Seung Jung Yu

Paper-based bioactive scaffolds for stem cell-mediated bone tissue engineering

Bioactive, functional scaffolds are required to improve the regenerative potential of stem cells for tissue reconstruction and functional recovery of damaged tissues. Here, we report a paper-based bioactive scaffold platform for stem cell culture and transplantation for bone reconstruction. The paper scaffolds are surface-engineered by an initiated chemical vapor deposition process for serial coating of a water-repellent and cell-adhesive polymer film, which ensures the long-term stability in cell culture medium and induces efficient cell attachment. The prepared paper scaffolds are compatible with general stem cell culture and manipulation techniques. An optimal paper type is found to provide structural, physical, and mechanical cues to enhance the osteogenic differentiation of human adipose-derived stem cells (hADSCs). A bioactive paper scaffold significantly enhances in vivo bone regeneration of hADSCs in a critical-sized calvarial bone defect. Stacking the paper scaffolds with osteogenically differentiated hADSCs and human endothelial cells resulted in vascularized bone formation in vivo. Our study suggests that paper possesses great potential as a bioactive, functional, and cost-effective scaffold platform for stem cell-mediated bone tissue engineering. To the best of our knowledge, this is the first study reporting the feasibility of a paper material for stem cell application to repair tissue defects.

Hydrogel-laden paper scaffold system for origami-based tissue engineering

Significance This work describes an intriguing strategy for the formation of hydrogel-laden multiform structures utilizing paper sheets and suggests a route for trachea tissue engineering. It combines concepts extracted from paper origami, functional thin polymer coating, and thin hydrogel layering on top of the paper scaffolds. A computer-aided design-based lock-and-key arrangement was used for folding the sheets into multiform structures with spatial arrangements. With encapsulating cells in hydrogel-laden paper, the scaffold system was able to deliver biological cues in vivo. In this work, we have successfully applied an origami-based tissue engineering approach to the trachea regeneration model. In this study, we present a method for assembling biofunctionalized paper into a multiform structured scaffold system for reliable tissue regeneration using an origami-based approach. The surface of a paper was conformally modified with a poly(styrene-co-maleic anhydride) layer via initiated chemical vapor deposition followed by the immobilization of poly-l-lysine (PLL) and deposition of Ca2+. This procedure ensures the formation of alginate hydrogel on the paper due to Ca2+ diffusion. Furthermore, strong adhesion of the alginate hydrogel on the paper onto the paper substrate was achieved due to an electrostatic interaction between the alginate and PLL. The developed scaffold system was versatile and allowed area-selective cell seeding. Also, the hydrogel-laden paper could be folded freely into 3D tissue-like structures using a simple origami-based method. The cylindrically constructed paper scaffold system with chondrocytes was applied into a three-ring defect trachea in rabbits. The transplanted engineered tissues replaced the native trachea without stenosis after 4 wks. As for the custom-built scaffold system, the hydrogel-laden paper system will provide a robust and facile method for the formation of tissues mimicking native tissue constructs.

Nanothin Coculture Membranes with Tunable Pore Architecture and Thermoresponsive Functionality for Transfer-Printable Stem Cell-Derived Cardiac Sheets

Coculturing stem cells with the desired cell type is an effective method to promote the differentiation of stem cells. The features of the membrane used for coculturing are crucial to achieving the best outcome. Not only should the membrane act as a physical barrier that prevents the mixing of the cocultured cell populations, but it should also allow effective interactions between the cells. Unfortunately, conventional membranes used for coculture do not sufficiently meet these requirements. In addition, cell harvesting using proteolytic enzymes following coculture impairs cell viability and the extracellular matrix (ECM) produced by the cultured cells. To overcome these limitations, we developed nanothin and highly porous (NTHP) membranes, which are ∼20-fold thinner and ∼25-fold more porous than the conventional coculture membranes. The tunable pore size of NTHP membranes at the nanoscale level was found crucial for the formation of direct gap junctions-mediated contacts between the cocultured cells. Differentiation of the cocultured stem cells was dramatically enhanced with the pore size-customized NTHP membrane system compared to conventional coculture methods. This was likely due to effective physical contacts between the cocultured cells and the fast diffusion of bioactive molecules across the membrane. Also, the thermoresponsive functionality of the NTHP membranes enabled the efficient generation of homogeneous, ECM-preserved, highly viable, and transfer-printable sheets of cardiomyogenically differentiated cells. The coculture platform developed in this study would be effective for producing various types of therapeutic multilayered cell sheets that can be differentiated from stem cells.

Effects of interfacial layer wettability and thickness on the coating morphology and sirolimus release for drug-eluting stent.

Drug-eluting stents (DESs) have been used to treat coronary artery diseases by placing in the arteries. However, current DESs still suffer from polymer coating defects such as delamination and peeling-off that follows stent deployment. Such coating defects could increase the roughness of DES and might act as a source of late or very late thrombosis and might increase the incident of restenosis. In this regard, we modified the cobalt-chromium (Co-Cr) alloy surface with hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) or hydrophobic poly(2-hydroxyethyl methacrylate)-grafted-poly(caprolactone) (PHEMA-g-PCL) brushes. The resulting surfaces were biocompatible and biodegradable, which could act as anchoring layer for the drug-in-polymer matrix coating. The two modifications were characterized by ATR-FTIR, XPS, water contact angle measurements, SEM and AFM. On the control and modified Co-Cr samples, a sirolimus (SRL)-containing poly(D,L-lactide) (PDLLA) were ultrasonically spray-coated, and the drug release was examined for 8weeks under physiological conditions. The results demonstrated that PHEMA as a primer coating improved the coating stability and degradation morphology, and drug release profile for short-term as compared to control Co-Cr, but fails after 7weeks in physiological buffer. On the other hand, the hydrophobic PHEMA-g-PCL brushes not only enhanced the stability and degradation morphology of the PDLLA coating layer, but also sustained SRL release for long-term. At 8-week of release test, the surface morphologies and release profiles of coated PDLLA layers verified the beneficial effect of hydrophobic PCL brushes as well as their thickness on coating stability. Our study concludes that 200nm thickness of PHEMA-g-PCL as interfacial layer affects the stability and degradation morphology of the biodegradable coating intensively to be applied for various biodegradable-based DESs.

Engineering the xylose-catabolizing Dahms pathway for production of poly(d-lactate-co-glycolate) and poly(d-lactate-co-glycolate-co-d-2-hydroxybutyrate) in Escherichia coli

Poly(lactate‐co‐glycolate), PLGA, is a representative synthetic biopolymer widely used in medical applications. Recently, we reported one‐step direct fermentative production of PLGA and its copolymers by metabolically engineered Escherichia coli from xylose and glucose. In this study, we report development of metabolically engineered E. coli strains for the production of PLGA and poly(d‐lactate‐co‐glycolate‐co‐d‐2‐hydroxybutyrate) having various monomer compositions from xylose as a sole carbon source. To achieve this, the metabolic flux towards Dahms pathway was modulated using five different synthetic promoters for the expression of Caulobacter crescentus XylBC. Further metabolic engineering to concentrate the metabolic flux towards d‐lactate and glycolate resulted in production of PLGA and poly(d‐lactate‐co‐glycolate‐co‐d‐2‐hydroxybutyrate) with various monomer fractions from xylose. The engineered E. coli strains produced polymers containing 8.8–60.9 mol% of glycolate up to 6.93 g l−1 by fed‐batch cultivation in a chemically defined medium containing xylose. Finally, the biocompatibility of poly(d‐lactate‐co‐glycolate‐co‐d‐2‐hydroxybutyrate) was confirmed by live/dead assay using human mesenchymal stem cells.

Chondroitin Sulfate-Based Biomineralizing Surface Hydrogels for Bone Tissue Engineering

Chondroitin sulfate (CS) is the major component of glycosaminoglycan in connective tissue. In this study, we fabricated methacrylated PEGDA/CS-based hydrogels with varying CS concentration (0, 1, 5, and 10%) and investigated them as biomineralizing three-dimensional scaffolds for charged ion binding and depositions. Due to its negative charge from the sulfate group, CS exhibited an osteogenically favorable microenvironment by binding charged ions such as calcium and phosphate. Particularly, ion binding and distribution within negatively charged hydrogel was dependent on CS concentration. Furthermore, CS dependent biomineralizing microenvironment induced osteogenic differentiation of human tonsil-derived mesenchymal stem cells in vitro. Finally, when we transplanted PEGDA/CS-based hydrogel into a critical sized cranial defect model for 8 weeks, 10% CS hydrogel induced effective bone formation with highest bone mineral density. This PEGDA/CS-based biomineralizing hydrogel platform can be utilized for in situ bone formation in addition to being an investigational tool for in vivo bone mineralization and resorption mechanisms.

Biofunctionalized titanium with anti-fouling resistance by grafting thermo-responsive polymer brushes for the prevention of peri-implantitis

In the last decade, titanium has been effectively used in the dental field for oral surgery as an implant material. However, disinfected Ti can be easily re-infected by the surrounding environment. Thus, a novel anti-fouling treatment for Ti implants is currently necessary. In this study, we designed an anti-fouling surface comprised of poly N-isopropylacylamide (PIPAAM) grafted Ti by introducing poly glycidyl methacrylate (pGMA) coating via an initiated chemical vapor deposition (iCVD) system to prevent bacterial infection. The results indicate that pristine Ti was well coated with pGMA with a film thickness of approximately 60 nm and uniformly grafted with PIPAAM. The bacteria were effectively detached after rinsing with a buffer solution at room temperature, while hADSCs were well attached on the surface treated Ti surface at oral temperature. All tests clearly confirm that our strategy may be a useful means of imparting anti-fouling characteristics to Ti in order to prevent bacterial adhesion and resultant peri-implantitis.

Hydrogel Functionalized Janus Membrane for Skin Regeneration

In this study, a hydrogel functionalized Janus membrane is developed and its capacity is examined as a wound dressing biomaterial. A hydrophobic fluoropolymer, poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate) (PHFDMA), is uniformly coated onto macroporous polyester membrane through initiated chemical vapor deposition process on both sides. PHFDMA-coated macroporous membrane exhibits antibacterial property, allows air permeation, and inhibits water penetration. Janus membrane property is obtained by exposing one side of PHFDMA coated membrane with 1 m KOH solution, which allows PHFDMA cleavage resulting in carboxylic acid residue. This carboxylic acid residue is then further functionalized with gelatin methacrylate-based photocrosslinkable hydrogel for moisture retention and growth factor release. When applied to full thickness dorsal skin defect model, functionalized hydrogel allows moisture retention and hydrophobic surface prevents exudate leaks via water repellence. Furthermore, hydrogel functionalized Janus membrane enhances the wound healing rate and induces thick epidermal layer formation. In conclusion, the multifunctional Janus membrane with hydrophobic outer surface and immobilized hydrogel on the other surface is fabricated for an innovative strategy for wound healing.

Prevention of Bacterial Colonization on Catheters by a One-Step Coating Process Involving an Antibiofouling Polymer in Water

As reports of multidrug resistant pathogens have increased, patients with implanted medical catheters increasingly need alternative solutions to antibiotic treatments. As most catheter-related infections are directly associated with biofilm formation on the catheter surface, which, once formed, is difficult to eliminate, a promising approach to biofilm prevention involves inhibiting the initial adhesion of bacteria to the surface. In this study, we report an amphiphilic, antifouling polymer, poly(DMA-mPEGMA-AA) that can facilely coat the surfaces of commercially available catheter materials in water and prevent bacterial adhesion to and subsequent colonization of the surface, giving rise to an antibiofilm surface. The antifouling coating layer was formed simply by dipping a model substrate (polystyrene, PET, PDMS, or silicon-based urinary catheter) in water containing poly(DMA-mPEGMA-AA), followed by characterization by X-ray photoelectron spectroscopy (XPS). The antibacterial adhesion properties of the polymer-coated surface were assessed for Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) growth under static (incubation in the presence of a bacterial suspension) and dynamic (bacteria suspended in a solution under flow) conditions. Regardless of the conditions, the polymer-coated surface displayed significantly reduced attachment of the bacteria (antiadhesion effect > ∼8-fold) compared to the bare noncoated substrates. Treatment of the implanted catheters with S. aureus in vivo further confirmed that the polymer-coated silicon urinary catheters could significantly reduce bacterial adhesion and biofilm formation in a bacterial infection animal model. Furthermore, the polymer-coated catheters did not induce hemolysis and were resistant to the adhesion of blood-circulating cells, indicative of high biocompatibility. Collectively, the present amphiphilic antifouling polymer is potentially useful as a coating platform that renders existing medical devices resistant to biofilm formation.