Photobiomodulation of Gingival Cells Challenged with Viable Oral Microbes

The oral cavity, a unique ecosystem harboring diverse microorganisms, maintains health through a balanced microflora. Disruption may lead to disease, emphasizing the protective role of gingival epithelial cells (GECs) in preventing harm from pathogenic oral microbes. Shifting GECs' response from proinflammatory to antimicrobial could be a novel strategy for periodontitis. Photobiomodulation therapy (PBMT), a nonpharmacologic host modulatory approach, is considered an alternative to drugs. While the host cell response induced by a single type of pathogen-associated molecular patterns (PAMPs) was widely studied, this model does not address the cellular response to intact microbes that exhibit multiple PAMPs that might modulate the response. Inspired by this, we developed an in vitro model that simulates direct interactions between host cells and intact pathogens and evaluated the effect of PBMT on the response of human gingival keratinocytes (HGKs) to challenge viable oral microbes at both the cellular and molecular levels. Our data demonstrated that LED pretreatment on microbially challenged HGKs with specific continuous wavelengths (red: 615 nm; near-infrared: 880 nm) induced the production of various antimicrobial peptides, enhanced cell viability and proliferation, promoted reactive oxygen species scavenging, and down-modulated proinflammatory activity. The data also suggest a potential explanation regarding the superior efficacy of near-infrared light treatment compared with red light in enhancing antimicrobial activity and reducing cellular inflammation of HGKs. Taken together, the findings suggest that PBMT enhances the overall barrier function of gingival epithelium while minimizing inflammation-mediated breakdown of the underlying structures.

A strategy for enhancing bioactivity and osseointegration with antibacterial effect by incorporating magnesium in polylactic acid based biodegradable orthopedic implant

Biodegradable orthopedic implants are essential for restoring the physiological structure and function of bone tissue while ensuring complete degradation after recovery. Polylactic acid (PLA), a biodegradable polymer, is considered a promising material due to its considerable mechanical properties and biocompatibility. However, further improvements are necessary to enhance the mechanical strength and bioactivity of PLA for reliable load-bearing orthopedic applications. In this study, a multifunctional PLA-based composite was fabricated by incorporating tricalcium phosphate (TCP) microspheres and magnesium (Mg) particles homogenously at a volume fraction of 40 %. This approach aims to enhance mechanical strength, accelerate pore generation, and improve biological and antibacterial performance. Mg content was incorporated into the composite at varying values of 1, 3, and 5 vol% (referred to as PLA/TCP-1 Mg, PLA/TCP-3 Mg, and PLA/TCP-5 Mg, respectively). The compressive strength and stiffness were significantly enhanced in all composites, reaching 87.7, 85.9, and 84.1 MPa, and 2.7, 3.0, and 3.1 GPa, respectively. The degradation test indicated faster elimination of the reinforcers as the Mg content increased, resulting in accelerated pore generation to induce enhanced osseointegration. Because PLA/TCP-3 Mg and PLA/TCP-5 Mg exhibited cracks in the PLA matrix due to rapid corrosion of Mg forming corrosion byproducts, to optimize the Mg particle content, PLA/TCP-1 Mg was selected for further evaluation. As determined by in vitro biological and antibacterial testing, PLA/TCP-1 Mg showed enhanced bioactivity with pre-osteoblast cells and exhibited antibacterial properties by suppressing bacterial colonization. Overall, the multifunctional PLA/TCP-Mg composite showed improved mechanobiological performance, making it a promising material for biodegradable orthopedic implants.

Antibacterial PLA/Mg composite with enhanced mechanical and biological performance for biodegradable orthopedic implants

Biodegradability, bone-healing rate, and prevention of bacterial infection are critical factors for orthopedic implants. Polylactic acid (PLA) is a good candidate biodegradable material; however, it has insufficient mechanical strength and bioactivity for orthopedic implants. Magnesium (Mg), has good bioactivity, biodegradability, and sufficient mechanical properties, similar to that of bone. Moreover, Mg has an inherent antibacterial property via a photothermal effect, which generates localized heat, thus preventing bacterial infection. Therefore, Mg is a good candidate material for PLA composites, to improve their mechanical and biological performance and add an antibacterial property. Herein, we fabricated an antibacterial PLA/Mg composite for enhanced mechanical and biological performance with an antibacterial property for application as biodegradable orthopedic implants. The composite was fabricated with 15 and 30 vol% of Mg homogeneously dispersed in PLA without the generation of a defect using a high-shear mixer. The composites exhibited an enhanced compressive strength of 107.3 and 93.2 MPa, and stiffness of 2.3 and 2.5 GPa, respectively, compared with those of pure PLA which were 68.8 MPa and 1.6 GPa, respectively. Moreover, the PLA/Mg composite at 15 vol% Mg exhibited significant improvement of biological performance in terms of enhanced initial cell attachment and cell proliferation, whereas the composite at 30 vol% Mg showed deteriorated cell proliferation and differentiation because of the rapid degradation of the Mg particles. In turn, the PLA/Mg composites exerted an antibacterial effect based on the inherent antibacterial property of Mg as well as the photothermal effect induced by near-infrared (NIR) treatment, which can minimize infection after implantation surgery. Therefore, antibacterial PLA/Mg composites with enhanced mechanical and biological performance may be a candidate material with great potential for biodegradable orthopedic implants.

3D-Printed Functional Hydrogel by DNA-Induced Biomineralization for Accelerated Diabetic Wound Healing

Chronic wounds in diabetic patients are challenging because their prolonged inflammation makes healing difficult, thus burdening patients, society, and health care systems. Customized dressing materials are needed to effectively treat such wounds that vary in shape and depth. The continuous development of 3D-printing technology along with artificial intelligence has increased the precision, versatility, and compatibility of various materials, thus providing the considerable potential to meet the abovementioned needs. Herein, functional 3D-printing inks comprising DNA from salmon sperm and DNA-induced biosilica inspired by marine sponges, are developed for the machine learning-based 3D-printing of wound dressings. The DNA and biomineralized silica are incorporated into hydrogel inks in a fast, facile manner. The 3D-printed wound dressing thus generates provided appropriate porosity, characterized by effective exudate and blood absorption at wound sites, and mechanical tunability indicated by good shape fidelity and printability during optimized 3D printing. Moreover, the DNA and biomineralized silica act as nanotherapeutics, enhancing the biological activity of the dressings in terms of reactive oxygen species scavenging, angiogenesis, and anti-inflammation activity, thereby accelerating acute and diabetic wound healing. These bioinspired 3D-printed hydrogels produce using a DNA-induced biomineralization strategy are an excellent functional platform for clinical applications in acute and chronic wound repair.

Manufacturing and Characterization of Dental Crowns Made of 5-mol% Yttria Stabilized Zirconia by Digital Light Processing

We herein report manufacturing of dental crowns made of 5-mol% yttria partially stabilized zirconia (5Y-PSZ) with desired mechanical properties, optical translucency and dimensional accuracy using digital light processing (DLP). To this end, all processing parameters were carefully controlled and optimized. First, 5Y-PSZ particles with a bimodal distribution were prepared via calcination of as-received granules and subsequent ball-milling and then used to formulate 5Y-PSZ suspensions with a high solid loading of 50 vol% required for high densification after sintering. Dispersant content was also optimized. To provide high dimensional accuracy, initial dimensions of dental crowns for 3D printing were precisely determined by considering increase and decrease in dimensions during photopolymerization and sintering, respectively. Photopolymerization time was also optimized for a given layer thickness of 50 μm to ensure good bonding between layers. A multi-step debinding schedule with a slow heating rate was employed to avoid formation of any defects. After sintering at 1500 °C for 2 h, 5Y-PSZ could be almost fully densified without noticeable defects within layers and at interfaces between layers. They had high relative densities (99.03 ± 0.39%) with a high cubic phase content (59.1%). These characteristics allowed for achievement of reasonably high mechanical properties (flexural strength = 625.4 ± 75.5 MPa and Weibull modulus = 7.9) and % transmittance (31.4 ± 0.7%). In addition, 5Y-PSZ dental crowns showed excellent dimensional accuracy (root mean square (RMS) for marginal discrepancy = 44.4 ± 10.8 μm and RMS for internal gap = 22.8 ± 1.6 μm) evaluated by the 3D scanning technique.

Digital Light Processing of Zirconia Suspensions Containing Photocurable Monomer/Camphor Vehicle for Dental Applications

This study reports the utility of solid camphor as a novel diluent in photocurable hexanediol diacrylate (HDDA) monomer to manufacture 4 mol% yttria partially stabilized zirconia (4Y-PSZ) components for dental applications by digital light processing (DLP). The use of a 65 wt% HDDA-35 wt% camphor solution allowed 4Y-PSZ suspensions to have reasonably low viscosities (1399 ± 55.8 mPa·s at a shear rate of 75 s^-1), measured by a cone/plate viscometer, at a high solid loading of 48 vol%, where 4Y-PSZ particles prepared by calcination of as-received 4Y-PSZ granules, followed by a ball-milling process, were used with assistance of a dispersant. These 4Y-PSZ suspensions could be successfully applied to our custom-made DLP machine for manufacturing 4Y-PSZ components. To this end, several processing parameters, including layer thickness of 4Y-PSZ suspension, UV illumination time for layer-by-layer photocuring process, and initial dimensions of 4Y-PSZ objects, were tightly controlled. As sintering temperature increased from 1300 °C to 1500 °C, relative density and grain size of 4Y-PSZ objects increased, and cubic phase content also increased. Thus, after sintering at the highest temperature of 1500 °C for 3 h, high mechanical properties (biaxial flexural strength = 911 ± 40.7 MPa, hardness = 1371 ± 14.4 H_v) and reasonably high optical transmittance (translucency parameter = 7.77 ± 0.32, contrast ratio = 0.809 ± 0.007), evaluated by a spectrophotometer, were obtained due to a high relative density (97.2 ± 1.38%), which would be useful for dental applications.

PCSK9 modulates the Wnt/beta-catenin signaling pathway in myocardial ischemia/reperfusion injury

Background

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a protein that affects cholesterol homeostasis. Recent research has found that PCSK9 has various effects on the heart that are unrelated to LDL cholesterol regulation. The Wnt/β-catenin signaling pathway plays a crucial role during heart development, and it is re-activated in response to cardiac injury. Low-density lipoprotein receptor-related proteins 5 (LRP5) act as co-receptors of Wnt ligands and are indispensable for Wnt/β-catenin signal transduction. However, it is not fully elucidated whether other members of the LDLR-superfamily may be targets of PCSK9.

Purpose

This study aimed to determine if LRP5 is a PCSK9 target, study the association between PCSK9 and Wnt/β-catenin signaling, and elucidate its effect on myocardial infarction in patients with ischemic cardiomyopathy.

Methods

The expression of Lrp5, phospho-β-catenin, total β-catenin was evaluated by western blot analysis, and the effects of overexpressed PCSK9 were tested under normoxia, hypoxia, or hypoxia/re-oxygenation (H/R) in mouse cardiomyocytes (HL-1). The transcriptional activity of β-catenin was assessed using the TOP-Flash/FOP-Flash luciferase reporter assay. In addition, the impact on various downstream targets of the Wnt/β-catenin signaling pathway was assessed using a quantitative real-time polymerase chain reaction. To examine whether PCSK9 regulates injury of cardiomyocytes in vivo, we subjected transgenic mice with cardiac-specific overexpression of PCSK9 (PCSK9 TG) and wild-type (WT) mice to either sham surgery or ischemia/reperfusion (I/R) surgery.

Results

Under hypoxic conditions, the Wnt/β-catenin signaling pathway-related genes were downregulated in HL-1 cells, as evidenced by lower Lrp5 and active phospho-β-catenin expression levels (0.5-fold, n=3, p<0.01). After H/R, the Wnt/β-catenin-related genes were recovered (1.5-fold, p<0.01) in the control group but not in the PCSK9 overexpressed group. In the luciferase reporter assay results, PCSK9 overexpression inhibited the recovery of β-catenin transcriptional activity after H/R, in contrast to the control group. Furthermore, mRNA levels of Axin2, Cyclin D1, which are the Wnt/β-catenin signaling downstream pathway targets, were down-regulated under hypoxia and recovered after H/R but did not recover in PCSK9 overexpressed cells. In the mouse I/R model, the overall protein levels of the Wnt/β-catenin signaling-related genes were down-regulated in PCSK9 TG mice compared to WT mice after I/R injury.

Conclusions

These results indicated that the regulation of PCSK9 is closely associated with the Wnt/β-catenin signaling pathway which may play a crucial role in damaged cardiomyocytes. It suggests that the regulation of PCSK9 could be a therapeutic target in patients with ischemic cardiomyopathy.

Funding Acknowledgement

Type of funding sources: None.

Improved Biocompatibility of Intra-Arterial Poly-L-Lactic Acid Stent by Tantalum Ion Implantation : 3-Month Results in a Swine Model

Objective

Biodegradable poly-L-lactic acid (PLLA) with a highly biocompatible surface via tantalum (Ta) ion implantation can be an innovative solution for the problems associated with current biodegradable stents. The purpose of this study is to develop a Ta-implanted PLLA stent for clinical use and to investigate its biological performance capabilities.

Methods

A series of in vitro and in vivo tests were used to assess the biological performance of bare and Ta-implanted PLLA stents. The re-endothelialization ability and thrombogenicity were examined through in vitro endothelial cell and platelet adhesion tests. An in vivo swine model was used to evaluate the effects of Ta ion implantation on subacute restenosis and thrombosis. Angiographic and histologic evaluations were conducted at one, two and three months post-treatment.

Results

The Ta-implanted PLLA stent was successfully fabricated, exhibiting a smooth surface morphology and modified layer integration. After Ta ion implantation, the surface properties were more favorable for rapid endothelialization and for less platelet attachment compared to the bare PLLA stent. In an in vivo animal test, follow-up angiography showed no evidence of in-stent stenosis in either group. In a microscopic histologic examination, luminal thrombus formation was significantly suppressed in the Ta-implanted PLLA stent group according to the 2-month follow-up assessment (21.2% vs. 63.9%, p=0.005). Cells positive for CD 68, a marker for the monocyte lineage, were less frequently identified around the Ta-implanted PLLA stent in the 1-month follow-up assessments.

Conclusion

The use of a Ta-implanted PLLA stent appears to promote re-endothelialization and anti-thrombogenicity.

Stable sol-gel hydroxyapatite coating on zirconia dental implant for improved osseointegration

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 (<1000 °C). The surface showed a nanoporous structure, and there was no crystalline phase other than HA and zirconia when the sintering temperature was 800 °C. The adhesion strength of the HA layer (>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.

Bifunctional poly (l-lactic acid)/hydrophobic silica nanocomposite layer coated on magnesium stents for enhancing corrosion resistance and endothelial cell responses

Biodegradable magnesium (Mg)-based vascular stents can overcome the limitations of conventional permanent metallic stents, such as late in-stent restenosis and thrombosis, but still have difficulty retarding degradation while providing adequate mechanical support to the blood vessel. We incorporated silica nanoparticles surface-functionalized with hexadecyltrimethoxysilane (mSiNP) into a poly (l-lactic acid) (PLLA) coating as a physical barrier to disturb the penetration of the corrosive medium as well as a bioactive source that releases silicon ions capable of stimulating endothelial cells. The corrosion resistance and biocompatibility of this bifunctional PLLA/mSiNP nanocomposite coating were investigated using different weight ratios of mSiNP. The nanocomposite coating containing more than 10 wt% of the mSiNP (PLLA/10mSiNP and PLLA/20mSiNP) significantly delayed the corrosion of the Mg substrate and exhibited favorable endothelial cell responses, compared to the pure PLLA coating. Specifically, the calculated corrosion rates of PLLA/10mSiNP and PLLA/20mSiNP decreased by half, indicating the durability of the coating after immersion in simulated body fluid for 12 days. Based on the in vitro cellular response, the incorporation of the mSiNPs into the PLLA coating significantly improved the endothelial cell responses to the Mg substrate, showing better initial cell surface coverage, migration, and proliferation rate than those of pure PLLA. These results indicate that the PLLA/mSiNP nanocomposite coatings have significant potential to improve the corrosion resistance and vascular compatibility of biodegradable Mg-based vascular stents.

Polydeoxyribonucleotide-delivering therapeutic hydrogel for diabetic wound healing

Patients with diabetes experience delayed wound healing because of the uncontrolled glucose level in their bloodstream, which leads to impaired function of white blood cells, poor circulation, decreased production and repair of new blood vessels. Treatment using polydeoxyribonucleotide (PDRN), which is a DNA extracted from the sperm cells of salmon, has been introduced to accelerate the healing process of diabetic wounds. To accelerate the wound-healing process, sustained delivery of PDRN is critical. In this study, taking advantage of the non-invasive gelation property of alginate, PDRN was loaded inside the hydrogel (Alg-PDRN). The release behavior of PDRN was altered by controlling the crosslinking density of the Alg hydrogel. The amount of PDRN was the greatest inside the hydrogel with the highest crosslinking density because of the decreased diffusion. However, there was an optimal degree of crosslinking for the effective release of PDRN. In vitro studies using human dermal fibroblasts and diabetes mellitus fibroblasts and an in ovo chorioallantoic membrane assay confirmed that the Alg-PDRN hydrogel effectively induced cell proliferation and expression of angiogenic growth factors and promoted new blood vessel formation. Its effectiveness for accelerated diabetic wound healing was also confirmed in an in-vivo animal experiment using a diabetic mouse model.

Biodegradable magnesium alloy (WE43) in bone-fixation plate and screw

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.

Enhanced biolubrication on biomedical devices using hyaluronic acid-silica nanohybrid hydrogels

In this work, highly lubricous hyaluronic acid-silica (HA-SiO₂) nanohybrid coatings were fabricated through a sequential process consisting of a sol-gel followed by electrophoretic deposition (EPD). SiO₂ nanoparticles were uniformly distributed in the coating layers, and the coating thickness was identified as approximately 1-2 μm regardless of the amount of SiO_2. Incorporation of SiO₂ into the HA polymer matrix enhanced the mechanical stability of the nanohybrid coatings, indicating greater interfacial bonding strength compared to HA coating layers alone. In addition, due to improved stability, the nanohybrid coatings showed excellent biolubrication properties, which were evaluated with a tribological experiment. These results indicate that the nanohybrid coatings have great potential to be used in biomedical applications that require superior biolubrication properties.

Bioactive and mechanically stable hydroxyapatite patterning for rapid endothelialization of artificial vascular graft

Polymeric vascular grafts have been widely used in the vascular regeneration field because of their ease of application. However, synthetic polymer grafts have the severe problem of low biocompatibility, which may cause delayed endothelialization and hyperplasia. In this study, we fabricated a linear hydroxyapatite (HA) pattern on a silicon wafer and then transferred the pattern to a poly(L-lactic)-acid (PLLA) film for use as a tubular vascular graft. The HA pattern with its characteristic needle-like shape was successfully embedded into the PLLA. The HA-patterned PLLA film exhibited superior mechanical stability compared with that of a HA-coated PLLA film under bending, elongation, and in vitro circulation conditions, suggesting its suitability for use as a tubular vascular graft. In addition, the HA pattern guided rapid endothelialization by promoting proliferation of endothelial cells and their migration along the pattern. The hemocompatibility of the HA-patterned PLLA was also confirmed, with substantially fewer platelets adhered on its surface. Overall, in addition to good mechanical stability, the HA-patterned PLLA exhibited enhanced biocompatibility and hemocompatibility compared with pure PLLA.

Digital Light Processing of Freeze-cast Ceramic Layers for Macroporous Calcium Phosphate Scaffolds with Tailored Microporous Frameworks

The objective of the present study is to demonstrate the versatility of the digital light processing (DLP) technique particularly when using a freeze-cast ceramic layer as the feedstock, which can manufacture porous calcium phosphate (CaP) scaffolds with arbitrarily designed macroporous structures with tailored microporous frameworks specially designed for bone scaffold applications. For this goal, we employed camphene-camphor as the freezing vehicle and porogen for the preparation of photocurable CaP suspensions containing diurethane dimethacrylate (UDMA) monomers. After freeze-casting, the CaP suspensions could be solidified at controlled temperatures (~33-38 °C) and then be photopolymerized by DLP. All produced CaP scaffolds fairly resembled the designed macroporous structures (the gyroid structure with two interpenetrating macropore networks). In addition, numerous micropores were created in the CaP filaments, while the microporosity increased with increasing the camphene-camphor amount from 40 vol % to 60 vol %. As a consequence, compressive strength and modulus of hierarchically porous CaP scaffolds decreased due to an increase in overall porosity. However, reasonable mechanical properties could be obtained at high porosities owing to the CaP frameworks constructed in a periodic manner. In addition, excellent water penetration capability, biocompatibility, and apatite-forming ability were obtained, which were attributed to the microporous CaP frameworks with good pore interconnectivity and large surface area.

Ta ion implanted nanoridge-platform for enhanced vascular responses

Bare metal stents are commonly used in interventional cardiology; they provide successful treatment because of their excellent mechanical properties, expandability ratios, and flexibility. However, their insufficient vascular affinity can induce the development of neointimal hyperplasia following arterial injury and subsequent smooth muscle cell overgrowth in the lumen of a stented vessel. Nanoengineering of the bare metal stent surface is a valuable strategy for eliciting favorable vascular responses. In this study, we introduce a target-ion-induced plasma sputtering (TIPS) technique to fabricate a platform with a favorable endothelial environment. This technique enables the simple single-step production of a Ta-implanted nanoridged surface on a stent with a complex 3D geometry that shows a clear tendency to become oriented parallel to the direction of blood flow. Moreover, the nanoridges developed show good structural integrity and mechanical stability, resulting in apparently stable morphologies under high strain rates. In vitro cellular responses to the Co-Cr, such as endothelialization, platelet activation, and blood coagulation, are considerably altered after TIPS treatment; endothelium formation is rapid and surface thrombogenicity is low. An in vivo rabbit iliac artery model is used to confirm that the nanoridged surface facilitates rapid re-endothelialization and limits the formation of neointima compared to the bare stent. These results indicate that the Ta ion implanted nanoridge platform fabricated using the TIPS technique has immense potential as a solution for in-stent restenosis and ensuring the long-term patency of bare metal stents.

Hyaluronic Acid-Based Hybrid Hydrogel Microspheres with Enhanced Structural Stability and High Injectability

For hydrogel injection applications, it is important to improve the strength and biostability of the hydrogel as well as its injectability to pass easily through the needle. Making gel microspheres is one approach to achieve these improvements. Granulization of a bulk hydrogel is a common procedure used to form microsized particles; however, the nonuniform size and shape cause an uneven force during injection, damaging the surrounding tissue and causing pain to the patients. In this study, injectable hyaluronic acid (HA)-based hybrid hydrogel microspheres were fabricated using a water-in-oil emulsion process. The injectability was significantly enhanced because of the relatively uniform size and spherical shape of the hydrogel formulates. In addition, the biostability and mechanical strength were also increased owing to the increased cross-linking density compared with that of conventionally fabricated gel microparticles. This tendency was further improved after in situ calcium phosphate precipitation. Our findings demonstrate the great potential of HA-based hydrogel microspheres for various clinical demands requiring injectable biomaterials.

3D Plotting using Camphene as Pore-regulating Agent to Produce Hierarchical Macro/micro-porous Poly(ε-caprolactone)/calcium phosphate Composite Scaffolds

This study demonstrates the utility of camphene as the pore-regulating agent for phase separation-based 3D plotting to produce hierarchical macro/micro-porous poly(ε-caprolactone) (PCL)-calcium phosphate (CaP) composite scaffolds, specifically featuring highly microporous surfaces. Unlike conventional particulate porogens, camphene is highly soluble in acetone, the solvent for PCL polymer, but insoluble in coagulation medium (water). In this study, this unique characteristic supported the creation of numerous micropores both within and at the surfaces of PCL and PCL-CaP composite filaments when using high camphene contents (40 and 50 wt%). In addition, the incorporation of the CaP particles into PCL solutions did not deteriorate the formation of microporous structures, and thus hierarchical macro/micro-porous PCL-CaP composite scaffolds could be successfully produced. As the CaP content increased, the in vitro biocompatibility, apatite-forming ability, and mechanical properties (tensile strength, tensile modulus, and compressive modulus) of the PCL-CaP composite scaffolds were substantially improved.

Enhanced Osseointegration Ability of Poly(lactic acid) via Tantalum Sputtering-Based Plasma Immersion Ion Implantation

Poly(lactic acid) (PLA) is the most utilized biodegradable polymer in orthopedic implant applications because of its ability to replace regenerated bone tissue via continuous degradation over time. However, the poor osteoblast affinity for PLA results in a high risk of early implant failure, and this issue remains one of the most difficult challenges with this technology. In this study, we demonstrate the use of a new technique in which plasma immersion ion implantation (PIII) is combined with a conventional DC magnetron sputtering. This technique, referred to as sputtering-based PIII (S-PIII), makes it possible to produce a tantalum (Ta)-implanted PLA surface within 30 s without any tangible degradation or deformation of the PLA substrate. Compared to a Ta-coated PLA surface, the Ta-implanted PLA showed twice the surface roughness and substantially enhanced adhesion stability in dry and wet conditions. The strong hydrophobic surface properties and biologically relatively inert chemical structure of PLA were ameliorated by Ta S-PIII treatment, which produced a moderate hydrophilic surface and enhanced cell-material interactions. Furthermore, in an in vivo evaluation in a rabbit distal femur implantation model, Ta-implanted PLA demonstrated significantly enhanced osseointegration and osteogenesis compared with bare PLA. These results indicate that the Ta-implanted PLA has great potential for orthopedic implant applications.

Biomimetic porous Mg with tunable mechanical properties and biodegradation rates for bone regeneration

The medical applications of porous Mg scaffolds are limited owing to its rapid corrosion, which dramatically decreases the mechanical strength of the scaffold. Mimicking the bone structure and composition can improve the mechanical and biological properties of porous Mg scaffolds. The Mg structure can also be coated with HA by an aqueous precipitation coating method to enhance both the corrosion resistance and the biocompatibility. However, due to the brittleness of HA coating layer, cracks tend to form in the HA coating layer, which may influence the corrosion and biological functionality of the scaffold. Consequently, in this study, hybrid poly(ether imide) (PEI)-SiO₂ layers were applied to the HA-coated biomimetic porous Mg to impart the structure with the high corrosion resistance associated with PEI and excellent bioactivity with SiO₂. The porosity of the Mg was controlled by adjusting the concentration of the sodium chloride (NaCl) particles used in the fabrication via the space-holder method. The mechanical measurements showed that the compressive strength and stiffness of the biomimetic porous Mg increased as the portion of the dense region increased. In addition, following results show that HA/(PEI-SiO₂) hybrid-coated biomimetic Mg is a promising biodegradable scaffold for orthopedic applications. In-vitro testing revealed that the proposed hybrid coating reduced the degradation rate and facilitated osteoblast spreading compared to HA- and HA/PEI-coating scaffolds. Moreover, in-vivo testing with a rabbit femoropatellar groove model showed improved tissue formation, reduced corrosion and degradation, and improved bone formation on the scaffold. STATEMENT OF SIGNIFICANCE: Porous Mg is a promising biodegradable scaffold for orthopedic applications. However, there are limitations in applying porous Mg for an orthopedic biomaterial due to its poor mechanical properties and susceptibility to rapid corrosion. Here, we strategically designed the structure and coating layer of porous Mg to overcome these limitations. First, porous Mg was fabricated by mimicking the bone structure which has a combined structure of dense and porous regions, thus resulting in an enhancement of mechanical properties. Furthermore, the biomimetic porous Mg was coated with HA/(PEI-SiO₂) hybrid layer to improve both corrosion resistance and biocompatibility. As the final outcome, with tunable mechanical and biodegradable properties, HA/(PEI-SiO₂)-coated biomimetic porous Mg could be a promising candidate material for load-bearing orthopedic applications.

Reduced fibrous capsule formation at nano-engineered silicone surfaces via tantalum ion implantation

Nano-engineered surface of silicone implant improves the biocompatibility and suppresses the fibrous capsule formation which is the most common side effect of polymeric implants.

Use of thioglycerol on porous polyurethane as an effective theranostic capping agent for bone tissue engineering

Thiolated biodegradable polyurethane (TG-DPU) was synthesized using a one-pot reaction with thioglycerol adopted as a functionalized chain extender. After characterization of the chemical structure of TG-DPU using proton nuclear magnetic resonance spectroscopy, bone morphogenetic protein (BMP-2) was loaded in the TG-DPU under oxidative conditions to form disulfides between the free thiol of TG-DPU and BMP-2. The interaction between TG-DPU and BMP-2, so-called bioconjugates, was investigated using X-ray photoelectron spectroscopy analysis; the appearance of disulfide (S–S) linkage indicated the formation of a polymer/growth factor conjugate system. The covalently linked bioconjugates provided stability with minimal loss during the drug delivery with prolonged release performance in in vitro release tests. The effects of the drugs delivered by TG-DPU were also confirmed by in vitro alkaline phosphatase tests using pre-osteoblasts and in vivo bone regeneration tests. The drugs effectively induced cell differentiation and promoted mature bone recovery.

Fluorine-ion-releasing injectable alginate nanocomposite hydrogel for enhanced bioactivity and antibacterial property

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.

Porous Calcium Phosphate Ceramic Scaffolds with Tailored Pore Orientations and Mechanical Properties Using Lithography-Based Ceramic 3D Printing Technique

This study demonstrates the usefulness of the lithography-based ceramic 3-dimensional printing technique with a specifically designed top-down process for the production of porous calcium phosphate (CaP) ceramic scaffolds with tailored pore orientations and mechanical properties. The processing parameters including the preparation of a photocurable CaP slurry with a high solid loading (φ = 45 vol%), the exposure time for photocuring process, and the initial designs of the porous scaffolds were carefully controlled. Three types of porous CaP scaffolds with different pore orientations (i.e., 0°/90°, 0°/45°/90°/135°, and 0°/30°/60°/90°/120°/150°) were produced. All the scaffolds exhibited a tightly controlled porous structure with straight CaP frameworks arranged in a periodic pattern while the porosity was kept constant. The porous CaP scaffold with a pore orientation of 0°/90° demonstrated the highest compressive strength and modulus due to a number of CaP frameworks parallel to the loading direction. On the other hand, scaffolds with multiple pore orientations may exhibit more isotropic mechanical properties regardless of the loading directions. The porous CaP scaffolds exhibited an excellent in vitro apatite-forming ability in a stimulated body fluid (SBF) solution. These findings suggest that porous CaP scaffolds with tailored pore orientations may provide tunable mechanical properties with good bone regeneration ability.

Ultrafast Single-Band Upconversion Luminescence in a Liquid-Quenched Amorphous Matrix

Achieving single-band upconversion is a challenging but rewarding approach to attain optimal performance in diverse applications, such as multiplexed molecular imaging, security coding, and nonlinear photonic devices. Here, highly efficient single-band upconversion luminescence in the green spectral regime (16.4 times increase in emission at 525 nm) accomplished by realizing minimal energy loss from two-photon upconversion in a newly synthesized liquid-quenched amorphous matrix is reported. In contrast to previously reported single-band upconversion, this phenomenon originates from the elevated transition probability of the host sensitive transition via changes in the host matrix's microstructure. The elevated transition probability facilitates ultrafast decay of upconversion luminescence with decay times as short as 0.2 µs, the fastest decay ever reported. The material in this study therefore has strong potential for use in photonic devices demanding high upconversion efficiency with a fast response time, which to date has been inaccessible using upconversion materials.

Coextrusion-Based 3D Plotting of Ceramic Pastes for Porous Calcium Phosphate Scaffolds Comprised of Hollow Filaments

This paper demonstrates the utility of coextrusion-based 3D plotting of ceramic pastes (CoEx-3DP) as a new type of additive manufacturing (AM) technique, which can produce porous calcium phosphate (CaP) ceramic scaffolds comprised of hollow CaP filaments. In this technique, green filaments with a controlled core/shell structure can be produced by coextruding an initial feedrod, comprised of the carbon black (CB) core and CaP shell, through a fine nozzle in an acetone bath and then deposited in a controlled manner according to predetermined paths. In addition, channels in CaP filaments can be created through the removal of the CB cores during heat-treatment. Produced CaP scaffolds had two different types of pores with well-defined geometries: three-dimensionally interconnected pores (~360 × 230 μm² in sizes) and channels (>100 μm in diameter) in hollow CaP filaments. The porous scaffolds showed high compressive strengths of ~12.3 ± 2.2 MPa at a high porosity of ~73 vol % when compressed parallel to the direction of the hollow CaP filaments. In addition, the mechanical properties of porous CaP scaffolds could be tailored by adjusting their porosity, for example, compressive strengths of 4.8 ± 1.1 MPa at a porosity of ~82 vol %. The porous CaP scaffold showed good biocompatibility, which was assessed by in vitro cell tests, where several the cells adhered to and spread actively with the outer and inner surfaces of the hollow CaP filaments.

Effective Wound Healing by Antibacterial and Bioactive Calcium-Fluoride-Containing Composite Hydrogel Dressings Prepared Using in Situ Precipitation

In this study, we report the development of a hyaluronic acid (HA)-based composite hydrogel containing calcium fluoride (CaF₂) with good biocompatibility and antibacterial properties for multifunctional wound dressing applications. CaF₂ was newly selected for incorporation within HA because it can release both Ca²⁺ and F^- ions, which are well-known ions for affecting cell proliferation and inhibiting bacterial growth, respectively. In particular, an in situ precipitation process enables easy control over the released amount of F^- ions by simply adjusting the precursor solutions (calcium chloride (CaCl₂) and ammonium fluoride (NH₄F)) used for the CaF₂ precipitation. CaF₂ particles were uniformly embedded within a HA-based pure hydrogel using an in situ precipitation process. Through variation of the CaCl₂ and NH₄F concentrations used in the precipitation as well as the precipitation time, composite hydrogels with different ion-release profiles were obtained. By controlling the precipitation time, especially for 10 min and after 30 min, large differences in the ion-release profiles as a function of CaF₂ concentration were observed. A shorter precipitation time resulted in faster release of fluoride, whereas for the 30 min and 1 h samples, sustained ion release was achieved. Colony tests and live/dead assays using Escherichia coli and Staphylococcus aureus revealed a lower density of bacteria on the CaF₂ composite hydrogels than on the pure hydrogel for both strains. In addition, improved cellular responses such as cell attachment and proliferation were also observed for the CaF₂ composite hydrogels compared to those for the pure hydrogel. Furthermore, the composite hydrogels exhibited excellent wound healing efficiency, as evidenced by an in vitro cell migration assay. Finally, monitoring of the wound closure changes using a full-thickness wound in a rat model revealed the accelerated wound healing capability of the CaF₂ composite hydrogels compared with that of the pure hydrogel. Based on our findings, these CaF₂ composite hydrogels show great potential for application as advanced hydrogel wound dressings with antibacterial properties and accelerated wound-healing capabilities.

In vitro and in vivo evaluation of polylactic acid-based composite with tricalcium phosphate microsphere for enhanced biodegradability and osseointegration

A biodegradable polylactic acid composite containing tricalcium phosphate microsphere was fabricated. The composite exhibited enhanced biocompatibility and a well-interconnected porous structure that enabled tissue ingrowth after degradation. The tricalcium phosphate microspheres had an average size of 106 ± 43 μm and were incorporated into the polylactic acid matrix using a high-shear mixer. The resulting bioactivity and hydrophilicity were enhanced to levels comparable to those of a polylactic acid composite containing tricalcium phosphate powder, which is a well-known material used in the medical field. An accelerated 30-day degradation test in HCl revealed successful generation of an open porous structure with ∼98% interconnectivity in the polylactic acid–tricalcium phosphate microsphere composite, demonstrating the potential of this material to induce enhanced osseointegration in the later stage of bone regeneration. The early stage osseointegration was also evaluated by implanting the composite in vivo using a rabbit femoral defect model. After 16 weeks of implantation, the bone-to-implant contact ratio of the polylactic acid–tricalcium phosphate microsphere composite was enhanced owing to tissue ingrowth through the generated pores near the surface.

Acceleration of the healing process of full-thickness wounds using hydrophilic chitosan-silica hybrid sponge in a porcine model

In this study, we evaluated the surface characterization of a novel chitosan-silica hybridized membrane and highlighted the substantial role of silica in the wound environment. The chemical coupling of chitosan and silica resulted in a more condensed network compared with pure chitosan, which was eventually able to stably maintain its framework, particularly in the wet state. In addition, we closely observed the wound-healing process along with the surface interaction between chitosan-silica and the wound site using large-surface-area wounds in a porcine model. Our evidence indicates that chitosan-silica exerts a synergetic effect of both materials to promote a remarkable wound-healing process. In particular, the silica in chitosan-silica accelerated wound closure including wound contraction, and re-epithelialization via enhancement of cell recruitment, epidermal maturity, neovascularization, and granulation tissue formation compared with pure chitosan and other commercial dressing materials. This advanced wound dressing material may lead to effective treatment for problematic cutaneous wounds and can be further applied for human skin regeneration.

Calcium Phosphate-Collagen Scaffold with Aligned Pore Channels for Enhanced Osteochondral Regeneration

This study reports the development of a bilayered scaffold with aligned channels produced via a sequential coextrusion and unidirectional freezing process to facilitate upward bone-marrow stem-cell migration. The biomimetic scaffold with collagen and biphasic calcium phosphate (BCP) layers is successfully fabricated with matching of the cartilage and bone layers. The aligned structure results in an enhancement of the compressive strength, and the channels enable tight anchoring of the collagen layers on the BCP scaffolds compared with a randomly structured porous scaffold. An in vitro evaluation demonstrates that the aligned channels guide the cells to attach on the surface in highly stretched shapes and migrate upward faster than the random structure. In addition, in vivo assessment reveals that the aligned channels yield superior osteochondral tissue regeneration compared with the random structure. Moreover, the channel diameter greatly affects the tissue regeneration, and the scaffold with a channel diameter of ≈270 µm exhibits the optimal regeneration because of sufficient nutrient supply and adequate tissue ingrowth. These findings indicate that the introduction of aligned channels to a bilayered scaffold provides an effective approach for osteochondral tissue regeneration.

Biocompatibility and Biocorrosion of Hydroxyapatite-Coated Magnesium Plate: Animal Experiment

Magnesium (Mg) has the advantage of being resorbed in vivo, but its resorption rate is difficult to control. With uncontrolled resorption, Magnesium as a bone fixation material has minimal clinical value. During resorption not only is the strength rapidly weakened, but rapid formation of metabolite also occurs. In order to overcome these disadvantages, hydroxyapatite (HA) surface coating of pure magnesium plate was attempted in this study. Magnesium plates were inserted above the frontal bone of Sprague-Dawley rats in both the control group (Bare-Mg group) and the experimental group (HA-Mg group). The presence of inflammation, infection, hydrogen gas formation, wound dehiscence, and/or plate exposure was observed, blood tests were performed, and the resorption rate and tensile strength of the retrieved metal plates were measured. The HA-Mg group showed no gas formation or plate exposure until week 12. However, the Bare-Mg group showed consistent gas formation and plate exposure beginning in week 2. WBC (White Blood Cell), BUN (Blood Urea Nitrogen), Creatinine, and serum magnesium concentration levels were within normal range in both groups. AST (Aspartate Aminotransferase) and ALT (Alanine Aminotransferase) values, however, were above normal range in some animals of both groups. The HA-Mg group showed statistically significant advantage in resistance to degradation compared to the Bare-Mg group in weeks 2, 4, 6, 8, and 12. Degradation of HA-Mg plates proceeded after week 12. Coating magnesium plates with hydroxyapatite may be a viable method to maintain their strength long enough to allow bony healing and to control the resorption rate during the initial period.

Production of Poly(ε-Caprolactone)/Hydroxyapatite Composite Scaffolds with a Tailored Macro/Micro-Porous Structure, High Mechanical Properties, and Excellent Bioactivity

We produced poro-us poly(ε-caprolactone) (PCL)/hydroxyapatite (HA) composite scaffolds for bone regeneration, which can have a tailored macro/micro-porous structure with high mechanical properties and excellent in vitro bioactivity using non-solvent-induced phase separation (NIPS)-based 3D plotting. This innovative 3D plotting technique can create highly microporous PCL/HA composite filaments by inducing unique phase separation in PCL/HA solutions through the non-solvent-solvent exchange phenomenon. The PCL/HA composite scaffolds produced with various HA contents (0 wt %, 10 wt %, 15 wt %, and 20 wt %) showed that PCL/HA composite struts with highly microporous structures were well constructed in a controlled periodic pattern. Similar levels of overall porosity (~78 vol %) and pore size (~248 µm) were observed for all the PCL/HA composite scaffolds, which would be highly beneficial to bone tissue regeneration. Mechanical properties, such as ultimate tensile strength and compressive yield strength, increased with an increase in HA content. In addition, incorporating bioactive HA particles into the PCL polymer led to remarkable enhancements in in vitro apatite-forming ability.

Novel Self-Assembly-Induced Gelation for Nanofibrous Collagen/Hydroxyapatite Composite Microspheres

This study demonstrates the utility of the newly developed self-assembly-induced gelation technique for the synthesis of porous collagen/hydroxyapatite (HA) composite microspheres with a nanofibrous structure. This new approach can produce microspheres of a uniform size using the droplets that form at the nozzle tip before gelation. These microspheres can have a highly nanofibrous structure due to the immersion of the droplets in a coagulation bath (water/acetone), in which the collagen aggregates in the solution can self-assemble into fibrils due to pH-dependent precipitation. Bioactive HA particles were incorporated into the collagen solutions, in order to enhance the bioactivity of the composite microspheres. The composite microspheres exhibited a well-defined spherical morphology and a uniform size for all levels of HA content (0 wt %, 10 wt %, 15 wt %, and 20 wt %). Collagen nanofibers-several tens of nanometers in size-were uniformly present throughout the microspheres and the HA particles were also well dispersed. The in vitro apatite-forming ability, assessed using the simulated body fluid (SBF) solution, increased significantly with the incorporation of HA into the composite microspheres.

Innovative micro-textured hydroxyapatite and poly(l-lactic)-acid polymer composite film as a flexible, corrosion resistant, biocompatible, and bioactive coating for Mg implants

The utility of a novel ceramic/polymer-composite coating with a micro-textured microstructure that would significantly enhance the functions of biodegradable Mg implants is demonstrated here. To accomplish this, bioactive hydroxyapatite (HA) micro-dots can be created by immersing a Mg implant with a micro-patterned photoresist surface in an aqueous solution containing calcium and phosphate ions. The HA micro-dots can then be surrounded by a flexible poly(l-lactic)-acid (PLLA) polymer using spin coating to form a HA/PLLA micro-textured coating layer. The HA/PLLA micro-textured coating layer showed an excellent corrosion resistance when it was immersed in a simulated body fluid (SBF) solution and good biocompatibility, which was assessed by in vitro cell tests. In addition, the HA/PLLA micro-textured coating layer had high deformation ability, where no apparent changes in the coating layer were observed even after a 5% elongation, which would be unobtainable using HA and PLLA coating layers; furthermore, this allowed the mechanically-strained Mg implant with the HA/PLLA micro-textured coating layer to preserve its excellent corrosion resistance and biocompatibility in vitro.

Polyurethane-silica hybrid foams from a one-step foaming reaction, coupled with a sol-gel process, for enhanced wound healing

Polyurethane (PU)-based dressing foams have been widely used due to their excellent water absorption capability, optimal mechanical properties, and unequaled economic advantage. However, the low bioactivity and poor healing capability of PU limit the applications of PU dressings in complex wound healing cases. To resolve this problem, this study was carried out the hybridization of bioactive silica nanoparticles with PU through a one-step foaming reaction that is coupled with the sol-gel process. The hybridization with silica did not affect the intrinsically porous microstructure of PU foams with silica contents of up to 10wt% and where 5-60nm silica nanoparticles were well dispersed in the PU matrix, despite slight agglomerations. The incorporated silica enhanced the mechanical performance of PU by proffering better flexibility and durability as well as maintaining good water absorption capabilities and the WVTR characteristics of pure PU foam. The silica of PU-10wt% Si foams was gradually dissolved and released under physiological conditions during a 14-day immersion period. The in vitro cell attachment and proliferation tests showed significant improvements in terms of the biocompatibility of PU-Si hybrid foams and demonstrated the effects of silica on cell growth. More significantly, the superior healing capability of PU-Si as a wound dressing in comparison to PU-treated wounds was verified through in vivo animal tests. Full-thickness wounds treated with PU-Si foams exhibited faster wound closure rates as well as accelerated collagen and elastin fiber regeneration in newly formed dermis, which was ultimately completely covered by a new epithelial layer. It is clear that PU-Si hybrid foams have considerable potential as a wound dressing material geared for accelerated, superior wound healing.

Biomimetic Coating of Hydroxyapatite on Glycerol Phosphate-Conjugated Polyurethane via Mineralization

In this study, glycerol phosphate was introduced into polyurethane (PU) to promote the coating stability of hydroxyapatite (HA) during its mineralization on the PU surface. Glycerol phosphate was successfully conjugated with the PU chain during polymerization. Phosphate groups in glycerol phosphate accelerated the nucleation of HA under calcium phosphate ion-rich conditions (concentrated simulated body fluid), resulting in the enhancement of structural stability. The robust interface between HA and PU also improved mechanical properties. Hydrophilic phosphate groups and bioactive HA improved in vitro cellular responses in terms of the attachment and proliferation of L929 fibroblasts and MC3T3-E1 preosteoblasts. Thus, the highly elastic and bioactive PU-gp-HA could be a promising candidate for tissue engineering applications that experience frequent deformation, including diverse cartilage replacements.

The Production of Porous Hydroxyapatite Scaffolds with Graded Porosity by Sequential Freeze-Casting

Porous hydroxyapatite (HA) scaffolds with porosity-graded structures were fabricated by sequential freeze-casting. The pore structures, compressive strengths, and biocompatibilities of the fabricated porous HA scaffolds were evaluated. The porosities of the inner and outer layers of the graded HA scaffolds were controlled by adjusting the initial HA contents of the casting slurries. The interface between the dense and porous parts was compact and tightly adherent. The porosity and compressive strengths of the scaffold were controlled by the relative thicknesses of the dense/porous parts. In addition, the porous HA scaffolds showed good biocompatibility in terms of preosteoblast cell attachment and proliferation. The results suggest that porous HA scaffolds with load-bearing parts have potential as bone grafts in hard-tissue engineering.