Cultivation of Exoelectrogenic Bacteria in Conductive DNA Nanocomposite Hydrogels Yields a Programmable Biohybrid Materials System

Antidiabetic Close Loop Based on Wearable DNA-Hydrogel Glucometer and Implantable Optogenetic Cells

Diabetes mellitus and its associated secondary complications have become a pressing global healthcare issue. The current integrated theranostic plan involves a glucometer-tandem pump. However, external condition-responsive insulin delivery systems utilizing rigid glucose sensors pose challenges in on-demand, long-term insulin administration. To overcome these challenges, we present a novel model of antidiabetic management based on printable metallo-nucleotide hydrogels and optogenetic engineering. The conductive hydrogels were self-assembled by bioorthogonal chemistry using oligonucleotides, carbon nanotubes, and glucose oxidase, enabling continuous glucose monitoring in a broad range (0.5-40 mM). The optogenetically engineered cells were enabled glucose regulation in type I diabetic mice via a far-red light-induced transgenic expression of insulin with a month-long avidity. Combining with a microchip-integrated microneedle patch, a prototyped close-loop system was constructed. The glucose levels detected by the sensor were received and converted by a wireless controller to modulate far-infrared light, thereby achieving on-demand insulin expression for several weeks. This study sheds new light on developing next-generation diagnostic and therapy systems for personalized and digitalized precision medicine.

Micromechanical Indentation Platform for Rapid Analysis of Viscoelastic Biomolecular Hydrogels

The advent of biomedical applications of soft bioinspired materials has entailed an increasing demand for streamlined and expedient characterization methods meant for both research and quality control objectives. Here, a novel measurement system for the characterization of biological hydrogels with volumes as low as 75 µL was developed. The system is based on an indentation platform equipped with micrometer drive actuators that allow the determination of both the fracture points and Young's moduli of relatively stiff polymers, including agarose, as well as the measurements of viscosity for exceptionally soft and viscous hydrogels, such as DNA hydrogels. The sensitivity of the method allows differentiation between DNA hydrogels produced by rolling circle amplification based on different template sequences and synthesis protocols. In addition, the polymerization kinetics of the hydrogels can be determined by time-resolved measurements, and the apparent viscosities of even more complex DNA-based nanocomposites can be measured. The platform presented here thus offers the possibility to characterize a broad variety of soft biomaterials in a targeted, fast, and cost-effective manner, holding promises for applications in fundamental materials science and ensuring reproducibility in the handling of complex materials.

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.

Recent progress in the characterization and application of exo-electrogenic microorganisms

Exo-electrogenic microorganisms are characterized by their special metabolic capability of transferring metabolic electrons out of their cell, into insoluble external electron acceptors such as iron or manganese oxides and electrodes, or vice versa take up electron from electrodes. Their conventional application is primarily limited to microbial fuel cells for electrical power generation and microbial electrolysis cells for the production of value-added products such as biohydrogen, biomethane and hydrogen peroxide. The utility of exo-electrogenic organisms has expanded into many other applications in recent times. Such examples include microbial desalination cells, microbial electro-synthesis cells producing value-added chemicals such as bio-butanol and their applications in other carbon sequestration technologies. Additionally, electrochemically-active organisms are now beginning to be employed in biosensor applications for environmental monitoring. Additionally, the utility of biocathodes in bio-electrochemical systems is also a novel application in catalyzing the cathodic oxygen reduction reaction to enhance their electrochemical performance. Advances have also been made in the expansion and use of other organisms such as the usage of photosynthetic microorganisms for the fabrication of self-sustained bio-electrochemical systems. This review attempts to provide a comprehensive picture of the state-of the art of exo-electrogenic organisms and their novel utility in bioelectrochemical systems.

Accurate quantification of DNA content in DNA hydrogels prepared by rolling circle amplification

Accurate quantification of polymerized DNA in rolling circle amplification (RCA)-based hydrogels is challenging due to the high viscosity of these materials, however, it can be achieved with a photometric nucleotide depletion assay or qPCR. We show that the DNA content strongly depends on the template sequence and correlates with the mechanical properties of the hydrogels.

Recent Implementations of Hydrogel-Based Microbial Electrochemical Technologies (METs) in Sensing Applications

Hydrogel materials have been used extensively in microbial electrochemical technology (MET) and sensor development due to their high biocompatibility and low toxicity. With an increasing demand for sensors across different sectors, it is crucial to understand the current state within the sectors of hydrogel METs and sensors. Surprisingly, a systematic review examining the application of hydrogel-based METs to sensor technologies has not yet been conducted. This review aimed to identify the current research progress surrounding the incorporation of hydrogels within METs and sensors development, with a specific focus on microbial fuel cells (MFCs) and microbial electrolysis cells (MECs). The manufacturing process/cost, operational performance, analysis accuracy and stability of typical hydrogel materials in METs and sensors were summarised and analysed. The current challenges facing the technology as well as potential direction for future research were also discussed. This review will substantially promote the understanding of hydrogel materials used in METs and benefit the development of electrochemical biosensors using hydrogel-based METs.

Functional Nanomaterial-Modified Anodes in Microbial Fuel Cells: Advances and Perspectives

Microbial fuel cell (MFC) is a promising approach that could utilize microorganisms to oxidize biodegradable pollutants in wastewater and generate electrical power simultaneously. Introducing advanced anode nanomaterials is generally considered as an effective way to enhance MFC performance by increasing bacterial adhesion and facilitating extracellular electron transfer (EET). This review focuses on the key advances of recent anode modification materials, as well as the current understanding of the microbial EET process occurring at the bacteria-electrode interface. Based on the difference in combination mode of the exoelectrogens and nanomaterials, anode surface modification, hybrid biofilm construction and single-bacterial surface modification strategies are elucidated exhaustively. The inherent mechanisms may help to break through the performance output bottleneck of MFCs by rational design of EET-related nanomaterials, and lead to the widespread application of microbial electrochemical systems.

Sprayable biofilm – Agarose hydrogels as 3D matrix for enhanced productivity in bioelectrochemical systems

Bio-based energy production utilizing renewable resources can be realized by exoelectrogenic organisms and their application in bioelectrochemical systems (BES). These organisms catalyze the direct conversion of chemical into electrical energy and are already widely used in bioelectronics and biosensing. However, the biofilm-electrode interaction is a factor that limits sufficient space-time-yields for industrial applications. In this study, a hydrogel matrix consisting of agarose fibers was utilized as a scaffold for S. oneidensis cells to improve anodic processes in BES. This synthetic, scalable biofilm reached a higher current density in BES in comparison to naturally formed biofilms. Complemented with carbon nanofibers and riboflavin, the application of this functionalized hydrogel containing S. oneidensis cells led to an overall 9.1-fold increase in current density to 1324 mA m⁻² in comparison to 145 mA m⁻² for the planktonic control. In addition, the synthetic biofilm can be applied by spraying onto surfaces using a novel spray applicator. The latter allows to apply the biofilm effortless on large surfaces which will facilitate scalability and thus industrial application.

Engineered living materials (ELMs) design: From function allocation to dynamic behavior modulation

Natural materials possess many distinctive "living" attributes, such as self-growth, self-healing, environmental responsiveness, and evolvability, that are beyond the reach of many existing synthetic materials. The emerging field of engineered living materials (ELMs) takes inspiration from nature and harnesses engineered living systems to produce dynamic and responsive materials with genetically programmable functionalities. Here, we identify and review two main directions for the rational design of ELMs: first, engineering of living materials with enhanced performances by incorporating functional material modules, including engineered biological building blocks (proteins, polysaccharides, and nucleic acids) or well-defined artificial materials; second, engineering of smart ELMs that can sense and respond to their surroundings by programming dynamic cellular behaviors regulated via cell-cell or cell-environment interactions. We next discuss the strengths and challenges of current ELMs and conclude by providing a perspective of future directions in this promising area.

DNA-Based Daisy Chain Rotaxane Nanocomposite Hydrogels as Dual-Programmable Dynamic Scaffolds for Stem Cell Adhesion

Interlocked DNA nanostructures perform programmable movements in nanoscales such as sliding, contraction, and expansion. However, utilizing nanoscaled interlocked movements to regulate the functions of larger length scaled matrix and developing their applications has not yet been reported. Herein we describe the assembly of DNA-based daisy chain rotaxane nanostructure (DNA-DCR) composed of two hollow DNA nanostructures as macrocycles, two interlocked axles and two triangular prism-shaped DNA structures as stoppers, in which three mechanical states─fixed extended state (FES), sliding state (SS), and fixed contracted state (FCS)─are characterized by using toehold-mediated strand displacement reaction (SDR). The DNA-DCRs are further used as nanocomposites and introduced into hydrogel matrix to produce interlocked hydrogels, which shows modulable stiffness by elongating the interlocked axles to regulate the hydrogel swelling with hybridization chain reaction (HCR) treatment. Then the DCR-hydrogels are employed as dynamic biointerfaces for human mesenchymal stem cells (hMSCs) adhesion studies. First, hMSCs showed lower cell density on bare DCR-hydrogel treated with HCR-initiated swelling for stiffness decreasing. Second, the cell adhesion ligand (RGD) modified DNA-DCRs are constructed for hydrogel functionalization. DCR^(RGD) hydrogel endows the mobility of RGDs by switching the mechanical states of DNA-DCR. HMSCs showed increased cell density on DCR^SS(RGD) hydrogel than on DCR^FCS(RGD) hydrogel. Therefore, our DNA-DCR nanocomposite hydrogel exhibit dual-programmable performances including swelling adjustment and offering sliding for incorporated ligands, which can be both utilized as dynamic scaffolds for regulating the stem cell adhesion. The dual-programmable cross-scale regulation from interlocked DNA nanostructures to hydrogel matrix was achieved, demonstrating a new pathway of DNA-based materials.

Acid-Resistant and Physiological pH-Responsive DNA Hydrogel Composed of A-Motif and i-Motif toward Oral Insulin Delivery

An acid-resistant DNA hydrogel that is stable in an extremely acidic environment with pH as low as 1.2 has not been reported before, largely due to the instability of DNA-hybridized structures. To achieve this, adenine (A)-rich and cytosine (C)-rich oligonucleotides are rationally designed and integrated to form copolymers with acrylamide monomers via free-radical polymerization. In an acidic environment (pH 1.2-6.0), the generated copolymers form a hydrogel state, which is cross-linked by parallel A-motif duplex configurations (pH 1.2-3.0) and quadruplex i-motif structures (pH 4.0-6.0) due to the protonation of A and C bases, respectively. Specifically, the protonated A-rich sequences under pH 1.2-3.0 form a stable parallel A-motif duplex cross-linking unit through reverse Hoogsteen interaction and electrostatic attraction. Hemi-protonated C bases under mildly acidic pH (4.0-6.0) form quadruplex i-motif cross-linking configuration via Hoogsteen interaction. Under physiological pH, both A and C bases deprotonated, resulting in the separation of A-motif and i-motif to A-rich and C-rich single strands, respectively, and thereby the dissociation of the DNA hydrogel into the solution state. The acid-resistant and physiological pH-responsive DNA hydrogel was further developed for oral drug delivery to the hostile acidic environment in the stomach (pH 1.2), duodenum (pH 5.0), and small intestine (pH 7.2), where the drug would be released and absorbed. As a proof of concept, insulin was encapsulated in the DNA hydrogel and orally administered to diabetic rats. In vitro and in vivo studies demonstrated the potential usage of the DNA hydrogel for oral drug delivery.

Conjugated Polyelectrolyte/Bacteria Living Composites in Carbon Paper for Biocurrent Generation

Successful practical implementation of bioelectrochemical systems requires developing affordable electrode structures that promote efficient electrical communication with microbes. Recent efforts have centered on immobilizing bacteria with organic semiconducting polymers on electrodes via electrochemical methods. This approach creates a fixed biocomposite that takes advantage of the increased electrode's electroactive surface area (EASA). Here, we demonstrate that a biocomposite comprising the water-soluble conjugated polyelectrolyte CPE-K and electrogenic Shewanella oneidensis MR-1 can self-assemble with carbon paper electrodes, thereby increasing its biocurrent extraction by ∼ 6-fold over control biofilms. A ∼ 1.5-fold increment in biocurrent extraction was obtained for the biocomposite on carbon paper relative to the biocurrent extracted from gold-coated counterparts. Electrochemical characterization revealed that the biocomposite stabilized with the carbon paper more quickly than atop flat gold electrodes. Cross-sectional images show that the biocomposite infiltrates inhomogeneously into the porous carbon structure. Despite an incomplete penetration, the biocomposite can take advantage of the large EASA of the electrode via long-range electron transport. These results show that previous success on gold electrode platforms can be improved when using more commercially viable and easily manipulated electrode materials. This article is protected by copyright. All rights reserved.

Formulation of DNA Nanocomposites: Towards Functional Materials for Protein Expression

DNA hydrogels are an emerging class of materials that hold great promise for numerous biotechnological applications, ranging from tissue engineering to targeted drug delivery and cell-free protein synthesis (CFPS). In addition to the molecular programmability of DNA that can be used to instruct biological systems, the formulation of DNA materials, e.g., as bulk hydrogels or microgels, is also relevant for specific applications. To advance the state of knowledge in this research area, the present work explores the scope of a recently developed class of complex DNA nanocomposites, synthesized by RCA polymerization of DNA-functionalized silica nanoparticles (SiNPs) and carbon nanotubes (CNTs). SiNP/CNT-DNA composites were produced as bulk materials and microgels which contained a plasmid with transcribable genetic information for a fluorescent marker protein. Using confocal microscopy and flow cytometry, we found that the materials are very efficiently taken up by various eukaryotic cell lines, which were able to continue dividing while the ingested material was evenly distributed to the daughter cells. However, no expression of the encoded protein occurred within the cells. While the microgels did not induce production of the marker protein even in a CFPS procedure with eukaryotic cell lysate, the bulk composites proved to be efficient templates for CFPS. This work contributes to the understanding of the molecular interactions between DNA composites and the functional cellular machinery. Implications for the use of such materials for CFPS procedures are discussed.

Artificial electrochemically active biofilm for improved sensing performance and quickly devising of water quality early warning biosensors

A major challenge for devising an electrochemically active biofilm (EAB)-based biosensor for real-time water quality early-warning is the formation of EAB that requires several days to weeks. Besides the onerous and time-consuming preparation process, the naturally formed EABs are intensively concerned as they can hardly deliver repeatable electrical signals even at identical experimental conditions. To address these concerns, this study employed sodium alginate as immobilization agent to encapsulate Shewanella oneidensis MR-1 and prepared EAB for devising a biosensor in a short period of less than 1 h. The artificial EAB were found capable of delivering highly consistent electrical signals with each other when fed with the same samples. Morphology and bioelectrochemical properties of the artificial EAB were investigated to provide interpretations for these findings. Different concentrations of bacteria and alginate in forming the EAB were investigated for their effects on the biosensor's sensitivity. Results suggested that lower concentration of bacteria would be beneficial until it increased to 0.06 (OD₆₆₀). Concentration of sodium alginate affected the sensitivity as well and 1% was found an optimum amount to serve in the formation of EAB. A long-term operation of the biosensor with artificial EAB for 110 h was performed. Clear warning signals for incoming toxicants were observed over random signal fluctuations. All results suggested that the artificial EAB electrode would support a rapid devised and highly sensitivity biosensor.

Harnessing the physicochemical properties of DNA as a multifunctional biomaterial for biomedical and other applications

The biological purpose of DNA is to store, replicate, and convey genetic information in cells. Progress in molecular genetics have led to its widespread applications in gene editing, gene therapy, and forensic science. However, in addition to its role as a genetic material, DNA has also emerged as a nongenetic, generic material for diverse biomedical applications. DNA is essentially a natural biopolymer that can be precisely programed by simple chemical modifications to construct materials with desired mechanical, biological, and structural properties. This review critically deciphers the chemical tools and strategies that are currently being employed to harness the nongenetic functions of DNA. Here, the primary product of interest has been crosslinked, hydrated polymers, or hydrogels. State-of-the-art applications of macroscopic, DNA-based hydrogels in the fields of environment, electrochemistry, biologics delivery, and regenerative therapy have been extensively reviewed. Additionally, the review encompasses the status of DNA as a clinically and commercially viable material and provides insight into future possibilities.

100th Anniversary of Macromolecular Science Viewpoint: Soft Materials for Microbial Bioelectronics

Bioelectronics brings together the fields of biology and microelectronics to create multifunctional devices with the potential to address longstanding technological challenges and change our way of life. Microbial electrochemical devices are a growing subset of bioelectronic devices that incorporate naturally occurring or synthetically engineered microbes into electronic devices and have broad applications including energy harvesting, chemical production, water remediation, and environmental and health monitoring. The goal of this Viewpoint is to highlight recent advances and ongoing challenges in the rapidly developing field of microbial bioelectronic devices, with an emphasis on materials challenges. We provide an overview of microbial bioelectronic devices, discuss the biotic-abiotic interface in these devices, and then present recent advances and ongoing challenges in materials related to electron transfer across the abiotic-biotic interface, microbial adhesion, redox signaling, electronic amplification, and device miniaturization. We conclude with a summary and perspective of the field of microbial bioelectronics.

Postsynthetic Functionalization of DNA-Nanocomposites with Proteins Yields Bioinstructive Matrices for Cell Culture Applications

We report on the directed postsynthetic functionalization of soft DNA nanocomposite materials with proteins. Using the example of the functionalization of silica nanoparticle-modified DNA polymer materials with agonists or antagonists of the epidermal growth factor receptor EGFR cell membrane receptor, we demonstrate that hierarchically structured interfaces to living cells can be established. Owing to the modular design principle, even complex DNA nanostructures can be integrated into the materials, thereby enabling the high-precision arrangement of ligands on the lower nanometer length scale. We believe that such complex biohybrid material systems can be used for new applications in biotechnology.