Kyobum Kim

Effects of Immobilized BMP-2 and Nanofiber Morphology on In Vitro Osteogenic Differentiation of hMSCs and In Vivo Collagen Assembly of Regenerated Bone

Engineering bone tissue is particularly challenging because of the distinctive structural features of bone within a complex biochemical environment. In the present study, we fabricated poly(L-lactic acid) (PLLA) electrospun nanofibers with random and aligned morphology immobilized with bone morphogenic protein-2 (BMP-2) and investigated how these signals modulate (1) in vitro osteogenic differentiation of human mesenchymal stem cells (hMSCs) and (2) in vivo bone growth rate, mechanical properties, and collagen assembly of newly formed bone. The orientation of adherent cells followed the underlying nanofiber morphology; however, nanofiber alignment did not show any difference in alkaline phosphate activity or in calcium mineralization of hMSCs after 14 days of in vitro culture in osteogenic differentiation media. In vivo bone regeneration was significantly higher in the nanofiber implanted groups (approximately 65-79%) as compared to the defect-only group (11.8 ± 0.2%), while no significant difference in bone regeneration was observed between random and aligned groups. However, nanoindentation studies of regenerated bone revealed Youngs modulus and contact hardness with anisotropic feature for aligned group as compared to random group. More importantly, structural analysis of collagen at de novo bone showed the ability of nanofiber morphology to guide collagen deposition. SEM and TEM images revealed regular, highly ordered collagen assemblies on aligned nanofibers as compared to random fibers, which showed irregular, randomly organized collagen deposition. Taken together, we conclude that nanofibers in the presence of osteoinductive signals are a potent tool for bone regeneration, and nanofiber alignment can be used for engineering bone tissues with structurally assembled collagen fibers with defined direction.

Transcriptome response of the Pacific oyster, Crassostrea gigas susceptible to thermal stress: A comparison with the response of tolerant oyster

Although oysters are exposed to seasonal temperature changes, they are frequently subjected to acute temperature stress during emersion due to their attachment on their rocky shore habitats. To understand the effect of acute temperature elevation on the whole transcriptome of susceptible Pacific oyster Crassostrea gigas over time, the oysters were exposed to temperatures ranging from the control 20°C to 32°C for 72 h. We compared the genome-wide patterns of mRNA expression of susceptible oysters with those obtained from thermotolerant oysters. RNA-seq identified differentially expressed stress responsive Gene Ontology (GO) terms and relevant transcripts following acute thermal stress. The clearest pattern between susceptible and tolerant oysters was the dramatic differences in transcriptional expression in the hsp70 gene family. GO terms and genes typically associated with oxygen binding were also repressed compared to those of tolerant oysters. This study provides insights into the significant differences in molecular response of susceptible C. gigas to acute heat stress, and the will further our understanding of the basis of molecular adaptation in the Pacific oyster.

Cytotoxicity of Gallium–Indium Liquid Metal in an Aqueous Environment

Eutectic gallium-indium alloy (EGaIn) liquid metal is highly conductive, moldable, and extremely deformable and has attracted significant attention for many applications, ranging from stretchable electronics to drug delivery. Even though EGaIn liquid metal is generally known to have low toxicity, the toxicity of the metal, rather than a salt form of Ga or In, has not been systematically studied yet. In this paper, we investigate the time-dependent concentration of the ions released from EGaIn liquid metal in an aqueous environment and their cytotoxicity to human cells. It is observed that only the Ga ion is dominantly released from EGaIn when no external agitation is applied, whereas the concentration of the In ion drastically increases with sonication. The cytotoxicity study reveals that all human cells tested are viable in the growth media with naturally released EGaIn ions, but the cytotoxicity becomes significant with sonication-induced EGaIn releasates. On the basis of the comparative study with other representative toxic elements, that is, Hg and Cd, it could be concluded that EGaIn is reasonably safe to use in an aqueous environment; however, it should be cautiously handled when any mechanical agitation is applied.

Overview of current standpoints in profiling of circulating tumor cells

The goal of this review is summarizing current technologies developed as the in vitro prognostic/diagnostic systems that can rapidly separate and detect circulating tumor cells (CTCs) from cancer patient’s blood (1–10 CTCs of 1 billion red blood cells) by labeled and non-labeled method. The review is focused on three major areas of CTC research (1) Summary of previous research on capturing of CTCs, (2) New development of the in vitro prognostic diagnosis system of cancer that is capable of rapid separation of CTCs, (3) Future direction on development of new technologies for CTC profiling. Current CTC researches have helped on identifying patients who may benefit from chemotherapy before treatment, patients who may benefit from continued chemotherapy, and leading to clinical development of CTC-guided chemotherapy strategies. We analyze the feasibility of clinical application of these current CTC research for the ultimate goal of increasing the survivability of cancer patient. The biomolecular assays of viable CTCs from cancer patient may elucidate the mechanism of metastasis and tumor initiating cells and also may have high impact on the development of personalized medicine to overcome the incurable diseases.

Bone morphogenetic protein-2 associated multiple growth factor delivery for bone tissue regeneration

Administration of growth factors (GFs) and cytokines to damaged bone tissue for the purpose of bone tissue regeneration has been investigated. Among GFs and cytokines, bone morphogenetic protein-2 (BMP-2) is one of the most important stimulatory factors for enhancing the osteoblastic differentiation of progenitor cells and promoting bone formation. Co-delivery of other GFs, including vascular endothelial growth factor, fibroblast growth factor, insulin-like growth factor, and stromal cell-derived factor, with BMP-2 is known to facilitate repair and remodeling of damaged bone tissue. These GFs stimulate various cellular activities, including angiogenesis, migration, proliferation, regulation of proteoglycan level, and stem cell recruitment. Although bone repair and regeneration are dynamic and complex physiological processes involving multiple cell types and cytokines in timed healing cascade stages, BMP-2-associated delivery of dual and/or multiple GFs could promote bone tissue regeneration based on the synergistic effects of GFs compared with single GF treatment. Current engineering approaches emphasize the importance of design parameters for GF delivery systems, such as optimization of the release profiles, stabilities, and bioactivities of cargo GFs, and the physico-chemical properties of scaffold/hydrogel materials. Therefore, this review summarizes BMP-2-associated GF combinations, biological functions, and current delivery strategies utilized in bone tissue engineering for the development of feasible clinical applications.

Perspectives on the nanotechnology applications of for the analytical detection of heavy metals in marine organisms

Heavy metals accumulate in organisms throughout the food chain and eventually end up in humans. Heavy metals can cause severe diseases and may even result in death. Therefore, concerns about heavy metal accumulation in marine organisms have increased in recent years. To determine solutions to this concern, the sensitive detection of heavy metals in marine organisms is required. Current detection techniques for heavy metals present in marine organisms have several limitations, such as complicated pre-treatment steps and a lengthy analysis time. Thus, there are increasing needs for the newly developed methods of detecting heavy metals in marine organisms. In this review, we focus here on (1) the current detection techniques available and (2) the application of newly emergent nanotechnology for the sensitive detection of heavy metals in marine organisms.

Engineered Co-culture Strategies Using Stem Cells for Facilitated Chondrogenic Differentiation and Cartilage Repair

Osteoarthritis (OA) is a chronic disease in elders and athletes due to limited regenerative capacities of cartilage tissues and subsequently insufficient recovery of damaged sites. Recent clinical treatments for OA have utilized progenitor cell-based therapies for cartilage tissue regeneration. Administration of a single type of cell population such as stem cells or chondrocytes does not guarantee a full recovery of cartilage defects. Therefore, current tissue engineering approaches using co-culture techniques have been developed to mimic complex and dynamic cellular interactions in native cartilage tissues and facilitate changes in cellular phenotypes into chondrogenesis. Therefore, this paper introduces recently developed co-culture systems using two major cell populations, mesenchymal stem cells (MSCs) and chondrocytes. Specifically, a series of examples to describe (1) synergistic in vitro activations of MSCs by paracrine signaling molecules from adult chondrocytes in co-culture systems and (2) functional in vivo tissue regeneration via co-administration of both cell types were reviewed. Based on these findings, it could be speculated that engineered co-culture systems using MSC/ chondrocyte is a promising and feasible cell-based OA therapy in clinical aspects.

Enhanced Skull Bone Regeneration by Sustained Release of BMP-2 in Interpenetrating Composite Hydrogels

Direct administration of bone morphogenetic protein-2 (BMP-2) for bone regeneration could cause various clinical side effects such as osteoclast activation, inflammation, adipogenesis, and bone cyst formation. In this study, thiolated gelatin/poly(ethylene glycol) diacrylate (PEGDA) interpenetrating (IPN) composite hydrogels were developed for guided skull bone regeneration. To promote bone regeneration, either polycation-based coacervates (Coa) or gelatin microparticles (GMPs) were incorporated within IPN gels as BMP-2 carriers. Both BMP-2 loaded Coa and BMP-2 loaded GMPs showed significantly enhanced in vitro alkaline phosphate (ALP) activity of human mesenchymal stem cells (hMSCs) than non-BMP-2 treated control. Moreover, BMP-2 loaded GMPs group exhibited statistically increased ALP activity compared to both bolus BMP-2 administration and BMP-2 loaded Coa group, indicating that our carriers could protect and maintain biological activity of cargo BMP-2. Sustained release kinetics of BMP-2 from IPN composite hydrogels could be controlled by different formulations. For in vivo bone regeneration, various IPN gel formulations (i.e., (1) control, (2) only hydrogel, (3) hydrogel with bolus BMP-2, (4) hydrogel with BMP-2-loaded Coa, and (5) hydrogel with BMP-2-loaded GMPs) were bilaterally implanted into 5 mm-sized rat calvarial defects. After 4 weeks, micro-CT and histological analysis were performed to evaluate new bone formation. Significantly higher scores for bony bridging and union were observed in BMP-2-loaded Coa and BMP-2-loaded GMP groups as compared to other formulations. In addition, rats treated with BMP-2-loaded GMPs showed a significantly higher ratio of bone volume/total volume and lower trabecular separation scores than others. Finally, rats treated with either Coa or GMP groups exhibited a significant increase in bone formation area, as assessed via histomorphometric analysis. Taken together, it could be concluded that Coa and GMPs were effective carriers to maintain the bioactivity of cargo BMP-2 during its sustained release. Consequently, our IPN composite hydrogel system that combines such BMP-2 carriers could effectively promote skull bone regeneration.

Development of Folate-Thioglycolate-Gold Nanoconjugates by Using Citric Acid-PEG Branched Polymer for Inhibition of MCF-7 Cancer Cell Proliferation

Development of folate (FA)-functionalized gold nanoparticles (AuNPs) has greatly increased in recent years due to their potential in cancer treatment. As surface functionalization of polymer-free AuNPs with thiol groups could result in agglomeration and precipitation, AuNPs should be stabilized with an efficient polymer. In this study, citric acid-PEG branched polymer (CPEG) acted as a reducing as well as stabilizing agent in the synthesis of AuNPs. The thiol group of thioglycolic acid (TGA) attached to CPEG-stabilized AuNPs and interacted with the free carboxylic acid group on the surface of TGA-AuNP nanoconjugates. Stable TGA-AuNP nanoconjugates were obtained only with CPEG-stabilized AuNPs and not with citrate-stabilized AuNPs. The carboxylic acid group on the surface of AuNPs was used to attach FA via an EDC/NHS coupling reaction to obtain FA-TGA-AuNP nanoconjugates. In vitro cytotoxicity studies indicated that FA-TGA-AuNPs were not toxic to normal cells up to a concentration of 200 μg/mL. However, FA-TGA-AuNP nanoconjugates effectively inhibited proliferation of MCF-7 cancer cells at a low concentration of 25 μg/mL after 3 days of incubation. The anticancer activity of FA-TGA-AuNPs was enhanced by incorporating the anticancer drug 5-fluorouracil into the nanoconjugates, which exhibited sustained drug release up to 5 days. Hence, the developed biocompatible FA-TGA-AuNPs could be used for specific killing of breast cancer cells.

Multiple growth factor delivery for skin tissue engineering applications

Administration of exogenous growth factors (GFs) to a damaged site has been investigated for skin tissue regeneration. Among the many types of GFs and cytokines, epidermal growth factor, vascular endothelial growth factor, platelet-derived growth factor, fibroblast growth factor, and hepatocyte growth factor could be specifically used for stimulating molecules in wound healing as well as for recovery of damaged skin tissues. It is speculated that delivered GFs could stimulate various cellular functions, including proliferation, migration, deposition of extracellular matrix molecules, and remodeling of collagen synthesis. Although the physiological wound healing process is complex, engineering strategies for proper delivery of multiple therapeutic GFs could enhance the quality and quantity of regenerated skin tissues. As compared to single delivery of a GF, recent studies have proven that any combination of multiple GFs and/or therapeutic chemical factors synergistically facilitates the regeneration of damaged skin tissues. In order to maximize the stability, bioactivity, intrinsic therapeutic functionality, and efficiency of internal delivery of cargo GFs, it is essential to utilize tissueengineered biomaterials and related composites as implantable platforms. Successful fabrication and development of skin tissue engineering applications as well as subsequent surgical implantation of these platforms might provide clinical treatment for superior skin regeneration. Therefore, the present review summarizes the biological functions, related signaling mechanisms, and recent developments of tissue engineering applications for multiple GF delivery.