Development of an Injectable Biphasic Hyaluronic Acid-Based Hydrogel With Stress Relaxation Properties for Cartilage Regeneration.

Biomimetic stress-relaxing hydrogels with reversible crosslinks attract significant attention for stem cell tissue regeneration compared with elastic hydrogels. However, stress-relaxing hyaluronic acid (HA)-based hydrogels fabricated using conventional technologies lack stability, biocompatibility, and mechanical tunability. Here, it is aimed to address these challenges by incorporating calcium or phosphate components into the HA backbone, which allows reversible crosslinking of HA with alginate to form interpenetrating networks, offering stability and mechanical tunability for mimicking cartilage. Diverse stress-relaxing hydrogels (τ1/2; SR50, 60-2000 s) are successfully prepared at ≈3 kPa stiffness with self-healing and shear-thinning abilities, favoring hydrogel injection. In vitro cell experiments with RNA sequencing analysis demonstrate that hydrogels tune chondrogenesis in a biphasic manner (hyaline or calcified) depending on the stress-relaxation properties and phosphate components. In vivo studies confirm the potential for biphasic chondrogenesis. These results indicate that the proposed stress-relaxing HA-based hydrogel with biphasic chondrogenesis (hyaline or calcified) is a promising material for cartilage regeneration.

Dual stimuli-responsive mesoporous silica nanoparticles for efficient loading and smart delivery of doxorubicin to cancer with RGD-integrin targeting.

The recent progress in nanoparticle applications, such as tumor-targeting, has enabled specific delivery of chemotherapeutics to malignant tissues with enhanced local efficacy while limiting side effects. However, existing delivery systems leave much room for improvement in terms of achieving enhanced colloidal stability in fluid medium, efficient targeting of intended sites, and effective release of therapeutic drugs into diseased cells. Here, an efficient stimuli-responsive nanocarrier for mammalian cells, termed RGD-NAMs, was developed, which enabled temperature- and pH-sensitive release of drug loads. The RGD-NAMs comprise two parts: a stimuli-responsive copolymer shell (NIBIm-AA-RGD) and drug-container core (MSNs). The RGD-NAMs have a stable drug-loading capacity with a marked difference in the release rate depending on the temperature and pH conditions. The RGD-NAMs also exhibit high colloidal stability in SBF (Stimulated body fluid) solutions and minimal toxicity in skeletal myoblasts (C2C12) and bovine arterial endothelial cells (BAEC). The doxorubicin-loaded RGD-NAMs induced a cytotoxic effect in a dose-dependent manner, which was furthered by an increase in temperature from 37 to 40 °C. Moreover, significant control of the release rate and the amount were achieved through pH change. This novel, smart drug-delivery system with high responsiveness to temperature and pH changes has wide application prospects in biomedical fields, including the theragnosis of tumors and vascular diseases.

Injectable remodeling hydrogels derived from alendronate-tethered alginate calcium complex for enhanced osteogenesis.

A combination of hydrogel materials, and therapeutic agents have been actively reported to facilitate bone defect healing. However, conventionally hydrogels using cross-linker would result in low stability of the hydrogel itself, loss of agents during cross-linking, and complexity of use. In this study, alendronate was tethered to an AlA to improve its bone healing and drug-loading stability. AlA was further functionalized with Ca2+ (AlACa). A mixture of AlACa and alginate formed AlAA hydrogel. The gelation time of AlAA was sufficient for injecting into the defect site. The hydrogel stiffness was controlled, while the stress-relaxation time was fixed. In vitro cell tests demonstrated that the AlAA promoted proliferation and differentiation behaviors. In particular, AlAA showed the best mechanical stiffness with appropriate stress-relaxation and cellular behavior, indicating that it would be beneficial as a scaffold in the bone tissue engineering field.

Wearable CNTs-based humidity sensors with high sensitivity and flexibility for real-time multiple respiratory monitoring.

Sensors, such as optical, chemical, and electrical sensors, play an important role in our lives. While these sensors already have widespread applications, such as humidity sensors, most are generally incompatible with flexible/inactive substrates and rely on conventional hard materials and complex manufacturing processes. To overcome this, we develop a CNT-based, low-resistance, and flexible humidity sensor. The core-shell structured CNT@CPM is prepared with Chit and PAMAM to achieve reliability, accuracy, consistency, and durability, resulting in a highly sensitive humidity sensor. The average response/recovery time of optimized sensor is only less than 20 s, with high sensitivity, consistent responsiveness, good linearity according to humidity rates, and low hysteresis (- 0.29 to 0.30 %RH). Moreover, it is highly reliable for long-term (at least 1 month), repeated bending (over 15,000 times), and provides accurate humidity measurement results. We apply the sensor to smart-wear, such as masks, that could conduct multi-respiratory monitoring in real-time through automatic ventilation systems. Several multi-respiratory monitoring results demonstrate its high responsiveness (less than 1.2 s) and consistent performance, indicating highly desirable for healthcare monitoring. Finally, these automatic ventilation systems paired with flexible sensors and applied to smart-wear can not only provide comfort but also enable stable and accurate healthcare in all environments.

Improved gliotransmission by increasing intracellular Ca2+ via TRPV1 on multi-walled carbon nanotube platforms.

BACKGROUND: Astrocyte is a key regulator of neuronal activity and excitatory/inhibitory balance via gliotransmission. Recently, gliotransmission has been identified as a novel target for neurological diseases. However, using the properties of nanomaterials to modulate gliotransmission has not been uncovered. RESULTS: We prepared non-invasive CNT platforms for cells with different nanotopography and properties such as hydrophilicity and conductivity. Using CNT platforms, we investigated the effect of CNT on astrocyte functions participating in synaptic transmission by releasing gliotransmitters. Astrocytes on CNT platforms showed improved cell adhesion and proliferation with upregulated integrin and GFAP expression. In addition, intracellular GABA and glutamate in astrocytes were augmented on CNT platforms. We also demonstrated that gliotransmitters in brain slices were increased by ex vivo incubation with CNT. Additionally, intracellular resting Ca2+ level, which is important for gliotransmission, was also increased via TRPV1 on CNT platforms. CONCLUSION: CNT can improve astrocyte function including adhesion, proliferation and gliotransmission by increasing resting Ca2+ level. Therefore, our study suggests that CNT would be utilized as a new therapeutic platform for central nervous system diseases by modulating gliotransmission.

Electrical and thermal stimulus-responsive nanocarbon-based 3D hydrogel sponge for switchable drug delivery.

Smart hydrogels that are responsive to various external (e.g. electrical and/or thermal) stimulation have become increasingly popular in recent years for simple, rapid, and precise drug delivery that can be controlled and turned on or off with external stimuli. For such a switchable drug delivery material, highly homogeneous dispersion and distribution of the hydrophobic, electrically conductive nanomaterials throughout a hydrophilic three-dimensional (3D) hydrogel network remains a challenge and is essential for achieving well-connected electrical and thermal conducting paths. Herein we developed electrical and thermal stimulus-responsive 3D hydrogels based on (i) carbon nanotubes (CNTs) as the core unit and an electrical/thermal conductor, (ii) chitosan (Chit) as the shell unit and a hydrophilic dispersant, and (iii) poly(NIPAAm-co-BBVIm) (pNIBBIm) as the drug carrier and a temperature-responsive copolymer. By formulating the CNT-core and Chit-shell units and constructing a CNT sponge framework, uniform distribution and 3D connectivity of the CNTs were improved. The 3D hydrogel based on the CNT sponge, namely the 3D frame CNT-Chit/pNIBBIm hydrogel, delivered approximately 37% of a drug, ketoprofen used for the treatment of musculoskeletal pain, during about 30% shrinkage after electrical and thermal switches on/off and exhibited the best potential for future use in a smart transdermal drug delivery system. The physicochemical, mechanical, electrical, thermal, and biocompatible characteristics of this nanocarbon-based 3D frame hydrogel led to remarkable electrical and thermal stimulus-responsive properties capable of developing an excellent controllable and switchable drug delivery platform for biomedical engineering and medicine applications.

Therapeutic tissue regenerative nanohybrids self-assembled from bioactive inorganic core / chitosan shell nanounits.

Natural inorganic/organic nanohybrids are a fascinating model in biomaterials design due to their ultra-microstructure and extraordinary properties. Here, we report unique-structured nanohybrids through self-assembly of biomedical inorganic/organic nanounits, composed of bioactive inorganic nanoparticle core (hydroxyapatite, bioactive glass, or mesoporous silica) and chitosan shell - namely Chit@IOC. The inorganic core thin-shelled with chitosan could constitute as high as 90%, strikingly contrasted with the conventional composites. The Chit@IOC nanohybrids were highly resilient under cyclic load and resisted external stress almost an order of magnitude effectively than the conventional composites. The nanohybrids, with the nano-roughened surface topography, could accelerate the cellular responses through stimulated integrin-mediated focal adhesions. The nanohybrids were also able to load multiple therapeutic molecules in the core and shell compartment and then release sequentially, demonstrating controlled delivery systems. The nanohybrids compartmentally-loaded with therapeutic molecules (dexamethasone, fibroblast growth factor 2, and phenamil) were shown to stimulate the anti-inflammatory, pro-angiogenic and osteogenic events of relevant cells. When implanted in the in vivo calvarium defect model with 3D-printed scaffold forms, the therapeutic nanohybrids were proven to accelerate new bone formation. Overall, the nanohybrids self-assembled from Chit@IOC nanounits, with their unique properties (ultrahigh inorganic content, nano-topography, high resilience, multiple-therapeutics delivery, and cellular activation), can be considered as promising 3D tissue regenerative platforms.

Biodegradable and injectable hydrogels as an immunosuppressive drug delivery system.

Cyclosporine A (CsA) is an extremely hydrophobic immunosuppressive drug, whose systemic administration to suppress the activity of T cells and T cell-based immune responses is frequently associated with a number of adverse drug reactions. Local delivery of CsA focused on a specific target organ has been proposed as a possible solution to this problem. In this study, we developed biodegradable sol-gel drug delivery systems, consisting of HA-Ca-Alg hydrogels combining hyaluronic acid calcium complex (HA-Ca) and sodium alginate (Alg-Na) components, for the local sustained delivery of CsA. A HA-Ca complex with very high degree of substitution was prepared by the acid-base reaction of hyaluronic acid and calcium acetate. The gelation was completed within about 2-45 min without external addition of calcium salts such as CaSO4 and CaCl2, indicating the high potential of the present hydrogel systems for drug delivery by injection in vivo. The HA-Ca system was characterized by high-resolution inductively coupled plasma-optical emission spectroscopy, 1H NMR, FT-IR, and thermogravimetric analysis methods. Moreover, the scanning electron microscopy analysis of the HA-Ca-Alg hydrogels showed an irregular porous morphology, with interconnected pores of 50-300 µm width. The sol-gel transition and the maximum viscosity (about 10,000 cP) of the HA-Ca-Alg hydrogels were characterized by examining the time evolution of the viscosity at 37 °C. The hydrolytic degradation of the HA-Ca-Alg hydrogel was also examined at 37 °C. CsA-encapsulated HA-Ca-Alg hydrogels exhibited sustained in vitro release of CsA over 14 days, which was confirmed through in vitro measurements of the activity of murine T cells over 2 weeks. These results show that the present injectable HA-Ca-Alg hydrogels can be used effectively for the sustained delivery of extremely hydrophobic immunosuppressive drugs, including CsA.

Small intestine- and colon-specific smart oral drug delivery system with controlled release characteristic.

In recent years, there has been a significant increase in strategies for the development of small intestine (and colon)-specific oral drug-delivery systems to maximize the efficiency of therapeutic agents and reduce side effects. However, only a few strategies are capable of working in the complicated environment of the human intestinal tract. In this study, the preparation of a basic pH/temperature-responsive co-polymer (p-NIVIm) and its in-vitro-drug delivery function in the pH range of 1-8 and temperature range of 25-42 °C are reported. The basic copolymer was prepared by radical copolymerization of N-isopropyl acryl amide (NIPAAm) and N-vinylimidazole (VIm). The lower critical solution temperature (LCST) of p-NIVIm was higher in stomach pH (~1.0) conditions (36.5-42 °C) and lower in small intestine and/or colon pH (~8.0) conditions (35.8-38.2 °C). The ability to uptake a model protein (BSA) at body temperature and to release it in conditions of 37 °C and pH 1-8 was determined. The drug loading capacity (0.231 mg per 1.0 mg copolymer) and efficiency (92.4%) were high at 37 °C/pH 7. The drug carrier showed a slow release pattern at pH 1 (~0.084 mg; ~35%) and then a sudden release pattern (~0.177 mg; ~73%) at pH 8. The cytotoxicity of p-NIVIm to MCF-7 cells in vitro was minimal at concentrations <168.9 µg/mL after 72 h. The prepared copolymer with its pH-/temperature-responsive protein-entrapping and -releasing behavior at body temperature may potentially be applied as a novel small intestine (and colon)-specific oral drug delivery system.

Carbon Nanotube Nanocomposites with Highly Enhanced Strength and Conductivity for Flexible Electric Circuits.

Carbon nanotubes (CNTs) have an important role in nanotechnology due to their unique properties, retaining the inherent material flexibility, superior strength, and electrical conductivity, unless the bottleneck of CNTs persists and the aggregated structure is overcome. Here, we report on the highly enhanced mechanical and electrical properties of the CNT-chitosan nanocomposites through homogeneous dispersion of CNTs into chitosan solution using a high-pressure homogenizer. The optimal condition is a 50% (w/w) chitosan-CNT film, providing about 7 nm thickness of homogeneous chitosan layer on CNTs, a good tensile strength of 51 MPa, high electrical conductivity under 16 Ω/sq, and a stable bending and folding performance. This CNT-chitosan nanocomposite with highly enhanced properties is an amenable material to fabricate structures of various shapes such as films, sensors, and circuits and also enables a simple and cost-effective approach to improve the performance of a device that presents the first flexible and soft electric circuits yet reported using only CNT-chitosan as the conductor.

Injectable hydrogels derived from phosphorylated alginic acid calcium complexes.

Phosphorylation of sodium alginate salt (NaAlg) was carried out using H3PO4/P2O5/Et3PO4 followed by acid-base reaction with Ca(OAc)2 to give phosphorylated alginic acid calcium complexes (CaPAlg), as a water dispersible alginic acid derivative. The modified alginate derivatives including phosphorylated alginic acid (PAlg) and CaPAlg were characterized by nuclear magnetic resonance spectroscopy for (1)H, and (31)P nuclei, high resolution inductively coupled plasma optical emission spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. CaPAlg hydrogels were prepared simply by mixing CaPAlg solution (2w/v%) with NaAlg solution (2w/v%) in various ratios (2:8, 4:6, 6:4, 8:2) of volume. No additional calcium salts such as CaSO4 or CaCl2 were added externally. The gelation was completed within about 3-40min indicating a high potential of hydrogel delivery by injection in vivo. Their mechanical properties were tested to be ≤6.7kPa for compressive strength at break and about 8.4kPa/mm for elastic modulus. SEM analysis of the CaPAlg hydrogels showed highly porous morphology with interconnected pores of width in the range of 100-800µm. Cell culture results showed that the injectable hydrogels exhibited comparable properties to the pure alginate hydrogel in terms of cytotoxicity and 3D encapsulation of cells for a short time period. The developed injectable hydrogels showed suitable physicochemical and mechanical properties for injection in vivo, and could therefore be beneficial for the field of soft tissue engineering.