Degradation rate of DNA scaffolds and bone regeneration

DNA hydrogels for bone regeneration

DNA-based biomaterials have been proposed for tissue engineering approaches due to their predictable assembly into complex morphologies and ease of functionalization. For bone tissue regeneration, the ability to bind Ca2+ and promote hydroxyapatite (HAP) growth along the DNA backbone combined with their degradation and release of extracellular phosphate, a known promoter of osteogenic differentiation, make DNA-based biomaterials unlike other currently used materials. However, their use as biodegradable scaffolds for bone repair remains scarce. Here, we describe the design and synthesis of DNA hydrogels, gels composed of DNA that swell in water, their interactions in vitro with the osteogenic cell lines MC3T3-E1 and mouse calvarial osteoblast, and their promotion of new bone formation in rat calvarial wounds. We found that DNA hydrogels can be readily synthesized at room temperature, and they promote HAP growth in vitro, as characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Osteogenic cells remain viable when seeded on DNA hydrogels in vitro, as characterized by fluorescence microscopy. In vivo, DNA hydrogels promote the formation of new bone in rat calvarial critical size defects, as characterized by micro-computed tomography and histology. This study uses DNA hydrogels as a potential therapeutic biomaterial for regenerating lost bone.

Evaluation of 'surgery-friendly' bone scaffold characteristics: 3D printed ductile BG/PCL scaffold with high inorganic content to repair critical bone defects

The repair of irregular and complex critical bone defects remains a challenge in clinical practice. The application of 3D-printed bioceramics particle/polymer composite scaffolds in bone tissue engineering has been widely studied. At present, the inorganic particle content of the composite scaffolds is generally low, resulting in poor osteogenic activity. However, scaffold with high inorganic content are highly brittle, difficult to operate during surgery, and cannot be in close contact with surrounding bones. Therefore, it is of great significance to design a 'surgery-friendly' scaffold with high bioceramic content and good ductility. In this study, we used the solvent method to add high concentration (wt% 70%) bioglass (BG) into polycaprolactone (PCL), and polyethylene glycol was used as plasticizer to prepare 70% BG/PCL composite scaffolds with high ductility using 3D printing technology.In vitroexperiments showed that the scaffold had good mechanical properties: easy extension, easy folding and strong compressive resistance. It also showed good performance in biocompatibility and osteogenic activity. It was further observed that compared with pure BG or PCL implantation, the scaffold with higher BG content could have more new bone tissue appeared after 12 weeks. All these results indicate that 3D-printed 70% BG/PCL scaffolds have great potential for personalized repair of bone defects.

3D-Printed Hybrid Collagen/GelMA Hydrogels for Tissue Engineering Applications

Bioprinting is an emerging technology involved in the fabrication of three-dimensional tissue constructs for the repair and regeneration of various tissues and organs. Collagen, a natural protein found abundantly in the extracellular matrix of several tissues, can be extracted from collagen-rich tissues of animals such as sheep, cows, rats, pigs, horses, birds, and marine animals. However, due to the poor printability of collagen bioinks, biocompatible collagen scaffolds that mimic the extracellular matrix (ECM) are difficult to fabricate using bioprinting techniques. Gelatin methacrylate (GelMA), a semi-synthetic polymer with tunable physical and chemical properties, has been found to be a promising biomaterial in various bioprinting applications. The printability of collagen can be improved by combining it with semi-synthetic polymers such as GelMA to develop hybrid hydrogels. Such hybrid hydrogels printed have also been identified to have enhanced mechanical properties. Hybrid GelMA meshes have not previously been prepared with collagen from ovine sources. This study provides a novel comparison between the properties of hybrid meshes with ovine skin and bovine hide collagen. GelMA (8% w/v) was integrated with three different concentrations (0.5%, 1%, and 2%) of bovine and ovine collagen forming hybrid hydrogels inks that were printed into meshes with enhanced properties. The maximum percentage of collagen suitable for integration with GelMA, forming hybrid hydrogels with a stable degradation rate was 1%. The water-soluble nature of ovine collagen promoted faster degradation of the hybrid meshes, although the structural crosslinking was identified to be higher than bovine hybrid meshes. The 1% bovine collagen hybrid meshes stood out in terms of their stable degradation rates.

Advancing bone tissue engineering one layer at a time: a layer-by-layer assembly approach to 3D bone scaffold materials

The layer-by-layer (LbL) assembly technique has shown excellent potential in tissue engineering applications. The technique is mainly based on electrostatic attraction and involves the sequential adsorption of oppositely charged electrolyte complexes onto a substrate, resulting in uniform single layers that can be rapidly deposited to form nanolayer films. LbL has attracted significant attention as a coating technique due to it being a convenient and affordable fabrication method capable of achieving a wide range of biomaterial coatings while keeping the main biofunctionality of the substrate materials. One promising application is the use of nanolayer films fabricated by LbL assembly in the development of 3-dimensional (3D) bone scaffolds for bone repair and regeneration. Due to their versatility, nanoscale films offer an exciting opportunity for tailoring surface and bulk property modification of implants for osseous defect therapies. This review article discusses the state of the art of the LbL assembly technique, and the properties and functions of LbL-assembled films for engineered bone scaffold application, combination of multilayers for multifunctional coatings and recent advancements in the application of LbL assembly in bone tissue engineering. The recent decade has seen tremendous advances in the promising developments of LbL film systems and their impact on cell interaction and tissue repair. A deep understanding of the cell behaviour and biomaterial interaction for the further development of new generations of LbL films for tissue engineering are the most important targets for biomaterial research in the field. While there is still much to learn about the biological and physicochemical interactions at the interface of nano-surface coated scaffolds and biological systems, we provide a conceptual review to further progress in the LbL approach to 3D bone scaffold materials and inform the future of LbL development in bone tissue engineering.

Construction of tissue-customized hydrogels from cross-linkable materials for effective tissue regeneration

Hydrogels are prevalent scaffolds for tissue regeneration because of their hierarchical architectures along with outstanding biocompatibility and unique rheological and mechanical properties. For decades, researchers have found that many materials (natural, synthetic, or hybrid) can form hydrogels using different cross-linking strategies. Traditional strategies for fabricating hydrogels include physical, chemical, and enzymatical cross-linking methods. However, due to the diverse characteristics of different tissues/organs to be regenerated, tissue-customized hydrogels need to be developed through precisely controlled processes, making the manufacture of hydrogels reliant on novel cross-linking strategies. Thus, hybrid cross-linkable materials are proposed to tackle this challenge through hybrid cross-linking strategies. Here, different cross-linkable materials and their associated cross-linking strategies are summarized. From the perspective of the major characteristics of the target tissues/organs, we critically analyze how different cross-linking strategies are tailored to fit the regeneration of such tissues and organs. To further advance this field, more appropriate cross-linkable materials and cross-linking strategies should be investigated. In addition, some innovative technologies, such as 3D bioprinting, the internet of medical things (IoMT), and artificial intelligence (AI), are also proposed to improve the development of hydrogels for more efficient tissue regeneration.

2D DNA nanoporous scaffold promotes osteogenic differentiation of pre-osteoblasts

Biofunctional materials with nanomechanical parameters similar to bone tissue may promote the adherence, migration, proliferation, and differentiation of pre-osteoblasts. In this study, deoxyribonucleic acid (DNA) nanoporous scaffold (DNA-NPS) was synthesized by the polymerization of rectangular and double-crossover (DX) DNA tiles. The diagonally precise polymerization of nanometer-sized DNA tiles (A + B) through sticky end cohesion gave rise to a micrometer-sized porous giant-sheet material. The synthesized DNA-NPS exhibited a uniformly distributed porosity with a size of 25 ± 20 nm. The morphology, dimensions, sectional profiles, 2-dimensional (2D) layer height, texture, topology, pore size, and mechanical parameters of DNA-NPS have been characterized by atomic force microscopy (AFM). The size and zeta potential of DNA-NPS have been characterized by the zeta sizer. Cell biocompatibility, proliferation, and apoptosis have been evaluated by flow cytometry. The AFM results confirmed that the fabricated DNA-NPS was interconnected and uniformly porous, with a surface roughness of 0.125 ± 0.08035 nm. The elastic modulus of the DNA-NPS was 22.45 ± 8.65 GPa, which was comparable to that of native bone tissue. DNA-NPS facilitated pre-osteoblast adhesion, proliferation, and osteogenic differentiation. These findings indicated the potential of 2D DNA-NPS in promoting bone tissue regeneration.

Characterization of Polycaprolactone Nanohydroxyapatite Composites with Tunable Degradability Suitable for Indirect Printing

Degradable bone implants are designed to foster the complete regeneration of natural tissue after large-scale loss trauma. Polycaprolactone (PCL) and hydroxyapatite (HA) composites are promising scaffold materials with superior mechanical and osteoinductive properties compared to the single materials. However, producing three-dimensional (3D) structures with high HA content as well as tuneable degradability remains a challenge. To address this issue and create homogeneously distributed PCL-nanoHA (nHA) scaffolds with tuneable degradation rates through both PCL molecular weight and nHA concentration, we conducted a detailed characterisation and comparison of a range of PCL-nHA composites across three molecular weight PCLs (14, 45, and 80 kDa) and with nHA content up to 30% w/w. In general, the addition of nHA results in an increase of viscosity for the PCL-nHA composites but has little effect on their compressive modulus. Importantly, we observe that the addition of nHA increases the rate of degradation compared to PCL alone. We show that the 45 and 80 kDa PCL-nHA groups can be fabricated via indirect 3D printing and have homogenously distributed nHA even after fabrication. Finally, the cytocompatibility of the composite materials is evaluated for the 45 and 80 kDa groups, with the results showing no significant change in cell number compared to the control. In conclusion, our analyses unveil several features that are crucial for processing the composite material into a tissue engineered implant.

DNA nanostructures as templates for biomineralization

Nature uses extracellular matrix scaffolds to organize biominerals into hierarchical structures over various length scales. This has inspired the design of biomimetic mineralization scaffolds, with DNA nanostructures being among the most promising. DNA nanotechnology makes use of molecular recognition to controllably give 1D, 2D and 3D nanostructures. The control we have over these structures makes them attractive templates for the synthesis of mineralized tissues, such as bones and teeth. In this Review, we first summarize recent work on the crystallization processes and structural features of biominerals on the nanoscale. We then describe self-assembled DNA nanostructures and come to the intersection of these two themes: recent applications of DNA templates in nanoscale biomineralization, a crucial process to regenerate mineralized tissues.

Functionalized DNA nanostructures as scaffolds for guided mineralization

The field of DNA nanotechnology uses synthetic DNA strands as building blocks for designing complex shapes in one-, two- and three-dimensions. Here, we investigate whether DNA nanostructures are feasible platforms for the precise organization of polyaspartic acid (pAsp), a known mineral carrier, with a goal towards biomimetic mineralization for enamel regeneration. We describe the preparation of DNA-pAsp conjugates and their subsequent assembly into ordered nanostructures. Covalent attachment of pAsp to DNA was noted to hinder DNA nanostructure formation past a certain threshold (50% pAsp) when tested on a previously published DNA system. However, a simplified double stranded DNA system (3sDH system) was more robust and efficient in its pAsp incorporation. In addition, the 3sDH system was successful in organizing mineral inducing groups in one dimension at repeating intervals of 28.7 ± 4.0 nm, as determined by atomic force microscopy. Our results demonstrate that DNA nanostructures can be functionalized with pAsp and act as a platform to investigate guided mineralization.

Design, synthesis and evaluation of DNA nano-cubes as a core material protected by the alginate coating for oral administration of anti-diabetic drug

Poor control towards glycemic levels among diabetic patients may lead to severe micro/ macro-vascular and neuropathic complexities. Proper functioning of alpha-beta cells of pancreases is required to attain long term glycemic control among type 2 diabetics. The recent developments to manage diabetes are focused on controlling the insulin-glucagon secretions from the pancreases. DPP-4 inhibitors class of drugs after elevating GLP-1/GIP (incretins) levels in the blood, not only raise the insulin levels but also suppress the glucagon level. Vildagliptin (VI) is a potent DPP-4 inhibitor with least adverse events compared to other DPP-4 inhibitors. We encapsulated VI into 3D nanocube that gets bind to the DNA due to secondary amine in its chemical structure. DNA-nanocube being negatively charged was incubated with the PLL to attain positive surface. Ultimately VI loaded nanocubes were coated with the negatively charged Na-alginate via electrostatic attraction method to get stable spherical nanospheres for oral delivery of VI. Nanospheres were evaluated physically through native PAGE analysis, DSC, TGA, dissolution testing, XRD and FTIR. We attained uniformed and spherical nanospheres with stable topology, nanoscale size precision (40–150 nm in diameter), Entrapment efficiency (up to 90%), prolonged drug release (13 ± 4 h) at basic pH, and superior oral antidiabetic effects with improved GLP1 and glycemic levels. The formulated nanospheres attained size uniformity and better therapeutic outcomes in terms of reduced adverse events and better control of glycemic levels than previously reported methods with decreased dosage frequency tested in Db/Db mice.