Non-viral delivery of an optogenetic tool into cells with self-healing hydrogel

Optogenetics and Targeted Gene Therapy for Retinal Diseases: Unravelling the Fundamentals, Applications, and Future Perspectives

With a common aim of restoring physiological function of defective cells, optogenetics and targeted gene therapies have shown great clinical potential and novelty in the branch of personalized medicine and inherited retinal diseases (IRDs). The basis of optogenetics aims to bypass defective photoreceptors by introducing opsins with light-sensing capabilities. In contrast, targeted gene therapies, such as methods based on CRISPR-Cas9 and RNA interference with noncoding RNAs (i.e., microRNA, small interfering RNA, short hairpin RNA), consists of inducing normal gene or protein expression into affected cells. Having partially leveraged the challenges limiting their prompt introduction into the clinical practice (i.e., engineering, cell or tissue delivery capabilities), it is crucial to deepen the fields of knowledge applied to optogenetics and targeted gene therapy. The aim of this in-depth and novel literature review is to explain the fundamentals and applications of optogenetics and targeted gene therapies, while providing decision-making arguments for ophthalmologists. First, we review the biomolecular principles and engineering steps involved in optogenetics and the targeted gene therapies mentioned above by bringing a focus on the specific vectors and molecules for cell signalization. The importance of vector choice and engineering methods are discussed. Second, we summarize the ongoing clinical trials and most recent discoveries for optogenetics and targeted gene therapies for IRDs. Finally, we then discuss the limits and current challenges of each novel therapy. We aim to provide for the first time scientific-based explanations for clinicians to justify the specificity of each therapy for one disease, which can help improve clinical decision-making tasks.

Injectable organo-hydrogels influenced by click chemistry as a paramount stratagem in the conveyor belt of pharmaceutical revolution

The field of injectable hydrogels has demonstrated a paramount headway in the myriad of biomedical applications and paved a path toward clinical advancements. The innate superiority of hydrogels emerging from organic constitution has exhibited dominance in overcoming the bottlenecks associated with inorganic-based hydrogels in the biological milieu. Inorganic hydrogels demonstrate various disadvantages, including limited biocompatibility, degradability, a cumbersome synthesis process, high cost, and ecotoxicity. The excellent biocompatibility, eco-friendliness, and manufacturing convenience of organo-hydrogels have demonstrated to be promising in therapizing biomedical complexities with low toxicity and augmented bioavailability. This report manifests the realization of biomimetic organo-hydrogels with the development of bioresponsive and self-healing injectable organo-hydrogels in the emerging pharmaceutical revolution. Furthermore, the influence of click chemistry in this regime as a backbone in the pharmaceutical conveyor belt has been suggested to scale up production. Moreover, we propose an avant-garde design stratagem of developing a hyaluronic acid (HA)-based injectable organo-hydrogel via click chemistry to be realized for its pharmaceutical edge. Ultimately, injectable organo-hydrogels that materialize from academia or industry are required to follow the standard set of rules established by global governing bodies, which has been delineated to comprehend their marketability. Thence, this perspective narrates the development of injectable organo-hydrogels via click chemistry as a prospective elixir to have in the arsenal of pharmaceuticals.

Adhesive and self-healing materials for central nervous system repair

The central nervous system (CNS) has a limited ability to regenerate after a traumatic injury or a disease due to the low capacity of the neurons to re-grow and the inhibitory environment formed in situ. Current therapies include the use of drugs and rehabilitation, which do not fully restore the CNS functions and only delay the pathology progression. Tissue engineering offers a simple and versatile solution for this problem through the use of bioconstructs that promote nerve tissue repair by bridging cavity spaces. In this approach, the choice of biomaterial is crucial. Herein, we present recent advances in the design and development of adhesive and self-healing materials that support CNS healing. The adhesive materials have the advantage of promoting recovery without the use of needles or sewing, while the self-healing materials have the capacity to restore the tissue integrity without the need for external intervention. These materials can be used alone or in combination with cells and/or bioactive agents to control the inflammation, formation of free radicals, and proteases activity. We discuss the advantages and drawbacks of different systems. The remaining challenges that can bring these materials to clinical reality are also briefly presented.

Antiviral and Antibacterial Sulfated Polysaccharide-Chitosan Nanocomposite Particles as a Drug Carrier

Drug delivery system (DDS) refers to the method of delivering drugs to the targeted sites with minimal risk. One popular strategy of DDS is using nanoparticles as a drug carrier, which are made from biocompatible and degradable polymers. Here, nanoparticles composed of Arthrospira-derived sulfated polysaccharide (AP) and chitosan were developed and expected to possess the capabilities of antiviral, antibacterial, and pH-sensitive properties. The composite nanoparticles, abbreviated as APC, were optimized for stability of morphology and size (~160 nm) in the physiological environment (pH = 7.4). Potent antibacterial (over 2 μg/mL) and antiviral (over 6.596 μg/mL) properties were verified in vitro. The pH-sensitive release behavior and release kinetics of drug-loaded APC nanoparticles were examined for various categories of drugs, including hydrophilic, hydrophobic, and protein drugs, under different pH values of the surroundings. Effects of APC nanoparticles were also evaluated in lung cancer cells and neural stem cells. The use of APC nanoparticles as a drug delivery system maintained the bioactivity of the drug to inhibit the proliferation of lung cancer cells (with ~40% reduction) and to relieve the growth inhibitory effect on neural stem cells. These findings indicate that the pH-sensitive and biocompatible composite nanoparticles of sulfated polysaccharide and chitosan well keep the antiviral and antibacterial properties and may serve as a promising multifunctional drug carrier for further biomedical applications.

Effects of hydrophilic fullerene nanoarchitectured structures on the behaviour of neural stem cells

The interaction between nanoarchitectonic fullerenes and cells is essential for their applications in the biological field. Herein we reported the preparation and investigation of the function of different types of water-dispersible self-assembled fullerenes. The hydrophobic self-assembled fullerenes were either surface-modified or chemically etched to become water dispersible. Different types of fullerenes were then examined for their effects on the behavior of neural stem cells (NSCs). Our results indicated that only the hydrophilic fullerene nanotubes (FNTs, diameter ∼480 nm) created by chemically etching were endocytosed by NSCs, which showed a spindle-like morphology after the uptake. Meanwhile, the FNTs did not increase the reactive oxygen species (ROS) production of the cells. The expression levels of neural-related genes (CNPase and β-tubulin) were upregulated 1.5-fold in the presence of FNTs. The differentiation of NSCs depended on the size, shape, and surface functional group of various fullerenes. Besides, the addition of FNTs in a chitosan self-healing hydrogel did not influence the integrity, injectability, and self-healing properties of the composite hydrogel. These results revealed that FNTs induced the neural differentiation of NSCs in the composite hydrogel. The addition of FNTs at a low concentration (50 μg mL^-1) was enough to create such effects in the composite hydrogel. The expression levels of the oligodendrocytic marker gene CNPase and the neuronal marker gene β-tubulin were increased remarkably by ∼14.5- and ∼8.4-fold, respectively, by the composite self-healing hydrogel containing 50 μg mL^-1 FNTs. The fullerene nanoarchitectured structures may have potential for use as nanovehicles and in neural tissue engineering in the future.

Environment tolerant, adaptable and stretchable organohydrogels: preparation, optimization, and applications

Multiple stretchable materials have been successively developed and applied to wearable devices, soft robotics, and tissue engineering. Organohydrogels are currently being widely studied and formed by dispersing immiscible hydrophilic/hydrophobic polymer networks or only hydrophilic polymer networks in an organic/water solvent system. In particular, they can not only inherit and carry forward the merits of hydrogels, but also have some unique advantageous features, such as anti-freezing and water retention abilities, solvent resistance, adjustable surface wettability, and shape memory effect, which are conducive to the wide environmental adaptability and intelligent applications. This review first summarizes the structure, preparation strategy, and unique advantages of the reported organohydrogels. Furthermore, organohydrogels can be optimized for electro-mechanical properties or endowed with various functionalities by adding or modifying various functional components owing to their modifiability. Correspondingly, different optimization strategies, mechanisms, and advanced developments are described in detail, mainly involving the mechanical properties, conductivity, adhesion, self-healing properties, and antibacterial properties of organohydrogels. Moreover, the applications of organohydrogels in flexible sensors, energy storage devices, nanogenerators, and biomedicine have been summarized, confirming their unlimited potential in future development. Finally, the existing challenges and future prospects of organohydrogels are provided.

Advances in hydrogel-based vascularized tissues for tissue repair and drug screening

The construction of biomimetic vasculatures within the artificial tissue models or organs is highly required for conveying nutrients, oxygen, and waste products, for improving the survival of engineered tissues in vitro. In recent times, the remarkable progress in utilizing hydrogels and understanding vascular biology have enabled the creation of three-dimensional (3D) tissues and organs composed of highly complex vascular systems. In this review, we give an emphasis on the utilization of hydrogels and their advantages in the vascularization of tissues. Initially, the significance of vascular elements and the regeneration mechanisms of vascularization, including angiogenesis and vasculogenesis, are briefly introduced. Further, we highlight the importance and advantages of hydrogels as artificial microenvironments in fabricating vascularized tissues or organs, in terms of tunable physical properties, high similarity in physiological environments, and alternative shaping mechanisms, among others. Furthermore, we discuss the utilization of such hydrogels-based vascularized tissues in various applications, including tissue regeneration, drug screening, and organ-on-chips. Finally, we put forward the key challenges, including multifunctionalities of hydrogels, selection of suitable cell phenotype, sophisticated engineering techniques, and clinical translation behind the development of the tissues with complex vasculatures towards their future development.

Biosensors to Monitor Cell Activity in 3D Hydrogel-Based Tissue Models

Three-dimensional (3D) culture models have gained relevant interest in tissue engineering and drug discovery owing to their suitability to reproduce in vitro some key aspects of human tissues and to provide predictive information for in vivo tests. In this context, the use of hydrogels as artificial extracellular matrices is of paramount relevance, since they allow closer recapitulation of (patho)physiological features of human tissues. However, most of the analyses aimed at characterizing these models are based on time-consuming and endpoint assays, which can provide only static and limited data on cellular behavior. On the other hand, biosensing systems could be adopted to measure on-line cellular activity, as currently performed in bi-dimensional, i.e., monolayer, cell culture systems; however, their translation and integration within 3D hydrogel-based systems is not straight forward, due to the geometry and materials properties of these advanced cell culturing approaches. Therefore, researchers have adopted different strategies, through the development of biochemical, electrochemical and optical sensors, but challenges still remain in employing these devices. In this review, after examining recent advances in adapting existing biosensors from traditional cell monolayers to polymeric 3D cells cultures, we will focus on novel designs and outcomes of a range of biosensors specifically developed to provide real-time analysis of hydrogel-based cultures.

Optogenetics for Understanding and Treating Brain Injury: Advances in the Field and Future Prospects

Optogenetics is emerging as an ideal method for controlling cellular activity. It overcomes some notable shortcomings of conventional methods in the elucidation of neural circuits, promotion of neuroregeneration, prevention of cell death and treatment of neurological disorders, although it is not without its own limitations. In this review, we narratively review the latest research on the improvement and existing challenges of optogenetics, with a particular focus on the field of brain injury, aiming at advancing optogenetics in the study of brain injury and collating the issues that remain. Finally, we review the most current examples of research, applying photostimulation in clinical treatment, and we explore the future prospects of these technologies.

Towards translational optogenetics

Optogenetics is widely used to interrogate the neural circuits underlying disease and has most recently been harnessed for therapeutic applications. The optogenetic toolkit consists of light-responsive proteins that modulate specific cellular functions, vectors for the delivery of the transgenes that encode the light-responsive proteins to targeted cellular populations, and devices for the delivery of light of suitable wavelengths at effective fluence rates. A refined toolkit with a focus towards translational uses would include efficient and safer viral and non-viral gene-delivery vectors, increasingly red-shifted photoresponsive proteins, nanomaterials that efficiently transduce near-infrared light deep into tissue, and wireless implantable light-delivery devices that allow for spatiotemporally precise interventions at clinically relevant tissue depths. In this Review, we examine the current optogenetics toolkit and the most notable preclinical and translational uses of optogenetics, and discuss future methodological and translational developments and bottlenecks.

Engineered Bacteriorhodopsin May Induce Lung Cancer Cell Cycle Arrest and Suppress Their Proliferation and Migration

Highly expressible bacteriorhodopsin (HEBR) is a light-triggered protein (optogenetic protein) that has seven transmembrane regions with retinal bound as their chromophore to sense light. HEBR has controllable photochemical properties and regulates activity on proton pumping. In this study, we generated HEBR protein and incubated with lung cancer cell lines (A549 and H1299) to evaluate if there was a growth-inhibitory effect with or without light illumination. The data revealed that the HEBR protein suppressed cell proliferation and induced the G0/G1 cell cycle arrest without light illumination. Moreover, the migration abilities of A549 and H1299 cells were reduced by ~17% and ~31% after incubation with HEBR (40 μg/mL) for 4 h. The Snail-1 gene expression level of the A549 cells was significantly downregulated by ~50% after the treatment of HEBR. In addition, HEBR significantly inhibited the gene expression of Sox-2 and Oct-4 in H1299 cells. These results suggested that the HEBR protein may inhibit cell proliferation and cell cycle progression of lung cancer cells, reduce their migration activity, and suppress some stemness-related genes. These findings also suggested the potential of HEBR protein to regulate the growth and migration of tumor cells, which may offer the possibility for an anticancer drug.

Strategic conceptualization and potential of self-healing polymers in biomedical field

Smart polymeric materials and hydrogels derived from acrylate, epoxy resins, etc. mimic the healing ability of natural organisms and biological cells by showing shape memory and tissue regenerative properties wherein, the healing ability in some of the materials is triggered by external stimuli like temperature, pH and light. This article provides an overview of various conceptual strategies and chemical and mechanical interactions involved in the different types of biomimetic self-healing materials to regain the deformed structure by repairing the cracked shape which play important role in contributing to the structural properties and functional recovery. Also, different chemical bonding like π-π interaction, ligand-metal, hydrogen bonding, etc. takes place at the molecular level for replenishing the damaged structure with greater bond strength. The regeneration ability of artificial self-healing polymeric materials not only shows use in material sciences, engineering but also exhibits a wide range of applications in site-specific drug delivery, skin grafting, implantation, dentistry and bone and tissue regeneration to restore injured surfaces with better biocompatibility, healing efficiency and higher tensile strength to serve as a next-generation material for amplifying the use in biomedical field.

Polypyrrole-Doped Conductive Self-Healing Composite Hydrogels with High Toughness and Stretchability

In recent years, hydrogels with self-healing capability and conductivity have become ideal materials for the design of electrodes, soft robotics, electronic skin, and flexible wearable devices. However, it is still a critical challenge to achieve the synergistic characteristics of high conductivity, excellent self-healing efficiency without any stimulations, and decent mechanical properties. Herein, we developed a ferric-ion (Fe³⁺) crosslinked acrylic acid and chitosan polymer hydrogel using embedded polypyrrole particles with features of high conductivity (2.61S·m^-1) and good mechanical performances (a tensile strength of 628%, a stress of 0.33 MPa, an elastic modulus of 0.146 MPa, and a toughness of 1.14 MJ·m^-3). In addition, the self-healing efficiency achieved 93% in tensile strength after healing in the air for 9 h without any external stimuli. Therefore, with these outstanding mechanical, self-healing, and conductive abilities all in one, it is possible to fabricate a new kind of soft material with wide applications.

Semi-Interpenetrating Polymer Network of Hyaluronan and Chitosan Self-Healing Hydrogels for Central Nervous System Repair

The repair of the central nervous system (CNS) is a major challenge because of the difficulty for neurons or axons to regenerate after damages. Injectable hydrogels have been developed to deliver drugs or cells for neural repair, but these hydrogels usually require conditional stimuli or additional catalysts to control the gelling process. Self-healing hydrogels, which can be injected locally to fill tissue defects after stable gelation, are attractive candidates for CNS treatment. In the current study, the self-healing hydrogel with a semi-interpenetrating polymer network (SIPN) was prepared by incorporation of hyaluronan (HA) into the chitosan-based self-healing hydrogel. The addition of HA allowed the hydrogel to pass through a narrow needle much more easily. As the HA content increased, the hydrogel showed a more packed nanostructure and a more porous microstructure verified by coherent small-angle X-ray scattering and scanning electron microscopy. The unique structure of SIPN hydrogel enhanced the spreading, migration, proliferation, and differentiation of encapsulated neural stem cells in vitro. Compared to the pristine chitosan-based self-healing hydrogel, the SIPN hydrogel showed better biocompatibility, CNS injury repair, and functional recovery evaluated by the traumatic brain injury zebrafish model and intracerebral hemorrhage rat model. We proposed that the SIPN of HA and chitosan self-healing hydrogel allowed an adaptable environment for cell spreading and migration and had the potential as an injectable defect support for CNS repair.

Natural Polymer-based Stimuli-responsive Hydrogels

The abilities of intelligent polymer hydrogels to change their structure and volume phase in response to external stimuli have provided new possibilities for various advanced technologies and great research and application potentials in the medical field. The natural polymer-based hydrogels have the advantages of environment-friendliness, rich sources and good biocompatibility. Based on their responsiveness to external stimuli, the natural polymer-based hydrogels can be classified into the temperature-responsive hydrogel, pH-responsive hydrogel, light-responsive hydrogel, electricresponsive hydrogel, redox-responsive hydrogel, enzyme-responsive hydrogel, magnetic-responsive hydrogel, multi-responsive hydrogel, etc. In this review, we have compiled some recent studies on natural polymer-based stimuli-responsive hydrogels, especially the hydrogels prepared from polysaccharides. The preparation methods, properties and applications of these hydrogels in the medical field are highlighted.

Optogenetics in the Era of Cerebral Organoids

The human brain has been deemed the most complex organ and has captivated neuroscientists for decades. Most studies of this organ have relied on reductionist model systems. Although all model systems are essentially wrong, cerebral organoids so far represent the closest recapitulation of human brain development and disease both in terms of cell diversity and organization. The optogenetic technique can be used in this context to study the functional neuroanatomy of the brain, to examine the neural circuits, and to determine the etiology of neurological disorders. In this opinion article, we suggest ways in which optogenetics can be combined with cerebral organoids to allow unprecedented precision and accuracy in studying normal and aberrant neurodevelopmental processes and, as well, neurodegenerative diseases.

Potential of Engineered Bacteriorhodopsins as Photoactivated Biomaterials in Modulating Neural Stem Cell Behavior

Bacteriorhodopsin (BR), a light-sensitive bacterial proton pump, has been demonstrated the capacity for regulating the neural activity in mammalian cells. Because of the difficulty in production and purification in large quantities, the BR proteins have neither been directly employed to biomedical applications nor verified the functionality by protein administration. Previously, we have invented a highly expressible bacteriorhodopsin (HEBR) and established the massive production protocol. In the current study, we mass-produced the two types of HEBR proteins that have normal or abnormal activity on the proton pumping, and then we treated murine neural stem cells (NSCs) with these HEBR proteins. We discovered that the cell behaviors including growth, metabolism, mitochondrial inner membrane potential, and differentiation were obviously affected in NSCs after the treatment of HEBR proteins. Particularly, these effects induced by HEBR proteins were correlated to their proton pump activity and could be altered by cell culture substrate materials. Current findings suggest that the engineered light-sensitive HEBR protein can serve as a biological material to directly influence the multiple behaviors of mammalian cells, which is further modified by the cell culture substrate material, revealing the versatile potential of HEBR protein in biomaterial applications.

Conductive Organohydrogels with Ultrastretchability, Antifreezing, Self-Healing, and Adhesive Properties for Motion Detection and Signal Transmission

Conductive hydrogels had demonstrated significant prospect in the field of wearable devices. However, hydrogels suffer from a huge limitation of freezing when the temperature falls below zero. Here, a novel conductive organohydrogel was developed by introducing polyelectrolytes and glycerol into hydrogels. The gel exhibited excellent elongation, self-healing, and self-adhesive performance for various materials. Moreover, the gel could withstand a low temperature of -20 °C for 24 h without freezing and still maintain good conductivity and self-healing properties. As a result, the sample could be applied for motion detection and signal transmission. For example, it can respond to finger movements and transmit network signals like network cables. Therefore, it was envisioned that the effective design strategy for conductive organohydrogels with antifreezing, toughness, self-healing, and self-adhesive properties would provide wide applications of flexible wearable devices.

Magnetic Regulation of Thermo-Chemotherapy from a Cucurbit[7]uril-Crosslinked Hybrid Hydrogel

The fabrication, characterization, and therapy efficiency of a noncovalent-bonded hydrogel network, which is assembled by utilizing cucurbit[7]uril as a supramolecular linker to "stick" superparamagnetic γ-Fe₂ O₃ nanoparticles onto the polymer backbone of catechol-functionalized chitosan are described. The unique barrel-shaped structure of cucurbit[7]uril not only facilitates host-guest recognition with the catechol derivatives, but also forms robust electrostatic interactions between its carbonyl portals and the γ-Fe₂ O₃ nanoparticles in a supramolecular manner, which leaves the physical and chemical properties of the nanoparticles intact. The γ-Fe₂ O₃ nanoparticles display vibrational movement and heat generation under an alternating magnetic field, endowing the formed hybrid supramolecular hydrogel with both thermo- and chemotherapy modalities, which are demonstrated both in vitro and in vivo. Here, a facile strategy is introduced to construct noncovalent interactions between a polymer matrix and the incorporated nanoparticles, which is amendable to a wide range of biomedical and industrial applications.

Thermoresponsive dendronized chitosan-based hydrogels as injectable stem cell carriers

A combination of dendronization and Schiff-base chemistry endows injectable chitosan hydrogels with thermoresponsiveness, self-healing abilities and enhanced mechanical properties under physiological conditions.

Optogenetic Modulation and Reprogramming of Bacteriorhodopsin-Transfected Human Fibroblasts on Self-Assembled Fullerene C60 Nanosheets

Fullerenes have unique biocompatibility and photoelectric properties and are candidate materials for biomedical applications. Several cell membrane proteins in nature such as bacteriorhodopsin also have photoelectric properties. Highly expressible bacteriorhodopsin (HEBR) is a novel light-sensitive opsin that has the potential to trigger neural activities through optogenetic modulation. Here, HEBR plasmids are delivered to human fibroblasts and the cells are exposed to C60 fullerene self-assembled 2D nanosheets. Results show that the above approach combined with light stimulation (3 s duration and three times per day) may promote reprogramming and differentiation of human fibroblasts into neural-like cells in 7 d without any neural induction medium. The special photoelectric properties of fullerenes as culture substrates and transfected HEBR on the cell membrane may provide a new optogenetic platform for regulating the location (C60 nanosheet) and time (frequency of light illumination) for human fibroblasts to become neural-like cells, and may be applied to improve neural regeneration in the future.

Synthesis and Biomedical Applications of Self-healing Hydrogels

Hydrogels, which are crosslinked polymer networks with high water contents and rheological solid-like properties, are attractive materials for biomedical applications. Self-healing hydrogels are particularly interesting because of their abilities to repair the structural damages and recover the original functions, similar to the healing of organism tissues. In addition, self-healing hydrogels with shear-thinning properties can be potentially used as the vehicles for drug/cell delivery or the bioinks for 3D printing by reversible sol-gel transitions. Therefore, self-healing hydrogels as biomedical materials have received a rapidly growing attention in recent years. In this paper, synthesis methods and repair mechanisms of self-healing hydrogels are reviewed. The biomedical applications of self-healing hydrogels are also described, with a focus on the potential therapeutic applications verified through in vivo experiments. The trends indicate that self-healing hydrogels with automatically reversible crosslinks may be further designed and developed for more advanced biomedical applications in the future.