Integrated Assembly and Photopreservation of Topographical Micropatterns.

Micromanipulation techniques that are capable of assembling nano/micromaterials into usable structures such as topographical micropatterns (TMPs) have proliferated rapidly in recent years, holding great promise in building artificial electronic and photonic microstructures. Here, a method is reported for forming TMPs based on optoelectronic tweezers in either "bottom-up" or "top-down" modes, combined with in situ photopolymerization to form permanent structures. This work demonstrates that the assembled/cured TMPs can be harvested and transferred to alternate substrates, and illustrates that how permanent conductive traces and capacitive circuits can be formed, paving the way toward applications in microelectronics. The integrated, optical assembly/preservation method described here is accessible, versatile, and applicable for a wide range of materials and structures, suggesting utility for myriad microassembly and microfabrication applications in the future.

Incorporating Wireless Strategies to Wearable Devices Enabled by a Photocurable Hydrogel for Monitoring Pressure Information.

Advances in emerging technologies for wireless collection and the timely analysis of various information captured by wearable devices are of growing interest. Herein, a crosslinked ionic hydrogel prepared by a facile photocuring process is proposed, which allows wearable devices to be further incorporated into two wireless integrated systems for pressure monitoring applications. The device exhibits a simplified structure by effectively sharing functional layers, rather than conventional two separate combinations, offering the salient performance of iontronic sensing and electrochromic properties to simultaneously quantify and visualize pressure. The developed smart patch system is demonstrated to monitor physiological signals in real-time utilizing the user interface of remote portable equipment with the Bluetooth protocol and on-site electrochromic displays. Moreover, a passive wireless system based on the magnetic coupling effect is designed, which can operate free from the battery and simultaneously acquire multiple pressure information. It is envisioned that the strategies would hold enormous potential for flexible electronics, versatile sensing platforms, and wireless on-body networks.

Cell-Laden Composite Hydrogel Bioinks with Human Bone Allograft Particles to Enhance Stem Cell Osteogenesis.

There is a growing demand for bone graft substitutes that mimic the extracellular matrix properties of the native bone tissue to enhance stem cell osteogenesis. Composite hydrogels containing human bone allograft particles are particularly interesting due to inherent bioactivity of the allograft tissue. Here, we report a novel photocurable composite hydrogel bioink for bone tissue engineering. Our composite bioink is formulated by incorporating human allograft bone particles in a methacrylated alginate formulation to enhance adult human mesenchymal stem cell (hMSC) osteogenesis. Detailed rheology and printability studies confirm suitability of our composite bioinks for extrusion-based 3D bioprinting technology. In vitro studies reveal high cell viability (~90%) for hMSCs up to 28 days of culture within 3D bioprinted composite scaffolds. When cultured within bioprinted composite scaffolds, hMSCs show significantly enhanced osteogenic differentiation as compared to neat scaffolds based on alkaline phosphatase activity, calcium deposition, and osteocalcin expression.

Exosomal OTULIN from M2 macrophages promotes the recovery of spinal cord injuries via stimulating Wnt/ß-catenin pathway-mediated vascular regeneration.

Vascularization following spinal cord injury (SCI) provides trophic support for rebuilding up and maintaining the homeostasis of neuronal networks, and the promotion of angiogenesis is beneficial for functional recovery after SCI. M2 macrophages have been reported to exhibit powerful pro-angiogenic functions during tissue repair. Exosomes are important paracrine mediators of their parent cells and play critical roles in tissue regeneration. However, the role of M2 macrophage-derived exosomes (M2-Exos) in SCI is still largely unknown. In the present study, we determined that M2-Exos could augment the angiogenic activities of spinal cord microvascular endothelial cells (SCMECs) in vitro. Hydrogel-mediated sustained release of M2-Exos significantly promoted vascular regeneration and functional recovery in mice after SCI. Furthermore, proteomics analysis showed that ubiquitin thioesterase otulin (OTULIN) protein was highly enriched in M2-Exos. Functional assays demonstrated that OTULIN protein was required for the M2-Exos-induced pro-angiogenic effects in SCMECs, as well as positive effects on vascular regeneration, cell proliferation, and functional recovery in the mouse model of SCI. Mechanically, OTULIN from M2-Exos could activate the Wnt/ß-catenin signaling by increasing the protein level of ß-catenin via inhibiting its ubiquitination and trigger the expression of angiogenesis-related genes that are reported to be the downstream targets of Wnt/ß-catenin signaling. Inhibition of the Wnt/ß-catenin signaling by ICG001 markedly attenuated the pro-angiogenic activities of M2-Exos in vitro/vivo. Our findings indicate that M2-Exos positively modulate vascular regeneration and neurological functional recovery after SCI by activating Wnt/ß-catenin signaling through the transfer of OTULIN protein. STATEMENT OF SIGNIFICANCE: M2 macrophages have been identified to promote vascular regeneration, cell proliferation and tissue growth after spinal cord injury (SCI), which is beneficial to the functional recovery. Exosomes are essential paracrine mediators involved in cell-to-cell communication and play important roles in tissue regeneration. In the present study, we revealed that M2 macrophages-derived exosomes (M2-Exos) could promote functional recovery post SCI by targeting angiogenesis. We demonstrated for the first time that OTULIN protein from M2-Exos mediated the angiogenic effects through activating Wnt/ß-catenin signaling and triggering the expression of angiogenic-related genes in spinal cord microvascular endothelial cells (SCMECs). The hydrogel-M2-Exos sustained released system provides potential therapeutic clues of local cell-free interventions for the treatment of SCI.

Highly elastomeric photocurable silk hydrogels.

A photocurable silk fibroin hydrogel is prepared, for the first time, using natural silk protein fibroin and biophotosensitizer riboflavin. Riboflavin is excited by ultraviolet light to generate a triplet state which is transferred to produce active oxygen radicals with singlet oxygen as the main component. Active oxygen radicals can induce chemical cross-linking of amino-, phenol- and other groups in the silk fibroin macromolecules to form a photocurable hydrogel. The different biophysical characterizations of the gelation of this modified fibroin protein solution were studied by using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, microplate reader and texture analyzer. The aggregate structures, surface morphologies, mechanical properties, light transmission and degradation properties of the gel were studied. The investigations showed that the silk fibroin/riboflavin hydrogels predominantly have random coils or alpha helix structures. These gels show resilience up to 90% after 80% compression and a light transmission of up to 97%. The cell culture experiment exhibits that the hydrogel has a satisfactory cytocompatibility.

Development of 3D printable conductive hydrogel with crystallized PEDOT:PSS for neural tissue engineering.

Bioelectronic devices enable efficient and effective communication between medical devices and human tissue in order to directly treat patients with various neurological disorders. Due to the mechanical similarity to human tissue, hydrogel-based electronic devices are considered to be promising for biological signal recording and stimulation of living tissues. Here, we report the first three-dimensionally (3D) printable conductive hydrogel that can be photocrosslinked while retaining high electrical conductivity. In addition, we prepared dorsal root ganglion (DRG) cell-encapsulated gelatin methacryloyl (GelMA) hydrogels which were integrated with the 3D printed conductive structure and evaluated for efficiency neural differentiation under electrical stimulation (ES). For enhanced electrical conductivity, a poly(3,4-ethylenedioxythiophene) (PEDOT): polystyrene sulfonate (PSS) aqueous solution was freeze-dried and mixed with polyethylene glycol diacrylate (PEGDA) as the photocurable polymer base. Next, the conductive hydrogel was patterned on the substrate by using a table-top stereolithography (SLA) 3D printer. The fabricated hydrogel was characterized for electrochemical conductivity. After printing with the PEDOT:PSS conductive solution, the patterned hydrogel exhibited decreased printing diameters with increasing of PEDOT:PSS concentration. Also, the resultant conductive hydrogel had significantly increased electrochemical properties with increasing PEDOT:PSS concentration. The 3D printed conductive hydrogel provides excellent structural support to systematically transfer the ES toward encapsulated DRG cells for enhanced neuronal differentiation. The results from this study indicate that the conductive hydrogel can be useful as a 3D printing material for electrical applications.

Integration of a Genetically Encoded Calcium Molecular Sensor into Photopolymerizable Hydrogels for Micro-Optrode-Based Sensing.

Genetically encoded molecular-protein sensors (GEMS) are engineered to sense and quantify a wide range of biological substances and events in cells, in vitro and even in vivo with high spatial and temporal resolution. Here, we aim to stably incorporate these proteins into a photopatternable matrix, while preserving their functionality, to extend the application of these proteins as spatially addressable optical biosensors. For this reason, we examined the fabrication of 3D hydrogel microtips doped with a genetically encoded fluorescent biosensor, GCaMP3, at the end of an optical fiber. Stable incorporation parameters of GCaMP3 into a photo-cross-linkable monomer matrix were investigated through a series of characterization and optimization experiments. Different precursor-solution formulations and irradiation parameters of in situ photopolymerization were tested to determine the factors affecting protein stability and sensor reproducibility during photoencapsulation. The microstructure and performance of hydrogel microtips were controlled by varying UV irradiation intensity as well as the molecular weight and concentration of the photocurable monomer, PEGDA (polyethylene glycol diacrylate), in precursor solution. Protein-doped hydrogel micro-optrodes (microtip sensors) were fabricated successfully and reproducibly at the distal end of optical fiber. Under optimized conditions, the bioactivity of GCaMP3 within a hydrogel matrix of micro-optrodes remained similar to that of the protein-free matrix in buffer. The limit of detection of protein optrodes for free calcium was also determined to be 4.3 nM. The hydrogel formulation and fabrication process demonstrated here using microtip optrodes can be easily adapted to other conformation-dependent protein biosensors and can be used in sensing applications.