Double Controlled Release of Therapeutic RNA Modules through Injectable DNA-RNA Hybrid Hydrogel

Nucleic acid-responsive smart systems for controlled cargo delivery

Stimulus-responsive delivery systems allow controlled, highly regulated, and efficient delivery of various cargos while minimizing side effects. Owing to the unique properties of nucleic acids, including the ability to adopt complex structures by base pairing, their easy synthesis, high specificity, shape memory, and configurability, they have been employed in autonomous molecular motors, logic circuits, reconfigurable nanoplatforms, and catalytic amplifiers. Moreover, the development of nucleic acid (NA)-responsive intelligent delivery vehicles is a rapidly growing field. These vehicles have attracted much attention in recent years due to their programmable, controllable, and reversible properties. In this work, we review several types of NA-responsive controlled delivery vehicles based on locks and keys, including DNA/RNA-responsive, aptamer-responsive, and CRISPR-responsive, and summarize their advantages and limitations.

DNA-based nanostructures for RNA delivery

RNA-based therapeutics have emerged as a promising approach for the treatment of various diseases, including cancer, genetic disorders, and infectious diseases. However, the delivery of RNA molecules into target cells has been a major challenge due to their susceptibility to degradation and inefficient cellular uptake. To overcome these hurdles, DNA-based nano technology offers an unprecedented opportunity as a potential delivery platform for RNA therapeutics. Due to its excellent characteristics such as programmability and biocompatibility, these DNA-based nanostructures, composed of DNA molecules assembled into precise and programmable structures, have garnered significant attention as ideal building materials for protecting and delivering RNA payloads to the desired cellular destinations. In this review, we highlight the current progress in the design and application of three DNA-based nanostructures: DNA origami, lipid-nanoparticle (LNP) technology related to frame guided assembly (FGA), and DNA hydrogel for the delivery of RNA molecules. Their biomedical applications are briefly discussed and the challenges and future perspectives in this field are also highlighted.

DNA Hydrogels with Programmable Condensation, Expansion, and Degradation for Molecular Carriers

Molecular carriers are necessary for the controlled release of drugs and genes to achieve the desired therapeutic outcomes. DNA hydrogels can be a promising candidate in this application with their distinctive sequence-dependent programmability, which allows precise encapsulation of specific cargo molecules and stimuli-responsive release of them at the target. However, DNA hydrogels are inherently susceptible to the degradation of nucleases, making them vulnerable in a physiological environment. To be an effective molecular carrier, DNA hydrogels should be able to protect encapsulated cargo molecules until they reach the target and release them once they are reached. Here, we develop a simple way of controlling the enzyme resistance of DNA hydrogels for cargo protection and release by using cation-mediated condensation and expansion. We found that DNA hydrogels condensed by spermine are highly resistant to enzymatic degradation. They become degradable again if expanded back to their original, uncondensed state by sodium ions interfering with the interaction between spermine and DNA. These controllable condensation, expansion, and degradation of DNA hydrogels pave the way for the development of DNA hydrogels as an effective molecular carrier.

Nucleic acids based integrated macromolecular complexes for SiRNA delivery: Recent advancements

The therapeutic potential of small interfering RNA (siRNA) is monumental, offering a pathway to silence disease-causing genes with precision. However, the delivery of siRNA to target cells in-vivo remains a formidable challenge, owing to degradation by nucleases, poor cellular uptake and immunogenicity. This overview examines recent advancements in the design and application of nucleic acid-based integrated macromolecular complexes for the efficient delivery of siRNA. We dissect the innovative delivery vectors developed in recent years, including lipid-based nanoparticles, polymeric carriers, dendrimer complexes and hybrid systems that incorporate stimuli-responsive elements for targeted and controlled release. Advancements in bioconjugation techniques, active targeting strategies and nanotechnology-enabled delivery platforms are evaluated for their contribution to enhancing siRNA delivery. It also addresses the complex interplay between delivery system design and biological barriers, highlighting the dynamic progress and remaining hurdles in translating siRNA therapies from bench to bedside. By offering a comprehensive overview of current strategies and emerging technologies, we underscore the future directions and potential impact of siRNA delivery systems in personalized medicine.

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.

Dual-functional DNA nanogels for anticancer drug delivery

DNA hydrogels with unique sequence programmability on nucleic acid framework manifest remarkable attributes, such as high payload capacities, biocompatibility and biosafety. The availability of DNA nanogels with multimodal functionalities remains limited due to the absence of facile gelation methods applicable at the nanometer scale. Here, we developed a one-step assembly of DNA dendrimers into nanogels (DNG) with couple hundred nanometers size. DNG showed robust stability against physical forces and biological degradation for easy purification and sustainable drug release. Long-term stability either in powder or aqueous solution endows DNG easy for shipping, handling and storage. By encoding dual functionalities into separate branches on DNA dendrimers, DNG can accommodate chemodrugs and aptamers with distinctive loading moduli. DNG significantly enhanced the drug efficacy against cancerous cells while minimizing cytotoxicity towards somatic cells, as demonstrated in vitro and in xenografted mice models of breast cancer. Thus, due to their facile assembly and storage, bi-entity encoding, and inherent biocompatibility, DNG exhibits immense prospects as nanoscale vesicles for the synergistic delivery of multimodal theranostics in anticancer treatments. STATEMENT OF SIGNIFICANCE: DNA nanogels were self-assembled via a facile protocol utilizing a DNA dendrimer structure. These nanogels displayed robust stability against physical forces, permitting long term storage in concentrated solutions or as a powder. Furthermore, they exhibited resilience to biological degradation, facilitating sustained drug release. The bi-entity encoded dendritic branches conferred dual functionalities, enabling both chemodrug encapsulation and the presentation of aptamers as targeting motifs. In vivo investigations confirmed the nanogels provide high efficacy in tumor targeting and chemotherapy with enhanced drug efficacy and reduced side effects.

Exploring the potential of polysaccharide-based hybrid hydrogel systems for their biomedical and therapeutic applications: A review

Hydrogels are a versatile category of biomaterials that have been widely applied in the fields of biomedicine for the last several decades. The three-dimensional polymeric crosslinked hydrophilic structures of the hydrogel can proficiently hold drugs, nanoparticles, and cells, making them a potential delivery system. However, disadvantages like low mechanical strength, poor biocompatibility, and unusual in-vivo biodegradation are associated with conventional hydrogels. To overcome these hurdles, hybrid hydrogels are designed using two or more structurally different polymeric units. Polysaccharides, characterized by their innate biocompatibility, biodegradability, and abundance, establish an ideal foundation for the development of these hybrid hydrogels. This review aims to discuss the studies that have utilized naturally occurring polysaccharides to prepare hybrid systems, which were aimed for various biomedical applications such as tissue engineering, bone and cartilage regeneration, wound healing, skin cancer treatment, antimicrobial therapy, osteoarthritis treatment, and drug delivery. Furthermore, this review extensively examines the properties of the employed polysaccharides within hydrogel matrices, emphasizing the advantageous characteristics that make them a preferred choice. Furthermore, the challenges associated with the commercial implementation of these systems are explored alongside an assessment of the current patent landscape.

A pH-responsive, injectable and self-healing chitosan-coumarin hydrogel based on Schiff base and hydrogen bonds

Smart hydrogels have shown great potential applications in disease treatment due to their controlled and local drug-release ability. Herein, a smart hydrogel with pH-responsive, injectable, and self-healing properties for controlled release of taxifolin (TFL) was prepared by freezing-thawing and photo-crosslinking methods. The crosslinking network of hydrogels (CS-CA hydrogels) was constructed by the hydrogen bonds, Schiff base bonds, and cyclobutane rings using chitosan (CS) and coumarin (CA) as raw materials. The CS-CA hydrogel demonstrated a compressive strength of 1.04 MPa, a self-healing efficiency of 99.9 %, and could maintain structural and functional integrity after injection. In addition, the drug release rate and shape of the CS-CA hydrogels were tunable due to its pH sensitivity. The TFL cumulative release reached 60 % within 12 h at pH = 4, and after equilibration, the cumulative release of TFL at pH = 4 (80 %) was significantly higher than at pH = 9.2 (50 %). The CCK8 experiment showed that the resulting hydrogel had no cytotoxicity. Meanwhile, subcutaneous implantation experiments in mice showed that the CS-CA hydrogels had favorable biodegradability and compatibility.

The microspheres/hydrogels scaffolds based on the proteins, nucleic acids, or polysaccharides composite as carriers for tissue repair: A review

There are many studies on specific macromolecules and their contributions to tissue repair. Macromolecules have supporting and protective effects in organisms and can help regrow, reshape, and promote self-repair and regeneration of damaged tissues. Macromolecules, such as proteins, nucleic acids, and polysaccharides, can be constructed into hydrogels for the preparation of slow-release drug agents, carriers for cell culture, and platforms for gene delivery. Hydrogels and microspheres are fabricated by chemical crosslinking or mixed co-deposition often used as scaffolds, drug carriers, or cell culture matrix, provide proper mechanical support and nutrient delivery, a well-conditioned environment that to promote the regeneration and repair of damaged tissues. This review provides a comprehensive overview of recent developments in the construction of macromolecules into hydrogels and microspheres based on the proteins, nucleic acids, polysaccharides and other polymer and their application in tissue repair. We then discuss the latest research trends regarding the advantages and disadvantages of these composites in repair tissue. Further, we examine the applications of microspheres/hydrogels in different tissue repairs, such as skin tissue, cartilage, tumor tissue, synovial, nerve tissue, and cardiac repair. The review closes by highlighting the challenges and prospects of microspheres/hydrogels composites.

Dancing with Nucleobases: Unveiling the Self-Assembly Properties of DNA and RNA Base-Containing Molecules for Gel Formation

Nucleobase-containing molecules are compounds essential in biology due to the fundamental role of nucleic acids and, in particular, G-quadruplex DNA and RNA in life. Moreover, some molecules different from nucleic acids isolated from different vegetal sources or microorganisms show nucleobase moieties in their structure. Nucleoamino acids and peptidyl nucleosides belong to this molecular class. Closely related to the above, nucleopeptides, also known as nucleobase-bearing peptides, are chimeric derivatives of synthetic origin and more rarely isolated from plants. Herein, the self-assembly properties of a vast number of structures, belonging to the nucleic acid and nucleoamino acid/nucleopeptide family, are explored in light of the recent scientific literature. Moreover, several technologically relevant properties, such as the hydrogelation ability of some of the nucleobase-containing derivatives, are reviewed in order to make way for future experimental investigations of newly devised nucleobase-driven hydrogels. Nucleobase-containing molecules, such as mononucleosides, DNA, RNA, quadruplex (G4)-forming oligonucleotides, and nucleopeptides are paramount in gel and hydrogel formation owing to their distinctive molecular attributes and ability to self-assemble in biomolecular nanosystems with the most diverse applications in different fields of biomedicine and nanotechnology. In fact, these molecules and their gels present numerous advantages, underscoring their significance and applicability in both material science and biomedicine. Their versatility, capability for molecular recognition, responsiveness to stimuli, biocompatibility, and biodegradability collectively contribute to their prominence in modern nanotechnology and biomedicine. In this review, we emphasize the critical role of nucleobase-containing molecules of different nature in pioneering novel materials with multifaceted applications, highlighting their potential in therapy, diagnostics, and new nanomaterials fabrication as required for addressing numerous current biomedical and nanotechnological challenges.

Injectable smart stimuli-responsive hydrogels: pioneering advancements in biomedical applications

Hydrogels have established their significance as prominent biomaterials within the realm of biomedical research. However, injectable hydrogels have garnered greater attention compared with their conventional counterparts due to their excellent minimally invasive nature and adaptive behavior post-injection. With the rapid advancement of emerging chemistry and deepened understanding of biological processes, contemporary injectable hydrogels have been endowed with an "intelligent" capacity to respond to various endogenous/exogenous stimuli (such as temperature, pH, light and magnetic field). This innovation has spearheaded revolutionary transformations across fields such as tissue engineering repair, controlled drug delivery, disease-responsive therapies, and beyond. In this review, we comprehensively expound upon the raw materials (including natural and synthetic materials) and injectable principles of these advanced hydrogels, concurrently providing a detailed discussion of the prevalent strategies for conferring stimulus responsiveness. Finally, we elucidate the latest applications of these injectable "smart" stimuli-responsive hydrogels in the biomedical domain, offering insights into their prospects.

Multifunctional rolling circle transcription-based nanomaterials for advanced drug delivery

As the up-and-comer in the development of RNA nanotechnology, RNA nanomaterials based on functionalized rolling circle transcription (RCT) have become promising carriers for drug production and delivery. This is due to RCT technology can self-produce polyvalent tandem nucleic acid prodrugs for intervention in intracellular gene expression and protein production. RNA component strands participating in de novo assembly enable RCT-based nanomaterials to exhibit good mechanical properties, biostability, and biocompatibility as delivery carriers. The biostability makes it to suitable for thermodynamically/kinetically favorable assembly, enzyme resistance and efficient expression in vivo. Controllable RCT system combined with polymers enables customizable and adjustable size, shape, structure, and stoichiometry of RNA building materials, which provide groundwork for the delivery of advanced drugs. Here, we review the assembly strategies and the dynamic regulation of RCT-based nanomaterials, summarize its functional properties referring to the bottom-up design philosophy, and describe its advancements in tumor gene therapy, synergistic chemotherapy, and immunotherapy. Last, we elaborate on the unique and practical value of RCT-based nanomaterials, namely "self-production and self-sale", and their potential challenges in nanotechnology, material science and biomedicine.

Self-assembly of a multimeric genomic hydrogel via multi-primed chain reaction of dual single-stranded circular plasmids for cell-free protein production

Recent technical advances in cell-free protein synthesis (CFPS) offer several advantages over cell-based expression systems, including the application of cellular machinery, such as transcription and translation, in the test tube. Inspired by the advantages of CFPS, we have fabricated a multimeric genomic DNA hydrogel (mGD-gel) via rolling circle chain amplification (RCCA) using dual single-stranded circular plasmids with multiple primers. The mGD-gel exhibited significantly enhanced protein yield. In addition, mGD-gel can be reused at least five times, and the shape of the mGD-gel can be easily manipulated without losing the feasibility of protein expression. The mGD-gel platform based on the self-assembly of multimeric genomic DNA strands (mGD strands) has the potential to be used in CFPS systems for a variety of biotechnological applications.

Small Molecule-Templated DNA Hydrogel with Record Stiffness Integrates and Releases DNA Nanostructures and Gene Silencing Nucleic Acids

Deoxyribonucleic acid (DNA) hydrogels are a unique class of programmable, biocompatible materials able to respond to complex stimuli, making them valuable in drug delivery, analyte detection, cell growth, and shape-memory materials. However, unmodified DNA hydrogels in the literature are very soft, rarely reaching a storage modulus of 10³  Pa, and they lack functionality, limiting their applications. Here, a DNA/small-molecule motif to create stiff hydrogels from unmodified DNA, reaching 10⁵  Pa in storage modulus is used. The motif consists of an interaction between polyadenine and cyanuric acid-which has 3-thymine like faces-into multimicrometer supramolecular fibers. The mechanical properties of these hydrogels are readily tuned, they are self-healing and thixotropic. They integrate a high density of small, nontoxic molecules, and are functionalized simply by varying the molecule sidechain. They respond to three independent stimuli, including a small molecule stimulus. These stimuli are used to integrate and release DNA wireframe and DNA origami nanostructures within the hydrogel. The hydrogel is applied as an injectable delivery vector, releasing an antisense oligonucleotide in cells, and increasing its gene silencing efficacy. This work provides tunable, stimuli-responsive, exceptionally stiff all-DNA hydrogels from simple sequences, extending these materials' capabilities.

Polymeric DNA Hydrogels and Their Applications in Drug Delivery for Cancer Therapy

The biomolecule deoxyribonucleic acid (DNA), which acts as the carrier of genetic information, is also regarded as a block copolymer for the construction of biomaterials. DNA hydrogels, composed of three-dimensional networks of DNA chains, have received considerable attention as a promising biomaterial due to their good biocompatibility and biodegradability. DNA hydrogels with specific functions can be prepared via assembly of various functional sequences containing DNA modules. In recent years, DNA hydrogels have been widely used for drug delivery, particularly in cancer therapy. Benefiting from the sequence programmability and molecular recognition ability of DNA molecules, DNA hydrogels prepared using functional DNA modules can achieve efficient loading of anti-cancer drugs and integration of specific DNA sequences with cancer therapeutic effects, thus achieving targeted drug delivery and controlled drug release, which are conducive to cancer therapy. In this review, we summarized the assembly strategies for the preparation of DNA hydrogels on the basis of branched DNA modules, hybrid chain reaction (HCR)-synthesized DNA networks and rolling circle amplification (RCA)-produced DNA chains, respectively. The application of DNA hydrogels as drug delivery carriers in cancer therapy has been discussed. Finally, the future development directions of DNA hydrogels in cancer therapy are prospected.

Crystallinity-tuned ultrasoft polymeric DNA networks for controlled release of anticancer drugs

Despite the vast interest in utilizing rolling circle amplification (RCA)-based DNA networks for bioapplications, precise control of the mechanical and physicochemical properties is highly challenging. To address this concern, we aimed to develop ultrasoft self-supporting polymerized DNA networks (pDNets) of variable crystallinities to manipulate sequence-mediated drug release efficiency. A controlled ratio of the inorganic magnesium pyrophosphate (MgPPi) crystal to the organic polymeric DNA resulted in the synthesis of pDNets of various nanoporosities. The number of crystal microstructures influencing drug localization and release pattern and the tunable mechanical properties influencing injectability and structural stability under physiological conditions were investigated. The pDNets exhibited ultrasoft properties with Young's moduli of 0.06-0.54 Pa; approximately 9-fold differences in mechanical properties were obtained by varying the degree of crystallinity. With functional DNA sequences, the developed platforms showed pH stimuli-responsive drug release profiles of the dynamic DNA structures and aptamer-specific cell target adhesion efficiency. Analyses of controlled delivery of anticancer therapeutics in vitro and in vivo revealed crystallinity-dependent antitumor efficacy without side effects. This strategy provides an effective one-pot enzymatic polymerization methodology and a favorable microenvironment for a three-dimensional DNA network based on demand-localized drug delivery.

Nucleic acid-based artificial nanocarriers for gene therapy

Nucleic acid nanotechnology is a powerful tool in the fields of biosensing and nanomedicine owing to their high editability and easy synthesis and modification. Artificial nucleic acid nanostructures have become an emerging research hotspot as gene carriers with low cytotoxicity and immunogenicity for therapeutic approaches. In this review, recent progress in the design and functional mechanisms of nucleic acid-based artificial nano-vectors especially for exogenous siRNA and antisense oligonucleotide delivery is summarized. Different types of DNA nanocarriers, including DNA junctions, tetrahedrons, origami, hydrogels and scaffolds, are introduced. The enhanced targeting strategies to improve the delivery efficacy are demonstrated. Furthermore, RNA based gene nanocarrier systems by self-assembly of short strands, rolling circle transcription, chemical crosslinking and using RNA motifs and DNA-RNA hybrids are demonstrated. Finally, the outlook and potential challenges are highlighted. The nucleic acid-based artificial nanocarriers offer a promising and precise tool for gene delivery and therapy.

Design and application of stimuli-responsive DNA hydrogels: A review

Deoxyribonucleic acid (DNA) hydrogels combine the properties of DNAs and hydrogels, and adding functionalized DNAs is key to the wide application of DNA hydrogels. In stimuli-responsive DNA hydrogels, the DNA transcends its application in genetics and bridges the gap between different fields. Specifically, the DNA acts as both an information carrier and a bridge in constructing DNA hydrogels. The programmability and biocompatibility of DNA hydrogel make it change macroscopically in response to a variety of stimuli. In order to meet the needs of different scenarios, DNA hydrogels were also designed into microcapsules, beads, membranes, microneedle patches, and other forms. In this study, the stimuli were classified into single biological and non-biological stimuli and composite stimuli. Stimuli-responsive DNA hydrogels from the past five years were summarized, including but not limited to their design and application, in particular logic gate pathways and signal amplification mechanisms. Stimuli-responsive DNA hydrogels have been applied to fields such as sensing, nanorobots, information carriers, controlled drug release, and disease treatment. Different potential applications and the developmental pro-spects of stimuli-responsive DNA hydrogels were discussed.

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DNA hydrogel, favored by researchers, combines properties of DNA and hydrogels.

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Both DNA and skeleton, having many response characteristics, can respond to stimuli.

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Sensing, nano robots, information carriers, drug delivery, and disease treatment uses.

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Three stimulus response types: single biological, single abiotic and compound.

Injectable DNA Hydrogel-Based Local Drug Delivery and Immunotherapy

Regulated drug delivery is an important direction in the field of medicine and healthcare research. In recent years, injectable hydrogels with good biocompatibility and biodegradability have attracted extensive attention due to their promising application in controlled drug release. Among them, DNA hydrogel has shown great potentials in local drug delivery and immunotherapy. DNA hydrogel is a three-dimensional network formed by cross-linking of hydrophilic DNA strands with extremely good biocompatibility. Benefiting from the special properties of DNA, including editable sequence and specificity of hybridization reactions, the mechanical properties and functions of DNA hydrogels can be precisely designed according to specific applications. In addition, other functional materials, including peptides, proteins and synthetic organic polymers can be easily integrated with DNA hydrogels, thereby enriching the functions of the hydrogels. In this review, we first summarize the types and synthesis methods of DNA hydrogels, and then review the recent research progress of injectable DNA hydrogels in local drug delivery, especially in immunotherapy. Finally, we discuss the challenges facing DNA hydrogels and future development directions.

Multimeric RNAs for efficient RNA-based therapeutics and vaccines

There has been a growing interest in RNA therapeutics globally, and much progress has been made in this area, which has been further accelerated by the clinical applications of RNA-based vaccines against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Following these successful clinical trials, various technologies have been developed to improve the efficacy of RNA-based drugs. Multimerization of RNA therapeutics is one of the most attractive approaches to ensure high stability, high efficacy, and prolonged action of RNA-based drugs. In this review, we offer an overview of the representative approaches for generating repetitive functional RNAs by chemical conjugation, structural self-assembly, enzymatic elongation, and self-amplification. The therapeutic and vaccine applications of engineered multimeric RNAs in various diseases have also been summarized. By outlining the current status of multimeric RNAs, the potential of multimeric RNA as a promising treatment strategy is highlighted.

Application of Nucleic Acid Frameworks in the Construction of Nanostructures and Cascade Biocatalysts: Recent Progress and Perspective

Nucleic acids underlie the storage and retrieval of genetic information literally in all living organisms, and also provide us excellent materials for making artificial nanostructures and scaffolds for constructing multi-enzyme systems with outstanding performance in catalyzing various cascade reactions, due to their highly diverse and yet controllable structures, which are well determined by their sequences. The introduction of unnatural moieties into nucleic acids dramatically increased the diversity of sequences, structures, and properties of the nucleic acids, which undoubtedly expanded the toolbox for making nanomaterials and scaffolds of multi-enzyme systems. In this article, we first introduce the molecular structures and properties of nucleic acids and their unnatural derivatives. Then we summarized representative artificial nanomaterials made of nucleic acids, as well as their properties, functions, and application. We next review recent progress on constructing multi-enzyme systems with nucleic acid structures as scaffolds for cascade biocatalyst. Finally, we discuss the future direction of applying nucleic acid frameworks in the construction of nanomaterials and multi-enzyme molecular machines, with the potential contribution that unnatural nucleic acids may make to this field highlighted.

Construction of a two-dimensional DNA-RNA hybridized membrane for collecting tumor-derived exosomes

Macroscopic nucleic acid-based structures have attracted much attention in biomedical fields. Here, we introduce a novel DNA-RNA hybridized membrane structure via enzymatic dual polymerization. The membrane exhibited enhanced rigidity and functionality. Encoded with an aptamer, the membrane showed great potential as a collecting platform of tumor-derived exosomes without additional labeling.

Aptamer-Modified Hydrogels

Hydrogels have attracted much attention especially due to their biocompatibility and their potential for stimulus responsiveness. By combining hydrogels with aptamers, biological recognition and responsiveness can be added to hydrogels, thereby opening path to advanced applications in biosensing and biomedicine. Within this chapter aptamers will be introduced and their contributions to biological responsiveness of hydrogels will be described. Especially the aptamer-based mechanisms that result in biological responsiveness will be explained and examples for the application of these mechanisms will be given ranging from rather simple sensing approaches to advanced materials for tissue engineering and drug delivery. Since aptamers are not only highly specific bioreceptors, but represent switchable structures that can be easily manipulated using well-known DNA techniques, the combination of aptamers and hydrogels facilitates the rational design of well-programmable and target-responsive smart hydrogels.