Biomedical subjects

Young Ha Kim

Publications and source records attributed to Young Ha Kim.

27 records · Page 2Linked to original sources

PubMed2003

In vivo conjunctival reconstruction using modified PLGA grafts for decreased scar formation and contraction.

The in vivo reconstruction of conjunctiva was investigated by using modified poly(lactide-co-glycolide) (PLGA) 50/50 scaffolds. The porous PLGA matrices were prepared by a solvent-casting particulate-leaching method with NaCl, then modified with collagen, hyaluronic acid (HA) or/and human amniotic membrane (AM) component. The growth of corneal epithelial cells and human stromal fibroblasts on the scaffolds was investigated in vitro. All the modified PLGA scaffolds demonstrated enhanced cell adhesion and proliferation as compared to PLGA untreated, and the number of cells proliferated after 1 week was increased in the order of PLGA<PLGA/collagen=PLGA/collagen/AM<PLGA/collagen/HA=PLGA/collagen/AM/HA, which was the same order as the adhesion of the cells onto the surfaces. Conjunctival wounds were created on the eyes of white rabbits bilaterally and PLGA/collagen/HA scaffolds were grafted for 4 weeks to evaluate the regeneration of ocular surface tissue at the wounds. At postoperative 4 weeks, all the wounds were completely covered with epithelial membranes. However, the contraction was minimal (6%) in the wound grafted with the modified PLGA, while that of the ungrafted wound was substantially large (25%). In addition, the collagen fibers regenerated within the scaffolds were characterized by a random array of a loose network that resembled natural conjunctiva. On the contrary, an aligned array of dense collagen fibers formed in the ungrafted wounds. Our results indicated that the modified PLGA graft as an acellular bed might allow the reconstruction of the damaged conjunctival tissue with less scar formation and contraction.

Animals↗

PubMed2003

Development and evaluation of an automated stainer for acid-fast bacilli.

The current strategy for the control of tuberculosis (TB) relies on early diagnosis, and smear microscopy is an essential component of the laboratory diagnosis of TB in most countries with a high prevalence of the disease. However, even simple smear microscopy examination is far from satisfactory because staining results can vary among individual technicians. In an effort to minimize variations in manual staining procedures, we developed an automated stainer for AFB and evaluated its usefulness in comparison with manual staining. The key feature of our automated stainer is a heating apparatus required for fixation and carbol-fuchsin staining. After smear slides are placed into the machine, the entire staining process is fully automated, from fixation to final washing and drying. With the automated methods, five slides can be fixed and stained in 21 min at consistent high quality. Using sputum samples from 91 TB patients, the staining results of the automated stainer were compared blindly with those of manual staining. The concordance rate between the two methods was 94.5%. In addition, there was no significant difference in the rate of detection of AFB in the sputum samples. Although further optimization of the auto staining procedures is required, the results indicate that the automated AFB stainer developed in this study looks promising for use in clinical mycobacteriology laboratory in order to minimize personal variation during AFB staining.

Equipment Design↗

PubMed2002

Anticoagulant activity of sulfonated polyrotaxanes as blood-compatible materials.

Polyrotaxanes, in which alpha-cyclodextrins (alpha-CDs) are threaded onto poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) triblock copolymers (Pluronic) capped with benzyloxycarbonyl(Z)-L-phenylalanine (Z-L-Phe), were prepared, and sulfopropyl groups were introduced to hydroxyl groups of alpha-CDs in the polyrotaxanes. The supramolecular structure and the chemical composition of the polyrotaxanes after the sulfonation were confirmed by 1H-NMR, 13C-NMR, and elemental analysis. Anticoagulant activity of the polyrotaxanes and sulfonated polyrotaxanes was measured by activated partial thromboplastin time (APTT). It was found that the polyrotaxanes and the sulfonated polyrotaxanes showed greater anticoagulant activity than Pluronic itself, suggesting that both the supramolecular structure of the polyrotaxanes and the sulfonated groups contribute to the inhibition of intrinsic coagulation factors. Finally, our designed polyrotaxanes are suggested to be a promising candidate when fabricating blood-compatible medical devices by blending with or coating on clinically used polymers.

Anticoagulants↗

PubMed2002

Effects of organic matrix proteins on the interfacial structure at the bone-biocompatible nacre interface in vitro.

The biocompatibility and potential osteoinductivity of nacre have favored its use as a bone-grafting material. The present study is to investigate the interfacial structure at the bone-nacre interface resulting from organic matrix proteins, which emphasizes the mechanism of bone-bonding ability and biocompatibility of the shell tissues such as nacre and biogenic calcite. To understand the interfacial reaction, the zeta potential measurements, provide for a unique method to quantify the actual state of the interface in situ, were used for synthetic and biogenic calcium carbonate suspensions with respect to pH and the organic matrix as an additive. The zeta potentials and surface charge density show that the organic matrix proteins are main charge regulators, resulting in the stabilized tissue properties as compared with synthetic crystals. Also, in forming calcium carbonate crystals with the additives, the conformation of organic matrix has an important role in the understanding of the newly formed interfacial structure. The result provides the primary role of the organic matrix proteins in controlling the formation of interfacial structure and biocompatibility with bone as well as the stability of biogenic tissues. And it gives a new insight into the usefulness of zeta potential measurement to describe the in vivo interaction between the bone and implants.

Adsorption↗

PubMed2002

Fibroblast adhesion and proliferation on poly(ethylene glycol) hydrogels crosslinked by hydrolyzable polyrotaxane.

Fibroblast culture was performed to evaluate cell adhesion and proliferation on poly(ethylene glycol) (PEG) hydrogels crosslinked by a hydrolyzable polyrotaxane. The polyrotaxane consisting of alpha-cyclodextrins (alpha-CDs) and PEG terminated by benzyloxycarbonyl (Z)-L-phenylalanine (L-Phe) via ester linkage was used as a multi-functional crosslinker in the PEG hydrogels. From the results of contact angle and small angle light scattering measurements, it was suggested that the surface and bulk structure of the PEG hydrogels were heterogeneous. Fibroblast adhesion and proliferation on the hydrogels was observed. The number of fibroblast adhesion on the hydrogels crosslinked by the polyrotaxane was proportional to contact angle values and correlation length, and was significantly higher than those crosslinked by alpha-CDs in spite of similar contact angle and correlation length. These findings suggest that the cells recognize the surface heterogeneity due to the polyrotaxane structure, and the number of cell adhesion and proliferation is controllable by the polyrotaxane content in feed.

3T3 Cells↗

PubMed2002

Improved blood compatibility and decreased VSMC proliferation of surface-modified metal grafted with sulfonated PEG or heparin.

Although the technique of coronary stenting has remarkably improved long-term results in recent years, (sub)acute thrombosis and late restenosis still remain problems to be solved. Metallic surfaces were regarded as thrombogenic, due to their positive surface charges, and stenosis resulted from the activation and proliferation of vascular smooth muscle cells (VSMCs). In this study, a unique surface modification method for metallic surfaces was studied using a self-assembled monolayer (SAM) technique. The method included the deposition of thin gold layers, the chemisorption of disulfides containing functional groups, and the subsequent coupling of PEG derivatives or heparin utilizing the functional groups of the disulfides. All the reactions were confirmed by ATR-FTIR and XPS. The surface modified with sulfonated PEG (Au-S-PEG-SO3) or heparinized PEG (Au-S-PEG-Hep) exhibited decreased static contact angles and therefore increased hydrophilicity to a great extent, which resulted from the coupling of PEG and the ionic groups attached. In vitro fibrinogen adsorption and platelet adhesion onto the Au-S-PEG-SO3 or Au-S-PEG-Hep surfaces decreased to a great extent, indicating enhanced blood compatibility. This decreased interaction of the modified surfaces should be attributed to the non-adhesive property of PEG and the synergistic effect of sulfonated PEG. The effect of the surface modification on the adhesion and proliferation of VSMCs was also investigated. The modified Au-S-PEG-SO3 or Au-S-PEG-Hep surfaces also exhibited decreased adhesion of VSMCs, while the deposited gold layer itself was effective. The enhanced blood compatibility and the decreased adhesion of VSMCs on the modified metallic surfaces may help to decrease thrombus formation and suppress restenosis. It would therefore be very useful to apply these modified surfaces to stents for improved functions. A long-term in vivo study using animal models is currently under way.

Animals↗

PubMedDate not supplied

Heparin conjugated polylactide as a blood compatible material.

A heparin-conjugated biodegradable polymer (PLA-heparin) by the direct coupling of heparin to polylactide (PLA) was synthesized and characterized. The surface exposed heparin content associated PLA-heparin was measured to be 0.067 microg/cm2. PLA-heparin coated surface has shown higher hydrophilicity rather than control PLA surface. The clotting time of PLA-heparin conjugate measured by activated partial thromboplastin time (APTT) was significantly prolonged as compared to PLA. The bioactivity of bound heparin measured by APTT corresponds to 17.4% of free heparin. It has been also demonstrated that the conjugation of heparin suppresses the protein adsorption as well as the platelet adhesion. These results indicate that the unique property of bound heparin has an inhibiting influence on the coagulation, plasma protein adsorption, and subsequent platelet adhesion systems. This novel PLA-heparin conjugate could be applied as blood/tissue compatible biodegradable materials for implantable medical devices and tissue engineering.

Biocompatible Materials↗

PubMedDate not supplied

Morphology of elastic poly(L-lactide-co-epsilon-caprolactone) copolymers and in vitro and in vivo degradation behavior of their scaffolds.

Very elastic PLCL [poly(L-lactide-co-epsilon-caprolactone), 50:50] copolymers were synthesized and extruded into porous tubular scaffolds (pore size 150 +/- 50 microm, porosity 90%) for the application to tissue engineering. The copolymers were basically random and amorphous. However, two T(g)'s (glass transition temperatures) were observed in dynamic mechanical thermal analysis and also in differential scanning calorimetry thermograms. Furthermore, microdomains (about 17 nm in size) were indicated on the small-angle X-ray scattering profile and finally confirmed by transmission electron microscopy. Therefore, the PLCL copolymer was probably composed of a soft matrix of mainly epsilon-caprolactone moieties and hard domains containing more L-lactide units to exhibit a rubberlike elasticity in virtue of the physically cross-linked structure. The smooth muscle cells seeded scaffolds were implanted into nude mice subcutaneously for up to 15 weeks to monitor the in vivo degradation. In addition, they were degraded in vitro in phosphate buffer solution (pH 7.4) for up to 1 year to compare the results each other. All the scaffolds degraded slowly in vivo and in vitro even in the form of a highly porous thin membrane. However, the degradation rate was somewhat faster for in vivo than for in vitro. This should be explained by enzymes that might have played a certain role in the degradation in the body. In addition, the epsilon-caprolactone moieties degraded faster than the L-lactide units did in these PLCL scaffolds, although their hydrophilicities are in the opposite order. This behavior appeared more prominently in the in vivo case. This should result from that the amorphous regions composed of mainly epsilon-caprolactone units might have been first attacked by water because water can penetrate into the amorphous regions easier than the hard domains containing more L-lactides.

Animals↗

PubMedDate not supplied

The extract of the flowers of Prunus persica, a new cosmetic ingredient, protects against solar ultraviolet-induced skin damage in vivo.

The flowers of Prunus persica Batsch have been used for skin disorders in East Asia from ancient times. In this investigation, the ethanol extract from this plant material was prepared and several major constituents were isolated. In addition, the protective effects of the extract were evaluated against solar ultraviolet (UV)-induced skin damage using in vivo animal models of UVB-induced erythema in guinea pigs and ear edema in ICR mice. From the extract, four kaempferol glycoside derivatives were successfully isolated and their contents were measured with HPLC. Among the derivatives isolated, the content of multiflorin B was highest (3.3%, w/w). The P. persica extract clearly inhibited UVB-induced erythema formation dose dependently when topically applied (IC(50) = 0.5 mg/cm(2)). It also inhibited UVB-induced ear edema (49% inhibition at 3.0 mg/ear). Moreover, multiflorin B inhibited UVB-induced erythema formation (80% inhibition at 0.3 mg/cm(2)), indicating that this compound is one of the active principles of the extract. All these results suggest that P. persica extract may be useful for protection against UVB-induced skin damage when topically applied.

Animals↗