Biomedical subjects

Hyeon Joo Kim

Publications and source records attributed to Hyeon Joo Kim.

9 recordsLinked to original sources

PubMed2006

Electrospun silk-BMP-2 scaffolds for bone tissue engineering.

Silk fibroin fiber scaffolds containing bone morphogenetic protein 2 (BMP-2) and/or nanoparticles of hydroxyapatite (nHAP) prepared via electrospinning were used for in vitro bone formation from human bone marrow-derived mesenchymal stem cells (hMSCs). BMP-2 survived the aqueous-based electrospinnig process in bioactive form. hMSCs were cultured for up to 31 days under static conditions in osteogenic media on the scaffolds (silk/PEO/BMP-2, silk/PEO/nHAP, silk/PEO/nHAP/BMP-2) and controls (silk/PEO, silk/PEO extracted). Electrospun silk fibroin-based scaffolds supported hMSC growth and differentiation toward osteogenic outcomes. The scaffolds with the co-processed BMP-2 supported higher calcium deposition and enhanced transcript levels of bone-specific markers than in the controls, indicating that these nanofibrous electrospun silk scaffolds were an efficient delivery system for BMP-2. X-ray diffraction (XRD) analysis revealed that the apatite formed on the silk fibroin/BMP-2 scaffolds had higher crystallinity than on the silk fibroin scaffold controls. In addition, nHAP particles were incorporated into the electrospun fibrous scaffolds during processing and improved bone formation. The coexistence of BMP-2 and nHAP in the electrospun silk fibroin fibers resulted in the highest calcium deposition and upregulation of BMP-2 transcript levels when compared with the other systems. The results suggest that electrospun silk-fibroin-based scaffolds are potential candidates for bone tissue engineering. Furthermore, the mild aqueous process required to spin the fibers offers an important option for delivery of labile cytokines and other components into the system.

Adult↗

PubMed2005

Biomaterial coatings by stepwise deposition of silk fibroin.

A completely aqueous, stepwise deposition process with Bombyx mori silk fibroin for the assembly of nanoscale thin film coatings is reported the first time. The focus of this work was to develop an understanding of the control of this deposition process and to characterize the films formed from a physicochemical perspective. The deposition process was monitored by UV spectrophotometry and research quartz crystal microbalance. Both absorbance and film thickness correlated linearly with the number of silk fibroin layers deposited, analogous to multilayered materials fabricated from conventional polyelectrolytes. The polymer adsorption process was stable and reproducible, with control of a single layer thickness ranging from a few to tens of nanometers, determined by the concentrations of silk fibroin, salt concentration in the dipping solution, and method of rinsing. The driving force for the assembly of silk fibroin onto the substrate was primarily hydrophobic interactions, while some electrostatic interactions were also involved. The difference with this approach from traditional polyelectrolyte layer-by-layer techniques is that an intervening drying step is used to control the structure and stability of the self-assembled silk fibroin. The assembled films were stable under physiological conditions and supported human bone marrow stem cell adhesion, growth, and differentiation. This approach offers new options to engineer biomaterial coatings as well as bulk materials with control of both interfacial properties conducive to specific cellular or tissue responses and the potential to entrap and deliver labile molecules or other components due to the all-aqueous process described.

Bone Marrow Cells↗

PubMed2005

Three-dimensional aqueous-derived biomaterial scaffolds from silk fibroin.

A new all-aqueous process is described to form three-dimensional porous silk fibroin matrices with control of structural and morphological features. The result of this process are scaffolds with controllable porosity and pore sizes that fully degrade in the presence of proteases, unlike prior methods to generate silk-based biomaterials that required the use of organic solvent treatments to impart control of structure and stability in aqueous environments, with low rates of proteolytic hydrolysis. A mechanism is proposed for this novel process that imparts physical stability via hydrophobic interactions. Adjusting the concentration of silk fibroin in water, and the particle size of granular NaCl used in the process, leads to the control of morphological and functional properties of the scaffolds. The aqueous-derived scaffolds had highly homogeneous and interconnected pores with pore sizes ranging from 470 to 940 microm, depending on the mode of preparation. The scaffolds had porosities >90% and compressive strength and modulus up to 320 +/- 10 and 3330 +/- 500 KPa, respectively, when formed from 10% aqueous solutions of fibroin. The scaffolds fully degraded upon exposure to protease during 21 days, unlike the scaffolds prepared from organic solvent processing. These new silk-based three-dimensional matrices provide useful properties as biomaterial matrices due to the all-aqueous mode of preparation, control of pore size, connectivity of pores, degradability and useful mechanical features. Importantly, this process offers an entirely new window of materials properties when compared with traditional silk fibroin-based materials.

Absorbable Implants↗

PubMed2005

Influence of macroporous protein scaffolds on bone tissue engineering from bone marrow stem cells.

The aim of this study was to investigate the effect of three-dimensional silk fibroin scaffold preparation methods (aqueous and solvent) on osteogenic responses by human bone marrow stem cells (hMSCs). Macroporous 3D protein scaffolds with similar sized pores of 900+/-50 microm were prepared either by an organic solvent process (hexafluoro-2-propanol, HFIP) or an aqueous process. hMSCs were expanded, seeded on the scaffolds, and cultured up to 28 days under static conditions in osteogenic media. hMSCs seeded onto the water-based silk scaffolds showed a significant increase in cell numbers (p<0.01) vs. the HFIP-prepared silk scaffolds. Significantly higher (p<0.01) alkaline phosphatase (ALPase) activity and calcium deposition were apparent after 28 days of culture in the water-based silk scaffolds when compared to the HFIP-derived silk scaffolds. Transcript levels for collagen type I (Col I), ALP, and osteopontin (OP) increased (p<0.05) in the water-based silk scaffolds in comparison to the HFIP-derived materials. At early stages of culture, increased expression of OP and collagen type II (Col II) were also observed in both scaffolds. Expression of Col II, MMP 13, Col I, and OP proteins increased in the water-based silk scaffolds in comparison to the HFIP-derived scaffolds while bone sialoprotein (BSP) proteins increased in the HFIP-derived silk scaffolds in comparison to the water-based scaffolds after 28 days of culture. Histological analysis showed the development of bone-like trabeculae with cuboid cells in an extracellular matrix (ECM) in the water-based silk scaffolds with more organization than in the HFIP-derived material after 28 days of culture. Alcian blue staining demonstrated the presence of proteoglycan in the ECM formed in the water-based scaffolds but not in the HFIP-prepared silk scaffolds. The results suggest that macroporous 3D aqueous-derived silk fibroin scaffolds provide improved bone-related outcomes in comparison to the HFIP-derived systems. These data illustrate the importance of materials processing on biological outcomes, as the same protein, silk fibroin, was used in both preparations.

Bone Substitutes↗

PubMed2005

Potential predictive markers for proliferative capacity of cultured human articular chondrocytes: PCNA and p21.

The purpose of this study was to investigate age-related changes in the proliferative ability of human articular chondrocytes in culture. In addition, the possible markers for the proliferative capacity of chondrocytes were examined. Chondrocytes obtained from human articular cartilages of young (under 40 years) or old (over 60 years) individuals were expanded until their growth was arrested. The number of cells and the type II collagen phenotype were determined together with the expression levels of proliferating cell nuclear antigen (PCNA) and p21(WAF1/CIP) along with the passages of cultured chondrocytes. The results showed that young chondrocytes had higher proliferative capacity and viability than old chondrocytes. The growth arrest and the cessation in the expression of type II collagen were accompanied by down-regulation of PCNA and up-regulation of p21(WAF1/CIP) levels in both young and old chondrocytes. Notably, the expression levels of PCNA and p21(WAF1/CIP) along with the passages were correlated inversely to each other and showed distinct patterns between young and old chondrocytes. These results suggest that senescence of human articular chondrocytes leads to the decrease in the proliferative capacity and phenotypic stability. In addition, PCNA and p21 could be molecular markers that represent the status of these age-related properties of human articular chondrocytes in vitro.

Adult↗

PubMed2002

Lateral decubitus HRCT: a simple technique to replace expiratory CT in children with air trapping.

OBJECTIVE: To evaluate the effectiveness of lateral decubitus high-resolution CT (HRCT) in detecting air trapping in children. MATERIALS AND METHODS: HRCT scans of 21 children with heterogeneous lung attenuation caused by air trapping (n = 10) or with infiltrative lung disease (n = 11) were reviewed retrospectively. The air-trapping disease included bronchiolitis obliterans (n = 7), bronchial obstruction due to mediastinal lymphoma (n = 1), endobronchial haemangioma (n = 1) and foreign body aspiration (n = 1). HRCT was performed in both lateral decubitus positions as well as the supine position. The attenuation (Hounsfield units; HU) was measured in both the hypo- and adjacent hyper-attenuating areas of the heterogeneous lung portion, and the difference of attenuation between these two areas was calculated in the supine and both lateral decubitus scans, respectively. The attenuation differences of the three scans were compared in each group. RESULTS: The attenuation difference was larger in the ipsilateral decubitus (207.95 +/- 105.24 HU) scans than in the contralateral (121.25 +/- 90.05 HU) or supine (162 +/- 94.01 HU) scans in the air-trapping group (P < 0.05). There were no significant differences among the three scans in the infiltrative lung disease group (P > 0.05). CONCLUSIONS: Lateral decubitus HRCT is an effective adjunct to standard HRCT in the evaluation of air trapping as a cause of mosaic lung attenuation in uncooperative paediatric patients.

Airway Obstruction↗

PubMed2002

Characterization of subpopulated articular chondrocytes separated by Percoll density gradient.

The aim of this study was to develop a method for fractionation of articular chondrocytes from the entire thickness of the tissue. Isolated chondrocytes from rabbit articular cartilage fractionated by centrifugation in a discontinuous Percoll gradient resulted in four cell fractions with two differing properties. The lowest-density fraction consisted mainly of large cells with small nuclei proliferated actively, maintained the chondrocytic phenotype, and secreted larger amounts of proteoglycan. In contrast, the highest-density fraction consisted of small cells with large nuclei proliferated slowly, did not express the chondrocytic phenotype, and produced larger amounts of interleukin 1-induced nitric oxide. Comparing our results with other previous reports, we find that fraction 1 cells are likely originated from the deep layer of the articular cartilage, whereas fraction 4 cells are tentatively categorized as chondrocytes from the superficial layer of cartilage. Centrifugal fractionation of articular chondrocytes via Percoll density gradient permits clear separation of these heterogeneous cells into different phenotypic populations and allows distinguishing of cells from the different layers of articular cartilage. This simple novel method will provide ready separation of articular chondrocytes for the investigation of the pathogenesis of articular cartilage.

Alkaline Phosphatase↗

PubMed2002

Diverse vacA allelic types of Helicobacter pylori in Korea and clinical correlation.

Helicobacter pylori has a diversity of vacA allelic types. The purpose of this study was to correlate the vacA status and the clinical outcome. After constructing specific primers for the vacA signal sequence, H. pylori-positive antral biopsy specimens were examined for the vacA status in 25 gastric ulcers, 31 duodenal ulcers, 22 gastric cancers, 42 chronic gastritis, and 8 gastroduodenal ulcers. The relationship between the vacA allele and the clinical disease was examined. The vacA genotype s1c/m1 is predominant in Korea (71/128, 55.5%). Other strains including s1b or s2 were not found in this study. s1c/m1 was more prominent in duodenal ulcers, than in gastric ulcers (p=0.041) and cancer (p=0.029). Seven out of 8 patients with gastric and coexistent duodenal ulcers had the s1c/m1 allele. No statistical differences in the positive rates of the s1a/m1, s1a/m2, and s1c/m2 alleles among the disease groups were found. In conclusion, s1c/m1 is the main vacA allele in Korea and it is particularly associated with duodenal ulcers.

Adolescent↗

PubMedDate not supplied

Fixation methods for implantable port chamber: comparative study using glue, self-stabilizing leg and suture fixations in rabbits.

OBJECTIVE: To evaluate the fixation strength and tissue reaction of the glue fixation and self-stabilizing leg fixation methods and to compare the results with those of the conventional tagging suture fixation method. MATERIALS AND METHODS: Twelve healthy rabbits were selected and three different methods of implanting the port chamber were employed on the back of each rabbit. A total of thirty six port chambers were implanted with these three different methods, viz. the glue fixation method using tissue adhesive, the self-stabilizing leg method using a self-expandable stabilizing leg, and the suture fixation method. The fixation strength and the gross and histopathologic changes of each fixation method were evaluated at three days, one week, two weeks and four weeks after port implantation. RESULTS: The glue fixation method showed a good fixation strength, which was similar to that of the tagging suture method (p = 0.3486). Five of the six ports (83%) implanted with the glue fixation method which were examined after two weeks showed cracks on the external surface, but this had no adverse effects on their function. A large amount of granulation tissue reaction was found at the bottom of the chamber (p = 0.0025). The fixation with the self-stabilizing leg showed relatively lower fixation strength (p = 0.0043), but no turning-over of the chamber occurred. The fixation strength improved with time after the first week, and minimal granulation tissue reaction was observed with this method. CONCLUSION: The glue fixation method exhibited equal fixation strength compared to the suture fixation, but showed cracking and a large amount of granulation tissue, whereas the fixation with a self-stabilizing leg showed weaker fixation strength.

Alloys↗