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Biodegradable stents made of magnesium (Mg) and its alloys have been developed to minimize persistent inflammation or in-stent restenosis, which are the main problems for permanent stents. However, their rapid corrosion behavior under physiological conditions leads to poor vascular compatibility and premature structural failure, which remains an important unsolved clinical problem. Herein, we demonstrate a new strategy for solving this problem by combining poly (ether imide) (PEI) coating and subsequent tantalum (Ta) ion implantation. The PEI coating covers the whole surface of the Mg stent uniformly via a spray coating technique and provides Mg with superior corrosion resistance and stable sirolimus-carrying ability. Ta ion implantation is conducted by a sputtering-based plasma immersion ion implantation technique only onto the luminal surface of the PEI-coated Mg stent. Its extremely short processing time (

Poly(ether imide) (PEI) has shown satisfactory corrosion protection capability with good adhesion strength as a coating for magnesium (Mg), a potential candidate of biodegradable orthopedic implant material. However, its innate hydrophobic property causes insufficient osteoblast affinity and a lack of osseointegration. Herein, we modify the physical and chemical properties of a PEI-coated Mg implant. A plasma immersion ion implantation technique is combined with direct current (DC) magnetron sputtering to introduce biologically compatible tantalum (Ta) onto the surface of the PEI coating. The PEI-coating layer is not damaged during this process owing to the extremely short processing time (30 s), retaining its high corrosion protection property and adhesion stability. The Ta-implanted layer (roughly 10-nm-thick) on the topmost PEI surface generates long-term surface hydrophilicity and favorable surface conditions for pre-osteoblasts to adhere, proliferate, and differentiate. Furthermore, in a rabbit femur study, the Ta/PEI-coated Mg implant demonstrates significantly enhanced bone tissue affinity and osseointegration capability. These results indicate that Ta/PEI-coated Mg is promising for achieving early mechanical fixation and long-term success in biodegradable orthopedic implant applications., Graphical abstract Image 1, Highlights • PEI coating with subsequent Ta ion implantation was prepared on WE43 Mg alloy implant. • The corrosion resistance of Mg alloy implant was improved by Ta embedded PEI coating. • The wettability of PEI coating layer was enhanced by embedded Ta on its top-surface. • Ta embedded PEI coating significantly improved in vitro and in vivo responses. • Ta embedded PEI-coated Mg is highly suitable as a biodegradable orthopedic implant material.

The purpose of the present study was to evaluate the mechanical strength and the absorption rate of WE43 material and to develop an absorbable metallic plate and screw for craniofacial application. The extruded WE43 plate and screw were evaluated using a LeFort I osteotomy canine model of 10 beagle dogs. Animals were divided into two groups: five dogs in the experimental group and five dogs in the control group. μCT was acquired at 4, 12, and 24 weeks. At 24 weeks after the operation, all animals were sacrificed, and histologic evaluation was performed. Swelling and gas formation were observed in three dogs in the experimental groups at 8 weeks. From 12 weeks, infraorbital fistula and inflammation were observed in three dogs in the experimental group, which gradually decreased and disappeared at 24 weeks. Other two dogs showed less gas formation at 12 weeks. The plates were completely absorbed, and gas formation was not observed at 24 weeks in these two dogs. New bone was well formed around the plates and screws in both groups. Histologic examination showed no specific differences between two groups. The mechanical strength of extruded WE43 was sufficient for mid‐facial application. Plates and screws made with appropriately treated WE43 have the potential to be useful clinically.

Aside from being known for its excellent mechanical properties and aesthetic effect, zirconia has recently attracted attention as a new dental implant material. Many studies have focused on hydroxyapatite (HA) coating for obtaining improved biocompatibility, however the coating stability was reduced by a byproduct produced during the high-temperature sintering process. In this study, to overcome this problem, we simply coated the zirconia surface with a sol–gel-derived hydroxyapatite (HA) layer and then sintered it at a varied temperature (40 MPa) was also appropriate as a dental implant application. In addition, in vitro cell experiments using a preosteoblast cell line revealed that the HA-coated zirconia surface acts as a preferable surface for cell attachment and proliferation than bare zirconia surface. In vivo animal experiments also demonstrated that the osteoconductivity of zirconia were dramatically enhanced by HA coating, which was comparable to that of Ti implant. These results suggest that the sol–gel-based HA-coated zirconia has a great potential for use as a dental implant material.

The surface characteristics of coronary stents play a pivotal role in inhibiting in-stent restenosis and late-stent thrombosis. In this study, a sol-gel-derived silica xerogel-chitosan hybrid coating was applied to Co-Cr stent and was reported, for the first time, as a biocompatible drug delivery tool in vascular stent application. A dense and uniform chitosan-silica xerogel hybrid coating (1-μm thick) was applied on bare Co-Cr material. Sirolimus was well incorporated into the hybrid coatings without re-crystallization. The chitosan-silica hybrid coating with 30 wt% silica xerogel showed better mechanical stability and good adhesive strength without any cracking or delamination. The chitosan-silica hybrid coated Co-Cr surface exhibited significantly improved wettability and corrosion resistance compared to the chitosan coated Co-Cr surface. In addition, the hybrid coating layer enabled efficient loading of sirolimus, owing to the unique mesoporous structure of silica xerogel, which further allowed the sustained release of sirolimus over 3 weeks. In-vitro tests with human umbilical cord vein endothelial cells and blood platelets confirmed that the chitosan-silica hybrid coating had excellent cytocompatibility and hemocompatibilty. Thus, this study demonstrated that the chitosan-silica hybrid material is a promising material for coating coronary stents, with minimal risk of in-stent restenosis and thrombogenicity.

The creation of a moist environment and promotion of cell proliferation and migration together with antibacterial property are critical to the wound-healing process. Alginate (Alg) is an excellent candidate for injectable wound dressing materials because it can form a gel in a mild environment. Taking advantage of its gelation property, an injectable nano composite hydrogel containing nano-sized (about 90 nm) calcium fluoride (CaF2) particles was developed using in-situ precipitation process. The amount of released fluorine (F−) ion from the nanocomposite hydrogel increased with increasing CaF2 content inside the composite hydrogel and the ions stimulated both the proliferation and migration of fibroblast cells in vitro. The antibacterial property of the composite hydrogel against E. coli and S. aureus was confirmed through colony formation test where the number of bacterial colonies significantly decreased compared to Alg hydrogel. The in vivo results based on a full-thickness wound model showed that the nanocomposite hydrogel effectively enhanced the deposition of the extracellular matrix compared to that of the Alg hydrogel. This study demonstrates the potential of this nanocomposite hydrogel as a bioactive injectable wound-dressing material with the ability to inhibit bacterial growth and stimulate cell proliferation and migration for accelerated wound healing.

Titanium (Ti) is used in dental applications owing to their excellent mechanical properties, corrosion resistance, and biocompatibility. However, postoperative bacterial infection may cause serious complications and remains one of the most difficult challenges hindering the development of long term Ti dental implants. Therefore, the desire for high quality dental care has led to significant interest in designing implant surfaces that offer stable antibacterial activity with excellent cellular response. In this study, we propose a simple and efficient approach for fabricating an antibacterial stabilized Ag nanostructure on a Ti surface, which is based on a two-step process involving target-ion induced plasma sputtering (TIPS) and Ag sputtering. The TIPS process generates a nanostructured Ti surface that provides a nanotemplate on which the Ag nanostructure may be deposited through Ag sputtering. The Ag nanoclusters adhere tightly to the TIPS-treated Ti (TIPS-Ti) nanostructured surface with no noticeable defects, and the amount of stabilized Ag deposited may be controlled by simply adjusting the Ag-sputtering time. The silver ion is released continuously from the Ag-TIPS-Ti surface for 7 d. The Ag nanostructured TIPS-Ti (Ag-TIPS-Ti) surface not only offers outstanding antibacterial activity toward Escherichia coli and Staphylococcus aureus over 12 h of culturing but also exhibits no severe cytotoxicity for fibroblast cells for up to 10 days. In particular, Ag stabilization by 10 s Ag-sputtering on TIPS-Ti provides the best balance between antibacterial activity and cellular performances, and the resulting fibroblast cell-attachment morphology and proliferation level are similar to those for a polished Ti surface. Therefore, the controllable antibacterial activity and fibroblast tissue affinity of the Ag-TIPS-Ti present a promising avenue for producing reliable, long term dental implants.

Surface patterns can be used as a selective coating platform on metal surfaces, in particular, under various deformation conditions because they induce local strain gradients along with pattern geometry. In this study, hard and flexible coating materials were introduced to regions with small and large deformations, respectively, on patterned magnesium (Mg) surfaces. Despite significant deformation, a polymer-ceramic coating on patterned Mg maintained its protection, as opposed to a ceramic coating on a flat Mg surface. Our proposed approach can be implemented in various Mg-based medical-device platforms by optimizing surface patterns on Mg depending on their loading conditions for clinical use. MOE (Min. of Education, S’pore)

For hard tissue engineering applications, biodegradable composite scaffolds have been extensively investigated because of their satisfactory mechanical properties and biocompatibility. Recently, 3D printing processes have received substantial attention in the tissue engineering field because of their ability to be customized for tissues that have suffered different types of loss or damage for each patient. However, previous studies on material extrusion-based techniques lack flexibility in the filler loading amount and cannot fulfill requirements that aim to enhance mechanical properties and biocompatibility. Herein, we propose a biodegradable polymer-based composite scaffolds with high ceramic loadings fabricated using the binder jetting (BJ) technique conjugated with capillary rise infiltration. A calcium sulfate hemihydrate (CSH) scaffold was fabricated using BJ-based 3D printing. Thereafter, CSH was transformed into biphasic calcium phosphate (BCP) using hydrothermal treatment, followed by heat treatment. Melted polycaprolactone (PCL) was infiltrated in the resulting BCP scaffold. BCP was then completely dispersed in the PCL matrix, and the calculated PCL loading in the BCP matrix exceeded 40 vol%. The PCL/BCP composite scaffold demonstrated the highest compressive strength, moduli, and toughness with the fracture mode shifted from brittle to less brittle. Moreover, a stable PCL/BCP surface promotes initial cell responses and shows sufficient proliferation and differentiation of pre-osteoblast cells.

A hyaluronic acid (HAc)-hydroxyapatite (HAp) nanocomposite (HAc-nanoHAp) hydrogel was fabricated through an in situ precipitation process for mechanical and biological enhancement as a soft tissue augmentation product. In this study, these composite hydrogel fillers were analyzed from three different perspectives and compared with pure HAc hydrogel for soft tissue augmentation application: (1) rheological behaviors, (2) in vivo lateral diffusion under mouse skin, and (3) wrinkle improvement in a photo-aged mouse model. HAc-nanoHAp provided great improvement to wrinkles because of its higher stiffness and gel cohesiveness in comparison with that of pure HAc. HAc-nanoHAp also presented great enhancement in strengthening the dermal matrix by stimulating the synthesis of collagen and elastin. Thus, HAc-nanoHAp filler has great potential as a soft tissue augmentation product, improving the biophysical and biological performance in skin tissue. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3315-3325, 2017.

Magnesium (Mg) and its alloys are promising materials for biodegradable drug-eluting stent applications, but their rapid corrosion remains a major challenge for clinical practice. Considerable efforts have been made to develop an efficient surface coating that can provide higher Mg stent corrosion resistance, sustained drug-delivery capability, and vascular compatibility. Herein, we introduce poly(ether imide) (PEI) and poly(lactic-co-glycolic acid) (PLGA) as surface coating polymers for WE43 Mg-alloy stent. Using a sequential spray-coating method, we developed a novel asymmetric stent coating comprising an inner surface coated with a PEI single layer and outer/side surfaces coated with sirolimus-loaded PLGA/PEI double layers. PEI coating layer has excellent adhesiveness to WE43 surface and considerably improves WE43 corrosion resistance and in vitro endothelial cell compatibility. PLGA/PEI double coating layer ensures a low release rate of sirolimus and stable surface morphology during drug-release process. Only vascular smooth muscle cells are directly affected by sirolimus owing to the asymmetric geometry of PLGA/PEI double coating, which has a satisfactory anti-proliferation effect. These results indicate that the developed asymmetrically PEI- and PLGA/PEI-coated WE43 stents have significant potential for achieving enhanced re-endothelialization and suppressed in-stent restenosis in vascular stent applications.

Environmentally benign processing technology of polymeric semiconductor is demonstrated to facilitate industrial application of organic electronics. By employing sodium dodecyl sulfate (SDS) as a surfactant and Poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) as a polymeric semiconductor, a water-borne colloid was synthesized and used for forming the active layer of a field effect transistor. Traditionally, this technology was not successful in realizing high charge carrier mobility, owing to difficulties in identifying an optimal temperature for eliminating the surfactant while maintaining the long-range-ordered π–π stacked structure of the semiconductors. In this work, by utilizing the liquid crystalline nature of the PBTTT, we identified the optimal thermal treatment condition (∼270 °C), which is sufficient both for eliminating the SDS and stimulating a second phase transition of the PBTTT. As a result, the PBTTT nanoparticle film cast from the water-borne colloid was successfully sintered to form continuously π–π stacked polymeric semiconductor films, whose high charge carrier mobility of 0.19 cm2/Vs, is comparable to those of organic solvents.

A simple, facile surface sol–gel method is introduced for the fabrication of zirconium oxide films for use as a dielectric layer of a solution-processed polymer field effect transistor (PFET). High dielectric strength is demonstrated for a zirconium oxide layer under room-temperature fabrication conditions using a surface sol–gel method without any post-treatments, which are typically needed in general sol–gel methods. X-ray photoemission spectroscopy showed that the fabricated zirconium oxide layer consists of inorganic ZrO2 and organic alkoxide groups, which can explain its marginal dielectric constant (∼9) and continuous film properties. In addition, by finishing the surface sol–gel synthesis at the stage of chemisorption, the hydrophobic nature of the final surface was retained, leading to a trap-free semiconductor/dielectric interface. As a result, the PFET made with a conventional polymeric semiconductor rendered nearly hysteresis-free and high mobility (0.3 cm2/V) characteristics at low voltage (

Ideal bone substitutes should ensure good integration with bone tissue and are therefore required to exhibit good mechanical stability and biocompatibility. Consequently, the high elastic modulus (similar to that of bone), thermoplasticity, and biocompatibility of poly(lactic acid) (PLA) make it well suited for the fabrication of such substitutes by fused filament fabrication (FFF)-based 3D printing. However, the demands of present-day applications require the mechanical and biological properties of PLA to be further improved. Herein, we fabricated PLA/Ti composite scaffolds by FFF-based 3D printing and used thermogravimetric analysis to confirm the homogenous dispersion of Ti particles in the PLA matrix at loadings of 5–20 vol%. Notably, the thermal stability of these composites and the crystallization temperature/crystallinity degree of PLA therein decreased with increasing Ti content, while the corresponding glass transition temperature and melting temperature concomitantly increased. The compressive and tensile strengths of PLA/Ti composites increased with Ti increasing loading until it reached 10 vol% and were within the range of real bone values, while the impact strengths of the above composites significantly exceeded that of pure PLA. The incorporation of Ti resulted in enhanced in vitro biocompatibility, promoting the initial attachment, proliferation, and differentiation of pre-osteoblast cells, which allowed us to conclude that the prepared PLA/Ti composite scaffolds with enhanced mechanical and biological properties are promising candidates for bone tissue engineering applications.

Considering the recent rapid growth of polymer field effect transistor (PFET) techniques and environmental pressure to avoid the use of toxic organic solvents in industrial processes, it is very important to develop colloids of semiconducting polymers in non-toxic solvents. Herein, we demonstrate the fabrication of surfactant-free, emulsion-dispersed nanoparticles of donor–acceptor copolymers. By optimizing the deposition methods of such semiconducting polymer colloids, high mobility (2.7 cm2/Vs) PFETs were fabricated via environmentally benign processes. Systematic analyses on the crystalline nature of the colloid-processed films revealed that the well-developed edge-on lamella structure comparable to that of the bulk polymer, was preserved during the colloid-fabrication processes.

Semiconducting polymer nanoparticles dispersed in water are synthesized by a novel method utilizing non-ionic surfactants. By developing a smart surfactant engineering technique involving a selective post-removal process of surfactants, an unprecedentedly high mobility of 2.51 cm(2) V(-1) s(-1) from a water-borne colloid is demonstrated for the first time.

Here, a novel strategy is reported to develop polymer field effect transistors using ethanol, propanol, and butanol—the most environmentally benign solvent except water—as processing solvents. From such environmentally benign processes, for the first time high-mobility (>1 cm2 V−1 s−1) polymer field effect transistors are demonstrated. These mobility values realized from “really green solvents” exceed those of conventional hydrogenated amorphous silicon semiconductors. To achieve this 1) stable sub-microparticles of conjugated polymers dispersed in alcohols are fabricated, 2) an aldehyde-assisted surface tension-depression methodology is developed to successfully form thin films from alcohol, and 3) the structural information of alcohol-dispersed sub-microparticles of semiconducting polymers is carefully characterized.

In this work, we fabricated a diketopyrrolopyrole-based donor-acceptor copolymer composite film. This is a high-mobility semiconductor component with a functionalized-graphene-oxide (GO) gas-adsorbing dopant, used as an active layer in gas-sensing organic-field-effect transistor (OFET) devices. The GO content of the composite film was carefully controlled so that the crystalline orientation of the semiconducting polymer could be conserved, without compromising its gas-adsorbing ability. The resulting optimized device exhibited high mobility (1 cm(2) V(-1) s(-1)) and revealed sensitive response during programmed exposure to various polar organic molecules (i.e., ethanol, acetone, and acetonitrile). This can be attributed to the high mobility of polymeric semiconductors, and also to their high surface-to-volume ratio of GO. The operating mechanism of the gas sensing GO-OFET is fully discussed in conjunction with charge-carrier trap theory. It was found that each transistor parameter (e.g., mobility, threshold voltage), responds independently to each gas molecule, which enables high selectivity of GO-OFETs for various gases. Furthermore, we also demonstrated practical GO-OFET devices that operated at low voltage (1.5 V), and which successfully responded to gas exposure.

We report on a new class of microliter-scale solution processes for fabricating highly uniform and large-area transistor arrays with extremely low consumption of semiconducting polymers. These processes are accomplished by applying a vertical phase separation of polymers with an environmentally benign solvent, a random copolymerization strategy between two highly conductive repeating units, and a meniscus-dragging deposition technique. The successful realization of these three processes, as confirmed by the structural and morphological in-depth characterizations, has enabled the fabrication of high-performance polymeric field-effect transistors that were uniformly distributed, without a single failure, on a 4 inch wafer using only 40 μg of semiconducting polymers. The resulting transistor arrays showed an average mobility of 0.28 cm2 V−1 s−1, with a low standard deviation of 0.04, as well as ultra-uniform near-zero threshold voltages. Our simple strategy shows great promise for fabricating large-scale organic electronic devices in the future using a truly low-cost process.

A hyaluronic acid (HAc)-hydroxyapatite (HAp) nanocomposite (HAc-nanoHAp) hydrogel was fabricated through an in situ precipitation process for mechanical and biological enhancement as a soft tissue augmentation product. In this study, these composite hydrogel fillers were analyzed from three different perspectives and compared with pure HAc hydrogel for soft tissue augmentation application: (1) rheological behaviors, (2) in vivo lateral diffusion under mouse skin, and (3) wrinkle improvement in a photo-aged mouse model. HAc-nanoHAp provided great improvement to wrinkles because of its higher stiffness and gel cohesiveness in comparison with that of pure HAc. HAc-nanoHAp also presented great enhancement in strengthening the dermal matrix by stimulating the synthesis of collagen and elastin. Thus, HAc-nanoHAp filler has great potential as a soft tissue augmentation product, improving the biophysical and biological performance in skin tissue. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3315-3325, 2017.

We show that selenophene-substitution can be an efficient synthetic strategy toward high charge carrier mobility of isoindigo (IID)-based copolymers when their side chains are optimized. A high mobility of 5.8 cm(2) V(-1) s(-1) is demonstrated by a strategically designed IID-based polymer, with both side-chain adjustment and selenophene-substitution.

The hole mobility of the widely studied diketopyrrolopyrole-based polymers (PDPPDTSE) was examined using space charge limited current (SCLC) and time of flight (TOF) methods. The mobility of the hole-only device based on PDPPDTSE was found to be dependent upon the e-field over the range of 10−3 to 10−2 cm2 V−1 s−1 with nearly identical Poole–Frenkel coefficients. In addition, we found that the mobility strongly depended on the thickness of the PDPPDTSE. By analyzing the temperature dependence of transport characteristics, we argued that the charge transport in this polymer was greatly influenced by trap distribution at the electrode/semiconductor interface.