Byung Woo Hwang

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.

Hyaluronate and its derivatives for customized biomedical applications

Since hyaluronate (HA) was firstly isolated from the vitreous of bovine eyes in 1934, HA has been widely investigated for various biomedical applications. As a naturally-occurring polysaccharide, HA has been used for joint lubrication and ocular treatment in its intact form due to the excellent biocompatibility, viscoelasticity, biodegradability, and hygroscopic properties. HA can be easily functionalized via the chemical modification of its carboxyl and hydroxyl groups. Recently, a variety of biological functions of HA have been explored and a number of customized applications have been investigated taking advantages of the interaction between HA and biological tissues. HA has been used for drug delivery to enhance the blood circulation time of drugs with target-specificity to HA receptors in the body. HA has been also used to prepare tissue engineering hydrogel scaffolds for the spatiotemporal control of encapsulated cells. In this review, we describe the key biological functions of HA in the body in terms of its structure, physical properties, biodistribution and interaction with HA receptors. After that, we describe unique advantages that allow HA to be applied in various biomedical fields. Finally, we report the conventional and newly emerging applications of HA and its derivatives under commercial development stages.

Effect of osteoconductive hyaluronate hydrogels on calvarial bone regeneration

BackgroundWithout exploitation of possibly immunogenic and carcinogenic bone morphogenetic protein, we developed simple but clinically feasible artificial bone graft using osteoconductive hyaluronate (HA) hydrogels and bioactive MegaGen synthetic bone (MGSB).MethodsHA hydrogels were synthesized by the crosslinking reaction between carboxyl groups of HA and amine groups of gelatin (GEL). Then, artificial bone grafts were prepared by mixing MGSB with HA-GEL hydrogels. The bone regeneration by the MGSB/HA-GEL hydrogel complex was assessed in the skull of New Zealand white male rabbits in 4 and 8 weeks.ResultsHA hydrogels were synthesized by the crosslinking reaction between carboxyl groups of HA and amine groups of gelatin (GEL). Then, artificial bone grafts were prepared by mixing MGSB with HA-GEL hydrogels. In vitro proliferation of preosteogenic cells was enhanced with increasing molecular weight of HA. In addition, histological analysis of dissected tissues with hematoxylin and eosin staining confirmed the effective in vivo bone regeneration by the MGSB/HA-GEL hydrogel complex. The MGSB/HA-GEL hydrogels were well resorbed and partially substituted to the lamellar bone after implantation for 8 weeks.ConclusionsThe novel artificial bone graft of MGSB/HA-GEL hydrogel complex for effective bone regeneration might be clinically feasible for further development.

Bioimaging and pulmonary applications of self-assembled Flt1 peptide-hyaluronic acid conjugate nanoparticles.

Despite wide exploitation of corticosteroid drugs for the treatment of asthma, the poor therapeutic effect on a neutrophilic subtype of asthma prohibits the full recovery of asthma patients. In this work, dexamethasone (Dexa) was loaded in Flt1 peptide-hyaluronic acid (HA) conjugate nanoparticles to overcome the limitation of corticosteroid resistance for the treatment of neutrophilic pulmonary inflammation. Flt1 peptide-HA conjugates are self-assembled to nanoparticles because of hydrophobic Flt1 peptide conjugated to HA by benzotriazol-1-yloxy-tris(dimethylamino)phosphonium hexafluorophosphate (BOP) chemistry. In vitro bioimaging showed efficient internalization of Flt1 peptide-HA conjugate nanoparticles into lung epithelial cells by HA-receptor mediated endocytosis. Also, ex vivo imaging for the biodistribution in ICR mice revealed long-term retention of Flt1 peptide-HA conjugate nanoparticles in deep lung tissues possibly due to mucoadhesive property of HA. On the basis of bioimaging results for pulmonary drug delivery applications, we prepared Dexa-loaded Flt1 peptide-HA conjugate nanoparticles. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) confirmed the formation of nanoparticles, which reduced cytokine levels of lipopolysaccharide (LPS)-stimulated cells more efficiently than free Dexa. Furthermore, according to the bronchoalveolar lavage (BAL) cellularity and histological analysis, Dexa loaded Flt1 peptide-HA conjugate nanoparticles showed remarkable therapeutic effects in both eosinophilic and neutrophilic asthma model mice.

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.

Smart Microbubble Eluting Theranostic Stent for Noninvasive Ultrasound Imaging and Prevention of Restenosis

A pH-responsive microbubble-eluting theranostic stent is developed for real-time ultrasound imaging of stent implanted blood vessels and dissolution of fat-rich plaques to prevent the blocking of blood vessels in rats. This smart theranostic stent can be effectively applied to facilitate noninvasive monitoring and prevent restenosis after stent implantation.

Hyaluronate modified upconversion nanoparticles for near infrared light-triggered on–off tattoo systems

An in vivo on–off tattoo system was developed using upconversion nanoparticles conjugated with hyaluronate (HA-UCNPs). Two-photon microscopy clearly visualized the transdermal delivery of HA-UCNPs into the deep skin tissue. Upon near-infrared light irradiation, invisible HA-UCNPs in the skin were visualized showing the feasibility as a new on–off tattoo system.

Upconversion Nanoparticles/Hyaluronate–Rose Bengal Conjugate Complex for Noninvasive Photochemical Tissue Bonding

The recent progress in photonic nanomaterials has contributed greatly to the development of photomedicines. However, the finite depth of light penetration is still a serious limitation, constraining their clinical applications. Here, we developed a poly(allylamine) (PAAm)-modified upconversion nanoparticle/hyaluronate-rose bengal (UCNP/PAAm/HA-RB) conjugate complex for photochemical bonding of deep tissue with near-infrared (NIR) light illumination. Compared to the conventional invasive treatment via suturing and stapling, the UCNP/PAAm/HA-RB conjugate complex could be noninvasively delivered into the deep tissue and accelerate the tissue bonding upon NIR light illumination. HA in the outer layer of the complex facilitated the penetration of RB into the collagen layer of the dermis. The NIR light triggered UCNP of NaYF4: Yb/Er (Y:Yb:Er = 78:20:2) in the complex to illuminate visible green light under the skin tissue. The activated RB in the HA-RB conjugate by the green light induced radical formation for the cross-linking of incised collagen matrix. An in vitro light propagation test and collagen fibrillogenesis analysis, an in vivo animal tissue bonding test, and an ex vivo tensile strength test of dissected skin tissues confirmed the successful photochemical tissue bonding effect of the UCNP/PAAm/HA-RB conjugate complex.

Supramolecular hydrogels encapsulating bioengineered mesenchymal stem cells for ischemic therapy

We developed supramolecular hyaluronate (HA) hydrogels to encapsulate genetically engineered mesenchymal stem cells (MSCs) for the treatment of limb ischemia. In vivo angiogenic factors could be produced stably by the bioengineered MSCs (BMSCs) within the supramolecular hydrogels showing effective vascular repair and enhanced blood perfusion.