Dissection of an ABC transporter LolCDE function analyzed by photo-crosslinking

The envelope of Escherichia coli contains approximately 100 different species of lipoproteins, most of which are localized to the inner leaflet of the outer membrane. The localization of lipoprotein (Lol) system, consisting of five Lol proteins, is responsible for the trafficking of lipoproteins to the outer membrane. LolCDE binds to lipoproteins destined for the outer membrane and transfers them to the periplasmic chaperone LolA. Although the cryo-EM structures of E. coli LolCDE have been reported, the mechanisms by which outer membrane lipoproteins are transferred to LolA remain elusive. In this study, we investigated the interaction between LolCDE and lipoproteins using site-specific photo-crosslinking. We introduced a photo-crosslinkable amino acid into different locations across the four helices which form the central lipoprotein-binding cavity, and identified domains that crosslink with peptidoglycan-associated lipoprotein (Pal) in vivo. Using one of the derivatives containing the photo-crosslinkable amino acid, we developed an in vitro system to analyze the binding of lipoproteins to LolCDE. Our results indicate that compound 2, a LolCDE inhibitor, does not inhibit the binding of lipoproteins to LolCDE, but rather promotes the dissociation of bound lipoproteins from LolCDE.

In Vitro and In Vivo Degradation of Photo-Crosslinked Poly(Trimethylene Carbonate-co-ε-Caprolactone) Networks

Three-armed poly(trimethylene carbonate) (PTMC) and poly(trimethylene carbonate-co-Ɛ-caprolactone) (P(TMC-co-ε-CL)) macromers with molecular weights of approximately 30 kg mol-1 are synthesized by ring-opening polymerization and subsequent functionalization with methacrylic anhydride. Networks are then prepared by photo-crosslinking. To investigate the in vitro and in vivo degradation properties of these photo-crosslinked networks and assess the effect of ε-caprolactone content on the degradation properties, PTMC networks, and copolymer networks with two different TMC:ε-CL ratios are prepared. PTMC networks degraded slowly, via an enzymatic surface erosion process, both in vitro and in vivo. Networks prepared from P(TMC-co-ε-CL) macromers with a 74:26 ratio are found to degrade slowly as well, via a surface erosion process, albeit at a higher rate compared to PTMC networks. Increasing the ε-CL content to a ratio of 52:48, resulted in a faster degradation. These networks lost their mechanical properties much sooner than the other networks. Thus, PTMC and P(TMC-co-ε-CL) networks are interesting networks for tissue engineering purposes and the exact degradation properties can be tuned by varying the TMC:ε-CL ratio, providing researchers with a tool to obtain copolymer networks with the desired degradation rate depending on the intended application.

A well plate-based GelMA photo-crosslinking system with tunable hydrogel mechanical properties to regulate the PTH-mediated osteogenic fate

Versatile and efficient regulation of the mechanical properties of the extracellular matrix is crucial not only for understanding the dynamic changes in biological systems, but also for obtaining precise and effective cellular responses in drug testing. In this study, we developed a well plate-based hydrogel photo-crosslinking system to effectively control the mechanical properties of hydrogels and perform high-throughput assays. We improved cell biocompatibility by using gelatin methacryloyl (GelMA) with a visible light photo-crosslinking method. Multiple cell-laden GelMA hydrogels were simultaneously and uniformly created using multi-arrayed 520 nm light-emitting diodes in a well plate format. The elastic modulus of the hydrogels can be widely adjusted (0.5-30 kPa) using a photo-crosslinking system capable of independently controlling the light intensity or exposure time for multiple samples. We demonstrate the feasibility of our system by observing enhanced bone differentiation of human mesenchymal stem cells (hMSCs) cultured on stiffer hydrogels. Additionally, we observed that the osteogenic fate of hMSCs, affected by the different mechanical properties of the gel, was regulated by parathyroid hormone (PTH). Notably, in response to PTH, hMSCs in a high-stiffness microenvironment upregulate osteogenic differentiation while exhibiting increased proliferation in a low-stiffness microenvironment. Overall, the developed system enables the generation of multiple cell-laden three-dimensional cell culture models with diverse mechanical properties and holds significant potential for expansion into drug testing.

Green Synthesis of UV-Reactive Polycarbonates from Levoglucosenone and 5-Hydroxymethyl Furfural

This study focuses on the synthesis of fully renewable polycarbonates (PCs) starting from cellulose-based platform molecules levoglucosenone (LGO) and 2,5-bis(hydroxymethyl)furan (BHMF). These unique bio-based PCs are obtained through the reaction of a citronellol-containing triol (Triol-citro) derived from LGO, with a dimethyl carbonate derivative of BHMF (BHMF-DC). Solvent-free polymerizations are targeted to minimize waste generation and promote an eco-friendly approach with a favorable environmental factor (E-factor). The choice of metal catalyst during polymerization significantly influences the polymer properties, resulting in high molecular weight (up to 755 kDa) when Na2 CO3 is employed as an inexpensive catalyst. Characterization using nuclear magnetic resonance confirms the successful incorporation of the furan ring and the retention of the terminal double bond of the citronellol pendant chain. Furthermore, under UV irradiation, the presence of both citronellol and furanic moieties induces singular structural changes, triggering the formation of three distinct structures within the polymer network, a phenomenon herein occurs for the first time in this type of polymer. These findings pave the way to new functional materials prepared from renewable monomers with tunable properties.

Effect of Residue Acrylic Monomers in Synthesized Solvent-Free Photoreactive Pressure-Sensitive Adhesives on the Main Properties of Transfer Tapes Applied to Joining Wooden Elements

This publication describes the influence of residue monomers in synthesized pressure-sensitive adhesives based on acrylics on their main properties-tack, peel adhesion, shear strength and shrinkage-in the form of transfer tapes used for joining wooden elements in the furniture industry. The discussed carrier-free adhesive tapes are synthesized via photo-crosslinking and photopolymerization with UV radiation of the photoreactive prepolymers sandwiched between two adhesive siliconized polyester films. The simultaneous crosslinking and polymerization processes carried out under UV lamps placed simultaneously above and below the crosslinked photoreactive polymer layer lead to the production of a carrier-free adhesive film. The preliminary target of these studies was to investigate how the intensity of UV radiation and the time of its exposure affect the viscosity of the photoreactive compositions and the content of unreacted monomers in them. Next, the influence of the crosslinking agent concentration and UV irradiation time on the content of unreacted monomers after the crosslinking process was tested. The last step of the studies was the investigation of the influence of the residue monomer concentration on the application properties of the obtained pressure-sensitive adhesive layers. The typical PSA application properties were tested on the wood samples: tack, peel adhesion, shear strength (cohesion) and shrinkage.

Covalent Capture and Selection of DNA-Encoded Chemical Libraries via Photo-Activated Lysine-Selective Crosslinkers

Covalent crosslinking probes have arisen as efficient toolkits to capture and elucidate biomolecular interaction networks. Exploiting the potential of crosslinking in DNA-encoded chemical library (DEL) selection methods significantly boosted bioactive ligand discovery in complex physiological contexts. Herein, we incorporated o-nitrobenzyl alcohol (o-NBA) as a photo-activated lysine-selective crosslinker into divergent DEL formats and achieved covalent capture of ligand-target interactions featuring improved crosslinking efficiency and site-specificity. In addition, covalent DEL selection was realized with the modularly designed o-NBA-functionalized mock libraries.

A Mucin-Based Bio-Ink for 3D Printing of Objects with Anti-Biofouling Properties

With its potential to revolutionize the field of personalized medicine by producing customized medical devices and constructs for tissue engineering at low costs, 3D printing has emerged as a highly promising technology. Recent advancements have sparked increasing interest in the printing of biopolymeric hydrogels. However, owing to the limited printability of those soft materials, the lack of variability in available bio-inks remains a major challenge. In this study, a novel bio-ink is developed based on functionalized mucin-a glycoprotein that exhibits a multitude of biomedically interesting properties such as immunomodulating activity and strong anti-biofouling behavior. To achieve sufficient printability of the mucin-based ink, its rheological properties are tuned by incorporating Laponite XLG as a stabilizing agent. It is shown that cured objects generated from this novel bio-ink exhibit mechanical properties partially similar to that of soft tissue, show strong anti-biofouling properties, good biocompatibility, tunable cell adhesion, and immunomodulating behavior. The presented findings suggest that this 3D printable bio-ink has a great potential for a wide range of biomedical applications, including tissue engineering, wound healing, and soft robotics.

Advances and challenges in identifying and characterizing G-quadruplex-protein interactions

G-quadruplexes (G4s) are peculiar nucleic acid secondary structures formed by DNA or RNA and are considered as fundamental features of the genome. Many proteins can specifically bind to G4 structures. There is increasing evidence that G4-protein interactions involve in the regulation of important cellular processes, such as DNA replication, transcription, RNA splicing, and translation. Additionally, G4-protein interactions have been demonstrated to be potential targets for disease treatment. In order to unravel the detailed regulatory mechanisms of G4-binding proteins (G4BPs), biochemical methods for detecting G4-protein interactions with high specificity and sensitivity are highly demanded. Here, we review recent advances in screening and validation of new G4BPs and highlight both their features and limitations.

A Photopolymerizable Biocompatible Hyaluronic Acid Hydrogel Promotes Early Articular Cartilage Repair in a Minipig Model In Vivo

Articular cartilage defects represent an unsolved clinical challenge. Photopolymerizable hydrogels are attractive candidates supporting repair. This study investigates the short-term safety and efficacy of two novel hyaluronic acid (HA)-triethylene glycol (TEG)-coumarin hydrogels photocrosslinked in situ in a clinically relevant large animal model. It is hypothesized that HA-hydrogel-augmented microfracture (MFX) is superior to MFX in enhancing early cartilage repair, and that the molar degree of substitution and concentration of HA affects repair. Chondral full-thickness defects in the knees of adult minipigs are treated with either 1) debridement (No MFX), 2) debridement and MFX, 3) debridement, MFX, and HA hydrogel (30% molar derivatization, 30 mg mL-1 HA; F3) (MFX+F3), and 4) debridement, MFX, and HA hydrogel (40% molar derivatization, 20 mg mL-1 HA; F4) (MFX+F4). After 8 weeks postoperatively, MFX+F3 significantly improves total macroscopic and histological scores compared with all other groups without negative effects, besides significantly enhancing the individual repair parameters "defect architecture," "repair tissue surface" (compared with No MFX, MFX), and "subchondral bone" (compared with MFX). These data indicate that photopolymerizable HA hydrogels enable a favorable metastable microenvironment promoting early chondrogenesis in vivo. This work also uncovers a mechanism for effective HA-augmented cartilage repair by combining lower molar derivatization with higher concentrations.

Construction and Catalytic Study of Affinity Peptide Orientation and Light Crosslinking Immobilized Sucrose Isomerase

A novel affinity peptide orientation and light-controlled covalent immobilized method was developed. Sucrose isomerase (SI) was selected as the model enzyme. Molecular simulation was first performed to select the targeted immobilization region. Subsequently, a short peptide (H2N-VNIGGX-COOH, VG) with high affinity to this region was rationally designed. Thereafter, 4-benzoyl-l-phenylalanine with the photosensitive group of benzophenone was introduced. Then, the affinity between the ligand and the SI was validated using molecular dynamics simulation. Thereafter, the SI was directionally immobilized onto the surface of the epoxy resin (EP) guided by VG via photo-crosslinking, and thus the oriented photo-crosslinking enzymes were obtained. The enzymatic activity, thermostability, and reusability of the affinity directional photo-crosslinked immobilized sucrose isomerase (hv-EP-VG-SI) were systematically studied. The oriented immobilization enzymes were significantly improved in recycling and heat resistance. Moreover, hv-EP-VG-SI retained more than 90% of the original activity and 50% of the activity after 11 cycles.

Sustained delivery of osteogenic growth peptide through injectable photoinitiated composite hydrogel for osteogenesis

One of the most challenging clinical issues continues to be the effective bone regeneration and rebuilding following bone abnormalities. Although osteogenic growth peptide (OGP) has been proven to be effective in promoting osteoblast activity, its clinical application is constrained by abrupt release and easily degradation. We developed a GelMA/HAMA dual network hydrogel loaded with OGP based on a combination of physical chain entanglement and chemical cross-linking effects to produce an efficient long-term sustained release of OGP. The hydrogel polymers were quickly molded under ultraviolet (UV) light and had the suitable physical characteristics, porosity structure and biocompatibility. Significantly, the GelMA/HAMA-OGP hydrogel could promote cell proliferation, adhesion, increase osteogenic-related gene and protein expression in vitro. In conclusion, the OGP sustained-release system based on GelMA/HAMA dual network hydrogel offers a fresh perspective on bone regeneration therapy.

Indolocarbazole-Based Photo-Crosslinkable Hole-Transporting Layer for Efficient Solution-Processed Organic Light-Emitting Diodes

We designed and synthesized a new indolocarbazole-based polymer, poly(N,N-diphenyl(5,11-dihexylindolo[3,2,1-jk]carbazol-2-yl)amine) (PICA), for solution-processed organic light-emitting diodes (OLEDs). The highest occupied and lowest unoccupied molecular orbital energy levels of this polymer, -5.25 and -2.46 eV, respectively, are suitable for hole transport from the anode to the emissive layer. PICA was photo-crosslinked by UV irradiation with ethane-1,2-diyl bis(4-azido-2,3,5,6-tetrafluorobenzoate) (FPA) as the photoinitiator. Successful crosslinking was confirmed by a decreased intensity in the azide-stretching FT-IR peak and solvent test with toluene (a suitable solvent for PICA). The PICA film photo-crosslinked with 3 wt% FPA showed enhanced solvent resistance (90%) compared to the non-crosslinked neat PICA film (<20%). Moreover, OLED devices using PICA-based hole-transporting layers exhibited better device performance (EQE/LE/PE: 8.88%/12.97/8.12 in red devices, 10.84%/38.47 cd/A/25.06 lm/W in green devices) than those using poly-TPD:FPA. We demonstrated that the photo-crosslinked PICA can be applied as a hole-transporting layer in solution-processed OLEDs.

Acceleration of the Deamination of Cytosine through Photo-Crosslinking

Herein, we report the major factor for deamination reaction rate acceleration, i.e., hydrophilicity, by using various 5-substituted target cytosines and by carrying out deamination at high temperatures. Through substitution of the groups at the 5'-position of the cytosine, the effect of hydrophilicity was understood. It was then used to compare the various modifications of the photo-cross-linkable moiety as well as the effect of the counter base of the cytosine to edit both DNA and RNA. Furthermore, we were able to achieve cytosine deamination at 37 °C with a half-life in the order of a few hours.

Flexible Organic Electronic Ion Pump for Flow-Free Phytohormone Delivery into Vasculature of Intact Plants

Plant vasculature transports molecules that play a crucial role in plant signaling including systemic responses and acclimation to diverse environmental conditions. Targeted controlled delivery of molecules to the vascular tissue can be a biomimetic way to induce long distance responses, providing a new tool for the fundamental studies and engineering of stress-tolerant plants. Here, a flexible organic electronic ion pump, an electrophoretic delivery device, for controlled delivery of phytohormones directly in plant vascular tissue is developed. The c-OEIP is based on polyimide-coated glass capillaries that significantly enhance the mechanical robustness of these microscale devices while being minimally disruptive for the plant. The polyelectrolyte channel is based on low-cost and commercially available precursors that can be photocured with blue light, establishing much cheaper and safer system than the state-of-the-art. To trigger OEIP-induced plant response, the phytohormone abscisic acid (ABA) in the petiole of intact Arabidopsis plants is delivered. ABA is one of the main phytohormones involved in plant stress responses and induces stomata closure under drought conditions to reduce water loss and prevent wilting. The OEIP-mediated ABA delivery triggered fast and long-lasting stomata closure far away from the delivery point demonstrating systemic vascular transport of the delivered ABA, verified delivering deuterium-labeled ABA.

Genetically encoded crosslinkers to address protein-protein interactions

Non-canonical amino acids (ncAAs) for photo- and chemical crosslinking are powerful biochemical tools for studying and manipulating interactions between proteins both in vitro and in intact cells. Since the first crosslinking ncAAs were genetically encoded about twenty years ago, the technology has now ripened beyond the proof-of-principle demonstrations and is contributing to the study of relevant biological questions in the frame of modern integrative approaches. Here, we provide an overview of available photo-activatable ncAA for photo-crosslinking and electrophilic ncAAs for genetically encoded chemical crosslinking (GECX), with a major focus on the most recent entries such as ncAAs for SuFEx click chemistry and photo-activatable ncAAs for chemical crosslinking. We present recent examples of the application of genetically encoded crosslinkers to capture protein-protein interactions and identify interaction partners in live cells, to investigate molecular mechanisms of protein function, to stabilize protein complexes for structural studies, to derive structural information about protein complexes from the physiological cell environment, up to perspective applications of GECX-ncAAs for the development of covalent drugs. This article is protected by copyright. All rights reserved.

FkpA enhances membrane protein folding using an extensive interaction surface

Outer membrane protein (OMP) biogenesis in gram-negative bacteria is managed by a network of periplasmic chaperones that includes SurA, Skp, and FkpA. These chaperones bind unfolded OMPs (uOMPs) in dynamic conformational ensembles to suppress aggregation, facilitate diffusion across the periplasm, and enhance folding. FkpA primarily responds to heat-shock stress, but its mechanism is comparatively understudied. To determine FkpA chaperone function in the context of OMP folding, we monitored the folding of three OMPs and found that FkpA, unlike other periplasmic chaperones, increases the folded yield but decreases the folding rate of OMPs. The results indicate that FkpA behaves as a chaperone and not as a folding catalyst to influence the OMP folding trajectory. Consistent with the folding assay results, FkpA binds all three uOMPs as determined by sedimentation velocity (SV) and photo-crosslinking experiments. We determine the binding affinity between FkpA and uOmpA171 by globally fitting SV titrations and find it to be intermediate between the known affinities of Skp and SurA for uOMP clients. Notably, complex formation steeply depends on the urea concentration, suggesting an extensive binding interface. Initial characterizations of the complex using photo-crosslinking indicate that the binding interface spans the entire FkpA molecule. In contrast to prior findings, folding and binding experiments performed using subdomain constructs of FkpA demonstrate that the full-length chaperone is required for full activity. Together these results support that FkpA has a distinct and direct effect on OMP folding that it achieves by utilizing an extensive chaperone-client interface to tightly bind clients.

Pinpointing the interaction site between semaphorin-3A and its inhibitory peptide

Semaphorin-3A (Sema-3A) is a chemorepellant protein with various biological functions, including kidney development. It interacts with a protein complex consisting of the receptors neuropilin-1 (NRP-1) and plexin-A1. After acute kidney injury, Sema-3A is overexpressed and secreted, leading to a loss of kidney function. The development of peptide inhibitors is a promising approach to modulate the interaction of Sema-3A with its receptor NRP-1. Few interaction points between these binding partners are known. However, an immunoglobulin-like domain-derived peptide of Sema-3A has shown a positive effect on cell proliferation. To specify these interactions between the peptide inhibitor and the Sema-3A-NRP-1 system, the peptides were modified with the photoactivatable amino acids 4-benzoyl-l-phenylalanine or photo-l-leucine by solid-phase peptide synthesis. Activity was tested by an enzyme-linked immunosorbent-based binding assay, and crosslinking experiments were analyzed by Western blot and mass spectrometry, demonstrating a specific binding site of the peptide at Sema-3A. The observed signals for Sema-3A-peptide interaction were found in a defined area of the Sema domain, which was also demonstrated to be involved in NRP-1 binding. The presented data identified the interaction site for further development of therapeutic peptides to treat acute kidney injury by blocking the Sema-3A-NRP-1 interaction.

Photo-Crosslinkable Inorganic/Organic Sulfur Polymers

Inverse vulcanization techniques are used to fabricate thermodynamically stable, sulfur polymers. Sulfur-based polymers exhibit higher refractive indices and improved transparency in the mid-wave infrared region compared with most organic polymers. Herein, the postsynthetic modification of sulfur polymers created via inverse vulcanization to generate novel, inorganic/organic photoresists is discussed. Amine-containing sulfur resins are postfunctionalized with cross-linkable alkynes. The sulfur-based materials undergo rapid photo-crosslinking to generate patternable films within 10 min under UV irradiation (365 nm). The development of these resins enables sulfur polymers to be utilized in processes where spatial and hierarchical control is necessary. The generation of this class of materials also expands on sulfur-based organic polymer systems with optical applications.

An interplay of matrix stiffness, dimensionality and adhesivity on cellular behavior

Cell-based assays are essentialin vitrotools for understanding basic cell biology, pathophysiology of diseases and mechanism of drug actions most cancer studies have utilized two-dimensional (2D) cell culture methods, which have their shortcomings including lack of cell- extracellular matrix interactions and three-dimensional (3D) geometry, and inaccurate representation of cell polarity. Hence, 3D matrices are being increasingly used to study the effect of 3D niche on cell behavior. Till date, very few systematic studies have been done to show comparison of cell behavior when seeded on the surface and encapsulated inside the matrix. In this study, we fabricated poly(ethylene glycol) (PEG) and gelatin-based matrices using UV mediated photo-polymerization to establish 2D and 3D cell culture methods using breast cancer MDA-MB-231 cells. We have found that the adhesion and spreading of cells on the gel surface is different from that when embedded in gels. The stiffness of poly (ethylene glycol) diacrylate (PEGDA)-gelatin methacryloyl (GelMA) hydrogels with lower concentration of GelMA is lower than that with higher GelMA; further, those with higher overall concentration of polymers (>5%) retain their mechanical integrity and do not degrade even after 7 d. Physical characterization of these matrices demonstrate their optimal pore size, mechanical stiffness and degradation, which are further tunable for tissue engineering, regenerative medicine, drug delivery and cancer studies. Additionally, these semi-synthetic PEGDA-GelMA matrices are transparent in nature, thereby, allowing easy imaging of cells in 3D. The system developed here can be used for short and long term cell culture and can be potentially explored for cell migration and metastasis studies.

Injectable Hydrogel Membrane for Guided Bone Regeneration

In recent years, multicomponent hydrogels such as interpenetrating polymer networks (IPNs) have emerged as innovative biomaterials due to the synergistic combination of the properties of each network. We hypothesized that an innovative non-animal IPN hydrogel combining self-setting silanized hydroxypropyl methylcellulose (Si-HPMC) with photochemically cross-linkable dextran methacrylate (DexMA) could be a valid alternative to porcine collagen membranes in guided bone regeneration. Calvaria critical-size defects in rabbits were filled with synthetic biphasic calcium phosphate granules in conjunction with Si-HPMC; DexMA; or Si-HPMC/DexMA experimental membranes; and in a control group with a porcine collagen membrane. The synergistic effect obtained by interpenetration of the two polymer networks improved the physicochemical properties, and the gel point under visible light was reached instantaneously. Neutral red staining of murine L929 fibroblasts confirmed the cytocompatibility of the IPN. At 8 weeks, the photo-crosslinked membranes induced a similar degree of mineral deposition in the calvaria defects compared to the positive control, with 30.5 ± 5.2% for the IPN and 34.3 ± 8.2% for the collagen membrane. The barrier effect appeared to be similar in the IPN test group compared with the collagen membrane. In conclusion, this novel, easy-to-handle and apply, photochemically cross-linkable IPN hydrogel is an excellent non-animal alternative to porcine collagen membrane in guided bone regeneration procedures.

Poly(glycidyl azide) as Photo-Crosslinker for Polymers

Crosslinking polymers to form networks is a universal and routinely applied strategy to improve their stability and endow them with solvent resistance, adhesion properties, etc. However, the chemical crosslinking of common commercial polymers, especially for those without functional groups, cannot be achieved readily. In this study, we utilized low-molecular weight poly(glycidyl azide) (GAP) as polymeric crosslinkers to crosslink various commercial polymers via simple ultraviolet light irradiation. The azide groups were shown to decompose upon photo-irradiation and be converted to highly reactive nitrene species, which are able to insert into carbon-hydrogen bonds and thus crosslink the polymeric matrices. This strategy was demonstrated successfully in several commercial polymers. In particular, it was found that the crosslinking is highly localized, which could endow the polymeric matrices with a decent degree of crosslinking without significantly influencing other properties, suggesting a novel and robust method to crosslink polymeric materials.

Filamented Light (FLight) Biofabrication of Highly Aligned Tissue-Engineered Constructs

Cell-laden hydrogels used in tissue engineering generally lack sufficient 3D topographical guidance for cells to mature into aligned tissues. A new strategy called filamented light (FLight) biofabrication rapidly creates hydrogels composed of unidirectional microfilament networks, with diameters on the length scale of single cells. Due to optical modulation instability, a light beam is divided optically into FLight beams. Local polymerization of a photoactive resin is triggered, leading to local increase in refractive index, which itself creates self-focusing waveguides and further polymerization of photoresin into long hydrogel microfilaments. Diameter and spacing of the microfilaments can be tuned from 2 to 30 µm by changing the coherence length of the light beam. Microfilaments show outstanding cell instructive properties with fibroblasts, tenocytes, endothelial cells, and myoblasts, influencing cell alignment, nuclear deformation, and extracellular matrix deposition. FLight is compatible with multiple types of photoresins and allows for biofabrication of centimeter-scale hydrogel constructs with excellent cell viability within seconds (<10 s per construct). Multidirectional microfilaments are achievable within a single hydrogel construct by changing the direction of FLight projection, and complex multimaterial/multicellular tissue-engineered constructs are possible by sequentially exchanging the cell-laden photoresin. FLight offers a transformational approach to developing anisotropic tissues using photo-crosslinkable biomaterials.

Fucoidan-based hydrogels particles as versatile carriers for diabetes treatment strategies

There is a current lack of fully efficient therapies for diabetes mellitus, a chronic disease where the metabolism of blood glucose is severely hindered by a deficit in insulin or cell resistance to this hormone. Therefore, it is crucial to develop new therapeutic strategies to treat this disease, including devices for the controlled delivery of insulin or encapsulation of insulin-producing cells. In this work, fucoidan (Fu) - a marine sulfated polysaccharide exhibiting relevant properties on reducing blood glucose and antioxidant and anti-inflammatory effects - was used for the development of versatile carriers envisaging diabetes advanced therapies. Fu was functionalized by methacrylation (MFu) using 8% and 12% (v/v) of methacrylic anhydride and further photocrosslinked using visible light in the presence of triethanolamine and eosin-y to produce hydrogel particles. Degree of methacrylation varied between 2.78 and 6.50, as determined by ¹HNMR, and the produced particles have an average diameter ranging from 0.63 to 1.3 mm (dry state). Insulin (5%) was added to MFu solution to produce drug-loaded particles and the release profile was assessed in phosphate buffer solution (PBS) and simulated intestinal fluid (SIF) for 24 h. Insulin was released in a sustained manner during the initial 8 h, reaching then a plateau, higher in PBS than in SIF, indicating that lower pH favors drug liberation. Moreover, the ability of MFu particles to serve as templates for the culture of human pancreatic cells was assessed using 1.1B4 cell line during up to 7 days. During the culture period studied, pancreatic beta cells were proliferating, with a global viability over 80% and tend to form pseudo-islets, thus suggesting that the proposed biomaterial could be a good candidate as versatile carrier for diabetes treatment as they sustain the release of insulin and support pancreatic beta cells viability.

Effects and Progress of Photo-Crosslinking Hydrogels in Wound Healing Improvement

Wound healing is a dynamic physiological process, including three stages: inflammation, tissue formation, and remodeling. The quality of wound healing is affected by many topical and systemic factors, while any small factor may affect the process. Therefore, improving the quality of wound healing is a complex and arduous challenge. Photo-crosslinking reaction using visible light irradiation is a novel method for hydrogel preparation. Photo-crosslinking hydrogels can be controlled in time and space, and are not interfered by temperature conditions, which have been widely used in the fields of medicine and engineering. This review aims to summarize the application of photo-crosslinking hydrogels in improving the quality of wound healing, mainly including the material design, application mechanism, and effect of photo-crosslinking hydrogels applied in wound healing, followed by the applicable animal models for experimental research. Finally, this review analyzes the clinical application prospects of photo-crosslinking hydrogels in the field of wound healing.

Simultaneous One-Pot Interpenetrating Network Formation to Expand 3D Processing Capabilities

The incorporation of a secondary network into traditional single-network hydrogels can enhance mechanical properties, such as toughness and loading to failure. These features are important for many applications, including as biomedical materials; however, the processing of interpenetrating polymer network (IPN) hydrogels is often limited by their multistep fabrication procedures. Here, a one-pot scheme for the synthesis of biopolymer IPN hydrogels mediated by the simultaneous crosslinking of two independent networks with light, namely: i) free-radical crosslinking of methacrylate-modified hyaluronic acid (HA) to form the primary network and ii) thiol-ene crosslinking of norbornene-modified HA with thiolated guest-host assemblies of adamantane and β-cyclodextrin to form the secondary network, is reported. The mechanical properties of the IPN hydrogels are tuned by changing the network composition, with high water content (≈94%) hydrogels exhibiting excellent work of fracture, tensile strength, and low hysteresis. As proof-of-concept, the IPN hydrogels are implemented as low-viscosity Digital Light Processing resins to fabricate complex structures that recover shape upon loading, as well as in microfluidic devices to form deformable microparticles. Further, the IPNs are cytocompatible with cell adhesion dependent on the inclusion of adhesive peptides. Overall, the enhanced processing of these IPN hydrogels will expand their utility across applications.

Covalent Networking of a Conjugated-Polymer Photocatalyst to Promote Exciton Diffusion in the Aqueous Phase for Efficient Hydrogen Production

A conjugated polymer particle in an aqueous phase is covalently networked in 3D by crosslinking with azide groups, leading to significantly enhanced activity-a high photocatalytic H₂ evolution rate (11 024 µmol g^-1 h^-1 (λ > 420 nm)) and a high apparent quantum yield (up to 0.8%). The reaction between the photoactive azide and the alkyl chains of the conjugated polymer provides more intact intermolecular polymeric interactions in the colloidal state, thus preventing physical swelling and inhibiting the recombination of photoproduced carriers. The covalent network efficiently promotes exciton diffusion, which greatly facilitates charge separation and transfer. The azide photo-crosslinking also leads to more compact and better-packed nanoparticles in the aqueous phase and efficient transfer of excitons to the outer surface of the nanoparticles, where photocatalytic reactions occur. These results show that photo-crosslinking can suppress the adverse effects of alkyl chains which inhibit photocatalytic performance. Therefore, covalent crosslinking is a promising strategy for the development of solar and hydrogen energy.

Switchable DNA-Encoded Chemical Library: Interconversion between Double- and Single-Stranded DNA Formats

DNA-Encoded Chemical Library (DEL) has attracted substantial attention due to the infinite possibility for hit discovery in both pharmaceutical companies and academia. The encoding method is the initial step of DEL construction and one of the cornerstones of DEL applications. Classified by the DNA format, the existing DEL encoding strategies could be categorized into single-stranded DNA-based strategies and double-stranded DNA-based strategies. The two DEL formats have their unique advantages but are usually incompatible with each other. To address this issue, we proposed the concept of interconversion between double- and single-stranded DEL based on the "reversible covalent headpiece (RCHP)" design, which combined maximum robustness of synthesis with extraordinary flexibility of applications in distinct setups. Future opportunities in this field were also proposed to advance DEL technology to a comprehensive drug discovery platform.

Fabrication of Antibacterial, Osteo-Inductor 3D Printed Aerogel-Based Scaffolds by Incorporation of Drug Laden Hollow Mesoporous Silica Microparticles into the Self-Assembled Silk Fibroin Biopolymer

In this study, the novel biomimetic aerogel-based composite scaffolds through a synergistic combination of wet chemical synthesis and advanced engineering approaches have successfully designed. To this aim, initially the photo-crosslinkable methacrylated silk fibroin (SF-MA) biopolymer and methacrylated hollow mesoporous silica microcapsules (HMSC-MA) as the main constituents of the novel composite aerogels were synthesized. Afterward, by incorporation of drug-loaded HMSC-MA into the self-assembled SF-MA, printable gel-based composite inks are developed. By exploiting micro-extrusion-based three-dimensional (3D) printing, SF-MA-HMSC composite gels are printed by careful controlling their viscosity to provide a means to control the shape fidelity of the resulted printed gel constructs. The developed scaffold has shown a multitude of interesting biophysical and biological performances. Namely, thanks to the photo-crosslinking of the gel components during the 3D printing, the scaffolds become mechanically more stable than the pristine SF scaffolds. Also, freeze-casting the printed constructs generates further interconnectivity in the printed pore struts resulting in the scaffolds with hierarchically organized porosities necessary for cell infiltration and growth. Importantly, HMSC incorporated scaffolds promote antibacterial drug delivery, cellular ingrowth and proliferation, promoting osteoblastic differentiation by inducing the expression of osteogenic markers and matrix mineralization. Finally, the osteoconductive, -inductive, and anti-infective composite aerogels are expected to act as excellent bone implanting materials with an extra feature of local and sustained release of drug for efficient therapy of bone-related diseases.

Direct homophilic interaction of LAMP2A with the two-domain architecture revealed by site-directed photo-crosslinks and steric hindrances in mammalian cells

LAMP1 (lysosomal-associated membrane protein 1) and LAMP2 are the most abundant protein components of lysosome membranes. Both LAMPs have common structures consisting of a large lumenal domain composed of two domains (N-domain and C-domain, which are membrane-distal and -proximal, respectively), both with the β-prism fold, a transmembrane domain, and a short cytoplasmic tail. LAMP2 is involved in various aspects of autophagy, and reportedly forms high-molecular weight complexes at the lysosomal membrane. We previously showed that LAMP2 molecules coimmunoprecipitated with each other, but whether the homophilic interaction is direct or indirect has remained to be elucidated. In the present study, we demonstrated the direct homophilic interaction of mouse LAMP2A molecules, using expanded genetic code technologies that generate photo-crosslinking and/or steric hindrance at specified interfaces. Specifically, the results suggested that LAMP2A molecules assemble by facing each other with one side of the β-prism (defined as side A) of the C-domains. The N-domain truncation, which increased the coimmunoprecipitation of LAMP2A molecules in our previous study, permitted the nonspecific involvement of both sides of the β-prism (side A and side B). Thus, the presence of the N-domain restricts the LAMP2A interactions to side A-specific. The truncation of LAMP2A impaired the recruitment of GAPDH (a CMA-substrate) fused to the HaloTag protein to the surface of late endosomes/lysosomes (LE/Lys) and affected a process that generates LE/Lys. The present study revealed that the homophilic interaction of LAMP2A is direct, and the side A-specific, homophilic interaction of LAMP2A is required for the functional aspects of LAMP2A.Abbreviations: Aloc-Lys: Nε-allyloxycarbonyl-l-lysine; CMA: chaperone-mediated autophagy; FFE: free-flow electrophoresis; GAPDH-HT: glyceraldehyde-3-phosphate dehydrogenase fused to HaloTag protein; LAMP1: lysosomal-associated membrane protein 1; LAMP2A: lysosomal-associated membrane protein 2A; LBPA: lysobisphosphatidic acid; LE/Lys: late endosome/lysosomes; MEFs: mouse embryonic fibroblasts; pBpa: p-benzoyl- l-phenylalanine.

Promoting Oral Mucosal Wound Healing with a Hydrogel Adhesive Based on a Phototriggered S-Nitrosylation Coupling Reaction

The wet and highly dynamic environment of the mouth makes local treatment of oral mucosal diseases challenging. To overcome this, a photo-crosslinking hydrogel adhesive is developed inspired by the success of light-curing techniques in dentistry. The adhesive operates on a fast (within 5 s) phototriggered S-nitrosylation coupling reaction and employs imine anchoring to connect to host tissues. Unlike other often-used clinical agents that adhere weakly and for short durations, this thin, elastic, adhesive, and degradable cyclic o-nitrobenzyl-modified hyaluronic acid gel protects mucosal wounds from disturbance by liquid rinsing, oral movement, and friction for more than 24 h. The results from both rat and pig oral mucosa repair models demonstrate that this new gel adhesive creates a favorable microenvironment for tissue repair and can shorten tissue healing time. This study thus illustrates a therapeutic strategy with the potential to advance the treatment of oral mucosal defects in the clinic.

Aggregation of Gold Nanoparticles Triggered by Hydrogen Peroxide-Initiated Chemiluminescence for Activated Tumor Theranostics

Developing endogenous photo-activated theranostic platforms to overcome the limitation of low tissue-penetration from external light sources is highly significant for cancer diagnosis and treatment. We report a H₂ O₂ -initiated chemiluminescence (CL)-triggered nanoparticle aggregation strategy to activate theranostic functions of gold nanoparticles (AuNPs) for effective tumor imaging and therapy. Two types of AuNPs (tAuNP & mAuNP) were designed and fabricated by conjugating 2,5-diphenyltetrazole and methacrylic acid onto the surface of AuNPs, respectively. Luminol was adsorbed onto the mAuNPs to afford self-illuminating mAuNP/Lu NPs that could produce strong CL by reaction with H₂ O₂ in the tumor microenvironment, which triggers significant aggregation of AuNPs resulting in enhanced accumulation and retention of AuNPs for activated photoacoustic imaging and photothermal therapy of tumors. We thus believe that this approach may offer a promising tool for effective tumor treatment.

Blue Light-Activated Riboflavin Phosphate Promotes Collagen Crosslinking to Modify the Properties of Connective Tissues

Reduced amounts of collagen and fragmented collagen fibers are characteristics of aging skin. Recently, user-friendly, at-home personal aesthetic devices using light-emitting diode (LED) light have been used for cost-effective and safe skin improvement. However, to dramatically improve the skin via collagen repair, we need to develop an LED-responsive photosensitizer. Corneal collagen crosslinking uses ultraviolet light to activate riboflavin phosphate (RFP) and is used in ophthalmology. RFP is a biocompatible photosensitizer derived from vitamin B₂. This study aimed to prove that RFP combined with blue light (BL) can increase collagen crosslinking density, improving its mechanical properties in skin tissue and enhancing skin elasticity. We confirmed the RFP-induced photo-crosslinking in pure collagen by studying changes in its dynamic modulus and matrix morphology using collagen hydrogels. We also measured the changes in the mechanical properties after applying photo-crosslinking on porcine skin. The Young’s modulus (1.07 ± 0.12 MPa) and tensile strength (11.04 ± 1.06 MPa) of the porcine skin after photo-crosslinking were 2.8 and 3.5 times better compared to those of normal porcine skin, respectively. Thus, photo-crosslinking through RFP and BL irradiation can be potentially used for skin improvement using aesthetic LED devices.

Synthesis and Cellular Labeling of Multifunctional Phosphatidylinositol Bis- and Trisphosphate Derivatives

We synthesized the first multifunctionalized phosphoinositide polyphosphate derivatives featuring a photo-removable protecting group ("cage"), a photo-crosslinkable diazirine group, and a terminal alkyne group useful for click chemistry. We demonstrate that the lipid derivatives readily enter cells. After photo-crosslinking, cell fixation and fluorescent tagging via click chemistry, we determined the intracellular location of the lipid derivatives before and after uncaging of the lipids. We find that there is rapid trafficking of PI(3,4)P2 and PI(3,4,5)P3 derivatives to the plasma membrane, opening the intriguing possibility that there is active transport of these lipids involved. We employed the photo-crosslinking and click chemistry functions to analyze the proteome of PI(3,4,5)P3 -binding proteins. From the latter, we validated by RNAi that the putative lipid binding proteins ATP11A and MPP6 are involved in the transport of PI(3,4,5)P3 to the plasma membrane.

Microchip Electrophoresis Assay for Calmodulin Binding Proteins

The calcium signaling protein calmodulin regulates numerous intracellular processes. We introduce a sensitive microchip assay to separate and detect calmodulin binding proteins. The assay utilizes an optimized microchip electrophoresis protein separation platform with laser-induced fluorescence detection. Fluorescence-labeled calmodulin modified with a photoreactive diazirine crosslinker allowed selective detection of calmodulin binding proteins. We demonstrate successful in-vitro crosslinking of calmodulin with two calmodulin binding proteins, calcineurin and nitric oxide synthase. We compare the efficacy of commonly applied electrophoretic separation modes: microchip capillary zone electrophoresis, microchip micellar electrokinetic chromatography/gel electrophoresis, and nanoparticle colloidal arrays. Out of the methods tested, polydymethylsiloxane/glass chips with microchip zone electrophoresis gave the poorest separation, whereas sieving methods in which electro-osmotic flow was suppressed gave the best separation of photoproducts of calmodulin conjugated with calmodulin binding proteins.

A short ORF-encoded transcriptional regulator

Recent technological advances have expanded the annotated protein coding content of mammalian genomes, as hundreds of previously unidentified, short open reading frame (ORF)-encoded peptides (SEPs) have now been found to be translated. Although several studies have identified important physiological roles for this emerging protein class, a general method to define their interactomes is lacking. Here, we demonstrate that genetic incorporation of the photo-crosslinking noncanonical amino acid AbK into SEP transgenes allows for the facile identification of SEP cellular interaction partners using affinity-based methods. From a survey of seven SEPs, we report the discovery of short ORF-encoded histone binding protein (SEHBP), a conserved microprotein that interacts with chromatin-associated proteins, localizes to discrete genomic loci, and induces a robust transcriptional program when overexpressed in human cells. This work affords a straightforward method to help define the physiological roles of SEPs and demonstrates its utility by identifying SEHBP as a short ORF-encoded transcription factor.

Utilization of GelMA with phosphate glass fibers for glial cell alignment

Glial cell alignment in tissue engineered constructs is essential for achieving functional outcomes in neural recovery. While gelatin methacrylate (GelMA) hydrogel offers superior biocompatibility along with permissive structure and tailorable mechanical properties, phosphate glass fibers (PGFs) can provide physical cues for directionality of neural growth. Aligned PGFs were fabricated by a melt quenching and fiber drawing method and utilized with synthesized GelMA hydrogel. The mechanical properties of GelMA and biocompatibility of the GelMA-PGFs composite were investigated in vitro using rat glial cells. GelMA with 86% methacrylation degree were photo-crosslinked using 0.1%wt photo-initiator (PI). Photocrosslinking under UV exposure for 60 s was used to produce hydrogels (GelMA-60). PGFs were introduced into the GelMA before crosslinking. Storage modulus and loss modulus of GelMA-60 was 24.73 ± 2.52 and 1.08 ± 0.23 kN/m² , respectively. Increased cell alignment was observed in GelMA-PGFs compared with GelMA hydrogel alone. These findings suggest GelMA-PGFs can provide glial cells with physical cues necessary to achieve cell alignment. This approach could further be used to achieve glial cell alignment in bioengineered constructs designed to bridge damaged nerve tissue.

A tri-functional amino acid enables mapping of binding sites for posttranslational-modification-mediated protein-protein interactions

Posttranslational modification (PTM), through the recruitment of effector proteins (i.e., "readers") that signal downstream events, plays key roles in regulating a variety of cellular processes. To understand how a PTM is recognized, it is necessary to find its readers and, importantly, the location of the binding pockets responsible for PTM recognition. Although various methods have been developed to identify PTM readers, it remains a challenge to directly map the PTM-binding regions, especially for intrinsically disordered domains. Here, we demonstrate a photo-crosslinkable, clickable, and cleavable tri-functional amino acid, ADdis-Cys, that when coupled with mass spectrometry (ADdis-Cys-MS) can not only identify PTM readers from complex proteomes but also simultaneously map their PTM-recognition modules. Using ADdis-Cys-MS, we successfully identify the binding sites of several reader-PTM interactions, among which we discover human C1QBP as a histone chaperone. This robust method should find wide applications in examining other histone or non-histone PTM-mediated protein-protein interactions.

Chemical Diversification of Simple Synthetic Antibodies

Antibodies possess properties that make them valuable as therapeutics, diagnostics, and basic research tools. However, antibody chemical reactivity and covalent antigen binding are constrained, or even prevented, by the narrow range of chemistries encoded in canonical amino acids. In this work, we investigate strategies for leveraging an expanded range of chemical functionality using yeast displayed antibodies containing noncanonical amino acids (ncAAs) in or near antibody complementarity determining regions (CDRs). To enable systematic characterization of the effects of ncAA incorporation on antibody function, we first investigated whether diversification of a single antibody loop would support the isolation of binding clones against immunoglobulins from three species. We constructed and screened a billion-member library containing canonical amino acid diversity and loop length diversity only within the third complementarity determining region of the heavy chain (CDR-H3). Isolated clones exhibited moderate affinities (double- to triple-digit nanomolar affinities) and, in several cases, single-species specificity, confirming that antibody specificity can be mediated by a single CDR. This constrained diversity enabled the utilization of additional CDRs for the installation of chemically reactive and photo-cross-linkable ncAAs. Binding studies of ncAA-substituted antibodies revealed that ncAA incorporation is reasonably well tolerated, with observed changes in affinity occurring as a function of ncAA side chain identity, substitution site, and the ncAA incorporation machinery used. Multiple azide-containing ncAAs supported copper-catalyzed azide-alkyne cycloaddition (CuAAC) and strain-promoted azide-alkyne cycloaddition (SPAAC) without the abrogation of binding function. Similarly, several alkyne substitutions facilitated CuAAC without the apparent disruption of binding. Finally, antibodies substituted with a photo-cross-linkable ncAA were evaluated for ultraviolet-mediated cross-linking on the yeast surface. Competition-based assays revealed position-dependent covalent linkages, strongly suggesting successful cross-linking. Key findings regarding CuAAC reactions and photo-cross-linking on the yeast surface were confirmed using soluble forms of ncAA-substituted clones. The consistency of findings on the yeast surface and in solution suggest that chemical diversification can be incorporated into yeast display screening approaches. Taken together, our results highlight the power of integrating the use of yeast display and ncAAs in search of proteins with "chemically augmented" binding functions. This includes strategies for systematically introducing small molecule functionality within binding protein structures and evaluating protein-based covalent target binding. The efficient preparation and chemical diversification of antibodies on the yeast surface open up new possibilities for discovering "drug-like" protein leads in high throughput.

Development of Porous and Flexible PTMC Membranes for In Vitro Organ Models Fabricated by Evaporation-Induced Phase Separation

Polymeric membranes are widely applied in biomedical applications, including in vitro organ models. In such models, they are mostly used as supports on which cells are cultured to create functional tissue units of the desired organ. To this end, the membrane properties, e.g., morphology and porosity, should match the tissue properties. Organ models of dynamic (barrier) tissues, e.g., lung, require flexible, elastic and porous membranes. Thus, membranes based on poly (dimethyl siloxane) (PDMS) are often applied, which are flexible and elastic. However, PDMS has low cell adhesive properties and displays small molecule ad- and absorption. Furthermore, the introduction of porosity in these membranes requires elaborate methods. In this work, we aim to develop porous membranes for organ models based on poly(trimethylene carbonate) (PTMC): a flexible polymer with good cell adhesive properties which has been used for tissue engineering scaffolds, but not in in vitro organ models. For developing these membranes, we applied evaporation-induced phase separation (EIPS), a new method in this field based on solvent evaporation initiating phase separation, followed by membrane photo-crosslinking. We optimised various processing variables for obtaining form-stable PTMC membranes with average pore sizes between 5 to 8 µm and water permeance in the microfiltration range (17,000-41,000 L/m2/h/bar). Importantly, the membranes are flexible and are suitable for implementation in in vitro organ models.

Crosslinking of Polylactide by High Energy Irradiation and Photo-Curing

Polylactide (PLA) is presently the most studied bioderived polymer because, in addition to its established position as a material for biomedical applications, it can replace mass production plastics from petroleum. However, some drawbacks of polylactide such as insufficient mechanical properties at a higher temperature and poor shape stability have to be overcome. One of the methods of mechanical and thermal properties modification is crosslinking which can be achieved by different approaches, both at the stage of PLA-based materials synthesis and by physical modification of neat polylactide. This review covers PLA crosslinking by applying different types of irradiation, i.e., high energy electron beam or gamma irradiation and UV light which enables curing at mild conditions. In the last section, selected examples of biomedical applications as well as applications for packaging and daily-use items are presented in order to visualize how a variety of materials can be obtained using specific methods.

Fabrication of Photo-Crosslinkable Poly(Trimethylene Carbonate)/Polycaprolactone Nanofibrous Scaffolds for Tendon Regeneration

BACKGROUND

The treatment of tendon injuries remains a challenging problem in clinical due to their slow and insufficient natural healing process. Scaffold-based tissue engineering provides a promising strategy to facilitate tendon healing and regeneration. However, many tissue engineering scaffolds have failed due to their poor and unstable mechanical properties. To address this, we fabricated nanofibrous polycaprolactone/methacrylated poly(trimethylene carbonate) (PCL/PTMC-MA) composite scaffolds via electrospinning.

MATERIALS AND METHODS

PTMC-MA was characterized by nuclear magnetic resonance. Fiber morphology of composite scaffolds was evaluated using scanning electron microscopy. The monotonic tensile test was performed for determining the mechanical properties of composite scaffolds. Cell viability and collagen deposition were assessed via PrestoBlue assay and enzyme-linked immunosorbent assay, respectively.

RESULTS

These PCL/PTMC-MA composite scaffolds had an increase in mechanical properties as PTMC-MA content increase. After photo-crosslinking, they showed further enhanced mechanical properties including creep resistance, which was superior to pure PCL scaffolds. It is worth noting that photo-crosslinked PCL/PTMC-MA (1:3) composite scaffolds had a Young's modulus of 31.13 ± 1.30 MPa and Max stress at break of 23.80 ± 3.44 MPa that were comparable with the mechanical properties of native tendon (Young's modulus 20-1200 MPa, max stress at break 5-100 MPa). In addition, biological experiments demonstrated that PCL/PTMC-MA composite scaffolds were biocompatible for cell adhesion, proliferation, and differentiation.

A GelMA-PEGDA-nHA Composite Hydrogel for Bone Tissue Engineering

A new gelatin methacrylamine (GelMA)-poly (ethylene glycol) diacrylate (PEGDA)-nano hydroxyapatite (nHA) composite hydrogel scaffold was developed using UV photo-crosslinking technology. The Ca²⁺ from nHA can form a [HO]Ca²⁺ [OH] bridging structure with the hydroxyl group in GelMA, thereby enhancing the stability. Compared with GelMA-PEGDA hydrogel, the addition of nHA can control the mechanical properties of the composite hydrogel and reduce the degradation rate. In vitro cell culture showed that osteoblast can adhere and proliferate on the surface of the hydrogel, indicating that the GelMA-PEGDA-nHA hydrogel had good cell viability and biocompatibility. Furthermore, GelMA-PEGDA-nHA has excellent injectability and rapid prototyping properties and is a promising 3D printed bone repair scaffold material.

IbpB-bound substrate release in living cells as revealed by unnatural amino acid-mediated photo-crosslinking

Small heat shock proteins (sHSPs) are known to bind non‐native substrates and prevent irreversible aggregation in an ATP‐independent manner. However, the dynamic interaction between sHSPs and their substrates in vivo is less studied. Here, by utilizing a genetically incorporated crosslinker, we characterized the interaction between sHSP IbpB and its endogenous substrates in living cells. Through photo‐crosslinking analysis of five Bpa variants of IbpB, we found that the substrate binding of IbpB in living cells is reversible upon short‐time exposure at 50 °C. Our data provide in vivo evidence that IbpB engages in dynamic substrate release under nonstress conditions and suggest that photo‐crosslinking may be a suitable method for investigating dynamic interaction between molecular chaperones and their substrates in living cells.

Site-Specific Incorporation of Genetically Encoded Photo-Crosslinkers Locates the Heteromeric Interface of a GPCR Complex in Living Cells

G protein-coupled receptors (GPCRs) are critical mediators of cell signaling. Although capable of activating G proteins in a monomeric form, numerous studies reveal a possible association of class A GPCRs into dimers/oligomers. The relative location of individual protomers within these GPCR complexes remains a topic of intense debate. We previously reported that class A serotonin 5-HT_2A receptor (5-HT_2AR) and class C metabotropic glutamate 2 receptor (mGluR2) are able to form a GPCR heterocomplex. By introducing the photoactivatable unnatural amino acid p-azido-L-phenylalanine (azF) at selected individual positions along the transmembrane (TM) segments of mGluR2, we delineate the residues that physically interact at the heteromeric interface of the 5-HT_2AR-mGluR2 complex. We show that 5-HT_2AR crosslinked with azF incorporated at the intracellular end of mGluR2's TM4, while no crosslinking was observed at other positions along TM1 and TM4. Together, these findings provide important insights into the structural arrangement of the 5-HT_2AR-mGluR2 complex.

Gelatin Hydrogels Reinforced by Absorbable Nanoparticles and Fibrils Cured In Situ by Visible Light for Tissue Adhesive Applications

Most gelatin hydrogels used in regenerative medicine applications today are fabricated by photocrosslinking due to the convenience and speed of this method. However, in most cases photoinitiators are used, which require UV light, which, in turn, can cause cell and tissue damage, or using functionalized gelatin. Recently, ruthenium (II) tris-bipyridyl chloride has been studied as an initiator that can induce dityrosine bond formation using visible light. In addition, continuous fibrils and small particles are often used to reinforce composite materials. Therefore, this study investigated the visible-light-induced photocrosslinking of native gelatin molecules via dityrosine bonds formation as well as gel reinforcement by collagen fibrils and mesoporous bioactive glass (MBG) particles. The results show that collagen and MBG exerted a synergistic effect on maintaining gel integrity with a dental LED curing light when the irradiation time was shortened to 30 s. Without the two reinforcing components, the gel could not form a geometric shape stable gel even when the exposure time was 120 s. The shear strength increased by 62% with the collagen and MBG compared with the blank control. Furthermore, our results demonstrate that the addition of collagen and MBG enhanced gel stability in an artificial saliva solution. These results demonstrate the considerable advantages of using tyrosine-containing biomolecules, and using a dental LED curing light for the crosslinking of hydrogels in terms of their suitability and feasibility for use as bioadhesives in confined clinical working space, such as the oral cavity, and in application as in situ-crosslinked injectable hydrogels.

Bifunctional Non-Canonical Amino Acids: Combining Photo-Crosslinking with Click Chemistry

Genetic code expansion is a powerful tool for the study of protein interactions, as it allows for the site-specific incorporation of a photoreactive group via non-canonical amino acids. Recently, several groups have published bifunctional amino acids that carry a handle for click chemistry in addition to the photo-crosslinker. This allows for the specific labeling of crosslinked proteins and therefore the pulldown of peptides for further analysis. This review describes the properties and advantages of different bifunctional amino acids, and gives an overview about current and future applications.

Functionalized Enzyme-Responsive Biomaterials to Model Tissue Stiffening in vitro

The mechanical properties of the cellular microenvironment play a crucial role in modulating cell function, and many pathophysiological processes are accompanied by variations in extracellular matrix (ECM) stiffness. Lysyl oxidase (LOx) is one of the enzymes involved in several ECM-stiffening processes. Here, we engineered poly(ethylene glycol) (PEG)-based hydrogels with controlled mechanical properties in the range typical of soft tissues. These hydrogels were functionalized featuring free primary amines, which allows an additional chemical LOx-responsive behavior with increase in crosslinks and hydrogel elastic modulus, mimicking biological ECM-stiffening mechanisms. Hydrogels with elastic moduli in the range of 0.5-4 kPa were obtained after a first photopolymerization step. The increase in elastic modulus of the functionalized and enzyme-responsive hydrogels was also characterized after the second-step enzymatic reaction, recording an increase in hydrogel stiffness up to 0.5 kPa after incubation with LOx. Finally, hydrogel precursors containing HepG2 (bioinks) were used to form three-dimensional (3D) in vitro models to mimic hepatic tissue and test PEG-based hydrogel biocompatibility. Hepatic functional markers were measured up to 7 days of culture, suggesting further use of such 3D models to study cell mechanobiology and response to dynamic variation of hydrogels stiffness. The results show that the functionalized hydrogels presented in this work match the mechanical properties of soft tissues, allow dynamic variations of hydrogel stiffness, and can be used to mimic changes in the microenvironment properties of soft tissues typical of inflammation and pathological changes at early stages (e.g., fibrosis, cancer).

Site-Specific Photo-Crosslinking Proteomics Reveal Regulation of IFITM3 Trafficking and Turnover by VCP/p97 ATPase

Interferon-induced transmembrane protein 3 (IFITM3) is a key interferon effector that broadly prevents infection by diverse viruses. However, the cellular factors that control IFITM3 homeostasis and antiviral activity have not been fully elucidated. Using site-specific photo-crosslinking and quantitative proteomic analysis, here we present the identification and functional characterization of VCP/p97 AAA-ATPase as a primary interaction partner of IFITM3. We show that IFITM3 ubiquitination at lysine 24 is crucial for VCP binding, trafficking, turnover, and engagement with incoming virus particles. Consistently, pharmacological inhibition of VCP/p97 ATPase activity leads to defective IFITM3 lysosomal sorting, turnover, and co-trafficking with virus particles. Our results showcase the utility of site-specific protein photo-crosslinking in mammalian cells and reveal VCP/p97 as a key cellular factor involved in IFITM3 trafficking and homeostasis.

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Photo-crosslinking proteomics identify VCP/p97 as an IFITM3-interacting protein

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Ubiquitination of IFITM3 is crucial for interaction with VCP

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Lysine 24 ubiquitination regulates IFITM3 trafficking and turnover

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Depletion or inhibition of VCP leads to delayed turnover and accumulation of IFITM3

Disulfide Crosslinked Hydrogels Made From the Hydra Stinging Cell Protein, Minicollagen-1

Minicollagens from cnidarian nematocysts are attractive potential building blocks for the creation of strong, lightweight and tough polymeric materials with the potential for dynamic and reconfigurable crosslinking to modulate functionality. In this study, the Hydra magnipapillata minicollagen-1 isoform was recombinantly expressed in bacteria, and a high throughput purification protocol was developed to generate milligram levels of pure protein without column chromatography. The resulting minicollagen-1 preparation demonstrated spectral properties similar to those observed with collagen and polyproline sequences as well as the ability to self-assemble into oriented fibers and bundles. Photo-crosslinking with Ru(II)( bpy ) 3 2 + was used to create robust hydrogels that were analyzed by mechanical testing. Interestingly, the minicollagen-1 hydrogels could be dissolved with reducing agents, indicating that ruthenium-mediated photo-crosslinking was able to induce disulfide metathesis to create the hydrogels. Together, this work is an important first step in creating minicollagen-based materials whose properties can be manipulated through static and reconfigurable post-translational modifications.

Photo-crosslinking: An Emerging Chemical Tool for Investigating Molecular Networks in Live Cells

Studying protein-protein interactions (PPIs) is useful for understanding cellular functions and mechanisms. Evaluating these PPIs under conditions as similar as possible to native conditions can be achieved using photo-crosslinking methods because of their on-demand ability to generate reactive species in situ by irradiation with UV light. Various fusion tag, metabolic incorporation, and amber codon suppression approaches using various crosslinkers containing aryl azide, benzophenone, and diazirines have been applied in live cells. Mass spectrometry and immunological techniques are used to identify crosslinked proteins based on their capture transient and context-dependent interactions. Herein we discuss various incorporation methods and crosslinkers that have been used for interactome mapping in live cells.