Hyuntae Jung

In situ supramolecular assembly and modular modification of hyaluronic acid hydrogels for 3D cellular engineering.

A facile in situ supramolecular assembly and modular modification of biocompatible hydrogels were demonstrated using cucurbit[6]uril-conjugated hyaluronic acid (CB[6]-HA), diaminohexane-conjugated HA (DAH-HA), and tags-CB[6] for cellular engineering applications. The strong and selective host-guest interaction between CB[6] and DAH made possible the supramolecular assembly of CB[6]/DAH-HA hydrogels in the presence of cells. Then, the 3D environment of CB[6]/DAH-HA hydrogels was modularly modified by the simple treatment with various multifunctional tags-CB[6]. Furthermore, we could confirm in situ formation of CB[6]/DAH-HA hydrogels under the skin of nude mice by sequential subcutaneous injections of CB[6]-HA and DAH-HA solutions. The fluorescence of modularly modified fluorescein isothiocyanate (FITC)-CB[6] in the hydrogels was maintained for up to 11 days, reflecting the feasibility to deliver the proper cues for cellular proliferation and differentiation in the body. Taken together, CB[6]/DAH-HA hydrogels might be successfully exploited as a 3D artificial extracellular matrix for various tissue engineering applications.

Reduction‐Sensitive, Robust Vesicles with a Non‐covalently Modifiable Surface as a Multifunctional Drug‐Delivery Platform

The design and synthesis of a novel reduction-sensitive, robust, and biocompatible vesicle (SSCB[6]VC) are reported, which is self-assembled from an amphiphilic cucurbit[6]uril (CB[6]) derivative that contains disulfide bonds between hexaethylene glycol units and a CB[6] core. The remarkable features of SSCB[6]VC include: 1) facile, non-destructive, non-covalent, and modular surface modification using exceptionally strong host-guest chemistry; 2) high structural stability; 3) facile internalization into targeted cells by receptor-mediated endocytosis, and 4) efficient triggered release of entrapped drugs in a reducing environment such as cytoplasm. Furthermore, a significantly increased cytotoxicity of the anticancer drug doxorubicin to cancer cells is demonstrated using doxorubicin-loaded SSCB[6]VC, the surface of which is decorated with functional moieties such as a folate-spermidine conjugate and fluorescein isothiocyanate-spermidine conjugate as targeting ligand and fluorescence imaging probe, respectively. SSCB[6]VC with such unique features can be used as a highly versatile multifunctional platform for targeted drug delivery, which may find useful applications in cancer therapy. This novel strategy based on supramolecular chemistry and the unique properties of CB[6] can be extended to design smart multifunctional materials for biomedical applications including gene delivery.

Three-dimensional bioprinting of multilayered constructs containing human mesenchymal stromal cells for osteochondral tissue regeneration in the rabbit knee joint

The use of cell-rich hydrogels for three-dimensional (3D) cell culture has shown great potential for a variety of biomedical applications. However, the fabrication of appropriate constructs has been challenging. In this study, we describe a 3D printing process for the preparation of a multilayered 3D construct containing human mesenchymal stromal cells with a hydrogel comprised of atelocollagen and supramolecular hyaluronic acid (HA). This construct showed outstanding regenerative ability for the reconstruction of an osteochondral tissue in the knee joints of rabbits. We found that the use of a mechanically stable, host-guest chemistry-based hydrogel was essential and allowed two different types of extracellular matrix (ECM) hydrogels to be easily printed and stacked into one multilayered construct without requiring the use of potentially harmful chemical reagents or physical stimuli for post-crosslinking. To the best of our knowledge, this is the first study to validate the potential of a 3D printed multilayered construct consisting of two different ECM materials (atelocollagen and HA) for heterogeneous tissue regeneration using an in vivo animal model. We believe that this 3D printing-based platform technology can be effectively exploited for regeneration of various heterogeneous tissues as well as osteochondral tissue.

3D Tissue Engineered Supramolecular Hydrogels for Controlled Chondrogenesis of Human Mesenchymal Stem Cells

Despite a wide investigation of hydrogels as an artificial extracellular matrix, there are few scaffold systems for the facile spatiotemporal control of mesenchymal stem cells (MSCs). Here, we report 3D tissue engineered supramolecular hydrogels prepared with highly water-soluble monofunctionalized cucurbit[6]uril-hyaluronic acid (CB[6]-HA), diaminohexane conjugated HA (DAH-HA), and drug conjugated CB[6] (drug-CB[6]) for the controlled chondrogenesis of human mesenchymal stem cells (hMSCs). The mechanical property of supramolecular HA hydrogels was modulated by changing the cross-linking density for the spatial control of hMSCs. In addition, the differentiation of hMSCs was temporally controlled by changing the release profiles of transforming growth factor-β3 (TGF-β3) and/or dexamethasone (Dexa) from the hydrolyzable Dexa-CB[6]. The effective chondrogenic differentiation of hMSCs encapsulated in the monoCB[6]/DAH-HA hydrogel with TGF-β3 and Dexa-CB[6] was confirmed by biochemical glycosaminoglycan content analysis, real-time quantitative PCR, histological, and immunohistochemical analyses. Taken together, we could confirm the feasibility of cytocompatible monoCB[6]/DAH-HA hydrogels as a platform scaffold with controlled drug delivery for cartilage regeneration and other various tissue engineering applications.

Cdk5 phosphorylates PLD2 to mediate EGF-dependent insulin secretion

Insulin secretion from pancreatic beta-cells is an important process that affects the regulation of glucose level in the blood. In our previous study, we suggested that epidermal growth factor (EGF) stimulates insulin secretion by activating phospholipase D2 (PLD2) [H.Y. Lee, K. Yea, J. Kim, B.D. Lee, Y.C. Chae, H.S. Kim, D.W. Lee, S.H. Kim, J.H. Cho, C.J. Jin, D.S. Koh, K.S. Park, P.G. Suh, S.H. Ryu, 2007. Epidermal Growth Factor Increases Insulin Secretion and Lowers Blood Glucose in Diabetic Mice. J. Cell. Mol. Med. 5:5]. However, the specific mechanism by which PLD2 activation leads to insulin secretion was not determined. In this study, we suggest that the phosphorylation and activation of PLD2 by cyclin-dependent kinase 5 (Cdk5) is critical for EGF-dependent insulin secretion. We found that a Cdk5 inhibitor, roscovitine, and dominant-negative Cdk5 inhibited EGF-dependent PLD2 activation and insulin secretion. EGF stimulation activated Cdk5 activity in rat insulinoma RINm5F cells, and PLD2 phosphorylation by Cdk5 was observed in vitro and in cells. The kinetics of PLD2 phosphorylation correlates with the interaction between PLD2 and Cdk5 and its effect on EGF signaling. We determined that the phosphorylation site of PLD2 was located at Ser(134). PLD2-S134A did not show EGF-dependent phosphorylation and activation by Cdk5. Furthermore, this mutant was unable to mediate EGF-dependent insulin secretion in pancreatic beta cell lines, suggesting that the phosphorylation of PLD2 at Ser(134) by Cdk5 is critical for this process. The study results suggest that PLD2 is a new substrate of Cdk5 and that the phosphorylation of PLD2 by Cdk5 is involved in EGF-dependent insulin secretion.

Al+Y codeposition using EB-PVD method for improvement of high-temperature oxidation resistance of TiAl

Abstract An “Al+Y codeposition” on TiAl by the single EB-PVD method has been developed to improve the oxidation resistance of TiAl. To determine the optimum codeposition condition, the Al+Y codepositions with various ratios of Al and Y are evaluated through the isothermal and cyclic oxidation tests. The oxidation resistance of TiAl can be improved extensively by the Al+Y codeposition due to the formation of a gradient coating of Al and Y. The Al+Y codeposition with the ratio of Al:2Y for evaporation source material is proved to be the best. With a proper ratio of Al:Y, the Al+Y codeposition forms two distinctive layers of the oxides during high-temperature oxidation; Al 2 O 3 in the inner layer and (Y, Al)O type oxide in the outer layer. In addition to the inner Al 2 O 3 layer, the formation of the outer (Y, Al)O type oxide layer further improves the stability of the coatings. The stability of the Al+Y codeposition greatly depends upon the alloying element of TiAl substrate or oxidation resistance of the TiAl substrate alloy. The non-alloyed TiAl shows a poor coating stability, whereas TiAl–2.8Nb and Alloy K5 show a good coating stability under severe thermal stresses during cyclic oxidation since a stable Al 2 O 3 can form on the surface of these alloys.

Self-assembled, covalently linked, hollow phthalocyanine nanospheres

A rational design and synthesis of covalently linked Pc nanospheres with a very thin shell and hollow interior, composed of approximately 12 000 Pc units on average, was demonstrated through thiol–ene “click” chemistry without using any templates or emulsifiers. The ZnPc nanospheres allow post-synthetic modification to improve their dispersibility in aqueous solution without altering the morphology of the nanospheres or the properties of ZnPc cores. More importantly, the ZnPc nanospheres showed higher singlet oxygen generation efficiency and in vitro phototoxicity than monomeric Pc molecules, suggesting that ZnPc nanospheres are potentially useful as a PS for PDT. We anticipate that the ZnPc nanospheres would allow other post-synthetic modifications such as the introduction of targeting ligands to deliver the nanospheres to specific target sites and perform a dual chemo- and photodynamic therapy by the encapsulation of therapeutic agents. The easy synthesis of a hollow spherical framework with a high Pc content, coupled with facile post-synthetic modification may allow Pc nanospheres to be a versatile platform for a diverse range of medical and non-medical applications.

Supramolecular hydrogels for long-term bioengineered stem cell therapy.

Synthetic hydrogels have been extensively investigated as artificial extracellular matrices (ECMs) for tissue engineering in vitro and in vivo. Crucial challenges for such hydrogels are sustaining long-term cytocompatible encapsulation and providing appropriate cues at the right place and time for spatio-temporal control of the cells. Here, in situ supramolecularly assembled and modularly modified hydrogels for long-term engineered mesenchymal stem cell (eMSC) therapy are reported using cucurbit[6]uril-conjugated hyaluronic acid (CB[6]-HA), diaminohexane conjugated HA (DAH-HA), and drug-conjugated CB[6] (drug-CB[6]). The eMSCs producing enhanced green fluorescence protein (EGFP) remain alive and emit the fluorescence within CB[6]/DAH-HA hydrogels in mice for more than 60 d. Furthermore, the long-term expression of mutant interleukin-12 (IL-12M) by eMSCs within the supramolecular hydrogels results in effective inhibition of tumor growth with a significantly enhanced survival rate. Taken together, these findings confirm the feasibility of supramolecular HA hydrogels as 3D artificial ECMs for cell therapies and tissue engineering applications.

Genetically engineered mesenchymal stem cell therapy using self-assembling supramolecular hydrogels

Stem cell therapy has attracted a great deal of attention for treating intractable diseases such as cancer, stroke, liver cirrhosis, and ischemia. Especially, mesenchymal stem cells (MSCs) have been widely investigated for therapeutic applications due to the advantageous characteristics of long life-span, facile isolation, rapid proliferation, prolonged transgene expression, hypo-immunogenicity, and tumor tropism. MSCs can exert their therapeutic effects by releasing stress-induced therapeutic molecules after their rapid migration to damaged tissues. Recently, to improve the therapeutic efficacy, genetically engineered MSCs have been developed for therapeutic transgene expression by viral gene transduction and non-viral gene transfection. In general, the number of therapeutic cells for injection should be more than several millions for effective cell therapy. Adequate carriers for the controlled delivery of MSCs can reduce the required cell numbers and extend the duration of therapeutic effect, which provide great benefits for chronic disease patients. In this review, we describe genetic engineering of MSCs, recent progress of self-assembling supramolecular hydrogels, and their applications to cell therapy for intractable diseases and tissue regeneration.