Hydrogels for RNA delivery.

RNA-based therapeutics have shown tremendous promise in disease intervention at the genetic level, and some have been approved for clinical use, including the recent COVID-19 messenger RNA vaccines. The clinical success of RNA therapy is largely dependent on the use of chemical modification, ligand conjugation or non-viral nanoparticles to improve RNA stability and facilitate intracellular delivery. Unlike molecular-level or nanoscale approaches, macroscopic hydrogels are soft, water-swollen three-dimensional structures that possess remarkable features such as biodegradability, tunable physiochemical properties and injectability, and recently they have attracted enormous attention for use in RNA therapy. Specifically, hydrogels can be engineered to exert precise spatiotemporal control over the release of RNA therapeutics, potentially minimizing systemic toxicity and enhancing in vivo efficacy. This Review provides a comprehensive overview of hydrogel loading of RNAs and hydrogel design for controlled release, highlights their biomedical applications and offers our perspectives on the opportunities and challenges in this exciting field of RNA delivery.

Microfluidic Organ-on-A-chip: A Guide to Biomaterial Choice and Fabrication.

Organ-on-A-chip (OoAC) devices are miniaturized, functional, in vitro constructs that aim to recapitulate the in vivo physiology of an organ using different cell types and extracellular matrix, while maintaining the chemical and mechanical properties of the surrounding microenvironments. From an end-point perspective, the success of a microfluidic OoAC relies mainly on the type of biomaterial and the fabrication strategy employed. Certain biomaterials, such as PDMS (polydimethylsiloxane), are preferred over others due to their ease of fabrication and proven success in modelling complex organ systems. However, the inherent nature of human microtissues to respond differently to surrounding stimulations has led to the combination of biomaterials ranging from simple PDMS chips to 3D-printed polymers coated with natural and synthetic materials, including hydrogels. In addition, recent advances in 3D printing and bioprinting techniques have led to the powerful combination of utilizing these materials to develop microfluidic OoAC devices. In this narrative review, we evaluate the different materials used to fabricate microfluidic OoAC devices while outlining their pros and cons in different organ systems. A note on combining the advances made in additive manufacturing (AM) techniques for the microfabrication of these complex systems is also discussed.

Mucus-Inspired Dynamic Hydrogels: Synthesis and Future Perspectives.

Mucus hydrogels at biointerfaces are crucial for protecting against foreign pathogens and for the biological functions of the underlying cells. Since mucus can bind to and host both viruses and bacteria, establishing a synthetic model system that can emulate the properties and functions of native mucus and can be synthesized at large scale would revolutionize the mucus-related research that is essential for understanding the pathways of many infectious diseases. The synthesis of such biofunctional hydrogels in the laboratory is highly challenging, owing to their complex chemical compositions and the specific chemical interactions that occur throughout the gel network. In this perspective, we discuss the basic chemical structures and diverse physicochemical interactions responsible for the unique properties and functions of mucus hydrogels. We scrutinize the different approaches for preparing mucus-inspired hydrogels, with specific examples. We also discuss recent research and what it reveals about the challenges that must be addressed and the opportunities to be considered to achieve desirable de novo synthetic mucus hydrogels.

Multi-Factors Cooperatively Actuated Photonic Hydrogel Aptasensors for Facile, Label-Free and Colorimetric Detection of Lysozyme.

Responsive two-dimensional photonic crystal (2DPC) hydrogels have been widely used as smart sensing materials for constructing various optical sensors to accurately detect different target analytes. Herein, we report photonic hydrogel aptasensors based on aptamer-functionalized 2DPC poly(acrylamide-acrylic acid-N-tert-butyl acrylamide) hydrogels for facile, label-free and colorimetric detection of lysozyme in human serum. The constructed photonic hydrogel aptasensors undergo shrinkage upon exposure to lysozyme solution through multi-factors cooperative actuation. Here, the specific binding between the aptamer and lysozyme, and the simultaneous interactions between carboxyl anions and N-tert-butyl groups with lysozyme, increase the cross-linking density of the hydrogel, leading to its shrinkage. The aptasensors' shrinkage decreases the particle spacing of the 2DPC embedded in the hydrogel network. It can be simply monitored by measuring the Debye diffraction ring of the photonic hydrogel aptasensors using a laser pointer and a ruler without needing sophisticated apparatus. The significant shrinkage of the aptasensors can be observed by the naked eye via the hydrogel size and color change. The aptasensors show good sensitivity with a limit of detection of 1.8 nM, high selectivity and anti-interference for the detection of lysozyme. The photonic hydrogel aptasensors have been successfully used to accurately determine the concentration of lysozyme in human serum. Therefore, novel photonic hydrogel aptasensors can be constructed by designing functional monomers and aptamers that can specifically bind target analytes.

Biocompatible Conductive Hydrogels: Applications in the Field of Biomedicine.

The impact of COVID-19 has rendered medical technology an important factor to maintain social stability and economic increase, where biomedicine has experienced rapid development and played a crucial part in fighting off the pandemic. Conductive hydrogels (CHs) are three-dimensional (3D) structured gels with excellent electrical conductivity and biocompatibility, which are very suitable for biomedical applications. CHs can mimic innate tissue's physical, chemical, and biological properties, which allows them to provide environmental conditions and structural stability for cell growth and serve as efficient delivery substrates for bioactive molecules. The customizability of CHs also allows additional functionality to be designed for different requirements in biomedical applications. This review introduces the basic functional characteristics and materials for preparing CHs and elaborates on their synthetic techniques. The development and applications of CHs in the field of biomedicine are highlighted, including regenerative medicine, artificial organs, biosensors, drug delivery systems, and some other application scenarios. Finally, this review discusses the future applications of CHs in the field of biomedicine. In summary, the current design and development of CHs extend their prospects for functioning as an intelligent and complex system in diverse biomedical applications.

Recent Advances in Polymer Additive Engineering for Diagnostic and Therapeutic Hydrogels.

Hydrogels are hydrophilic polymer materials that provide a wide range of physicochemical properties as well as are highly biocompatible. Biomedical researchers are adapting these materials for the ever-increasing range of design options and potential applications in diagnostics and therapeutics. Along with innovative hydrogel polymer backbone developments, designing polymer additives for these backbones has been a major contributor to the field, especially for expanding the functionality spectrum of hydrogels. For the past decade, researchers invented numerous hydrogel functionalities that emerge from the rational incorporation of additives such as nucleic acids, proteins, cells, and inorganic nanomaterials. Cases of successful commercialization of such functional hydrogels are being reported, thus driving more translational research with hydrogels. Among the many hydrogels, here we reviewed recently reported functional hydrogels incorporated with polymer additives. We focused on those that have potential in translational medicine applications which range from diagnostic sensors as well as assay and drug screening to therapeutic actuators as well as drug delivery and implant. We discussed the growing trend of facile point-of-care diagnostics and integrated smart platforms. Additionally, special emphasis was given to emerging bioinformatics functionalities stemming from the information technology field, such as DNA data storage and anti-counterfeiting strategies. We anticipate that these translational purpose-driven polymer additive research studies will continue to advance the field of functional hydrogel engineering.

Composite Peptide-Agarose Hydrogels for Robust and High-Sensitivity 3D Immunoassays.

Canonical immunoassays rely on highly sensitive and specific capturing of circulating biomarkers by interacting biomolecular baits. In this frame, bioprobe immobilization in spatially discrete three-dimensional (3D) spots onto analytical surfaces by hydrogel encapsulation was shown to provide relevant advantages over conventional two-dimensional (2D) platforms. Yet, the broad application of 3D systems is still hampered by hurdles in matching their straightforward fabrication with optimal functional properties. Herein, we report on a composite hydrogel obtained by combining a self-assembling peptide (namely, Q3 peptide) with low-temperature gelling agarose that is proved to have simple and robust application in the fabrication of microdroplet arrays, overcoming hurdles and limitations commonly associated with 3D hydrogel assays. We demonstrate the real-case scenario feasibility of our 3D system in the profiling of Covid-19 patients' serum IgG immunoreactivity, which showed remarkably improved signal-to-noise ratio over canonical assays in the 2D format and exquisite specificity. Overall, the new two-component hydrogel widens the perspectives of hydrogel-based arrays and represents a step forward towards their routine use in analytical practices.

Target DNA- and pH-responsive DNA hydrogel-based capillary assay for the optical detection of short SARS-CoV-2 cDNA.

DNA is recognized as a powerful biomarker for clinical diagnostics because its specific sequences are closely related to the cause and development of diseases. However, achieving rapid, low-cost, and sensitive detection of short-length target DNA still remains a considerable challenge. Herein, we successfully combine the catalytic hairpin assembly (CHA) technique with capillary action to develop a new and cost-effective method, a target DNA- and pH-responsive DNA hydrogel-based capillary assay, for the naked eye detection of 24 nt short single-stranded target DNA. Upon contact of target DNA, three individual hairpin DNAs hybridize with each other to sufficiently amplify Y-shaped DNA nanostructures (Y-DNA) until they are completely consumed via CHA cycling reactions. Each arm of the resultant Y-DNA contains sticky ends with i-motif DNA structure-forming sequences that can be self-assembled in an acidic environment (pH 5.0) to form target DNA- and pH-responsive DNA hydrogels by means of i-motif DNA-driven crosslinking. When inserting a capillary tube in the resultant solution, the liquid level inside clearly reduces due to the decrease in capillary force induced by the gels. In this way, the developed assay demonstrates sensitive and quantitative detection, with a detection limit of approximately 10 pM of 24 nt short complementary DNA (cDNA) targeting SARS-CoV-2 RNA genes at room temperature within 1 h. The assay is further shown to successfully detect target cDNA in serum, and it is also applied to detect several types of target sequences. Requiring no analytic equipment, precise temperature control, or enzymatic reactions, the developed DNA hydrogel-based capillary assay has potential as a promising naked eye detection platform for target DNA in resource-limited clinical settings.

Airway Delivery of Hydrogel-Encapsulated Niclosamide for the Treatment of Inflammatory Airway Disease.

Repurposing of the anthelminthic drug niclosamide was proposed as an effective treatment for inflammatory airway diseases such as asthma, cystic fibrosis, and chronic obstructive pulmonary disease. Niclosamide may also be effective for the treatment of viral respiratory infections, such as SARS-CoV-2, respiratory syncytial virus, and influenza. While systemic application of niclosamide may lead to unwanted side effects, local administration via aerosol may circumvent these problems, particularly when the drug is encapsulated into small polyethylene glycol (PEG) hydrospheres. In the present study, we examined whether PEG-encapsulated niclosamide inhibits the production of mucus and affects the pro-inflammatory mediator CLCA1 in mouse airways in vivo, while effects on mucociliary clearance were assessed in excised mouse tracheas. The potential of encapsulated niclosamide to inhibit TMEM16A whole-cell Cl- currents and intracellular Ca2+ signalling was assessed in airway epithelial cells in vitro. We achieved encapsulation of niclosamide in PEG-microspheres and PEG-nanospheres (Niclo-spheres). When applied to asthmatic mice via intratracheal instillation, Niclo-spheres strongly attenuated overproduction of mucus, inhibited secretion of the major proinflammatory mediator CLCA1, and improved mucociliary clearance in tracheas ex vivo. These effects were comparable for niclosamide encapsulated in PEG-nanospheres and PEG-microspheres. Niclo-spheres inhibited the Ca2+ activated Cl- channel TMEM16A and attenuated mucus production in CFBE and Calu-3 human airway epithelial cells. Both inhibitory effects were explained by a pronounced inhibition of intracellular Ca2+ signals. The data indicate that poorly dissolvable compounds such as niclosamide can be encapsulated in PEG-microspheres/nanospheres and deposited locally on the airway epithelium as encapsulated drugs, which may be advantageous over systemic application.

3D culture of cancer cells in alginate hydrogel beads as an effective technique for emergency cell storage and transportation in the pandemic era.

Due to the restrictions in accessing research laboratories and the challenges in providing proper storage and transportation of cells during the COVID-19 pandemic, having an effective and feasible mean to solve these challenges would be of immense help. Therefore, we developed a 3D culture setting of cancer cells using alginate beads and tested its effectiveness in different storage and transportation conditions. The viability and proliferation of cancer cells were assessed using trypan blue staining and quantitative CCK-8 kit, respectively. The developed beads allowed cancer cells survival up to 4 weeks with less frequent maintenance measures such as change of the culture media or subculture of cells. In addition, the recovery of cancer cells and proliferation pattern were significantly faster with better outcomes in the developed 3D alginate beads compared to the standard cryopreservation of cells or the 2D culture conditions. The 3D alginate beads also supported the viability of cells while the shipment at room temperature for a duration of up to 5 days with no humidity or CO2  support. Therefore, 3D culture in alginate beads can be used to store or ship biological cells with ease at room temperature with minimal preparations.

Rheological stability of carbomer in hydroalcoholic gels: Influence of alcohol type.

OBJECTIVE: The main objective of this paper is to analyse and attempt to understand the nature of rheological changes observed and the dynamics of Carbopol NF 980 hydroalcoholic gels neutralized specifically by triethanol amine (TEA), both as a function of time and alcohol type to probe time stabilities and ageing effects in such carbopol gel systems. The rheological changes and dynamics of 3 carbopol gel systems were observed; the gels included a water-based, ethanol-based, and isopropyl alcohol-based gel. It is hoped that this study shall shed light on the dynamical nature and the microstructural evolution of such networked gel systems, which were maintained under closed isothermal conditions and left completely unperturbed. The experimental results can provide the information necessary to understand and proposes plausible mechanisms guiding this dynamical behaviour in hydroalcoholic carbopol gels. METHODS: A TA instrument mechanical rheometer was used to measure the viscosity and storage and loss modulus, and a pH meter was utilized to determine the changes in each sample over the period. RESULTS: Studying the differences in the gel structures upon initial preparation illustrated that the ethanol and isopropyl alcohol (IPA) gels differed from the water-based gel in terms of viscosity, G', and G″, with the IPA gel displaying the lowest viscosity and moduli values across all shear rates. All the three gel systems exhibited strong shear thinning characteristics and were reminiscent of yield stress type found in colloidal gels. The water-based gel compared to the hydroalcoholic gels was strongly G' dominated, with the magnitude of the difference between G' and G″ observed to be much higher. This reflects that initial formation of the water-based gel structure possesses a much more rigid structure with a high elastic modulus component dominating. This also suggests that the water-based gel structure displayed stronger interactions between the carbopol particles when compared to those of the hydroalcoholic gels. Over the 30-day period, it was observed that the ethanol and water-based gels did not reveal any appreciable viscosity changes, with only an approximate 12% and 7% change from day 1 to 30, respectively. It was observed that the IPA systems' viscosity drastically increased over the period, with an approximately 77% change from day 1 to 30. The water and ethanol-based gels also exhibited very similar rheological behaviour over the entire time period with G' dominating G″. The G″ values of the water and ethanol-based gels decreased slightly at the end of day 30 by 10% and 16%, respectively, while the G' values for each sample remained essentially unchanged, increasing only 0.06% for the water-based gel, and increasing 1.4% for the ethanol-based gel. This further confirms the relatively stable gel structures attained. For the isopropyl gel system, the storage modulus of the system exhibited an average percent increase of approximately 16% from day 1 to day 30, but interestingly the loss modulus varied the least amongst all the gel systems, with only a 3% increase. The increase in G' reflects upon the evolution of a more rigid structure by day 30 for the IPA gel. This observation is clearly consistent with the corresponding increase in viscosity observed in the IPA gel. None of the gels tested displayed a consistent pH over the period. The pH of the hydroalcoholic gels was higher than that of the water-based gel for a majority of the period. The greatest fluctuations in pH were observed for the water and IPA gels, even though the water-based gel had one of the most stable rheological profiles out of the samples tested. The water, ethanol, and IPA gels' pH increased approximately 25%, 6%, and 5%, respectively, from day 1 to day 30. CONCLUSION: The rheological and pH study of the 3 hand sanitizer systems over a 30-day period allowed for rational insights into the plausible reasons responsible for driving the observed rheological changes in these unperturbed systems. For the water-based gel, we hypothesize that the changes observed are due to physical ageing, where the gel structure has evolved over time to eventually progress towards a more stabilized framework structure. The pH of the gel upon formation was on the lower side. Such a lower pH influences the formation of a gel, which is comparatively less swollen and occupies a slightly lesser volume, and thereby points to a much less compacted gel network structure or alternatively, a more fluid structure. If the particles moved around more, the system was not initially in a state of low energy, causing increased particle movement, and in turn, physical ageing. This could be responsible for the development of a physically altered structure over time. The gel structure dynamically attempts to minimize its free energy by becoming more rigid, which has been observed as being manifested in the decrease of both the viscosity and the G″. For the hydroalcoholic gels, we conjecture that ageing observed was a result of chemical ageing, and the alcohol type employed in the preparation is primarily responsible for exhibiting this effect. The polarities of ethyl alcohol and isopropyl alcohol are key to the stabilization of such resultant network structures which get formed because of neutralization. It has been observed in previous studies that with decreasing polarity, there was an increase in the neutralization needed to obtain the development of a structure half as well developed as the final resultant structure. Isopropyl alcohol is a much less polar solvent compared to ethanol and water, and therefore required higher levels of TEA as the base to neutralize the system. We conjecture that the charged TEA cationic species had a greater propensity to get exchanged with bulk solution in the vicinity of the polymer into the bulk solution, and that the pH fluctuation observed indicated a kinetic exchange process over time, causing the viscosity and moduli profiles to increase along with the pH. At this time though, further investigations need to be carried out to truly understand the underlying instability, and thus dynamics for gel systems of this type.

OBJECTIF: L'objectif principal de cet article est d'analyser et de tenter de comprendre la nature des changements rhéologiques observés et la dynamique des gels hydroalcooliques Carbopol NF 980 neutralisés spécifiquement par l'amine triéthanol (TEA), à la fois en fonction du temps et du type d'alcool pour sonder les stabilités temporelles et les effets du vieillissement dans de tels systèmes de gel carbopol. Les changements rhéologiques et la dynamique de 3 systèmes de gel de carbopol ont été observés ; les gels comprenaient un gel à base d'eau, d'éthanol et d'alcool isopropylique. On espère que cette étude éclairera la nature dynamique et l'évolution microstructurale de ces systèmes de gel en réseau, qui ont été maintenus dans des conditions isothermes fermées et laissés complètement imperturbables. Les résultats expérimentaux peuvent fournir les informations nécessaires pour comprendre et proposer des mécanismes plausibles guidant ce comportement dynamique dans les gels hydroalcooliques de carbopol. MÉTHODE: Un rhéomètre TA mécanique a été utilisé pour mesurer la viscosité, le module de stockage et de perte, et un pH-mètre a été utilisé pour déterminer les changements dans chaque échantillon au cours de la période. RÉSULTATS: L'étude des différences dans les structures du gel lors de la préparation initiale a montré que les gels d'éthanol et d'alcool isopropylique (IPA) différaient du gel à base d'eau en termes de viscosité, G' et G'' le gel IPA affichant les valeurs de viscosité et de modules les plus faibles pour tous les taux de cisaillement. Les trois systèmes de gel présentaient de fortes caractéristiques d'amincissement par cisaillement et rappelaient le type de contrainte d'élasticité que l'on trouve dans les gels colloïdaux. Le gel à base d'eau par rapport aux gels hydroalcooliques était fortement dominé par G', l'ampleur de la différence entre G' et G'' présentant une importance beaucoup plus élevée. Cela reflète le fait que la formation initiale de la structure de gel à base d'eau possède une structure beaucoup plus rigide avec un composant de module élastique élevé dominant. Cela suggère également que la structure du gel à base d'eau présentait des interactions plus fortes entre les particules de carbopol par rapport à celles des gels hydroalcooliques. Au cours de la période de 30 jours, il a été observé que l'éthanol et les gels à base d'eau n'ont révélé aucun changement de viscosité appréciable, avec seulement un changement approximatif de 12% et 7% du jour 1 au jour 30, respectivement. Il a été observé que la viscosité des systèmes IPA a considérablement augmenté au cours de la période, avec un changement d'environ 77% du jour 1 au jour 30. Les gels à base d'eau et d'éthanol ont également montré un comportement rhéologique très similaire sur toute la période, G' dominant G''. Les valeurs G'' des gels à base d'eau et d'éthanol ont légèrement diminué à la fin de la journée 30 de 10% et 16%, respectivement, tandis que les valeurs G' pour chaque échantillon sont restées essentiellement inchangées, n'augmentant que de 0,06% pour le gel à base d'eau et augmentant de 1,4% pour le gel à base d'éthanol. Cela confirme en outre les structures de gel relativement stables atteintes. Pour le système de gel isopropylique, le module de stockage du système a montré une augmentation moyenne d'environ 16% du jour 1 au jour 30, mais il est intéressant de noter que le module de perte variait le moins parmi tous les systèmes de gel, avec seulement une augmentation de 3%. L'augmentation de G' reflète l'évolution d'une structure plus rigide au jour 30 pour le gel IPA. Cette observation est clairement cohérente avec l'augmentation correspondante de la viscosité observée dans le gel IPA. Aucun des gels testés n'a montré un pH constant sur la période. Le pH des gels hydroalcooliques était supérieur à celui du gel à base d'eau pendant la majeure partie de la période. Les plus grandes fluctuations de pH ont été observées pour les gels d'eau et d'IPA, même si le gel à base d'eau avait l'un des profils rhéologiques les plus stables parmi les échantillons testés. Le pH de l'eau, de l'éthanol et des gels IPA a augmenté d'environ 25%, 6% et 5%, respectivement, du jour 1 au jour 30. CONCLUSION: L'étude rhéologique et pH des 3 systèmes de désinfectant pour les mains sur une période de 30 jours a permis d'obtenir des informations rationnelles sur les raisons plausibles responsables des changements rhéologiques observés dans ces systèmes non perturbés. Pour le gel à base d'eau, nous émettons l'hypothèse que les changements observés sont dus au vieillissement physique, où la structure du gel a évolué au fil du temps pour éventuellement progresser vers une structure plus stabilisée. Le pH du gel lors de la formation était dans la partie inférieure. Un pH aussi bas influence la formation d'un gel, qui est comparativement moins gonflé et occupe un volume légèrement inférieur, et indique ainsi une structure de réseau de gel beaucoup moins compactée ou autrement dit, une structure plus fluide. Si les particules se déplaçaient davantage, le système n'était pas initialement dans un état de faible énergie, ce qui entraînait une augmentation du mouvement des particules et, à son tour, un vieillissement physique. Cela pourrait être responsable du développement d'une structure physiquement modifiée au fil du temps. La structure du gel tente dynamiquement de minimiser son énergie libre en devenant plus rigide, ce qui a été observé comme se manifestant par la diminution de la viscosité et du G'' Pour les gels hydroalcooliques, nous pensons que le vieillissement observé était le résultat d'un vieillissement chimique, et le type d'alcool utilisé dans la préparation est principalement responsable de cet effet. Les polarités de l'alcool éthylique et de l'alcool isopropylique sont essentielles à la stabilisation de ces structures de réseau résultantes qui se forment en raison de la neutralisation. Il a été observé dans des études antérieures qu'avec la diminution de la polarité, il y avait une augmentation de la neutralisation nécessaire pour obtenir le développement d'une structure à moitié aussi bien développée que la structure résultante finale. L'alcool isopropylique est un solvant beaucoup moins polaire que l'éthanol et l'eau, et nécessitait donc des niveaux plus élevés de TEA comme base pour neutraliser le système. Nous pensons que les espèces cationiques TEA chargées avaient une plus grande propension à être échangées avec une solution en vrac à proximité du polymère, dans la solution en vrac, et que la fluctuation du pH observée indiquait un processus d'échange cinétique au fil du temps, entraînant une augmentation des profils de viscosité et de modules avec le pH. À l'heure actuelle, cependant, des recherches supplémentaires doivent être menées pour vraiment comprendre l'instabilité sous-jacente, et donc la dynamique des systèmes de gel de ce type.

Hydrogel-Based Slow Release of a Receptor-Binding Domain Subunit Vaccine Elicits Neutralizing Antibody Responses Against SARS-CoV-2.

The development of effective vaccines that can be rapidly manufactured and distributed worldwide is necessary to mitigate the devastating health and economic impacts of pandemics like COVID-19. The receptor-binding domain (RBD) of the SARS-CoV-2 spike protein, which mediates host cell entry of the virus, is an appealing antigen for subunit vaccines because it is efficient to manufacture, highly stable, and a target for neutralizing antibodies. Unfortunately, RBD is poorly immunogenic. While most subunit vaccines are commonly formulated with adjuvants to enhance their immunogenicity, clinically-relevant adjuvants Alum, AddaVax, and CpG/Alum are found unable to elicit neutralizing responses following a prime-boost immunization. Here, it has been shown that sustained delivery of an RBD subunit vaccine comprising CpG/Alum adjuvant in an injectable polymer-nanoparticle (PNP) hydrogel elicited potent anti-RBD and anti-spike antibody titers, providing broader protection against SARS-CoV-2 variants of concern compared to bolus administration of the same vaccine and vaccines comprising other clinically-relevant adjuvant systems. Notably, a SARS-CoV-2 spike-pseudotyped lentivirus neutralization assay revealed that hydrogel-based vaccines elicited potent neutralizing responses when bolus vaccines did not. Together, these results suggest that slow delivery of RBD subunit vaccines with PNP hydrogels can significantly enhance the immunogenicity of RBD and induce neutralizing humoral immunity.

Engineering Polysaccharide-Based Hydrogel Photonic Constructs: From Multiscale Detection to the Biofabrication of Living Optical Fibers.

Solid-state optics has been the pillar of modern digital age. Integrating soft hydrogel materials with micro/nanooptics could expand the horizons of photonics for bioengineering. Here, wet-spun multilayer hydrogel fibers are engineered through ionic-crosslinked natural polysaccharides that serve as multifunctional platforms. The resulting flexible hydrogel structure and reversible crosslinking provide tunable design properties such as adjustable refractive index and fusion splicing. Modulation of the optical readout via physical stimuli, including shape, compression, and multiple optical inputs/outputs is demonstrated. The unique permeability of the hydrogels is also combined with plasmonic nanoparticles for molecular detection of SARS-CoV-2 in fiber-coupled biomedical swabs. A tricoaxial 3D printing nozzle is then employed for the continuous fabrication of living optical fibers. Light interaction with living cells enables the quantification and digitalization of complex biological phenomena such as 3D cancer progression and drug susceptibility. These fibers pave the way for advances in biomaterial-based photonics and biosensing platforms.

Synthetic hydrogel nanoparticles for sepsis therapy.

Sepsis is a life-threatening condition caused by the extreme release of inflammatory mediators into the blood in response to infection (e.g., bacterial infection, COVID-19), resulting in the dysfunction of multiple organs. Currently, there is no direct treatment for sepsis. Here we report an abiotic hydrogel nanoparticle (HNP) as a potential therapeutic agent for late-stage sepsis. The HNP captures and neutralizes all variants of histones, a major inflammatory mediator released during sepsis. The highly optimized HNP has high capacity and long-term circulation capability for the selective sequestration and neutralization of histones. Intravenous injection of the HNP protects mice against a lethal dose of histones through the inhibition of platelet aggregation and migration into the lungs. In vivo administration in murine sepsis model mice results in near complete survival. These results establish the potential for synthetic, nonbiological polymer hydrogel sequestrants as a new intervention strategy for sepsis therapy and adds to our understanding of the importance of histones to this condition.

Highly Selective Multiplex Quantitative Polymerase Chain Reaction with a Nanomaterial Composite Hydrogel for Precise Diagnosis of Viral Infection.

As viruses have been threatening global public health, fast diagnosis has been critical to effective disease management and control. Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) is now widely used as the gold standard for detecting viruses. Although a multiplex assay is essential for identifying virus types and subtypes, the poor multiplicity of RT-qPCR makes it laborious and time-consuming. In this paper, we describe the development of a multiplex RT-qPCR platform with hydrogel microparticles acting as independent reactors in a single reaction. To build target-specific particles, target-specific primers and probes are integrated into the particles in the form of noncovalent composites with boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs). The thermal release characteristics of DNA, primer, and probe from the composites of primer-BNNT and probe-CNT allow primer and probe to be stored in particles during particle production and to be delivered into the reaction. In addition, BNNT did not absorb but preserved the fluorescent signal, while CNT protected the fluorophore of the probe from the free radicals present during particle production. Bicompartmental primer-incorporated network (bcPIN) particles were designed to harness the distinctive properties of two nanomaterials. The bcPIN particles showed a high RT-qPCR efficiency of over 90% and effective suppression of non-specific reactions. 16-plex RT-qPCR has been achieved simply by recruiting differently coded bcPIN particles for each target. As a proof of concept, multiplex one-step RT-qPCR was successfully demonstrated with a simple reaction protocol.

Engineering Hydrogel-Based Biomedical Photonics: Design, Fabrication, and Applications.

Light guiding and manipulation in photonics have become ubiquitous in events ranging from everyday communications to complex robotics and nanomedicine. The speed and sensitivity of light-matter interactions offer unprecedented advantages in biomedical optics, data transmission, photomedicine, and detection of multi-scale phenomena. Recently, hydrogels have emerged as a promising candidate for interfacing photonics and bioengineering by combining their light-guiding properties with live tissue compatibility in optical, chemical, physiological, and mechanical dimensions. Herein, the latest progress over hydrogel photonics and its applications in guidance and manipulation of light is reviewed. Physics of guiding light through hydrogels and living tissues, and existing technical challenges in translating these tools into biomedical settings are discussed. A comprehensive and thorough overview of materials, fabrication protocols, and design architectures used in hydrogel photonics is provided. Finally, recent examples of applying structures such as hydrogel optical fibers, living photonic constructs, and their use as light-driven hydrogel robots, photomedicine tools, and organ-on-a-chip models are described. By providing a critical and selective evaluation of the field's status, this work sets a foundation for the next generation of hydrogel photonic research.

Clinical Translational Potential in Skin Wound Regeneration for Adipose-Derived, Blood-Derived, and Cellulose Materials: Cells, Exosomes, and Hydrogels.

Acute and chronic skin wounds due to burns, pressure injuries, and trauma represent a substantial challenge to healthcare delivery with particular impacts on geriatric, paraplegic, and quadriplegic demographics worldwide. Nevertheless, the current standard of care relies extensively on preventive measures to mitigate pressure injury, surgical debridement, skin flap procedures, and negative pressure wound vacuum measures. This article highlights the potential of adipose-, blood-, and cellulose-derived products (cells, decellularized matrices and scaffolds, and exosome and secretome factors) as a means to address this unmet medical need. The current status of this research area is evaluated and discussed in the context of promising avenues for future discovery.

Reversed-engineered human alveolar lung-on-a-chip model.

Here, we present a physiologically relevant model of the human pulmonary alveoli. This alveolar lung-on-a-chip platform is composed of a three-dimensional porous hydrogel made of gelatin methacryloyl with an inverse opal structure, bonded to a compartmentalized polydimethylsiloxane chip. The inverse opal hydrogel structure features well-defined, interconnected pores with high similarity to human alveolar sacs. By populating the sacs with primary human alveolar epithelial cells, functional epithelial monolayers are readily formed. Cyclic strain is integrated into the device to allow biomimetic breathing events of the alveolar lung, which, in addition, makes it possible to investigate pathological effects such as those incurred by cigarette smoking and severe acute respiratory syndrome coronavirus 2 pseudoviral infection. Our study demonstrates a unique method for reconstitution of the functional human pulmonary alveoli in vitro, which is anticipated to pave the way for investigating relevant physiological and pathological events in the human distal lung.

A rapid diagnosis of SARS-CoV-2 using DNA hydrogel formation on microfluidic pores.

The coronavirus disease 2019 (COVID-19) pandemic has been a major public health challenge in 2020. Early diagnosis of COVID-19 is the most effective method to control disease spread and prevent further mortality. As such, a high-precision and rapid yet economic assay method is urgently required. Herein, we propose an innovative method to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using isothermal amplification of nucleic acids on a mesh containing multiple microfluidic pores. Hybridization of pathogen DNA and immobilized probes forms a DNA hydrogel by rolling circle amplification and, consequently, blocks the pores to prevent fluid movement, as observed. Following optimization of several factors, including pore size, mesh location, and precision microfluidics, the limit of detection (LOD) for SARS-CoV-2 was determined to be 0.7 aM at 15-min incubation. These results indicate rapid, easy, and effective detection with a moderate-sized LOD of the target pathogen by remote point-of-care testing and without the requirement of any sophisticated device.

Hydrogel particles improve detection of SARS-CoV-2 RNA from multiple sample types.

Here we present a rapid and versatile method for capturing and concentrating SARS-CoV-2 from contrived transport medium and saliva samples using affinity-capture magnetic hydrogel particles. We demonstrate that the method concentrates virus from 1 mL samples prior to RNA extraction, substantially improving detection of virus using real-time RT-PCR across a range of viral titers (100-1,000,000 viral copies/mL) and enabling detection of virus using the 2019 nCoV CDC EUA Kit down to 100 viral copies/mL. This method is compatible with commercially available nucleic acid extraction kits (i.e., from Qiagen) and a simple heat and detergent method that extracts viral RNA directly off the particle, allowing a sample processing time of 10 min. We furthermore tested our method in transport medium diagnostic remnant samples that previously had been tested for SARS-CoV-2, showing that our method not only correctly identified all positive samples but also substantially improved detection of the virus in low viral load samples. The average improvement in cycle threshold value across all viral titers tested was 3.1. Finally, we illustrate that our method could potentially be used to enable pooled testing, as we observed considerable improvement in the detection of SARS-CoV-2 RNA from sample volumes of up to 10 mL.