Dually Crosslinked Supramolecular Hydrogel for Cancer Biomarker Sensing

Hydrogel for light delivery in biomedical applications

Traditional optical waveguides or mediums are often silica-based materials, but their applications in biomedicine and healthcare are limited due to the poor biocompatibility and unsuitable mechanical properties. In term of the applications in human body, a biocompatible hydrogel system with excellent optical transparency and mechanical flexibility could be beneficial. In this review, we explore the different designs of hydrogel-based optical waveguides derived from natural and synthetic sources. We highlighted key developments such as light emitting contact lenses, implantable optical fibres, biosensing systems, luminating and fluorescent materials. Finally, we expand further on the challenges and perspectives for hydrogel waveguides to achieve clinical applications.

Stereogenic Harmony Fabricated Mechanoresponsive Homochiral Triphenylalanine Analogues with Synergistic Antibacterial Performances: A Potential Weapon for Dermal Wound Management

The wound recovery phenomenon remains as one of the long challenging concerns worldwide. In search of user-friendly dressing materials, in this report, we fabricated a rational combinatorial strategy utilizing stereogenic harmony in a triphenylalanine fragment and appending it to δ-amino valeric acid at the N-terminus (hydrogelators I-VII) such that a potential scaffold could be fished out from the design. Our investigations revealed that all the hydrogelators displayed not only excellent self-healing performance as well as high mechanical strength at physiological pH but also mechanical stress-triggered gel-sol-gel transition properties. The structural and morphological investigation confirmed the presence of β-sheet-like assemblies stabilized by intermolecular H-bonding and π-π interactions. Moreover, these scaffolds showed substantial antibacterial as well as antifungal efficacy against common wound pathogens, i.e, four Gram-positive bacteria (Staphylococcus aureus, Streptococcus mutans, B. subtilis, E. fecalis), four Gram-negative bacteria (Escherichia coli, Klebsiella pneumonia, P. aerugonosa, Proteus spp.), and two fungal strains (C. albicans and A. niger). The manifestation of consistent antioxidant properties might be due to the enhancement of amphiphilicity in hydrogelators, which has led to the generation of reactive oxygen species (ROS) in a facile manner, a probable mechanism to damage the microbial membrane, the driving force behind the antimicrobial efficacy. Also, the constructs exhibited proteolytic resistance and remarkable biocompatibility toward mammalian cells. Thus, based on the above benchmarks, the homochiral hydrogelator IV was seived out from a pool of seven, and we proceeded toward its in vivo evaluation using full-thickness excisional wounds in Wister rats. The scaffolds also accentuated the re-epithelialization as well in comparison to the negative control, thereby facilitating the wound closure process in a very short span of time (10 days). Overall, our in vitro and in vivo analysis certifies hydrogelator IV as an ideal dressing material that might hold immense promise for future wound care management.

Solvent-resolved self-assemblies of cholesteryl-cyanostilbene conjugates with photo- and thermo-responsiveness

It remains challenging to construct multifunctional chiral stimulus-responsive molecules and to modulate their morphology at the nanoscale. In this paper, we synthesized a novel chiral molecule with both photoactive and potentially bioactive properties and found that the morphological changes of its self-assembly were influenced by solvent polarity and light exposure. This work enabled the synthesized molecule to undergo Z-E isomerization efficiently under light irradiation by introducing highly oriented hydrogen bonds into the cyanostilbene part. The photoisomerization of the cyanostilbene part from Z- to E-type was further exploited, leading to morphological changes from nanohelices to vesicles with chiroptical evolution. The light-modulated supramolecular chirality and nanostructure provide a green and efficient method for the design of responsive chiral materials.

Hydrogel-Film-Fabricated Fluorescent Biosensors with Aggregation-Induced Emission for Albumin Detection through the Real-Time Modulation of a Vortex Fluidic Device

Hydrogels have various promising prospects as a successful platform for detecting biomarkers, and human serum albumin (HSA) is an important biomarker in the diagnosis of kidney diseases. However, the difficult-to-control passive diffusion kinetics of hydrogels is a major factor affecting detection performance. This study focuses on using hydrogels embedded with aggregation-induced emission (AIE) fluorescent probe TC426 to detect HSA in real time. The vortex fluidic device (VFD) technology is used as a rotation strategy to control the reaction kinetics and micromixing during measurement. The results show that the introduction of VFD could significantly accelerate its fluorescence response and effectively improve the diffusion coefficient, while VFD processing could regulate passive diffusion into active diffusion, offering a new method for future sensing research.

Surface Plasmon Resonance (SPR) Sensor for Cancer Biomarker Detection

A biomarker is a physiological observable marker that acts as a stand-in and, in the best-case scenario, forecasts a clinically significant outcome. Diagnostic biomarkers are more convenient and cost-effective than directly measuring the ultimate clinical outcome. Cancer is among the most prominent global health problems and a major cause of morbidity and death globally. Therefore, cancer biomarker assays that are trustworthy, consistent, precise, and verified are desperately needed. Biomarker-based tumor detection holds a lot of promise for improving disease knowledge at the molecular scale and early detection and surveillance. In contrast to conventional approaches, surface plasmon resonance (SPR) allows for the quick and less invasive screening of a variety of circulating indicators, such as circulating tumor DNA (ctDNA), microRNA (miRNA), circulating tumor cells (CTCs), lipids, and proteins. With several advantages, the SPR technique is a particularly beneficial choice for the point-of-care identification of biomarkers. As a result, it enables the timely detection of tumor markers, which could be used to track cancer development and suppress the relapse of malignant tumors. This review emphasizes advancements in SPR biosensing technologies for cancer detection.

Exploring Supramolecular Interactions between the Extracellular-Matrix-Derived Minimalist Bioactive Peptide and Nanofibrillar Cellulose for the Development of an Advanced Biomolecular Scaffold

It has been increasingly evident over the last few years that bioactive peptide hydrogels in conjugation with polymer hydrogels are emerging as a new class of supramolecular materials suitable for various biomedical applications owing to their specificity, tunability, and nontoxicity toward the biological system. Despite their unique biocompatible features, both polymer- and peptide-based scaffolds suffer from certain limitations, which restrict their use toward developing efficient matrices for controlling cellular behavior. The peptide hydrogels usually form soft matrices with low mechanical strength, whereas most of the polymer hydrogels lack biofunctionality. In this direction, combining polymers with peptides to develop a conjugate hydrogel can be explored as an emergent approach to overcome the limitations of the individual components. The polymer will provide high mechanical strength, whereas the biofunctionality of the material can be induced by the bioactive peptide sequence. In this study, we utilized TEMPO-oxidized nanofibrillar cellulose as the polymer counterpart, which was co-assembled with a short N-cadherin mimetic bioactive peptide sequence, Nap-HAVDI, to fabricate an NFC-peptide conjugate hydrogel. Interestingly, the mechanical strength of the peptide hydrogel was found to be significantly improved by combining the peptide with the NFC in the conjugate hydrogel. The addition of the peptide into the NFC also reduced the pore size within NFC matrices, which further helped in improving cellular adhesion, survival, and proliferation. Furthermore, the cells grown on the NFC and NFC-peptide hybrid hydrogel demonstrated normal expression of cytoskeleton proteins, i.e., β-tubulin in C6 cells and actin in L929 cells, respectively. The selective response of neuronal cells toward the specific bioactive peptide was further observed through a protein expression study. Thus, our study demonstrated the collective role of the cellulose-peptide composite material that revealed superior physical properties and biological response of this composite scaffold, which may open up a new platform for biomedical applications.

Multiplex Chroma Response Wearable Hydrogel Patch: Visual Monitoring of Urea in Body Fluids for Health Prognosis

Visual wearable devices can rapid intuitively monitor biomarkers in body fluids to indicate the human health status and provide valuable reference for further medical diagnosis. However, unavoidable interference factors such as skin color, natural light, and background luminescence can interfere with the visualization accuracy of flexible wearable devices, limiting their practical sensing application. Here, we designed a wearable sensing patch via an embedded upconversion optical probe in a 3D porous polyacrylamide hydrogel, exhibiting a multiplex chroma response to urea based on the inner filter effect, which overcomes the susceptibility to external conditions due to its near-infrared excited luminescence and improves the resolution and accuracy of visual sensing. Furthermore, a highly compatible portable sensing platform combined with a smartphone was designed to achieve in situ rapid quantitative analysis of urea. The limit of detection values of the upconversion optical probe and hydrogel sensor are as low as 1.4 and 30 μM respectively, exhibiting the practicality in different scenarios. The designed sensing patch provides a convenient and accurate sensing strategy for the detection of biomarkers in body fluids and has the potential to be developed into a point-of-care device to provide disease early warning and clinical diagnosis.

Supramolecular Room-Temperature Phosphorescent Hydrogel Based on Hexamethyl Cucurbit[5]uril for Cell Imaging

The host-guest interaction between hexamethyl cucurbit[5]uril (HmeQ[5]) and 1,4-diaminobenzene (DB) was investigated, and a new low-molecular-weight supramolecular gel was prepared by a simple heating/mixing cooling method. The structure and properties of the supramolecular gel were characterized. Results revealed that DB molecules did not enter the cavity of HmeQ[5] and that hydrogen bonding between the carbonyl group at the HmeQ[5] port and the DB amino groups, together with dipole-dipole interactions and outer wall interactions, were the main driving forces for the formation of the supramolecular gel. The HmeQ[5]/DB gel system exhibits temperature sensitivity. The phosphor 6-bromo-2-naphthol (BrNp) was embedded in the gel to give the gel fluorescent phosphorescence double emission. The double emission ability at room temperature can be attributed to the ordered microstructure of the supramolecular gel, which effectively avoids the nonradiative transition of BrNp. Meanwhile, HmeQ[5]/DB-BrNp has good biocompatibility and low biotoxicity, which is compatible with HeLa cells to achieve cytoplasmic staining of HeLa in the red channel. The supramolecular gels constructed by this supramolecular assembly strategy not only have good temperature sensitivity but also extend the application of Q[n]s in biomedical fields.

Hydrogel-Based Biosensors

There is an increasing interest in sensing applications for a variety of analytes in aqueous environments, as conventional methods do not work reliably under humid conditions or they require complex equipment with experienced operators. Hydrogel sensors are easy to fabricate, are incredibly sensitive, and have broad dynamic ranges. Experiments on their robustness, reliability, and reusability have indicated the possible long-term applications of these systems in a variety of fields, including disease diagnosis, detection of pharmaceuticals, and in environmental testing. It is possible to produce hydrogels, which, upon sensing a specific analyte, can adsorb it onto their 3D-structure and can therefore be used to remove them from a given environment. High specificity can be obtained by using molecularly imprinted polymers. Typical detection principles involve optical methods including fluorescence and chemiluminescence, and volume changes in colloidal photonic crystals, as well as electrochemical methods. Here, we explore the current research utilizing hydrogel-based sensors in three main areas: (1) biomedical applications, (2) for detecting and quantifying pharmaceuticals of interest, and (3) detecting and quantifying environmental contaminants in aqueous environments.

Recent advances in host-guest supramolecular hydrogels for biomedical applications

The recognition-directed host-guest interaction is recognized as a valuable tool for creating supramolecular polymers. Functional hydrogels constructed through the dynamic and reversible host-guest complexation are endowed with a great many appealing features, such as superior self-healing, injectability, flexibility, stimuli-responsiveness and biocompatibility, which are crucial for biological and medicinal applications. With numerous topological structures and host-guest combinations established previously, recent breakthroughs in this area mostly focus on further improvement and fine-tuning of various properties for practical utilizations. The current contribution provides a comprehensive overview of the latest developments in host-guest supramolecular hydrogels, with a particular emphasis on the innovative molecular-level design strategies and hydrogel formation methodologies targeting at a wide range of active biomedical domains, including drug delivery, 3D printing, wound healing, tissue engineering, artificial actuators, biosensors, etc. Furthermore, a brief conclusion and discussion on the steps forward to bring these smart hydrogels to clinical practice is also presented.

Tuning Surface Plasmon Resonance Responses through Size and Crosslinking Control of Multivalent Protein Binding-Capable Nanoscale Hydrogels

Surface plasmon resonance (SPR) phenomena have been widely studied to detect biomolecules because of their high sensitivity and ability to determine biomolecular interactions with kinetic information. However, highly selective detection in specific concentration ranges relevant to target biomolecules is still a challenging task. Recently, we developed bioresponsive nanoscale hydrogels to selectively intensify SPR signals through multivalent protein binding (MPB) events with target biomolecules, including IL-2, where we were able to demonstrate exceptional selectivity for target biomolecules with minimal responses to nonspecific and monovalent binding events. In this work, we systematically explored the relationship between the physical properties of MPB-capable nanoscale hydrogels and their SPR response induced in the presence of the programmed cell death protein 1 antibody (PD-1Ab) as a model target biomolecule. First, we developed a synthetic protocol by controlling various reaction parameters to construct a library of nanoscale poly(N-isopropylacrylamide-co-acrylic acid) hydrogels (NHs) with different sizes (from 400 nm to 1 μm) and degrees of crosslinking (from 2 to 8%). Then, by incorporating MPB-capable PD-1 receptors onto the surface of NHs to form PD-1-responsive nanoscale hydrogels (PNHs), the hydrogel size and crosslinking dependency of their SPR responses were investigated. Our results reveal the appropriate hydrogel size regime and degree of crosslinking for effective PD-1Ab detection at specific concentrations range between a few nM and 1 μM. Overall, our study demonstrates that by tuning the physical properties of the nanoscale hydrogel matrix, the sensitivity and detection range of MPB-based SPR sensors can be modulated to potentially benefit clinical applications such as monitoring diverse therapeutic biomolecules.

Plasmonic nanomaterials with responsive polymer hydrogels for sensing and actuation

Plasmonic nanomaterials have become an integral part of numerous technologies, where they provide important functionalities spanning from extraction and harvesting of light in thin film optical devices to probing of molecular species and their interactions on biochip surfaces. More recently, we witness increasing research efforts devoted to a new class of plasmonic nanomaterials that allow for on-demand tuning of their properties by combining metallic nanostructures and responsive hydrogels. This review addresses this recently emerged vibrant field, which holds potential to expand the spectrum of possible applications and deliver functions that cannot be achieved by separate research in each of the respective fields. It aims at providing an overview of key principles, design rules, and current implementations of both responsive hydrogels and metallic nanostructures. We discuss important aspects that capitalize on the combination of responsive polymer networks with plasmonic nanostructures to perform rapid mechanical actuation and actively controlled nanoscale confinement of light associated with resonant amplification of its intensity. The latest advances towards the implementation of such responsive plasmonic nanomaterials are presented, particularly covering the field of plasmonic biosensing that utilizes refractometric measurements as well as plasmon-enhanced optical spectroscopy readout, optically driven miniature soft actuators, and light-fueled micromachines operating in an environment resembling biological systems.

Nanomaterial-based biosensor developing as a route toward in vitro diagnosis of early ovarian cancer

The grand challenges of ovarian cancer early diagnosis have led to an alarmingly high mortality rate from ovarian cancer (OC) in the past half century. In vitro diagnosis (IVD) has great potential in the early diagnosis of OC through non-invasive and dynamic analysis of biomarkers. However, common IVDs often fail to provide reliable test results due to lack of sensitivity, specificity, and convenience. In recent years, the discovery of new biomarkers and the progress of nanomaterials can solve the shortcomings of traditional IVD for early OC. These emerging biosensors based on nanomaterials offer great improvements in convenience, speed, selectivity, and sensitivity of IVD. In this review, we firstly systematically summarized the limits of commercial IVD biosensors of OC and the latest discovery of new biomarkers for OC. The representative optimization strategies for six potential ovarian cancer biomarkers are systematically discussed with emphasis on nanomaterial selection and the design of detection principles. Then, various strategies adopted by emerging biosensors based on nanomaterials are also introduced in detail, including optical, electrochemical, microfluidic, and surface plasmon sensors. Finally, current challenges of early OC IVD are proposed, and future research directions on this promising field are also discussed.

•

Failure to diagnose OC early will lead to high mortality.

•

The detection of OC-related biomarkers by IVD method will achieve early diagnosis of OC.

•

The development of nanomaterials-based biosensors is expected to enhance efficiency of detection.

•

Strategies and progress for nanomaterials-based biosensors are systematically reviewed.

Shaping Macromolecules for Sensing Applications—From Polymer Hydrogels to Foldamers

Sensors are tools for detecting, recognizing, and recording signals from the surrounding environment. They provide measurable information on chemical or physical changes, and thus are widely used in diagnosis, environment monitoring, food quality checks, or process control. Polymers are versatile materials that find a broad range of applications in sensory devices for the biomedical sector and beyond. Sensory materials are expected to exhibit a measurable change of properties in the presence of an analyte or a stimulus, characterized by high sensitivity and selectivity of the signal. Signal parameters can be tuned by material features connected with the restriction of macromolecule shape by crosslinking or folding. Gels are crosslinked, three-dimensional networks that can form cavities of different sizes and forms, which can be adapted to trap particular analytes. A higher level of structural control can be achieved by foldamers, which are macromolecules that can attain well-defined conformation in solution. By increasing control over the three-dimensional structure, we can improve the selectivity of polymer materials, which is one of the crucial requirements for sensors. Here, we discuss various examples of polymer gels and foldamer-based sensor systems. We have classified and described applied polymer materials and used sensing techniques. Finally, we deliberated the necessity and potential of further exploration of the field towards the increased selectivity of sensory devices.

Reversible Protein Capture and Release by Redox-Responsive Hydrogel in Microfluidics

Stimuli-responsive hydrogels have a wide range of potential applications in microfluidics, which has drawn great attention. Double cross-linked hydrogels are very well suited for this application as they offer both stability and the required responsive behavior. Here, we report the integration of poly(N-isopropylacrylamide) (PNiPAAm) hydrogel with a permanent cross-linker (N,N'-methylenebisacrylamide, BIS) and a redox responsive reversible cross-linker (N,N'-bis(acryloyl)cystamine, BAC) into a microfluidic device through photopolymerization. Cleavage and re-formation of disulfide bonds introduced by BAC changed the cross-linking densities of the hydrogel dots, making them swell or shrink. Rheological measurements allowed for selecting hydrogels that withstand long-term shear forces present in microfluidic devices under continuous flow. Once implemented, the thiol-disulfide exchange allowed the hydrogel dots to successfully capture and release the protein bovine serum albumin (BSA). BSA was labeled with rhodamine B and functionalized with 2-(2-pyridyldithio)-ethylamine (PDA) to introduce disulfide bonds. The reversible capture and release of the protein reached an efficiency of 83.6% in release rate and could be repeated over 3 cycles within the microfluidic device. These results demonstrate that our redox-responsive hydrogel dots enable the dynamic capture and release of various different functionalized (macro)molecules (e.g., proteins and drugs) and have a great potential to be integrated into a lab-on-a-chip device for detection and/or delivery.

Lanthanide upconversion and downshifting luminescence for biomolecules detection

Biomolecules play critical roles in biological activities and are closely related to various disease conditions. The reliable, selective and sensitive detection of biomolecules holds much promise for specific and rapid biosensing. In recent years, luminescent lanthanide probes have been widely used for monitoring the activity of biomolecules owing to their long luminescence lifetimes and line-like emission which allow time-resolved and ratiometric analyses. In this review article, we concentrate on recent advances in the detection of biomolecule activities based on lanthanide luminescent systems, including upconversion luminescent nanoparticles, lanthanide-metal organic frameworks, and lanthanide organic complexes. We also introduce the latest remarkable accomplishments of lanthanide probes in the design principles and sensing mechanisms, as well as the forthcoming challenges and perspectives for practical achievements.

Dually cross-linked single networks: structures and applications

Cross-linked polymers have attracted an immense attention over the years, however, there are many flaws of these systems, e.g. softness and brittleness; such materials possess non-adjustable properties and cannot recover from damage and thus are limited in their practical applications. Supramolecular chemistry offers a variety of dynamic interactions that when integrated into polymeric gels endow the systems with reversibility and responsiveness to external stimuli. A combination of different cross-links in a single gel could be the key to tackle these drawbacks, since covalent or chemical cross-linking serve to maintain the permanent shape of the material and to improve overall mechanical performance, whereas non-covalent cross-links impart dynamicity, reversibility, stimuli-responsiveness and often toughness to the material. In the present review we sought to give a comprehensive overview of the progress in design strategies of different types of dually cross-linked single gels made by researchers over the past decade as well as the successful implementations of these advances in many demanding fields where versatile multifunctional materials are required, such as tissue engineering, drug delivery, self-healing and adhesive systems, sensors as well as shape memory materials and actuators.

Triple-Modulated Chiral Inversion of Co-Assembly System Based on Alanine Amphiphile and Cyanostilbene Derivative

The construction of chiroptical materials with controllable chirality is of special importance in biology and chemistry. Although tunable chirality can be realized in various systems, it remains a fundamental challenge to realize multimodulated chiral inversion. Herein, we report that chiral alanine derivative and fluorescent cyanostilbene derivative co-assemble to prepare supramolecular chiral systems, where twist nanofibers with totally inverted supramolecular chirality and circularly polarized luminescence are obtained through stoichiometric modulation. The supramolecular handedness can be inverted by means of altering the cooling rate and incorporating metal ions. The mechanism study reveals that the synergistic effect among hydrogen bonds, coordination interactions, and π-π stacking interactions contributes to the chirality inversion. This work establishes an effective strategy to precisely modulate supramolecular chirality in multiple ways, which shows great potential in developing smart chiroptical materials capable of achieving complex functionalities.