Smart and Functionalized Development of Nucleic Acid-Based Hydrogels: Assembly Strategies, Recent Advances, and Challenges

Nano revolution of DNA nanostructures redefining cancer therapeutics-A comprehensive review

DNA nanostructures are a promising tool in cancer treatment, offering an innovative way to improve the effectiveness of therapies. These nanostructures can be made solely from DNA or combined with other materials to overcome the limitations of traditional single-drug treatments. There is growing interest in developing nanosystems capable of delivering multiple drugs simultaneously, addressing challenges such as drug resistance. Engineered DNA nanostructures are designed to precisely deliver different drugs to specific locations, enhancing therapeutic effects. By attaching targeting molecules, these nanostructures can recognize and bind to cancer cells, increasing treatment precision. This approach offers tailored solutions for targeted drug delivery, enabling the delivery of multiple drugs in a coordinated manner. This review explores the advancements and applications of DNA nanostructures in cancer treatment, with a focus on targeted drug delivery and multi-drug therapy. It discusses the benefits and current limitations of nanoscale formulations in cancer therapy, categorizing DNA nanostructures into pure forms and hybrid versions optimized for drug delivery. Furthermore, the review examines ongoing research efforts and translational possibilities, along with challenges in clinical integration. By highlighting the advancements in DNA nanostructures, this review aims to underscore their potential in improving cancer treatment outcomes.

Oligo-Adenine and Cyanuric Acid Supramolecular DNA-Based Hydrogels Exhibiting Acid-Resistance and Physiological pH-Responsiveness

Expanding the functions and applications of DNA by integrating noncanonical bases and structures into biopolymers is a continuous scientific effort. An adenine-rich strand (A-strand) is introduced as functional scaffold revealing, in the presence of the low-molecular-weight cofactor cyanuric acid (CA, pKa 6.9), supramolecular hydrogel-forming efficacies demonstrating multiple pH-responsiveness. At pH 1.2, the A-strand transforms into a parallel A-motif duplex hydrogel cross-linked by AH+-H+A units due to the protonation of adenine (pKa 3.5). At pH 5.2, and in the presence of coadded CA, a helicene-like configuration is formed between adenine and protonated CA, generating a parallel A-CA triplex cross-linked hydrogel. At pH 8.0, the hydrogel undergoes transition into a liquid state by deprotonation of CA cofactor units and disassembly of A-CA triplex into its constituent components. Density functional theory calculations and molecular dynamics simulations, supporting the structural reconfigurations of A-strand in the presence of CA, are performed. The sequential pH-stimulated hydrogel states are rheometrically characterized. The hydrogel framework is loaded with fluorescein-labeled insulin, and the pH-stimulated release of insulin from the hydrogel across the pH barriers present in the gastrointestinal tract is demonstrated. The results provide principles for future application of the hydrogel for oral insulin administration for diabetes.

Construction Strategy of Functionalized Liposomes and Multidimensional Application

Liposomes are widely used in the biological field due to their good biocompatibility and surface modification properties. With the development of biochemistry and material science, many liposome structures and their surface functional components have been modified and optimized one by one, pushing the liposome platform from traditional to functionalized and intelligent, which will better satisfy and expand the needs of scientific research. However, a main limiting factor effecting the efficiency of liposomes is the complicated environmental conditions in the living body. Currently, in order to overcome the above problem, functionalized liposomes have become a very promising strategy. In this paper, binding strategies of liposomes with four main functional elements, namely nucleic acids, antibodies, peptides, and stimuli-responsive motif have been summarized for the first time. In addition, based on the construction characteristics of functionalized liposomes, such as drug-carrying, targeting, long-circulating, and stimulus-responsive properties, a comprehensive overview of their features and respective research progress are presented. Finally, the paper critically presents the limitations of these functionalized liposomes in the current applications and also prospectively suggests the future development directions, aiming to accelerate realization of their industrialization.

Recent Progress of Supramolecular Chemotherapy Based on Host-Guest Interactions

Chemotherapy is widely recognized as an effective approach for treating cancer due to its ability to eliminate cancer cells using chemotherapeutic drugs. However, traditional chemotherapy suffers from various drawbacks, including limited solubility and stability of drugs, severe side effects, low bioavailability, drug resistance, and challenges in tracking treatment efficacy. These limitations greatly hinder its widespread clinical application. In contrast, supramolecular chemotherapy, which relies on host-guest interactions, presents a promising alternative by offering highly efficient and minimally toxic anticancer drug delivery. In this review, an overview of recent advancements in supramolecular chemotherapy based on host-guest interactions is provided. The significant role it plays in guiding cancer therapy is emphasized. Drawing on a wealth of cutting-edge research, herein, a timely and valuable resource for individuals interested in the field of supramolecular chemotherapy or cancer therapy, is presented. Furthermore, this review contributes to the progression of the field of supramolecular chemotherapy toward clinical application.

A Nucleic Acid-Based LYTAC Plus Platform to Simultaneously Mediate Disease-Driven Protein Downregulation

Protein degradation techniques, such as proteolysis-targeting chimeras (PROTACs) and lysosome-targeting chimeras (LYTACs), have emerged as promising therapeutic strategies for the treatment of diseases. However, the efficacy of current protein degradation methods still needs to be improved to address the complex mechanisms underlying diseases. Herein, a LYTAC Plus hydrogel engineered is proposed by nucleic acid self-assembly, which integrates a gene silencing motif into a LYTAC construct to enhance its therapeutic potential. As a proof-of-concept study, vascular endothelial growth factor receptor (VEGFR)-binding peptides and mannose-6 phosphate (M6P) moieties into a self-assembled nucleic acid hydrogel are introduced, enabling its LYTAC capability. Small interference RNAs (siRNAs) is then employed that target the angiopoietin-2 (ANG-2) gene as cross-linkers for hydrogel formation, giving the final LYTAC Plus hydrogel gene silencing ability. With dual functionalities, the LYTAC Plus hydrogel demonstrated effectiveness in simultaneously reducing the levels of VEGFR-2 and ANG-2 both in vitro and in vivo, as well as in improving therapeutic outcomes in treating neovascular age-related macular degeneration in a mouse model. As a general material platform, the LYTAC Plus hydrogel may possess great potential for the treatment of various diseases and warrant further investigation.

Programming the Assembly of Oligo-Adenine with Coralyne into a pH-Responsive DNA Hydrogel

External stimuli-responsive DNA hydrogels present interesting platforms for drug loading and triggered release. Typically, drug molecules are encapsulated within three-dimensionally hybridized DNA networks. However, the utilization of drug molecules as cofactors to facilitate the directed assembly of DNA strands into hydrogel frameworks and their subsequent controlled release remains to be explored. Herein, we introduce the guided assembly of oligo-adenine (A-strand) into an acidic pH-responsive DNA hydrogel using an anticancer drug, coralyne (COR), as a low-molecular-weight cofactor. At pH 7, COR orchestrates the assembly of A-strand into an antiparallel duplex configuration cross-linked by A-COR-A units at a stoichiometric ratio of one COR cofactor per four adenine bases, resulting in a DNA hydrogel characterized by A-COR-A duplex bridges. At pH 4-5, the instability of A-COR-A units results in the disintegration of the duplex into its constituent components, leading to the release of COR and simultaneous dissociation of the DNA hydrogel matrix. This study introduces a method by which drug molecules, exemplified here by COR, facilitate the direct formation of a supramolecular cofactor-DNA complex, subsequently leading to the creation of a stimuli-responsive DNA hydrogel. This approach may inspire future investigations into DNA hydrogels tailored for controlled drug encapsulation and release applications.

Preparation Strategies, Functional Regulation, and Applications of Multifunctional Nanomaterials-Based DNA Hydrogels

With the extensive attention of DNA hydrogels in biomedicine, biomaterial, and other research fields, more and more functional DNA hydrogels have emerged to match the various needs. Incorporating nanomaterials into the hydrogel network is an emerging strategy for functional DNA hydrogel construction. Surprisingly, nanomaterials-based DNA hydrogels can be engineered to possess favorable properties, such as dynamic mechanical properties, excellent optical properties, particular electrical properties, perfect encapsulation properties, improved magnetic properties, and enhanced antibacterial properties. Herein, the preparation strategies of nanomaterials-based DNA hydrogels are first highlighted and then different nanomaterial designs are used to demonstrate the functional regulation of DNA hydrogels to achieve specific properties. Subsequently, representative applications in biosensing, drug delivery, cell culture, and environmental protection are introduced with some selected examples. Finally, the current challenges and prospects are elaborated. The study envisions that this review will provide an insightful perspective for the further development of functional DNA hydrogels.

Rational Design of DNA Hydrogels Based on Molecular Dynamics of Polymers

In recent years, DNA has emerged as a fascinating building material to engineer hydrogel due to its excellent programmability, which has gained considerable attention in biomedical applications. Understanding the structure-property relationship and underlying molecular determinants of DNA hydrogel is essential to precisely tailor its macroscopic properties at molecular level. In this review, the rational design principles of DNA molecular networks based on molecular dynamics of polymers on the temporal scale, which can be engineered via the backbone rigidity and crosslinking kinetics, are highlighted. By elucidating the underlying molecular mechanisms and theories, it is aimed to provide a comprehensive overview of how the tunable DNA backbone rigidity and the crosslinking kinetics lead to desirable macroscopic properties of DNA hydrogels, including mechanical properties, diffusive permeability, swelling behaviors, and dynamic features. Furthermore, it is also discussed how the tunable macroscopic properties make DNA hydrogels promising candidates for biomedical applications, such as cell culture, tissue engineering, bio-sensing, and drug delivery.

Self-Immolative Hydrogels with Stimulus-Mediated On-Off Degradation

Hydrogels are of interest for a wide range of applications from sensors to drug delivery and tissue engineering. Self-immolative polymers, which depolymerize from end-to-end following a single backbone or end-cap cleavage, offer advantages such as amplification of the stimulus-mediated cleavage event through a cascade degradation process. It is also possible to change the active stimulus by changing only a single end-cap or linker unit. However, there are very few examples of self-immolative polymer hydrogels, and the reported examples exhibited relatively poor stability in their nontriggered state or slow degradation after triggering. Described here is the preparation of hydrogels composed of self-immolative poly(ethyl glyoxylate) (PEtG) and poly(ethylene glycol) (PEG). Hydrogels formed from 2 kg/mol 4-arm PEG and 1.2 kg/mol PEtG with a light-responsive linker end-cap had high gel content (90%), an equilibrium water content of 89%, and a compressive modulus of 26 kPa. The hydrogel degradation could be turned on and off repeatedly through alternating cycles of irradiation and dark storage. Similar cycles could also be used to control the release of the anti-inflammatory drug celecoxib. These results demonstrate the potential for self-immolative hydrogels to afford a high degree of control over responses to stimuli in the context of smart materials for a variety of applications.

CRISPR/Cas9 Genome Editing for Tissue-Specific In Vivo Targeting: Nanomaterials and Translational Perspective

Clustered randomly interspaced short palindromic repeats (CRISPRs) and its associated endonuclease protein, i.e., Cas9, have been discovered as an immune system in bacteria and archaea; nevertheless, they are now being adopted as mainstream biotechnological/molecular scissors that can modulate ample genetic and nongenetic diseases via insertion/deletion, epigenome editing, messenger RNA editing, CRISPR interference, etc. Many Food and Drug Administration-approved and ongoing clinical trials on CRISPR adopt ex vivo strategies, wherein the gene editing is performed ex vivo, followed by reimplantation to the patients. However, the in vivo delivery of the CRISPR components is still under preclinical surveillance. This review has summarized the nonviral nanodelivery strategies for gene editing using CRISPR/Cas9 and its recent advancements, strategic points of view, challenges, and future aspects for tissue-specific in vivo delivery of CRISPR/Cas9 components using nanomaterials.

Optimization of guanosine-based hydrogels with boric acid derivatives for enhanced long-term stability and cell survival

Tissue defects can lead to serious health problems and often require grafts or transplants to repair damaged soft tissues. However, these procedures can be complex and may not always be feasible due to a lack of available tissue. Hydrogels have shown potential as a replacement for tissue grafts due to their ability to support cell survival and encapsulate biomolecules such as growth factors. In particular, guanosine-based hydrogels have been explored as a potential solution, but they often exhibit limited stability which hampers their use in the biofabrication of complex grafts. To address this issue, we explored the use of borate ester chemistry and more complex boric acid derivatives to improve the stability and properties of guanosine-based hydrogels. We hypothesized that the aromatic rings in these derivatives would enhance the stability and printability of the hydrogels through added π-π stack interactions. After optimization, 13 compositions containing either 2-naphthylboronic acid or boric acid were selected. Morphology studies shows a well-defined nanofibrilar structure with good printable properties (thixotropic behaviour, print fidelity and printability). Moreover, the pH of all tested hydrogels was within the range suitable for cell viability (7.4–8.3). Nevertheless, only the boric acid-based formulations were stable for at least 7 days. Thus, our results clearly demonstrated that the presence of additional aromatic rings did actually impair the hydrogel properties. We speculate that this is due to steric hindrance caused by adjacent groups, which disrupt the correct orientation of the aromatic groups required for effective π-π stack interactions of the guanosine building block. Despite this drawback, the developed guanosine-boric acid hydrogel exhibited good thixotropic properties and was able to support cell survival, proliferation, and migration. For instance, SaOS-2 cells planted on these printed structures readily migrated into the hydrogel and showed nearly 100% cell viability after 7 days. In conclusion, our findings highlight the potential of guanosine-boric acid hydrogels as tissue engineering scaffolds that can be readily enhanced with living cells and bioactive molecules. Thus, our work represents a significant advancement towards the development of functionalized guanosine-based hydrogels.

A DNA-Micropatterned Surface for Propagating Biomolecular Signals by Positional on-off Assembly of Catalytic Nanocompartments

Signal transduction is pivotal for the transfer of information between and within living cells. The composition and spatial organization of specified compartments are key to propagating soluble signals. Here, a high-throughput platform mimicking multistep signal transduction which is based on a geometrically defined array of immobilized catalytic nanocompartments (CNCs) that consist of distinct polymeric nanoassemblies encapsulating enzymes and DNA or enzymes alone is presented. The dual role of single entities or tandem CNCs in providing confined but communicating spaces for complex metabolic reactions and in protecting encapsulated compounds from denaturation is explored. To support a controlled spatial organization of CNCs, CNCs are patterned by means of DNA hybridization to a microprinted glass surface. Specifically, CNC-functionalized DNA microarrays are produced where individual reaction compartments are kept in close proximity by a distinct geometrical arrangement to promote effective communication. Besides a remarkable versatility and robustness, the most prominent feature of this platform is the reversibility of DNA-mediated CNC-anchoring which renders it reusable. Micropatterns of polymer-based nanocompartment assemblies offer an ideal scaffold for the development of the next generation responsive and communicative soft-matter analytical devices for applications in catalysis and medicine.

Stimuli-Responsive Self-Degradable DNA Hydrogels: Design, Synthesis, and Applications

DNA hydrogels play an increasingly important role in biomedicine and bioanalysis applications. Due to their high programmability, multifunctionality and biocompatibility, they are often used as effective carriers for packing drugs, cells, or other bioactive cargoes in vitro and in vivo. However, the stability of the DNA hydrogels prevents their in-demand rapid release of cargoes to achieve a full therapeutic effect in time. For bioanalysis, the generation of signals sometimes needs the DNA hydrogel to be rapidly degraded when sensing target molecules. To meet these requirements, stimulus-responsive DNA hydrogels are designed. By responding to different stimuli, self-degradable DNA hydrogels can switch from gel to solution for quantitative bioanalysis and precision cargo delivery. This review summarizes the recently developed innovative methods for designing stimuli-responsive self-degradable DNA hydrogels and showed their applications in the bioanalysis and biomedicines fields. Challenges, as well as prospects, are also discussed.

Nucleoside-Based Supramolecular Hydrogels: From Synthesis and Structural Properties to Biomedical and Tissue Engineering Applications

Supramolecular hydrogels are of great interest in tissue scaffolding, diagnostics, and drug delivery due to their biocompatibility and stimuli-responsive properties. In particular, nucleosides are promising candidates as building blocks due to their manifold noncovalent interactions and ease of chemical modification. Significant progress in the field has been made over recent years to allow the use of nucleoside-based supramolecular hydrogels in the biomedical field, namely drug delivery and 3D bioprinting. For example, their long-term stability, printability, functionality, and bioactivity have been greatly improved by employing more than one gelator, incorporating different cations, including silver for antibacterial activity, or using additives such as boric acid or even biomolecules. This now permits their use as bioinks for 3D printing to produce cell-laden scaffolds with specified geometries and pore sizes as well as a homogeneous distribution of living cells and bioactive molecules. We have summarized the latest advances in nucleoside-based supramolecular hydrogels. Additionally, we discuss their synthesis, structural properties, and potential applications in tissue engineering and provide an outlook and future perspective on ongoing developments in the field.

Fast Transport and Transformation of Biomacromolecular Substances via Thermo-Stimulated Active "Inhalation-Exhalation" Cycles of Hierarchically Structured Smart pNIPAM-DNA Hydrogels

Although smart hydrogels hold great promise in biosensing and biomedical applications, their response to external stimuli is governed by the passive diffusion-dependent substance transport between hydrogels and environments and within the 3D hydrogel matrices, resulting in slow response to biomacromolecules and limiting their extensive applications. Herein, inspired by the respiration systems of organisms, an active strategy to achieve highly efficient biomolecular substance transport through the thermo-stimulated "inhalation-exhalation" cycles of hydrogel matrices is demonstrated. The cryo-structured poly(N-isopropylacrylamide) (pNIPAM)-DNA hydrogels, composed of functional DNA-tethered pNIPAM networks and free-water-containing macroporous channels, exhibit thermally triggered fast and reversible shrinking/swelling cycles with high-volume changes, which drive the formation of dynamic water stream to accelerate the intake of external substances and expelling of endogenous substances, thus promoting the functional properties of hydrogel systems. Demonstrated by catalytic DNAzyme and CRISPR-Cas12a-incorporating hydrogels, significantly enhanced catalytic efficiency with up to 280% and 390% is achieved, upon the introduction of active "inhalation-exhalation" cycles, respectively. Moreover, remotely near-infrared (NIR)-triggering of "inhalation-exhalation" cycles is achieved after the introduction of NIR-responsive MXene nanosheets into the hydrogel matrix. These hydrogel systems with enhanced substance transport and transformation properties hold promise in the development of more effective biosensing and therapeutic systems.

Advances in the Translation of Electrochemical Hydrogel-Based Sensors

Novel biomaterials for bio- and chemical sensing applications have gained considerable traction in the diagnostic community with rising trends of using biocompatible and lowly cytotoxic material. Hydrogel-based electrochemical sensors have become a promising candidate for their swellable, nano-/microporous, and aqueous 3D structures capable of immobilizing catalytic enzymes, electroactive species, whole cells, and complex tissue models, while maintaining tunable mechanical properties in wearable and implantable applications. With advances in highly controllable fabrication and processability of these novel biomaterials, the possibility of bio-nanocomposite hydrogel-based electrochemical sensing presents a paradigm shift in the development of biocompatible, "smart," and sensitive health monitoring point-of-care devices. Here, recent advances in electrochemical hydrogels for the detection of biomarkers in vitro, in situ, and in vivo are briefly reviewed to demonstrate their applicability in ideal conditions, in complex cellular environments, and in live animal models, respectively, to provide a comprehensive assessment of whether these biomaterials are ready for point-of-care translation and biointegration. Sensors based on conductive and nonconductive polymers are presented, with highlights of nano-/microstructured electrodes that provide enhanced sensitivity and selectivity in biocompatible matrices. An outlook on current challenges that shall be addressed for the realization of truly continuous real-time sensing platforms is also presented.

Fabrication Strategies Towards Hydrogels for Biomedical Application: Chemical and Mechanical Insights

This review aims at giving selected chemical and mechanical insights on design criteria that should be taken into account in hydrogel production for biomedical applications. Particular emphasis will be given to the chemical aspects involved in hydrogel design: macromer chemical composition, cross-linking strategies and chemistry towards "conventional" and smart/stimuli responsive hydrogels. Mechanical properties of hydrogels in view of regenerative medicine applications will also be considered.

Construction of Sol-Gel Phase-Reversible Hydrogels with Tunable Properties with Native Nanofibrous Protein as Building Blocks

Reversible sol-gel transforming behaviors combined with tunable mechanical properties are vital demands for developing biomaterials. However, it remains challenging to correlate these properties with the hydrogels constructed by denatured protein as building blocks. Herein, taking advantage of naturally high-affinity coordination environments consisting of i, i + 4 His-Glu motifs offered by paramyosin, a ubiquitous nanofibrous protein, we found that Zn²⁺ rather than Ca²⁺ or Mg²⁺ has the ability to trigger the self-assembly of native abalone paramyosin (AbPM) into protein hydrogels under benign conditions, while the addition of EDTA induces the hydrogels back into protein monomers, indicative of a reversible process. By using such sol-gel reversible property, the AbPM gels can serve as a vehicle to encapsulate bioactive molecules such as curcumin, thereby protecting it from degradation from thermal and photo treatment. Notably, based on the high conserved structure of native AbPM, the mechanical property and biological activity of the fabricated AbPM hydrogels can be fined-tuned by its noncovalent interaction with small molecules. All these findings raise the possibility that native paramyosin can be explored as a new class of protein hydrogels which exhibit favorable properties that the traditional hydrogels constructed by denatured protein building blocks do not have.

Self-assembly hydrogels of therapeutic agents for local drug delivery

Advanced drug delivery systems are of vital importance to enhance therapeutic efficacy. Among various recently developed formulations, self-assembling hydrogels composed of therapeutic agents have shown promising potential for local drug delivery owing to their excellent biocompatibility, high drug-loading efficiency, low systemic toxicity, and sustained drug release behavior. In particular, therapeutic agents self-assembling hydrogels with well-defined nanostructures are beneficial for direct delivery to the target site via injection, not only improving drug availability, but also extending their retention time and promoting cellular uptake. In brief, the self-assembly approach offers better opportunities to improve the precision of pharmaceutical treatment and achieve superior treatment efficacies. In this review, we intend to cover the recent developments in therapeutic agent self-assembling hydrogels. First, the molecular structures, self-assembly mechanisms, and application of self-assembling hydrogels are systematically outlined. Then, we summarize the various self-assembly strategies, including the single therapeutic agent, metal-coordination, enzyme-instruction, and co-assembly of multiple therapeutic agents. Finally, the potential challenges and future perspectives are discussed. We hope that this review will provide useful insights into the design and preparation of therapeutic agent self-assembling hydrogels.

Programmable DNA Hydrogels as Artificial Extracellular Matrix

The cell microenvironment plays a crucial role in regulating cell behavior and fate in physiological and pathological processes. As the fundamental component of the cell microenvironment, extracellular matrix (ECM) typically possesses complex ordered structures and provides essential physical and chemical cues to the cells. Hydrogels have attracted much attention in recapitulating the ECM. Compared to natural and synthetic polymer hydrogels, DNA hydrogels have unique programmable capability, which endows the material precise structural customization and tunable properties. This review focuses on recent advances in programmable DNA hydrogels as artificial extracellular matrix, particularly the pure DNA hydrogels. It introduces the classification, design, and assembly of DNA hydrogels, and then summarizes the state-of-the-art achievements in cell encapsulation, cell culture, and tissue engineering with DNA hydrogels. Ultimately, the challenges and prospects for cellular applications of DNA hydrogels are delivered.

Myelosuppression Alleviation and Hematopoietic Regeneration by Tetrahedral-Framework Nucleic-Acid Nanostructures Functionalized with Osteogenic Growth Peptide

As major complications of chemoradiotherapy, myelosuppression and hematopoietic-system damage severely affect immunologic function and can delay or even terminate treatment for cancer patients. Although several specific cytokines have been used for hematopoiesis recovery, their effect is limited, and they may increase the risk of tumor recurrence. In this study, osteogenic growth peptide functionalized tetrahedral framework nucleic-acid nanostructures (OGP-tFNAs) are prepared; they combine the positive hematopoiesis stimulating effect of OGP and the drug carrying function of tFNAs. The potential of OGP-tFNAs for hematopoietic stimulation and microenvironment regulation is investigated. It is shown that OGP-tFNAs can protect bone marrow stromal cells from 5-fluorouracil (5-FU)-induced DNA damage and apoptosis. OGP-tFNAs pretreatment activates the extracellularly regulated protein kinase signal and downregulates apoptosis-related proteins. OGP-tFNAs also alleviate the chemotherapy-induced inhibition of hematopoiesis-related cytokine expression, which is crucial for hematopoiesis reconstitution. In conclusion, OGP-tFNAs can protect hematopoietic cells and their microenvironment from chemotherapy-induced injuries and myelosuppression, while promoting hematopoiesis regeneration.

Cell-specific aptamers as potential drugs in therapeutic applications: A review of current progress

Cell-specific aptamers are a promising emerging player in the field of disease therapy. This paper reviews the multidimensional research progress made in terms of their classification, modification, and application. Based on the target location of cell-specific aptamers, it is defined and classified cell-specific aptamers into three groups including aptamers for cell surface markers, aptamers for intracellular components, and aptamers for extracellular components. Moreover, the modification methods of aptamers to achieve improved stability and affinity are concluded. In addition, recent advances in the application of cell-specific aptamers are discussed, mainly focusing on the increasing research attraction of cell state improving helpers and cell recruitment mediators in the improvement of cellular microenvironments to achieve successful disease therapy. This review also highlights 11 types of clinical aptamer drugs. Finally, the challenges and future directions of potential clinical applications are presented. In summary, we believe that cell-specific aptamers are promising drugs in disease therapy.

Designer DNA biomolecules as a defined biomaterial for 3D bioprinting applications

DNA has excellent features such as the presence of functional and targeted molecular recognition motifs, tailorability, multifunctionality, high-precision molecular self-assembly, hydrophilicity, and outstanding biocompatibility. Due to these remarkable features, DNA has emerged as a leading next-generation biomaterial of choice to make hydrogels by self-assembly. In recent times, novel routes for the chemical synthesis of DNA, advances in tailorable designs, and affordable production ways have made DNA as a building block material for various applications. These advanced features have made researchers continuously explore the interesting properties of pure and hybrid DNA for 3D bioprinting and other biomedical applications. This review article highlights the topical advancements in the use of DNA as an ideal bioink for the bioprinting of cell-laden three-dimensional tissue constructs for regenerative medicine applications. Various bioprinting techniques and emerging design approaches such as self-assembly, nucleotide sequence, enzymes, and production cost to use DNA as a bioink for bioprinting applications are described. In addition, various types and properties of DNA hydrogels such as stimuli responsiveness and mechanical properties are discussed. Further, recent progress in the applications of DNA in 3D bioprinting are emphasized. Finally, the current challenges and future perspectives of DNA hydrogels in 3D bioprinting and other biomedical applications are discussed.

Fusion of binary split allosteric aptasensor for the ultra-sensitive and super-rapid detection of malachite green

The complicated labeling procedure and high cost of split aptasensors have hitherto limited their application in the detection of hazardous substances. Herein we report the first examples of label-free aptasensors based on the fusion of a binary split G-quadruplex and malachite green (MG) aptamer, transducing recognition events into fluorescent signals through the allosteric regulation of the aptamer to achieve selective and sensitive detection. Specifically, RNA MGA was successfully converted into DNA MGA with comparable affinity and improved stability, thereby overcoming the limitations of poor stability and high expense. We subsequently split the DNA MGA and attached them to a G-rich DNA sequence at the 5' and 3' ends, to construct the binary split allosteric aptasensor. The performance of the binary split aptasensor for MG detection was significantly improved based on proposed allosteric regulation strategy, and the reconfiguration capability of the aptamers upon binding with targets was proven, providing the binary split aptasensor with superior sensitivity and selectivity. This sensing method has a wide dynamic detection range of 5 nmol·L^-1 to 500 μmol·L^-1, with a low limit of detection (LOD) of 4.17 nmol·L^-1, and achieves the ultra-sensitive and super-rapid detection of MG. This newly proposed aptasensor is equipped with the advantages of being label-free, time saving and economical. More importantly, this successful construction of a fused aptasensor expands the principles of split aptasensor design and provides a universal platform for the detection of environmental contaminants.

Recent Advances in Stimuli-Responsive DNA-Based Hydrogels

Stimuli-responsive DNA-based hydrogels are attracting growing interest because of their smart responsiveness, excellent biocompatibility, regulated biodegradability, and programmable design properties. Integration of reconfigurable DNA architectures and switchable supramolecular moieties (as cross-linkers) in hydrogels by responding to external stimuli provides an ideal approach for the reversible tuning structural and mechanical properties of the hydrogels, which can be exploited in the development of intelligent DNA-based materials. This review highlights recent advances in the design of responsive pure DNA hydrogels, DNA-polymer hybrid hydrogels, and autonomous DNA-based hydrogels with transient behaviors. A variety of chemically and physically triggered DNA-based stimuli-responsive hydrogels and their versatile applications in biosensing, biocatalysis, cell culture and separation, drug delivery, shape memory, self-healing, and robotic actuators are summarized. Finally, we address the key challenges that the field will face in the coming years, and future prospects are identified.

Aptamer-Functionalized Binary-Drug Delivery System for Synergetic Obesity Therapy

The targeted delivery of phytochemicals that promote energy expenditure for obesity therapy remains a challenge. This study assembled a functionalized adipo-8 aptamer loaded with allicin using isothermal rolling-circle techniques to form a synergistic adipocyte-targeted binary-drug delivery system for treating obesity. The functionalized adipo-8 aptamer efficiently protected allicin from adsorption, showing significant potential to encapsulate, transport, and release molecular cargos into white adipose tissue. Introducing the negatively charged allicin, a phytochemical able to induce adipose tissue browning, reduced the diameters of DNA-nanoflower from 770 to 380 nm and increased cellular uptake efficiency up to 118.7%. The intracellular distribution observed via confocal microscopy confirmed the successful receptor recognition mediated by aptamers in the DNA-nanoflower-allicin (NFA) framework as well as its excellent stability to escape from lysosomes. In vivo results demonstrated that subcutaneous administration of NFA effectively promoted adipocyte browning and systematic energy expenditure with minimal side effects. Furthermore, the G-quadruplex in the mitochondrial uncoupling protein-1 promoter was found to be an interactive allicin target for regulating thermogenesis to combat obesity.

Smart Nucleic Acid Hydrogels with High Stimuli-Responsiveness in Biomedical Fields

Due to their hydrophilic, biocompatible and adjustability properties, hydrogels have received a lot of attention. The introduction of nucleic acids has made hydrogels highly stimuli-responsiveness and they have become a new generation of intelligent biomaterials. In this review, the development and utilization of smart nucleic acid hydrogels (NAHs) with a high stimulation responsiveness were elaborated systematically. We discussed NAHs with a high stimuli-responsiveness, including pure NAHs and hybrid NAHs. In particular, four stimulation factors of NAHs were described in details, including pH, ions, small molecular substances, and temperature. The research progress of nucleic acid hydrogels in biomedical applications in recent years is comprehensively discussed. Finally, the opportunities and challenges facing the future development of nucleic acid hydrogels are also discussed.