell NHL, 33 were analyzed. Six patients who experienced early treatment mortality without full lymphocyte recovery were excluded. We chose absolute lymphocyte count (ALC) recovery as 1000 cells/microl as a cutoff value. ALC recovery day was defined as the first of 3 consecutive days with ALC above 1000 cells/microl. Univariate analysis revealed that age younger than 45 years, good international prognostic index, chemosensitive disease prior to APBSCT, and early ALC recovery (1000 cells/microl within 25 days of APBSCT) were predictors of prolonged survival. Multivariate analyses confirmed that chemosensitive disease prior to APBSCT and early ALC recovery were strongly associated with better overall survival (OS) (P=0.005 and 0.011, respectively) and progression-free survival (PFS) (P<0.001 and P=0.013, respectively). Our finding, that ALC recovery > or =1000 cells/microl is an independent predictor of OS and PFS in T-cell NHL after APBSCT, suggests that earlier immune recovery may contribute to longer survival.

Adolescent↗
PubMed2004

Response to antiviral treatment in hepatitis C virus-associated marginal zone lymphomas.

A link between chronic hepatitis C virus (HCV) infection and low-grade B-cell lymphomas has been suggested by epidemiological studies. Marginal zone lymphomas (MZLs) including splenic lymphomas with villous lymphocytes are among the most frequently reported subgroups in the setting of chronic HCV infection. In this study, we examined the effect of antiviral treatment in eight patients with HCV-associated MZL. We found that five out of eight patients have responded to interferon alpha and ribavirin. In some cases, hematologic responses were correlated to virologic responses. In addition, we report a case of large granular lymphocyte leukemia occurring in association with MZL and HCV, and responding to interferon and ribavirin. We suggest that there is an etiologic link between HCV and antigen-driven lymphoproliferative disorders.

Adult↗