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

Insights on the role of cryoprotectants in enhancing the properties of bioinks required for cryobioprinting of biological constructs

Preservation and long-term storage of readily available cell-laden tissue-engineered products are major challenges in expanding their applications in healthcare. In recent years, there has been increasing interest in the development of off-the-shelf tissue-engineered products using the cryobioprinting approach. Here, bioinks are incorporated with cryoprotective agents (CPAs) to allow the fabrication of cryopreservable tissue constructs. Although this method has shown potential in the fabrication of cryopreservable tissue-engineered products, the impact of the CPAs on the viscoelastic behavior and printability of the bioinks at cryo conditions remains unexplored. In this study, we have evaluated the influence of CPAs such as glycerol and dimethyl sulfoxide (DMSO) on the rheological properties of pre-crosslinked alginate bioinks for cryoprinting applications. DMSO-incorporated bioinks showed a reduction in viscosity and yield stress, while the addition of glycerol improved both the properties due to interactions with the calcium chloride used for pre-crosslinking. Further, tube inversion and printability experiments were performed to identify suitable concentrations and cryobioprinting conditions for bioinks containing CPAs & pre-crosslinked with CaCl2. Finally, based on the printability analysis & cell recovery results, 10% glycerol was used for cryobioprinting and preservation of cell-laden constructs at -80 °C and the viability of cells within the printed structures were evaluated after recovery. Cell viability results indicate that the addition of 10% glycerol to the pre-crosslinked bioink significantly improved cell viability compared to bioinks without CPAs, confirming the suitability of the developed bioink combination to fabricate tissue constructs for on-demand applications.

3D-printed constructs deliver bioactive cargos to expedite cartilage regeneration

Cartilage is solid connective tissue that recovers slowly from injury, and pain and dysfunction from cartilage damage affect many people. The treatment of cartilage injury is clinically challenging and there is no optimal solution, which is a hot research topic at present. With the rapid development of 3D printing technology in recent years, 3D bioprinting can better mimic the complex microstructure of cartilage tissue and thus enabling the anatomy and functional regeneration of damaged cartilage. This article reviews the methods of 3D printing used to mimic cartilage structures, the selection of cells and biological factors, and the development of bioinks and advances in scaffold structures, with an emphasis on how 3D printing structure provides bioactive cargos in each stage to enhance the effect. Finally, clinical applications and future development of simulated cartilage printing are introduced, which are expected to provide new insights into this field and guide other researchers who are engaged in cartilage repair.

From Bioreactor to Bulk Rheology: Achieving Scalable Production of Highly Concentrated Circular DNA

DNA serves as a model system in polymer physics due to its ability to be obtained as a uniform polymer with controllable topology and nonequilibrium behavior. Currently, a major obstacle in the widespread adoption of DNA is obtaining it on a scale and cost basis that accommodates bulk rheology and high-throughput screening. To address this, recent advancements in bioreactor-based plasmid DNA production is coupled with anion exchange chromatography producing a unified approach to generating gram-scale quantities of monodisperse DNA. With this method, 1.1 grams of DNA is obtained per batch to generate solutions with concentrations up to 116 mg mL-1. This solution of uniform supercoiled and relaxed circular plasmid DNA, is roughly 69 times greater than the overlap concentration. The utility of this method is demonstrated by performing bulk rheology measurements at sample volumes up to 1 mL on DNA of different lengths, topologies, and concentrations. The measured elastic moduli are orders of magnitude larger than those previously reported for DNA and allowed for the construction of a time-concentration superposition curve that spans 12 decades of frequency. Ultimately, these results can provide important insights into the dynamics of ring polymers and the nature of highly condensed DNA dynamics.

Reversible and Fully Controllable Generation of Organo-Soluble DNA (osDNA)

The present work describes a complete and reversible transformation of DNA's properties allowing solubilization in organic solvents and subsequent chemical modifications that are otherwise not possible in an aqueous medium. Organo-soluble DNA (osDNA) moieties are generated by covalently linking a dsDNA fragment to a polyether moiety with a built-in mechanism, rendering the process perfectly reversible and fully controllable. The precise removal of the polyether moiety frees up the initial DNA fragment, unaltered, both in sequence and nature. The solubility of osDNA was confirmed in six organic solvents of decreasing polarity and six types of osDNAs. As a proof of concept, in the context of DNA-encoded library (DEL) technology, an amidation reaction was successfully performed on osDNA in 100% DMSO. The development of osDNA opens up entirely new avenues for any DNA applications that could benefit from working in nonaqueous solutions, including chemical transformations.

Carboxymethyl cellulose-agarose hydrogel in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nanofibers: A novel tissue engineered skin graft

Healing chronic and critical-sized full-thickness wounds is a major challenge in the healthcare sector. Scaffolds prepared using electrospinning and hydrogels serve as effective treatment options for wound healing by mimicking the native skin microenvironment. Combining synthetic nanofibers with tunable hydrogel properties can effectively overcome limitations in skin scaffolds made only with nanofibers or hydrogels. In this study, a biocompatible hybrid scaffold was developed for wound healing applications using poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanofibers embedded with hydrogel made of 2 % carboxymethyl cellulose (CMC) blended with 1 % agarose. Hybrid scaffolds, characterized for surface morphology, swellability, porosity, and degradation, were found to be suitable for wound healing. Furthermore, the incorporation of CMC-agarose hydrogel into nanofibers significantly enhanced their mechanical strength compared to PHBV nanofibers alone (p < 0.05). Extract cytotoxicity and direct cytotoxicity tests showed that the hybrid scaffolds developed in this study are cytocompatible (>75 % viability). Furthermore, human adult dermal fibroblasts (HDFa) and human adult immortalized keratinocytes (HaCaT) adhesion, viability, and proliferation studies revealed that the hybrid scaffolds exhibited a significant increase in cell proliferation over time, similar to PHBV nanofibers. Finally, the developed hybrid scaffolds were evaluated in rat full-thickness wounds, demonstrating their ability to promote full-thickness wound healing with reepithelialization and epidermis closure.

Tuning thermoresponsive properties of carboxymethyl cellulose (CMC)-agarose composite bioinks to fabricate complex 3D constructs for regenerative medicine

3D bioprinting has emerged as a viable tool to fabricate 3D tissue constructs with high precision using various bioinks which offer instantaneous gelation, shape fidelity, and cytocompatibility. Among various bioinks, cellulose is the most abundantly available natural polymer & widely used as bioink for 3D bioprinting applications. To mitigate the demanding crosslinking needs of cellulose, it is frequently chemically modified or blended with other polymers to develop stable hydrogels. In this study, we have developed a thermoresponsive, composite bioink using carboxymethyl cellulose (CMC) and agarose in different ratios (9:1, 8:2, 7:3, 6:4, and 5:5). Among the tested combinations, the 5:5 ratio showed better gel formation at 37 °C and were further characterized for physicochemical properties. Cytocompatibility was assessed by in vitro extract cytotoxicity assay (ISO 10993-5) using skin fibroblasts cells. CMC-agarose (5:5) bioink was successfully used to fabricate complex 3D structures through extrusion bioprinting and maintained over 80 % cell viability over seven days. Finally, in vivo studies using rat full-thickness wounds showed the potential of CMC-agarose bulk and bioprinted gels in promoting skin regeneration. These results indicate the cytocompatibility and suitability of CMC-agarose bioinks for tissue engineering and 3D bioprinting applications.

Embedded 3D bioprinting - An emerging strategy to fabricate biomimetic & large vascularized tissue constructs

Three-dimensional bioprinting is an advanced tissue fabrication technique that allows printing complex structures with precise positioning of multiple cell types layer-by-layer. Compared to other bioprinting methods, extrusion bioprinting has several advantages to print large-sized tissue constructs and complex organ models due to large build volume. Extrusion bioprinting using sacrificial, support and embedded strategies have been successfully employed to facilitate printing of complex and hollow structures. Embedded bioprinting is a gel-in-gel approach developed to overcome the gravitational and overhanging limits of bioprinting to print large-sized constructs with a micron-scale resolution. In embedded bioprinting, deposition of bioinks into the microgel or granular support bath will be facilitated by the sol-gel transition of the support bath through needle movement inside the granular medium. This review outlines various embedded bioprinting strategies and the polymers used in the embedded systems with advantages, limitations, and efficacy in the fabrication of complex vascularized tissues or organ models with micron-scale resolution. Further, the essential requirements of support bath systems like viscoelasticity, stability, transparency and easy extraction to print human scale organs are discussed. Additionally, the organs or complex geometries like vascular constructs, heart, bone, octopus and jellyfish models printed using support bath assisted printing methods with their anatomical features are elaborated. Finally, the challenges in clinical translation and the future scope of these embedded bioprinting models to replace the native organs are envisaged.

Ultrasound-triggered in situ gelation with ROS-controlled drug release for cartilage repair

Cartilage defects are usually caused by acute trauma and chronic degeneration. However, it is still a great challenge to improve the repair of articular cartilage defects due to the limited self-regeneration capacity of such defects. Herein, a novel ROS-responsive in situ nanocomposite hydrogel loaded with kartogenin (KGN) and bone marrow-derived stem cells (BMSCs) was designed and constructed via the enzymatic reaction of fibrinogen and thrombin. Meanwhile, a ROS-responsive thioketal (TK)-based liposome was synthesized to load the chondrogenesis-inducing factor KGN, the bioenzyme thrombin and an ultrasound-sensitive agent PpIX. Under ultrasound stimulation, the TK-based liposome was destroyed, followed by in situ gelation of fibrinogen and thrombin. Moreover, sustained release of KGN was realized by regulating the ultrasound conditions. Importantly, ROS generation and KGN release within the microenvironment of the in situ fibrin hydrogel significantly promoted chondrogenic differentiation of BMSCs via the Smad5/mTOR signalling pathway and effectively improved cartilage regeneration in a rat articular cartilage defect model. Overall, the novel in situ nanocomposite hydrogel with ROS-controlled drug release has great potential for efficient cartilage repair.

Additive manufacturing of peripheral nerve conduits - Fabrication methods, design considerations and clinical challenges

Tissue-engineered nerve guidance conduits (NGCs) are a viable clinical alternative to autografts and allografts and have been widely used to treat peripheral nerve injuries (PNIs). Although these NGCs are successful to some extent, they cannot aid in native regeneration by improving native-equivalent neural innervation or regrowth. Further, NGCs exhibit longer recovery period and high cost limiting their clinical applications. Additive manufacturing (AM) could be an alternative to the existing drawbacks of the conventional NGCs fabrication methods. The emergence of the AM technique has offered ease for developing personalized three-dimensional (3D) neural constructs with intricate features and higher accuracy on a larger scale, replicating the native feature of nerve tissue. This review introduces the structural organization of peripheral nerves, the classification of PNI, and limitations in clinical and conventional nerve scaffold fabrication strategies. The principles and advantages of AM-based techniques, including the combinatorial approaches utilized for manufacturing 3D nerve conduits, are briefly summarized. This review also outlines the crucial parameters, such as the choice of printable biomaterials, 3D microstructural design/model, conductivity, permeability, degradation, mechanical property, and sterilization required to fabricate large-scale additive-manufactured NGCs successfully. Finally, the challenges and future directions toward fabricating the 3D-printed/bioprinted NGCs for clinical translation are also discussed.

Carboxymethyl cellulose-agarose-gelatin: A thermoresponsive triad bioink composition to fabricate volumetric soft tissue constructs

Polysaccharide based hydrogels have been predominantly utilized as ink materials for 3D bioprinting due to biocompatibility and cell responsive features. However, most hydrogels require extensive crosslinking due to poor mechanical properties leading to limited printability. To improve printability without using cytotoxic crosslinkers, thermoresponsive bioinks could be developed. Agarose is a thermoresponsive polysaccharide with upper critical solution temperature (UCST) for sol-gel transition at 35-37 °C. Therefore, we hypothesized that a triad of carboxymethyl cellulose(C)-agarose(A)-gelatin(G) could be a suitable thermoresponsive ink for printing since they undergo instantaneous gelation without any addition of crosslinkers after bioprinting. The blend of agarose-carboxymethyl cellulose was mixed with 1% w/v, 3% w/v and 5% w/v gelatin to optimize the triad ratio for hydrogel formation. It was observed that a blend (C2-A0.5-G1 and C2-A1-G1) containing 2% w/v carboxymethyl cellulose, 0.5% or 1% w/v agarose and 1% w/v gelatin formed better hydrogels with higher stability for up to 21 days in DPBS at 37 °C. Further, C2-A0.5-G1 and C2-A1-G1hydrogels showed higher storage modulus 762 ± 182 Pa & 2452 ± 430 Pa, higher porosity of 96.98 ± 2% & 98.2 ± 0.8% and swellability of 1518 ± 68% & 1587 ± 25% respectively. To evaluate the in vitro potential of these bioink formulations, indirect and direct cytotoxicity were determined using NCTC clone 929 (mouse fibroblast cells) and HADF (primary human adult dermal fibroblast) cells as per the ISO 10993-5 standards. Importantly, the printability of these bioinks was confirmed using extrusion bioprinting by successfully printing different complex 3D patterns.

Efficient dual crosslinking of protein-in-polysaccharide bioink for biofabrication of cardiac tissue constructs

Myocardial infarction (MI) is a lethal cardiac disease that causes most of the mortality across the world. MI is a consequence of plaque in the arterial walls of heart, which eventually result in occlusion and ischemia to the myocardial tissues due to inadequate nutrient and oxygen supply. As an efficient alternative to the existing treatment strategies for MI, 3D bioprinting has evolved as an advanced tissue fabrication technique where the cell-laden bioinks are printed layer-by-layer to create functional cardiac patches. In this study, a dual crosslinking strategy has been utilized towards 3D bioprinting of myocardial constructs by using a combination of alginate and fibrinogen. Herein, pre-crosslinking of the physically blended alginate-fibrinogen bioinks with CaCl₂ enhanced the shape fidelity and printability of the printed structures. Physicochemical properties of the bioinks such as rheology, fibrin distribution, swelling ratio and degradation behaviour, were determined post-printing for only ionically crosslinked & dual crosslinked constructs and found to be ideal for bioprinting of cardiac constructs. Human ventricular cardiomyocytes (AC 16) exhibited a significant increase in cell proliferation on day 7 and 14 in AF-DMEM-20 mM CaCl₂ bioink when compared to A-DMEM-20 mM CaCl₂ (p < 0.05). Furthermore, myocardial patches containing neonatal ventricular rat myocytes (NVRM) showed >80 % viability and also expressed sarcomeric alpha actinin & connexin 43. These results indicate that the dual crosslinking strategy was cytocompatible and also possess the potential to be used for biofabrication of thick myocardial constructs for regenerative medicine applications.

Hyaluronic Acid as Bioink and Hydrogel Scaffolds for Tissue Engineering Applications

Bioprinting is an additive manufacturing technique that focuses on developing living tissue constructs using bioinks. Bioink is crucial in determining the stability of printed patterns, which remains a major challenge in bioprinting. Thus, the choices of bioink composition, modifications, and cross-linking methods are being continuously researched to augment the clinical translation of bioprinted constructs. Hyaluronic acid (HA) is a naturally occurring polysaccharide with the repeating unit of N-acetyl-glucosamine and d-glucuronic acid disaccharides. It is present in the extracellular matrix (ECM) of tissues (skin, cartilage, nerve, muscle, etc.) with a wide range of molecular weights. Due to the nature of its chemical structure, HA could be easily subjected to chemical modifications and cross-linking that would enable better printability and stability. These interesting properties have made HA an ideal choice of bioinks for developing tissue constructs for regenerative medicine applications. In this Review, the physicochemical properties, reaction chemistry involved in various cross-linking strategies, and biomedical applications of HA have been elaborately discussed. Further, the features of HA bioinks, emerging strategies in HA bioink preparations, and their applications in 3D bioprinting have been highlighted. Finally, the current challenges and future perspectives in the clinical translation of HA-based bioinks are outlined.

Advances in DNA Supramolecular Hydrogels for Tissue Engineering

Deoxyribonucleic acid (DNA) is a biological macromolecule that plays a genetic role in cells. DNA molecules with specific recognition, self-assembly capabilities, and sequence programmability have become an excellent construction material for micro- and nanostructures. Based on DNA self-assembly technology, a series of molecular devices and materials are constructed. Among them, DNA hydrogels with the advantages of good biocompatibility, biodegradability, and containing designable stimuli-responsive units have attracted much attention. This review introduces the formation strategy of DNA supramolecular hydrogels, and focuses on its applications in tissue engineering, including cell encapsulation, cell culture, cell capture and release, wound dressings, and tissue growth. The unique properties and application prospects of DNA supramolecular hydrogels in tissue engineering are also discussed.

DNA-Based Molecular Machines

Artificial molecular machines have found widespread applications ranging from fundamental studies to biomedicine. More recent advances in exploiting unique physical and chemical properties of DNA have led to the development of DNA-based artificial molecular machines. The unprecedented programmability of DNA provides a powerful means to design complex and sophisticated DNA-based molecular machines that can exert mechanical force or motion to realize complex tasks in a controllable, modular fashion. This Perspective highlights the potential and strategies to construct artificial molecular machines using double-stranded DNA, functional nucleic acids, and DNA frameworks, which enable improved control over reaction pathways and motion behaviors. We also outline the challenges and opportunities of using DNA-based molecular machines for biophysics, biosensing, and biocomputing.

Advances in electrospinning and 3D bioprinting strategies to enhance functional regeneration of skeletal muscle tissue

Skeletal muscles are essential for body movement, and the loss of motor function due to volumetric muscle loss (VML) limits the mobility of patients. Current therapeutic approaches are insufficient to offer complete functional recovery of muscle damages. Tissue engineering provides viable ways to fabricate scaffolds to regenerate damaged tissues. Hence, tissue engineering options are explored to address existing challenges in the treatment options for muscle regeneration. Electrospinning is a widely employed fabrication technique to make muscle mimetic nanofibrous scaffolds for tissue regeneration. 3D bioprinting has also been utilized to fabricate muscle-like tissues in recent times. This review discusses the anatomy of skeletal muscle, defects, the healing process, and various treatment options for VML. Further, the advanced strategies in electrospinning of natural and synthetic polymers are discussed, along with the recent developments in the fabrication of hybrid scaffolds. Current approaches in 3D bioprinting of skeletal muscle tissues are outlined with special emphasis on the combination of electrospinning and 3D bioprinting towards the development of fully functional muscle constructs. Finally, the current challenges and future perspectives of these convergence techniques are discussed.

Heavy Metal Ions Detection Using Nanomaterials-Based Aptasensors

Heavy metals ions as metallic pollutants are a growing global issue due to their adverse effects on the aquatic ecosystem, and human health. Unfortunately, conventional detection methods such as atomic absorption spectrometry exhibit a relatively low limit of detection and hold numerous disadvantages, and therefore, the development of an efficient method for in-situ and real-time detection of heavy metal residues is of great importance. The aptamer-based sensors offer distinct advantages over antibodies and emerged as a robust sensing platform against various heavy metals due to their high sensitivity, ease of production, simple operations, excellent specificity, better stability, low immunogenicity, and cost-effectiveness. The nucleic acid aptamers in conjugation with nanomaterials can bind to the metal ions with good specificity/selectivity and can be used for on-site monitoring of metal ion residues. This review aimed to provide background information about nanomaterials-based aptasensor, recent advancements in aptamer conjunction on nanomaterials surface, the role of nanomaterials in improving signal transduction, recent progress of nanomaterials-based aptasening procedures (from 2010 to 2022), and future perspectives toward the practical applications of nanomaterials-based aptasensors against hazardous metal ions for food safety and environmental monitoring.