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

Bioprinting spatially guided functional 3D neural circuits with agarose-xanthan gum copolymer hydrogels

Engineered three-dimensional (3D) tissue models are being used as predictive human in vitro assays for drug discovery and development. Tissue engineering technologies such as bioprinting are now available which use mixtures of polymeric hydrogels and cells for the construction of biomimetic engineered 3D tissue models. Many of the polymeric hydrogels used for bioprinting require post-printing processing steps which might hinder their application directly in multi-well plate platforms, thus limiting their utility in a drug screening setting. Here we describe an agarose and xanthan gum copolymer hydrogel (AG-XG) that has optimal rheological properties for high shape fidelity with extrusion-based printing, has long term stability in cell culture conditions, and is "ready-to-use" after printing, not requiring post-printing processing treatments, making it ideal for applications in multi-well plate format. This AG-XG hydrogel is non-degradable and has non-cell permissive features which makes it ideal to create customized spatially guided cellular patterns to enhance relevant tissue geometry and function. As a proof-of-concept, we show that a bioprinted AG-XG hydrogel casting mold significantly enhances functional connectivity of an engineered 3D neural circuit model made using human iPSC-derived GABAergic and dopaminergic neurons and astrocytes. The bioprinted AG-XG mold promotes the formation of strong functional synaptic connections between two spatially separated neuronal regions, as measured with calcium and optogenetic-based fluorescent biosensors with a customized fiber photometry device. The high shape fidelity of the AG-XG hydrogels described here enables the biofabrication of precisely positioned and spatially designed cellular models, in muti well-based platforms used for drug screening. The process of printing these AG-XG hydrogels uses commercially available extrusion-based bioprinters and can therefore be easily implemented in translational laboratories doing tissue modeling and drug screening without the need of additional specialized bioengineering equipment.

Electrochemical β-lactamase immunostrip sensor with 3D hydrogel-paper scaffold for rapid detection & post-antibiotic therapy monitoring in drug-resistant bloodstream infections

BACKGROUND

The increasing prevalence of drug-resistant bacterial bloodstream infections, particularly those caused by Methicillin-resistant Staphylococcus aureus (MRSA), presents a critical global healthcare challenge. Current diagnostic methods often lack the speed and sensitivity necessary for timely antibiotic interventions, leading to poor patient outcomes and increased resistance due to misuse of broad-spectrum antibiotics. Existing platforms rarely combine rapid detection, low detection limits, and real-time therapy monitoring, leaving a crucial gap in effective infection management.

RESULTS

This study introduces an electrochemical immunostrip sensor for the rapid detection of β-lactamase (BL), an enzyme associated with drug resistance. Using a novel 3D hydrogel-paper scaffold, the sensor achieves a detection limit of 0.146 mU/ml and accurately detects BL-producing pathogens, including MRSA, from clinical samples with bacterial loads as low as 102 CFU/ml. The platform provides post culture detection results within 1 h, post antibiotic therapy monitoring within 4 h and demonstrates high specificity (∼100 %) by differentiating BL-producing strains from non-producing isolates.

SIGNIFICANCE AND NOVELTY

This study introduces a new electrochemical smart immunostrip sensor integrated with a 3D hydrogel-paper scaffold for β-lactamase detection, which offers high sensitivity and specificity. Unlike conventional diagnostics, it enables user-friendly, rapid, cost-effective detection within 1 h post-blood culture and real-time antibiotic therapy monitoring in just 4 h, transforming clinically actionable point-of-care (POC) management of drug-resistant bloodstream infections.

Tailoring of agarose hydrogel to modulate its 3D bioprintability and mechanical properties for stem cell mediated bone tissue engineering

The intense gelling characteristics and viscosity constraints of agarose limit its utility as a sole ink material in 3D printing. This study presents the development of agarose bioink designed for cell-laden printing, featuring controlled printability, exceptional stiffness, and cell-responsiveness achieved via the insertion of photochemically reactive methacrylate groups. This chemical modification transforms the dense agarose network into a thinner structure, effecting a gentle thermogelling property that enhances the printability and facile cell encapsulation. Herein we examine the interplay between the degree of substitution and concentration variations to determine the optimal hydrogel composition. The best bioink composition possessed a lower shear modulus (storage modulus G' = 11.6 Pa) at 37 °C, assuring better bioprintability, while it possessed a Young's modulus of 1.4 ± 0.10 MPa in the crosslinked state, which is the highest reported in the natural single-matrix hydrogel systems. Studies with mesenchymal stem cells (MSC) confirmed that it is a good cell encapsulation matrix, achieving 111 % cell viability at 72 h. The bioprinted constructs promoted the osteogenic differentiation of MSC, as evidenced by mineralization and secretion of bone-related matrix. The gene expression analysis indicated that osteogenic marker expressions exhibited at least a two-fold increase on day 14 relative to the control group.

Optimization of Gelatin and Crosslinker Concentrations in a Gelatin/Alginate-Based Bioink with Potential Applications in a Simplified Skin Model

Three-dimensional bioprinting allows for the fabrication of structures mimicking tissue architecture. This study aimed to develop a gelatin-based bioink for a bioprinted simplified skin model. The bioink printability and chemical-physical properties were evaluated by varying the concentrations of gelatin (10, 15, and 20%) in a semi-crosslinked alginate-based bioink and calcium chloride (100, 150, and 200 mM) in post-printing crosslinking. For increasing the gelatin concentration, the gelatin-based formulations have a shear thinning behavior with increasing viscosity, and the filament bending angle increases, the spreading ratio value approaches 1, and the shape fidelity and the printing resolution improve. However, the formulation containing 20% of gelatin was not homogeneous, resulting also in poor printability properties. The morphology of the pores, degradation, and swelling depend on gelatin and CaCl2 concentrations, but not in a significant way. The samples containing 15% of gelatin and crosslinked with 150 mM CaCl2 have been selected for the bioprinting of a bilayer skin model containing human fibroblasts and keratinocytes. The model showed a homogeneous distribution of viable and proliferating cells over up to 14 days of in vitro culture. The gelatin-based bioink allowed for the 3D bioprinting of a simplified skin model, with potential applications in the bioactivity of pro-reparative molecules and drug evaluation.

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.

Nanocellulose-based hydrogels as versatile materials with interesting functional properties for tissue engineering applications

Tissue engineering has emerged as a remarkable field aiming to restore or replace damaged tissues through the use of biomimetic constructs. Among the diverse materials investigated for this purpose, nanocellulose-based hydrogels have garnered attention due to their intriguing biocompatibility, tunable mechanical properties, and sustainability. Over the past few years, numerous research works have been published focusing on the successful use of nanocellulose-based hydrogels as artificial extracellular matrices for regenerating various types of tissues. The review emphasizes the importance of tissue engineering, highlighting hydrogels as biomimetic scaffolds, and specifically focuses on the role of nanocellulose in composites that mimic the structures, properties, and functions of the native extracellular matrix for regenerating damaged tissues. It also summarizes the types of nanocellulose, as well as their structural, mechanical, and biological properties, and their contributions to enhancing the properties and characteristics of functional hydrogels for tissue engineering of skin, bone, cartilage, heart, nerves and blood vessels. Additionally, recent advancements in the application of nanocellulose-based hydrogels for tissue engineering have been evaluated and documented. The review also addresses the challenges encountered in their fabrication while exploring the potential future prospects of these hydrogel matrices for biomedical applications.

Patterned PVA Hydrogels with 3D Petri Dish® Micro-Molds of Varying Topography for Spheroid Formation of HeLa Cancer Cells: In Vitro Assessment

Cell spheroids are an important three-dimensional (3D) model for in vitro testing and are gaining interest for their use in clinical applications. More natural 3D cell culture environments that support cell-cell interactions have been created for cancer drug discovery and therapy applications, such as the scaffold-free 3D Petri Dish® technology. This technology uses reusable and autoclavable silicone micro-molds with different topographies, and it conventionally uses gelled agarose for hydrogel formation to preserve the topography of the selected micro-mold. The present study investigated the feasibility of using a patterned Poly(vinyl alcohol) hydrogel using the circular topography 12-81 (9 × 9 wells) micro-mold to form HeLa cancer cell spheroids and compare them with the formed spheroids using agarose hydrogels. PVA hydrogels showed a slightly softer, springier, and stickier texture than agarose hydrogels. After preparation, Fourier transform infrared (FTIR) spectra showed chemical interactions through hydrogen bonding in the PVA and agarose hydrogels. Both types of hydrogels favor the formation of large HeLa spheroids with an average diameter of around 700-800 µm after 72 h. However, the PVA spheroids are more compact than those from agarose, suggesting a potential influence of micro-mold surface chemistry on cell behavior and spheroid formation. This was additionally confirmed by evaluating the spheroid size, morphology, integrity, as well as E-cadherin and Ki67 expression. The results suggest that PVA promotes stronger cell-to-cell interactions in the spheroids. Even the integrity of PVA spheroids was maintained after exposure to the drug cisplatin. In conclusion, the patterned PVA hydrogels were successfully prepared using the 3D Petri Dish® micro-molds, and they could be used as suitable platforms for studying cell-cell interactions in cancer drug therapy.

Efficacy of 3D printed anatomically equivalent thermoplastic polyurethane guide conduits in promoting the regeneration of critical-sized peripheral nerve defects

Three-dimensional (3D) printing is an emerging tool for creating patient-specific tissue constructs analogous to the native tissue microarchitecture. In this study, anatomically equivalent 3D nerve conduits were developed using thermoplastic polyurethane (TPU) by combining reverse engineering and material extrusion (i.e. fused deposition modeling) technique. Printing parameters were optimized to fabricate nerve-equivalent TPU constructs. The TPU constructs printed with different infill densities supported the adhesion, proliferation, and gene expression of neuronal cells. Subcutaneous implantation of the TPU constructs for three months in rats showed neovascularization with negligible local tissue inflammatory reactions and was classified as a non-irritant biomaterial as per ISO 10993-6. To performin vivoefficacy studies, nerve conduits equivalent to rat's sciatic nerve were fabricated and bridged in a 10 mm sciatic nerve transection model. After four months of implantation, the sensorimotor function and histological assessments revealed that the 3D printed TPU conduits promoted the regeneration in critical-sized peripheral nerve defects equivalent to autografts. This study proved that TPU-based 3D printed nerve guidance conduits can be created to replicate the complicated features of natural nerves that can promote the regeneration of peripheral nerve defects and also show the potential to be extended to several other tissues for regenerative medicine applications.

Nanomaterials-Based Hybrid Bioink Platforms in Advancing 3D Bioprinting Technologies for Regenerative Medicine

3D bioprinting is recognized as the ultimate additive biomanufacturing technology in tissue engineering and regeneration, augmented with intelligent bioinks and bioprinters to construct tissues or organs, thereby eliminating the stipulation for artificial organs. For 3D bioprinting of soft tissues, such as kidneys, hearts, and other human body parts, formulations of bioink with enhanced bioinspired rheological and mechanical properties were essential. Nanomaterials-based hybrid bioinks have the potential to overcome the above-mentioned problem and require much attention among researchers. Natural and synthetic nanomaterials such as carbon nanotubes, graphene oxides, titanium oxides, nanosilicates, nanoclay, nanocellulose, etc. and their blended have been used in various 3D bioprinters as bioinks and benefitted enhanced bioprintability, biocompatibility, and biodegradability. A limited number of articles were published, and the above-mentioned requirement pushed us to write this review. We reviewed, explored, and discussed the nanomaterials and nanocomposite-based hybrid bioinks for the 3D bioprinting technology, 3D bioprinters properties, natural, synthetic, and nanomaterial-based hybrid bioinks, including applications with challenges, limitations, ethical considerations, potential solution for future perspective, and technological advancement of efficient and cost-effective 3D bioprinting methods in tissue regeneration and healthcare.

The Method of Direct and Reverse Phase Portraits as a Tool for Systematizing the Results of Studies of Phase Transitions in Solutions of Thermosensitive Polymers

It is shown that a more than significant amount of experimental data obtained in the field of studying systems based on thermosensitive hydrophilic polymers and reflected in the literature over the past decades makes the issue of their systematization and classification relevant. This, in turn, makes relevant the question of choosing the appropriate classification criteria. It is shown that the basic classification feature can be the number of phase transition stages, which can vary from one to four or more depending on the nature of the temperature-sensitive system. In this work, the method of inverse phase portraits is proposed for the first time. It was intended, among other things, to identify the number of phase transition stages. Moreover, the accuracy of this method significantly exceeds the accuracy of the previously used method of direct phase portraits since, for the first time, the operation of numerical differentiation is replaced by the operation of numerical integration. A specific example of the application of the proposed method for the analysis of a previously studied temperature-sensitive system is presented. It is shown that this method also allows for a quantitative comparison between the results obtained by the differential calorimetry method and the turbidimetry method. Issues related to increasing the resolution of the method of direct phase portraits are discussed.

An overview of nasal cartilage bioprinting: from bench to bedside

Nasal cartilage diseases and injuries are known as significant challenges in reconstructive medicine, affecting a substantial number of individuals worldwide. In recent years, the advent of three-dimensional (3D) bioprinting has emerged as a promising approach for nasal cartilage reconstruction, offering potential breakthroughs in the field of regenerative medicine. This paper provides an overview of the methods and challenges associated with 3D bioprinting technologies in the procedure of reconstructing nasal cartilage tissue. The process of 3D bioprinting entails generating a digital 3D model using biomedical imaging techniques and computer-aided design to integrate both internal and external scaffold features. Then, bioinks which consist of biomaterials, cell types, and bioactive chemicals, are applied to facilitate the precise layer-by-layer bioprinting of tissue-engineered scaffolds. After undergoing in vitro and in vivo experiments, this process results in the development of the physiologically functional integrity of the tissue. The advantages of 3D bioprinting encompass the ability to customize scaffold design, enabling the precise incorporation of pore shape, size, and porosity, as well as the utilization of patient-specific cells to enhance compatibility. However, various challenges should be considered, including the optimization of biomaterials, ensuring adequate cell viability and differentiation, achieving seamless integration with the host tissue, and navigating regulatory attention. Although numerous studies have demonstrated the potential of 3D bioprinting in the rebuilding of such soft tissues, this paper covers various aspects of the bioprinted tissues to provide insights for the future development of repair techniques appropriate for clinical use.

3D Printing of Polysaccharide-Based Hydrogel Scaffolds for Tissue Engineering Applications: A Review

In tissue engineering, 3D printing represents a versatile technology employing inks to construct three-dimensional living structures, mimicking natural biological systems. This technology efficiently translates digital blueprints into highly reproducible 3D objects. Recent advances have expanded 3D printing applications, allowing for the fabrication of diverse anatomical components, including engineered functional tissues and organs. The development of printable inks, which incorporate macromolecules, enzymes, cells, and growth factors, is advancing with the aim of restoring damaged tissues and organs. Polysaccharides, recognized for their intrinsic resemblance to components of the extracellular matrix have garnered significant attention in the field of tissue engineering. This review explores diverse 3D printing techniques, outlining distinctive features that should characterize scaffolds used as ideal matrices in tissue engineering. A detailed investigation into the properties and roles of polysaccharides in tissue engineering is highlighted. The review also culminates in a profound exploration of 3D polysaccharide-based hydrogel applications, focusing on recent breakthroughs in regenerating different tissues such as skin, bone, cartilage, heart, nerve, vasculature, and skeletal muscle. It further addresses challenges and prospective directions in 3D printing hydrogels based on polysaccharides, paving the way for innovative research to fabricate functional tissues, enhancing patient care, and improving quality of life.

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.

Emerging perspectives on 3D printed bioreactors for clinical translation of engineered and bioprinted tissue constructs

3D printed/bioprinted tissue constructs are utilized for the regeneration of damaged tissues and as in vitro models. Most of the fabricated 3D constructs fail to undergo functional maturation in conventional in vitro settings. There is a challenge to provide a suitable niche for the fabricated tissue constructs to undergo functional maturation. Bioreactors have emerged as a promising tool to enhance tissue maturation of the engineered constructs by providing physical/biological cues along with a controlled nutrient supply under dynamic in vitro conditions. Bioreactors provide an ambient microenvironment most appropriate for the development of functionally matured tissue constructs by promoting cell proliferation, differentiation, and maturation for transplantation and drug screening applications. Due to the huge cost and limited availability of commercial bioreactors, there is a need to develop strategies to make customized bioreactors. Additive manufacturing (AM) may be a viable tool to fabricate custom designed bioreactors with better efficiency and at low cost. In this review, we have extensively discussed the importance of bioreactors in functionalizing tissue engineered/3D bioprinted scaffolds for bone, cartilage, skeletal muscle, nerve, and vascular tissue. In addition, the importance and fabrication of customized 3D printed bioreactors for the maturation of tissue engineered constructs are discussed in detail. Finally, the current challenges and future perspectives in translating commercial and custom 3D printed bioreactors for clinical applications are outlined.