Recent trends in bioinks for 3D printing

Photocurable biomaterials labeled with luminescent sensors dedicated to bioprinting

In the present study, we focused on the development and characterization of formulations that function as biological inks. These inks were doped with coumarin derivatives to act as molecular luminescent sensors that allow the monitoring of the kinetics of in situ photopolymerization in 3D (DLP) printing and bioprinting using pneumatic extrusion techniques, making it possible to study the changes in the system in real time. The efficiency of the systems was tested on compositions containing monomers: poly(ethylene glycol) diacrylates and photoinitiators: 2,4,6-trimethylbenzoyldi-phenylphosphinate and lithium phenyl-2,4,6-trimethylbenzoylphosphinate. The selected formulations were spectroscopically characterized and examined for their photopolymerization kinetics and rheological properties. This is important because of the fact that spectroscopic characterization, examination of photopolymerization kinetics, and rheological properties provide valuable insights into the behaviour of photocurable resin dedicated for 3D printing processes. The next step involved printing tests on commercially available 3D printers. In turn, printing carried out as part of the work on commercially available 3D printers further verified the effectiveness of the formulations. Moreover the formulation components and the resulting 3D objects were tested for their antiproliferative effects on the selected Chinese hamster ovary cell line, CHO-K1.

Study on Printability Evaluation of Alginate/Silk Fibroin/Collagen Double-Cross-Linked Inks and the Properties of 3D Printed Constructs

In recent years, biological 3D printing has garnered increasing attention for tissue and organ repair. The challenge with 3D-printing inks is to combine mechanical properties as well as biocompatibility. Proteins serve as vital structural components in living systems, and utilizing protein-based inks can ensure that the materials maintain the necessary biological activity. In this study, we incorporated two natural biomaterials, silk fibroin (SF) and collagen (COL), into a low-concentration sodium alginate (SA) solution to create novel composite inks. SF and COL were modified with glycidyl methacrylate (GMA) to impart photo-cross-linking properties. The UV light test and 1H NMR results demonstrated successful curing of silk fibroin (SF) and collagen (COL) after modification and grafting. Subsequently, the printability of modified silk fibroin (RSFMA)/SA with varying concentration gradients was assessed using a set of three consecutive printing models, and the material's properties were tested. The research results prove that the addition of RSFMA and ColMA enhances the printability of low-concentration SA solutions, with the Pr values increasing from 0.85 ± 0.02 to 0.90 ± 0.03 and 0.92 ± 0.02, respectively, and the mechanical strength increasing from 0.19 ± 0.01 to 0.28 ± 0.01 and 0.38 ± 0.01 MPa; cytocompatibility has also been improved. Furthermore, rheological tests indicated that all of the inks exhibited shear thinning properties. CCK-8 experiments demonstrated that the addition of ColMA increased the cytocompatibility of the ink system. Overall, the utilization of SF and COL-modified SA materials as inks represents a promising advancement in 3D-printed ink technology.

Advancements in Ocular Therapy: A Review of Emerging Drug Delivery Approaches and Pharmaceutical Technologies

Eye disorders affect a substantial portion of the global population, yet the availability of efficacious ophthalmic drug products remains limited. This can be partly ascribed to a number of factors: (1) inadequate understanding of physiological barriers, treatment strategies, drug and polymer properties, and delivery systems; (2) challenges in effectively delivering drugs to the anterior and posterior segments of the eye due to anatomical and physiological constraints; and (3) manufacturing and regulatory hurdles in ocular drug product development. The present review discusses innovative ocular delivery and treatments, encompassing implants, liposomes, nanoparticles, nanomicelles, microparticles, iontophoresis, in situ gels, contact lenses, microneedles, hydrogels, bispecific antibodies, and gene delivery strategies. Furthermore, this review also introduces advanced manufacturing technologies such as 3D printing and hot-melt extrusion (HME), aimed at improving bioavailability, reducing therapeutic dosages and side effects, facilitating the design of personalized ophthalmic dosage forms, as well as enhancing patient compliance. This comprehensive review lastly offers insights into digital healthcare, market trends, and industry and regulatory perspectives pertaining to ocular product development.

Advancing Cartilage Tissue Engineering: A Review of 3D Bioprinting Approaches and Bioink Properties

Articular cartilage is crucial in human physiology, and its degeneration poses a significant public health challenge. While recent advancements in 3D bioprinting and tissue engineering show promise for cartilage regeneration, there remains a gap between research findings and clinical application. This review critically examines the mechanical and biological properties of hyaline cartilage, along with current 3D manufacturing methods and analysis techniques. Moreover, we provide a quantitative synthesis of bioink properties used in cartilage tissue engineering. After screening 181 initial works, 33 studies using extrusion bioprinting were analyzed and synthesized, presenting results that indicate the main materials, cells, and methods utilized for mechanical and biological evaluation. Altogether, this review motivates the standardization of mechanical analyses and biomaterial assessments of 3D bioprinted constructs to clarify their chondrogenic potential.

Emerging technologies in regenerative medicine: The future of wound care and therapy

Wound healing, an intricate biological process, comprises orderly phases of simple biological processed including hemostasis, inflammation, angiogenesis, cell proliferation, and ECM remodeling. The regulation of the shift in these phases can be influenced by systemic or environmental conditions. Any untimely transitions between these phases can lead to chronic wounds and scarring, imposing a significant socio-economic burden on patients. Current treatment modalities are largely supportive in nature and primarily involve the prevention of infection and controlling inflammation. This often results in delayed healing and wound complications. Recent strides in regenerative medicine and tissue engineering offer innovative and patient-specific solutions. Mesenchymal stem cells (MSCs) and their secretome have gained specific prominence in this regard. Additionally, technologies like tissue nano-transfection enable in situ gene editing, a need-specific approach without the requirement of complex laboratory procedures. Innovating approaches like 3D bioprinting and ECM bioscaffolds also hold the potential to address wounds at the molecular and cellular levels. These regenerative approaches target common healing obstacles, such as hyper-inflammation thereby promoting self-recovery through crucial signaling pathway stimulation. The rationale of this review is to examine the benefits and limitations of both current and emerging technologies in wound care and to offer insights into potential advancements in the field. The shift towards such patient-centric therapies reflects a paradigmatic change in wound care strategies.

A narrative review: 3D bioprinting of cultured muscle meat and seafood products and its potential for the food industry

The demand for meat and seafood products has been globally increasing for decades. To address the environmental, social, and economic impacts of this trend, there has been a surge in the development of three-dimensional (3D) food bioprinting technologies for lab-grown muscle food products and their analogues. This innovative approach is a sustainable solution to mitigate the environmental risks associated with climate change caused by the negative impacts of indiscriminative livestock production and industrial aquaculture. This review article explores the adoption of 3D bioprinting modalities to manufacture lab-grown muscle food products and their associated technologies, cells, and bioink formulations. Additionally, various processing techniques, governing the characteristics of bioprinted food products, nutritional compositions, and safety aspects as well as its relevant ethical and social considerations, were discussed. Although promising, further research and development is needed to meet standards and translate into several industrial areas, such as the food and renewable energy industries. In specific, optimization of animal cell culture conditions, development of serum-free media, and bioreactor design are essential to eliminate the risk factors but achieve the unique nutritional requirements and consumer acceptance. In short, the advancement of 3D bioprinting technologies holds great potential for transforming the food industry, but achieving widespread adoption will require continued innovation, rigorous research, and adherence to ethical standards to ensure safety, nutritional quality, and consumer acceptance.

Innovative 3D bioprinting approaches for advancing brain science and medicine: a literature review

The rapid advancements in 3D printing technology have revolutionized the field of tissue engineering, particularly in the development of neural tissues for the treatment of nervous system diseases. Brain neural tissue, composed of neurons and glial cells, plays a crucial role in the functioning of the brain, spinal cord, and peripheral nervous system by transmitting nerve impulses and processing information. By leveraging 3D bioprinting and bioinks, researchers can create intricate neural scaffolds that facilitate the proliferation and differentiation of nerve cells, thereby promoting the repair and regeneration of damaged neural tissues. This technology allows for the precise spatial arrangement of various cell types and scaffold materials, enabling the construction of complex neural tissue models that closely mimic the natural architecture of the brain. Human-induced pluripotent stem cells (hiPSCs) have emerged as a groundbreaking tool in neuroscience research and the potential treatment of neurological diseases. These cells can differentiate into diverse cell types within the nervous system, including neurons, astrocytes, microglia, oligodendrocytes, and Schwann cells, providing a versatile platform for studying neural networks, neurodevelopment, and neurodegenerative disorders. The use of hiPSCs also opens new avenues for personalized medicine, allowing researchers to model diseases and develop targeted therapies based on individual patient profiles. Despite the promise of direct hiPSC injections for therapeutic purposes, challenges such as poor localization and limited integration have led to the exploration of biomaterial scaffolds as supportive platforms for cell delivery and tissue regeneration. This paper reviews the integration of 3D bioprinting technologies and bioink materials in neuroscience applications, offering a unique platform to create complex brain and tissue architectures that mimic the mechanical, architectural, and biochemical properties of native tissues. These advancements provide robust tools for modelling, repair, and drug screening applications. The review highlights current research, identifies research gaps, and offers recommendations for future studies on 3D bioprinting in neuroscience. The investigation demonstrates the significant potential of 3D bioprinting to fabricate brain-like tissue constructs, which holds great promise for regenerative medicine and drug testing models. This approach offers new avenues for studying brain diseases and potential treatments.

Meta-analysis of the make-up and properties of in vitro models of the healthy and diseased blood-brain barrier

In vitro models of the human blood-brain barrier (BBB) are increasingly used to develop therapeutics that can cross the BBB for treating diseases of the central nervous system. Here we report a meta-analysis of the make-up and properties of transwell and microfluidic models of the healthy BBB and of BBBs in glioblastoma, Alzheimer's disease, Parkinson's disease and inflammatory diseases. We found that the type of model, the culture method (static or dynamic), the cell types and cell ratios, and the biomaterials employed as extracellular matrix are all crucial to recapitulate the low permeability and high expression of tight-junction proteins of the BBB, and to obtain high trans-endothelial electrical resistance. Specifically, for models of the healthy BBB, the inclusion of endothelial cells and pericytes as well as physiological shear stresses (~10-20 dyne cm-2) are necessary, and when astrocytes are added, astrocytes or pericytes should outnumber endothelial cells. We expect this meta-analysis to facilitate the design of increasingly physiological models of the BBB.

Gelatin-Sodium Alginate Hydrogels Cross-Linked by Squaric Acid and Dialdehyde Starch as a Potential Bio-Ink

Hydrogels as biomaterials possess appropriate physicochemical and mechanical properties that enable the formation of a three-dimensional, stable structure used in tissue engineering and 3D printing. The integrity of the hydrogel composition is due to the presence of covalent or noncovalent cross-linking bonds. Using various cross-linking methods and agents is crucial for adjusting the properties of the hydrogel to specific biomedical applications, e.g., for direct bioprinting. The research subject was mixtures of gel-forming polymers: sodium alginate and gelatin. The polymers were cross-linked ionically with the addition of CaCl2 solutions of various concentrations (10%, 5%, 2.5%, and 1%) and covalently using squaric acid (SQ) and dialdehyde starch (DAS). Initially, the polymer mixture's composition and the hydrogel cross-linking procedure were determined. The obtained materials were characterized by mechanical property tests, swelling degree, FTIR, SEM, thermal analysis, and biological research. It was found that the tensile strength of hydrogels cross-linked with 1% and 2.5% CaCl2 solutions was higher than after using a 10% solution (130 kPa and 80 kPa, respectively), and at the same time, the elongation at break increased (to 75%), and the stiffness decreased (Young Modulus is 169 kPa and 104 kPa, respectively). Moreover, lowering the concentration of the CaCl2 solution from 10% to 1% reduced the final material's toxicity. The hydrogels cross-linked with 1% CaCl2 showed lower degradation temperatures and higher weight losses than those cross-linked with 2.5% CaCl2 and therefore were less thermally stable. Additional cross-linking using SQ and DAS had only a minor effect on the strength of the hydrogels, but especially the use of 1% DAS increased the material's elasticity. All tested hydrogels possess a 3D porous structure, with pores of irregular shape and heterogenic size, and their swelling degree initially increased sharply to the value of approx. 1000% during the first 6 h, and finally, it stabilized at a level of 1200-1600% after 24 h. The viscosity of 6% gelatin and 2% alginate solutions with and without cross-linking agents was similar, and they were only slightly shear-thinning. It was concluded that a mixture containing 2% sodium alginate and 6% gelatin presented optimal properties after gel formation and lowering the concentration of the CaCl2 solution to 1% improved the hydrogel's biocompatibility and positively influenced the cross-linking efficiency. Moreover, chemical cross-linking by DAS or SQ additionally improved the final hydrogel's properties and the mixture's printability. In conclusion, among the tested systems, the cross-linking of 6% gelatin-2% alginate mixtures by 1% DAS addition and 1% CaCl2 solution is optimal for tissue engineering applications and potentially suitable for 3D printing.

Unleashing the power of silk-based proteins as biomaterials for cutting-edge drug delivery: a comprehensive review

Silk proteins, viz., sericin, fibroin and their modified forms etc., have been thoroughly researched as natural biopolymers for the development of varied nanomaterials exhibiting diverse biomedical applications. The silk proteins are extracted from the cocoons by degumming and treatment with soaps, followed by dissolution and dialysis against water. These proteins exhibit distinct mechanical and physicochemical characteristics including biocompatibility, controlled biodegradability, self-assembling traits, chemical modifiability, and adaptability, thus making it an ideal drug delivery vehicle. In this regard, silk protein-derived drug delivery systems have been reported as efficient carrier to encapsulate and stabilize the wide variety of pharmacological molecules, enzymes, proteins, vaccines, and even DNA, allowing them to remain active for a longer period of time. Further, different delivery carriers researched employing these proteins for multitude of applications include hydrogels, sponges, fibres, scaffolds and particulate delivery systems. Additionally, the chemical modification of silk proteins has further opened avenues for development of other modified silk proteins with improved physicochemical traits and hence exhibiting enormous potential in development of varied bioenhanced carrier systems. The current article thus provides the holistic information of characteristics, types of silk protein-based delivery carriers, and their fabrication techniques, while emphasizing the applications of different silk proteins in biomedicine and drug delivery.

Application of 3D-Printed Bioinks in Chronic Wound Healing: A Scoping Review

Chronic wounds, such as diabetic foot ulcers, pressure ulcers, and venous ulcers, pose significant clinical challenges and burden healthcare systems worldwide. The advent of 3D bioprinting technologies offers innovative solutions for enhancing chronic wound care. This scoping review evaluates the applications, methodologies, and effectiveness of 3D-printed bioinks in chronic wound healing, focusing on bioinks incorporating living cells to facilitate wound closure and tissue regeneration. Relevant studies were identified through comprehensive searches in databases, including PubMed, Scopus, and Web of Science databases, following strict inclusion criteria. These studies employ various 3D bioprinting techniques, predominantly extrusion-based, to create bioinks from natural or synthetic polymers. These bioinks are designed to support cell viability, promote angiogenesis, and provide structural integrity to the wound site. Despite these promising results, further research is necessary to optimize bioink formulations and printing parameters for clinical application. Overall, 3D-printed bioinks offer a transformative approach to chronic wound care, providing tailored and efficient solutions. Continued development and refinement of these technologies hold significant promise for improving chronic wound management and patient outcomes.

Experimental Study on Compatibility of Human Bronchial Epithelial Cells in Collagen-Alginate Bioink for 3D Printing

This paper reports an experimental study on the compatibility of human bronchial epithelial (HBE) cells in a collagen-alginate bioink. The compatibility was assessed using the culture well method with three bioink compositions prepared from a 10% alginate solution and neutralized TeloCol-10 mg/mL collagen stock solution. Cell viability, quantified by (live cell count-dead cell count)/live cell count within the HBE cell-laden hydrogel, was evaluated using the live/dead assay method from Day 0 to Day 6. Experimental results demonstrated that the collagen-alginate 4:1 bioink composition exhibited the highest cell viability on Day 6 (85%), outperforming the collagen-alginate 1:4 bioink composition and the alginate bioink composition, which showed cell viability of 75% and 45%, respectively. Additionally, the live cell count was highest for the collagen-alginate 4:1 bioink composition on Day 0, a trend that persisted through Days 1 to 6, underscoring its superior performance in maintaining cell viability and promoting cell proliferation. These findings show that the compatibility of HBE cells with the collagen-alginate 4:1 bioink composition was higher compared with the other two bioink compositions.

Recent advances in implantable sensors and electronics using printable materials for advanced healthcare

This review article focuses on the recent printing technological progress in healthcare, underscoring the significant potential of implantable devices across diverse applications. Printing technologies have widespread use in developing health monitoring devices, diagnostic systems, and surgical devices. Recent years have witnessed remarkable progress in fabricating low-profile implantable devices, driven by advancements in printing technologies and nanomaterials. The importance of implantable biosensors and bioelectronics is highlighted, specifically exploring printing tools using bio-printable inks for practical applications, including a detailed examination of fabrication processes and essential parameters. This review also justifies the need for mechanical and electrical compatibility between bioelectronics and biological tissues. In addition to technological aspects, this article delves into the importance of appropriate packaging methods to enhance implantable devices' performance, compatibility, and longevity, which are made possible by integrating cutting-edge printing technology. Collectively, we aim to shed light on the holistic landscape of implantable biosensors and bioelectronics, showcasing their evolving role in advancing healthcare through innovative printing technologies.

In vitro co-culture models for studying organoids-macrophages interaction: the golden technology of cancer immunotherapy

Macrophages, as the largest immune cell group in tumour tissues, play a crucial role in influencing various malignant behaviours of tumour cells and tumour immune evasion. As the research on macrophages and cancer immunotherapy develops, the importance of appropriate research models becomes increasingly evident. The development of organoids has bridged the gap between traditional two-dimensional (2D) cultures and animal experiments. Recent studies have demonstrated that organoids exhibit similar physiological characteristics to the source tissue and closely resemble the in vivo genome and molecular markers of the source tissue or organ. However, organoids still lack an immune component. Developing a co-culture model of organoids and macrophages is crucial for studying the interaction and mechanisms between tumour cells and macrophages. This paper presents an overview of the establishment of co-culture models, the current research status of organoid macrophage interactions, and the current status of immunotherapy. In addition, the application prospects and shortcomings of the model are explained. Ultimately, it is hoped that the co-culture model will offer a preclinical testing platform for maximising a precise cancer immunotherapy strategy.

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.

Fabrication of k-Carrageenan/Alginate/Carboxymethyl Cellulose basedScaffolds via 3D Printing for Potential Biomedical Applications

Three-dimensional (3D) printing technology was able to generate great attention because of its unique methodology and for its major potential to manufacture detailed and customizable scaffolds in terms of size, shape and pore structure in fields like medicine, pharmaceutics and food. This study aims to fabricate an ink entirely composed of natural polymers, alginate, k-carrageenan and carboxymethyl cellulose (AkCMC). Extrusion-based 3D printing was used to obtain scaffolds based on a crosslinked interpenetrating polymer network from the alginate, k-carrageenan, carboxymethyl cellulose and glutaraldehide formulation using CaCl2, KCl and glutaraldehyde in various concentrations of acetic acid. The stabile bonding of the crosslinked scaffolds was assessed using infrared spectroscopy (FT-IR) as well as swelling, degradation and mechanical investigations. Moreover, morphology analysis (µCT and SEM) confirmed the 3D printed samples' porous structure. In the AkCMC-GA objects crosslinked with the biggest acetic acid concentration, the values of pores and walls are the highest, at 3.9 × 10-2 µm-1. Additionally, this research proves the encapsulation of vitamin B1 via FT-IR and UV-Vis spectroscopy. The highest encapsulation efficiency of vitamin B1 was registered for the AkCMC-GA samples crosslinked with the maximum acetic acid concentration. The kinetic release of the vitamin was evaluated by UV-Vis spectroscopy. Based on the results of these experiments, 3D printed constructs using AkCMC-GA ink could be used for soft tissue engineering applications and also for vitamin B1 encapsulation.

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.

Recent trends in 3D bioprinting technology for skeletal muscle regeneration

Skeletal muscle is a pro-regenerative tissue, that utilizes a tissue-resident stem cell system to effect repair upon injury. Despite the demonstrated efficiency of this system in restoring muscle mass after many acute injuries, in conditions of severe trauma such as those evident in volumetric muscle loss (VML) (>20 % by mass), this self-repair capability is unable to restore tissue architecture, requiring interventions which currently are largely surgical. As a possible alternative, the generation of artificial muscle using tissue engineering approaches may also be of importance in the treatment of VML and muscle diseases such as dystrophies. Three-dimensional (3D) bioprinting has been identified as a promising technique for regeneration of the complex architecture of skeletal muscle. This review discusses existing treatment strategies following muscle damage, recent progress in bioprinting techniques, the bioinks used for muscle regeneration, the immunogenicity of scaffold materials, and in vitro and in vivo maturation techniques for 3D bio-printed muscle constructs. The pros and cons of these bioink formulations are also highlighted. Finally, we present the current limitations and challenges in the field and critical factors to consider for bioprinting approaches to become more translationa and to produce clinically relevant engineered muscle. STATEMENT OF SIGNIFICANCE: This review discusses the physiopathology of muscle injuries and existing clinical treatment strategies for muscle damage, the types of bioprinting techniques that have been applied to bioprinting of muscle, and the bioinks commonly used for muscle regeneration. The pros and cons of these bioinks are highlighted. We present a discussion of existing gaps in the literature and critical factors to consider for the translation of bioprinting approaches and to produce clinically relevant engineered muscle. Finally, we provide insights into what we believe will be the next steps required before the realization of the application of tissue-engineered muscle in humans. We believe this manuscript is an insightful, timely, and instructive review that will guide future muscle bioprinting research from a fundamental construct creation approach, down a translational pathway to achieve the desired impact in the clinic.

Design approaches for 3D cell culture and 3D bioprinting platforms

The natural habitat of most cells consists of complex and disordered 3D microenvironments with spatiotemporally dynamic material properties. However, prevalent methods of in vitro culture study cells under poorly biomimetic 2D confinement or homogeneous conditions that often neglect critical topographical cues and mechanical stimuli. It has also become increasingly apparent that cells in a 3D conformation exhibit dramatically altered morphological and phenotypical states. In response, efforts toward designing biomaterial platforms for 3D cell culture have taken centerstage over the past few decades. Herein, we present a broad overview of biomaterials for 3D cell culture and 3D bioprinting, spanning both monolithic and granular systems. We first critically evaluate conventional monolithic hydrogel networks, with an emphasis on specific experimental requirements. Building on this, we document the recent emergence of microgel-based 3D growth media as a promising biomaterial platform enabling interrogation of cells within porous and granular scaffolds. We also explore how jammed microgel systems have been leveraged to spatially design and manipulate cellular structures using 3D bioprinting. The advent of these techniques heralds an unprecedented ability to experimentally model complex physiological niches, with important implications for tissue bioengineering and biomedical applications.

3D bioprinting of liver models: A systematic scoping review of methods, bioinks, and reporting quality

Background

Effective communication is crucial for broad acceptance and applicability of alternative methods in 3R biomedical research and preclinical testing. 3D bioprinting is used to construct intricate biological structures towards functional liver models, specifically engineered for deployment as alternative models in drug screening, toxicological investigations, and tissue engineering. Despite a growing number of reviews in this emerging field, a comprehensive study, systematically assessing practices and reporting quality for bioprinted liver models is missing.

Methods

In this systematic scoping review we systematically searched MEDLINE (Ovid), EMBASE (Ovid) and BioRxiv for studies published prior to June 2nd, 2022. We extracted data on methodological conduct, applied bioinks, the composition of the printed model, performed experiments and model applications. Records were screened for eligibility and data were extracted from included articles by two independent reviewers from a panel of seven domain experts specializing in bioprinting and liver biology. We used RAYYAN for the screening process and SyRF for data extraction. We used R for data analysis, and R and Graphpad PRISM for visualization.

Results

Through our systematic database search we identified 1042 records, from which 63 met the eligibility criteria for inclusion in this systematic scoping review. Our findings revealed that extrusion-based printing, in conjunction with bioinks composed of natural components, emerged as the predominant printing technique in the bioprinting of liver models. Notably, the HepG2 hepatoma cell line was the most frequently employed liver cell type, despite acknowledged limitations. Furthermore, 51% of the printed models featured co-cultures with non-parenchymal cells to enhance their complexity. The included studies offered a variety of techniques for characterizing these liver models, with their primary application predominantly focused on toxicity testing. Among the frequently analyzed liver markers, albumin and urea stood out. Additionally, Cytochrome P450 (CYP) isoforms, primarily CYP3A and CYP1A, were assessed, and select studies employed nuclear receptor agonists to induce CYP activity.

Conclusion

Our systematic scoping review offers an evidence-based overview and evaluation of the current state of research on bioprinted liver models, representing a promising and innovative technology for creating alternative organ models. We conducted a thorough examination of both the methodological and technical facets of model development and scrutinized the reporting quality within the realm of bioprinted liver models. This systematic scoping review can serve as a valuable template for systematically evaluating the progress of organ model development in various other domains. The transparently derived evidence presented here can provide essential support to the research community, facilitating the adaptation of technological advancements, the establishment of standards, and the enhancement of model robustness. This is particularly crucial as we work toward the long-term objective of establishing new approach methods as reliable alternatives to animal testing, with extensive and versatile applications.

Cellular therapies for bone repair: current insights

Mesenchymal stem cells are core to bone homeostasis and repair. They both provide the progenitor cells from which bone cells are formed and regulate the local cytokine environment to create a pro-osteogenic environment. Dysregulation of these cells is often seen in orthopaedic pathology and can be manipulated by the physician treating the patient. This narrative review aims to describe the common applications of cell therapies to bone healing whilst also suggesting the future direction of these techniques.

Three-Dimensional Bioprinting of GelMA Hydrogels with Culture Medium: Balancing Printability, Rheology and Cell Viability for Tissue Regeneration

Three-dimensional extrusion bioprinting technology aims to become a fundamental tool for tissue regeneration using cell-loaded hydrogels. These biomaterials must have highly specific mechanical and biological properties that allow them to generate biosimilar structures by successive layering of material while maintaining cell viability. The rheological properties of hydrogels used as bioinks are critical to their printability. Correct printability of hydrogels allows the replication of biomimetic structures, which are of great use in medicine, tissue engineering and other fields of study that require the three-dimensional replication of different tissues. When bioprinting cell-loaded hydrogels, a small amount of culture medium can be added to ensure adequate survival, which can modify the rheological properties of the hydrogels. GelMA is a hydrogel used in bioprinting, with very interesting properties and rheological parameters that have been studied and defined for its basic formulation. However, the changes that occur in its rheological parameters and therefore in its printability, when it is mixed with the culture medium necessary to house the cells inside, are unknown. Therefore, in this work, a comparative study of GelMA 100% and GelMA in the proportions 3:1 (GelMA 75%) and 1:1 (GelMA 50%) with culture medium was carried out to determine the printability of the gel (using a device of our own invention), its main rheological parameters and its toxicity after the addition of the medium and to observe whether significant differences in cell viability occur. This raises the possibility of its use in regenerative medicine using a 3D extrusion bioprinter.

A 3D In-vitro model of the human dentine interface shows long-range osteoinduction from the dentine surface

Emerging regenerative cell therapies for alveolar bone loss have begun to explore the use of cell laden hydrogels for minimally invasive surgery to treat small and spatially complex maxilla-oral defects. However, the oral cavity presents a unique and challenging environment for in vivo bone tissue engineering, exhibiting both hard and soft periodontal tissue as well as acting as key biocenosis for many distinct microbial communities that interact with both the external environment and internal body systems, which will impact on cell fate and subsequent treatment efficacy. Herein, we design and bioprint a facile 3D in vitro model of a human dentine interface to probe the effect of the dentine surface on human mesenchymal stem cells (hMSCs) encapsulated in a microporous hydrogel bioink. We demonstrate that the dentine substrate induces osteogenic differentiation of encapsulated hMSCs, and that both dentine and β-tricalcium phosphate substrates stimulate extracellular matrix production and maturation at the gel-media interface, which is distal to the gel-substrate interface. Our findings demonstrate the potential for long-range effects on stem cells by mineralized surfaces during bone tissue engineering and provide a framework for the rapid development of 3D dentine-bone interface models.

Silk fibroin-based inks for in situ 3D printing using a double crosslinking process

The shortage of tissues and organs for transplantation is an urgent clinical concern. In situ 3D printing is an advanced 3D printing technique aimed at printing the new tissue or organ directly in the patient. The ink for this process is central to the outcomes, and must meet specific requirements such as rapid gelation, shape integrity, stability over time, and adhesion to surrounding healthy tissues. Among natural materials, silk fibroin exhibits fascinating properties that have made it widely studied in tissue engineering and regenerative medicine. However, further improvements in silk fibroin inks are needed to match the requirements for in situ 3D printing. In the present study, silk fibroin-based inks were developed for in situ applications by exploiting covalent crosslinking process consisting of a pre-photo-crosslinking prior to printing and in situ enzymatic crosslinking. Two different silk fibroin molecular weights were characterized and the synergistic effect of the covalent bonds with shear forces enhanced the shift in silk secondary structure toward β-sheets, thus, rapid stabilization. These hydrogels exhibited good mechanical properties, stability over time, and resistance to enzymatic degradation over 14 days, with no significant changes over time in their secondary structure and swelling behavior. Additionally, adhesion to tissues in vitro was demonstrated.

A review of biomacromolecule-based 3D bioprinting strategies for structure-function integrated repair of skin tissues

When skin is damaged or affected by diseases, it often undergoes irreversible scar formation, leading to aesthetic concerns and psychological distress for patients. In cases of extensive skin defects, the patient's life can be severely compromised. In recent years, 3D printing technology has emerged as a groundbreaking approach to skin tissue engineering, offering promising solutions to various skin-related conditions. 3D bioprinting technology enables the precise fabrication of structures by programming the spatial arrangement of cells within the skin tissue and subsequently printing skin replacements either in a 3D bioprinter or directly at the site of the defect. This study provides a comprehensive overview of various biopolymer-based inks, with a particular emphasis on chitosan (CS), starch, alginate, agarose, cellulose, and fibronectin, all of which are natural polymers belonging to the category of biomacromolecules. Additionally, it summarizes artificially synthesized polymers capable of enhancing the performance of these biomacromolecule-based bioinks, thereby composing hybrid biopolymer inks aimed at better application in skin tissue engineering endeavors. This review paper examines the recent advancements, characteristics, benefits, and limitations of biological 3D bioprinting techniques for skin tissue engineering. By utilizing bioinks containing seed cells, hydrogels with bioactive factors, and biomaterials, complex structures resembling natural skin can be accurately fabricated in a layer-by-layer manner. The importance of biological scaffolds in promoting skin wound healing and the role of 3D bioprinting in skin tissue regeneration processes is discussed. Additionally, this paper addresses the challenges and constraints associated with current 3D bioprinting technologies for skin tissue and presents future perspectives. These include advancements in bioink formulations, full-thickness skin bioprinting, vascularization strategies, and skin appendages bioprinting.

Human mesenchymal stromal cells-laden crosslinked hyaluronic acid-alginate bioink for 3D bioprinting applications in tissue engineering

Three-dimensional (3D) bioprinting is considered one of the most advanced tools to build up materials for tissue engineering. The aim of this work was the design, development and characterization of a bioink composed of human mesenchymal stromal cells (hMSC) for extrusion through nozzles to create these 3D structures that might potentially be apply to replace the function of damaged natural tissue. In this study, we focused on the advantages and the wide potential of biocompatible biomaterials, such as hyaluronic acid and alginate for the inclusion of hMSC. The bioink was characterized for its physical (pH, osmolality, degradation, swelling, porosity, surface electrical properties, conductivity, and surface structure), mechanical (rheology and printability) and biological (viability and proliferation) properties. The developed bioink showed high porosity and high swelling capacity, while the degradation rate was dependent on the temperature. The bioink also showed negative electrical surface and appropriate rheological properties required for bioprinting. Moreover, stress-stability studies did not show any sign of physical instability. The developed bioink provided an excellent environment for the promotion of the viability and growth of hMSC cells. Our work reports the first-time study of the effect of storage temperature on the cell viability of bioinks, besides showing that our bioink promoted a high cell viability after being extruded by the bioprinter. These results support the suggestion that the developed hMSC-composed bioink fulfills all the requirements for tissue engineering and can be proposed as a biological tool with potential applications in regenerative medicine and tissue engineering.

Computational Fluid Dynamics Analysis and Empirical Evaluation of Carboxymethylcellulose/Alginate 3D Bioprinting Inks for Screw-Based Microextrusion

Three-dimensional microextrusion bioprinting technology uses pneumatics, pistons, or screws to transfer and extrude bioinks containing biomaterials and cells to print biological tissues and organs. Computational fluid dynamics (CFD) analysis can simulate the flow characteristics of bioinks in a control volume, and the effect on cell viability can be predicted by calculating the physical quantities. In this study, we developed an analysis system to predict the effect of a screw-based dispenser system (SDS) on cell viability in bioinks through rheological and CFD analyses. Furthermore, carboxymethylcellulose/alginate-based bioinks were used for the empirical evaluation of high-viscous bioinks. The viscosity of bioinks was determined by rheological measurement, and the viscosity coefficient for the CFD analysis was derived from a correlation equation by non-linear regression analysis. The mass flow rate derived from the analysis was successfully validated by comparison with that from the empirical evaluation. Finally, the cell viability was confirmed after bioprinting with bioinks containing C2C12 cells, suggesting that the developed SDS may be suitable for application in the field of bioengineering. Consequently, the developed bioink analysis system is applicable to a wide range of systems and materials, contributing to time and cost savings in the bioengineering industry.

In Situ Bioprinting: Process, Bioinks, and Applications

Traditional tissue engineering methods face challenges, such as fabrication, implantation of irregularly shaped scaffolds, and limited accessibility for immediate healthcare providers. In situ bioprinting, an alternate strategy, involves direct deposition of biomaterials, cells, and bioactive factors at the site, facilitating on-site fabrication of intricate tissue, which can offer a patient-specific personalized approach and align with the principles of precision medicine. It can be applied using a handled device and robotic arms to various tissues, including skin, bone, cartilage, muscle, and composite tissues. Bioinks, the critical components of bioprinting that support cell viability and tissue development, play a crucial role in the success of in situ bioprinting. This review discusses in situ bioprinting techniques, the materials used for bioinks, and their critical properties for successful applications. Finally, we discuss the challenges and future trends in accelerating in situ printing to translate this technology in a clinical settings for personalized regenerative medicine.

Contribution of the ELRs to the development of advanced in vitro models

Developing in vitro models that accurately mimic the microenvironment of biological structures or processes holds substantial promise for gaining insights into specific biological functions. In the field of tissue engineering and regenerative medicine, in vitro models able to capture the precise structural, topographical, and functional complexity of living tissues, prove to be valuable tools for comprehending disease mechanisms, assessing drug responses, and serving as alternatives or complements to animal testing. The choice of the right biomaterial and fabrication technique for the development of these in vitro models plays an important role in their functionality. In this sense, elastin-like recombinamers (ELRs) have emerged as an important tool for the fabrication of in vitro models overcoming the challenges encountered in natural and synthetic materials due to their intrinsic properties, such as phase transition behavior, tunable biological properties, viscoelasticity, and easy processability. In this review article, we will delve into the use of ELRs for molecular models of intrinsically disordered proteins (IDPs), as well as for the development of in vitro 3D models for regenerative medicine. The easy processability of the ELRs and their rational design has allowed their use for the development of spheroids and organoids, or bioinks for 3D bioprinting. Thus, incorporating ELRs into the toolkit of biomaterials used for the fabrication of in vitro models, represents a transformative step forward in improving the accuracy, efficiency, and functionality of these models, and opening up a wide range of possibilities in combination with advanced biofabrication techniques that remains to be explored.

The Evolution of Technology-Driven In Vitro Models for Neurodegenerative Diseases

The alteration in the neural circuits of both central and peripheral nervous systems is closely related to the onset of neurodegenerative disorders (NDDs). Despite significant research efforts, the knowledge regarding NDD pathological processes, and the development of efficacious drugs are still limited due to the inability to access and reproduce the components of the nervous system and its intricate microenvironment. 2D culture systems are too simplistic to accurately represent the more complex and dynamic situation of cells in vivo and have therefore been surpassed by 3D systems. However, both models suffer from various limitations that can be overcome by employing two innovative technologies: organ-on-chip and 3D printing. In this review, an overview of the advantages and shortcomings of both microfluidic platforms and extracellular matrix-like biomaterials will be given. Then, the combination of microfluidics and hydrogels as a new synergistic approach to study neural disorders by analyzing the latest advances in 3D brain-on-chip for neurodegenerative research will be explored.

3D printed arrowroot starch-gellan scaffolds for wound healing applications

Skin, the largest organ in the body, blocks the entry of environmental pollutants into the system. Any injury to this organ allows infections and other harmful substances into the body. 3D bioprinting, a state-of-the-art technique, is suitable for fabricating cell culture scaffolds to heal chronic wounds rapidly. This study uses starch extracted from Maranta arundinacea (Arrowroot plant) (AS) and gellan gum (GG) to develop a bioink for 3D printing a scaffold capable of hosting animal cells. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction analysis (XRD) prove that the isolated AS is analogous to commercial starch. The cell culture scaffolds developed are superior to the existing monolayer culture. Infrared microscopy shows the AS-GG interaction and elucidates the mechanism of hydrogel formation. The physicochemical properties of the 3D-printed scaffold are analyzed to check the cell adhesion and growth; SEM images have confirmed that the AS-GG printed scaffold can support cell growth and proliferation, and the MTT assay shows good cell viability. Cell behavioral and migration studies reveal that cells are healthy. Since the scaffold is biocompatible, it can be 3D printed to any shape and structure and will biodegrade in the requisite time.

Plant-derived exosomes: a green approach for cancer drug delivery

Plant-derived exosomes (PDEs) are natural extracellular vesicles (EVs). In the current decade, they have been highlighted for cancer therapeutic development. Cancer is a global health crisis and it requires an effective, affordable, and less side effect-based treatment. Emerging research based on PDEs suggests that they have immense potential to be considered as a therapeutic option. Research evidences indicate that PDEs' internal molecular cargos show impressive cancer prevention activity with less toxicity. PDEs-based drug delivery systems overcome several limitations of traditional drug delivery tools. Extraction of PDEs from plant sources employ diverse methodologies, encompassing ultracentrifugation, immunoaffinity, size-based isolation, and precipitation, each with distinct advantages and limitations. The core constituents of PDEs comprise of lipids, proteins, DNA, and RNA. Worldwide, a few clinical trials on plant-derived exosomes are underway, and regulatory affairs for their use as therapeutic agents are still not understood with clarity. This review aims to comprehensively analyze the current state of research on plant-derived exosomes as a promising avenue for drug delivery, highlighting anticancer activity, challenges, and future orientation in effective cancer therapeutic development.

In situ polymer gelation in confined flow controls intermittent dynamics

Polymer flows through pores, nozzles and other small channels govern engineered and naturally occurring dynamics in many processes, from 3D printing to oil recovery in the earth's subsurface to a wide variety of biological flows. The crosslinking of polymers can change their material properties dramatically, and it is advantageous to know a priori whether or not crosslinking polymers will lead to clogged channels or cessation of flow. In this study, we investigate the flow of a common biopolymer, alginate, while it undergoes crosslinking by the addition of a crosslinker, calcium, driven through a microfluidic channel at constant flow rate. We map the boundaries defining complete clogging and flow as a function of flow rate, polymer concentration, and crosslinker concentration. Interestingly, the boundaries of the dynamic behavior qualitatively match the thermodynamic jamming phase diagram of attractive colloidal particles. That is, polymer clogging occurs in a region analogous to colloids in a jammed state, while the polymer flows in regions corresponding to colloids in a liquid phase. However, between the dynamic regimes of complete clogging and unrestricted flow, we observe a remarkable phenomenon in which the crosslinked polymer intermittently clogs the channel. This pattern of deposition and removal of a crosslinked gel is simultaneously highly reproducible, long-lasting, and controllable by system parameters. Higher concentrations of polymer and cross-linker result in more frequent ablation, while gels formed at lower component concentrations ablate less frequently. Upon ablation, the eluted gel maintains its shape, resulting in micro-rods several hundred microns long. Our results suggest both rich dynamics of intermittent flows in crosslinking polymers and the ability to control them.

Dynamics of Nanocomposite Hydrogel Alignment during 3D Printing to Develop Tissue Engineering Technology

Taking inspiration from spider silk protein spinning, we developed a method to produce tough filaments using extrusion-based 3D bioprinting and salting-out of the protein. To enhance both stiffness and ductility, we have designed a blend of partially crystalline, thermally sensitive natural polymer gelatin and viscoelastic G-polymer networks, mimicking the components of spider silk. Additionally, we have incorporated inorganic nanoparticles as a rheological modifier to fine-tune the 3D printing properties. This self-healing nanocomposite hydrogel exhibits exceptional mechanical properties, biocompatibility, shear thinning behavior, and a well-controlled gelation mechanism for 3D printing.

Xeno-Free 3D Bioprinted Liver Model for Hepatotoxicity Assessment

Three-dimensional (3D) bioprinting is one of the most promising methodologies that are currently in development for the replacement of animal experiments. Bioprinting and most alternative technologies rely on animal-derived materials, which compromises the intent of animal welfare and results in the generation of chimeric systems of limited value. The current study therefore presents the first bioprinted liver model that is entirely void of animal-derived constituents. Initially, HuH-7 cells underwent adaptation to a chemically defined medium (CDM). The adapted cells exhibited high survival rates (85-92%) after cryopreservation in chemically defined freezing media, comparable to those preserved in standard medium (86-92%). Xeno-free bioink for 3D bioprinting yielded liver models with high relative cell viability (97-101%), akin to a Matrigel-based liver model (83-102%) after 15 days of culture. The established xeno-free model was used for toxicity testing of a marine biotoxin, okadaic acid (OA). In 2D culture, OA toxicity was virtually identical for cells cultured under standard conditions and in CDM. In the xeno-free bioprinted liver model, 3-fold higher concentrations of OA than in the respective monolayer culture were needed to induce cytotoxicity. In conclusion, this study describes for the first time the development of a xeno-free 3D bioprinted liver model and its applicability for research purposes.

Rapid Volumetric Additive Manufacturing in Solid State: A Demonstration to Produce Water-Content-Dependent Cooling/Heating/Water-Responsive Shape Memory Hydrogels

In this study, we demonstrate the feasibility of rapid volumetric additive manufacturing in the solid state. This additive manufacturing technology is particularly useful in outer space missions (microgravity) and/or for harsh environment (e.g., on ships and vehicles during maneuvering, or on airplanes during flight). A special thermal gel is applied here to demonstrate the concept, that is, ultraviolet crosslinking in the solid state. The produced hydrogels are characterized and the water-content-dependent heating/cooling/water-responsive shape memory effect is revealed. Here, the shape memory feature is required to eliminate the deformation induced in the process of removing the uncrosslinked part from the crosslinked part in the last step of this additive manufacturing process.

Optical absorbance profilometry for tracking time-resolved particle redistribution in high volume fraction colloidal droplets

The distribution of components within colloidal suspensions is important in many complex biological and industrial fluids. A convenient method of measuring such distributions in low-volume-fraction suspensions is that of optical absorbance. Here we introduce a time-dependent validity criterion allowing extended use of optical absorbance to track colloidal distribution in high volume fraction suspensions. We define our validity criterion and show its use on a range of volume fractions from 15 to 55%, and also on larger micron sized particles, common for biological cells. Within the validity criterion, we establish the evaporative time duration in which the material's intrinsic coefficient of extinction can be treated as constant. This method enables rapid, low-cost, time-based study of the advective flow of suspended particulates, enabling advection to be straightforwardly measured from digital imaging. The residue profile predicted using our method in two test systems is compared with conventional laser profilometry measurements of the final evaporated residue, with good agreement at most radial positions.

Urethral Microenvironment Adapted Sodium Alginate/Gelatin/Reduced Graphene Oxide Biomimetic Patch Improves Scarless Urethral Regeneration

The nasty urine microenvironment (UME) is an inherent obstacle that hinders urethral repair due to fibrosis and swelling of the oftentimes adopted hydrogel-based biomaterials. Here, using reduced graphene oxide (rGO) along with double-freeze-drying to strengthen a 3D-printed patch is reported to realize scarless urethral repair. The sodium alginate/gelatin/reduced graphene oxide (SA/Gel/rGO) biomaterial features tunable stiffness, degradation profile, and anti-fibrosis performance. Interestingly, the 3D-printed alginate-containing composite scaffold is able to respond to Ca2+ present in the urine, leading to enhanced structural stability and strength as well as inhibiting swelling. The investigations present that the swelling behaviors, mechanical properties, and anti-fibrosis efficacy of the SA/Gel/rGO patch can be modulated by varying the concentration of rGO. In particular, rGO in optimal concentration shows excellent cell viability, migration, and proliferation. In-depth mechanistic studies reveal that the activation of cell proliferation and angiogenesis-related proteins, along with inhibition of fibrosis-related gene expressions, play an important role in scarless repair by the 3D-printed SA/Gel/rGO patch via promoting urothelium growth, accelerating angiogenesis, and minimizing fibrosis in vivo. The proposed strategy has the potential of resolving the dilemma of necessary biomaterial stiffness and unwanted fibrosis in urethral repair.

Polysaccharide-based hydrogels for medical devices, implants and tissue engineering: A review

Hydrogels are highly biocompatible biomaterials composed of crosslinked three-dimensional networks of hydrophilic polymers. Owing to their natural origin, polysaccharide-based hydrogels (PBHs) possess low toxicity, high biocompatibility and demonstrate in vivo biodegradability, making them great candidates for use in various biomedical devices, implants, and tissue engineering. In addition, many polysaccharides also show additional biological activities such as antimicrobial, anticoagulant, antioxidant, immunomodulatory, hemostatic, and anti-inflammatory, which can provide additional therapeutic benefits. The porous nature of PBHs allows for the immobilization of antibodies, aptamers, enzymes and other molecules on their surface, or within their matrix, potentiating their use in biosensor devices. Specific polysaccharides can be used to produce transparent hydrogels, which have been used widely to fabricate ocular implants. The ability of PBHs to encapsulate drugs and other actives has been utilized for making neural implants and coatings for cardiovascular devices (stents, pacemakers and venous catheters) and urinary catheters. Their high water-absorption capacity has been exploited to make superabsorbent diapers and sanitary napkins. The barrier property and mechanical strength of PBHs has been used to develop gels and films as anti-adhesive formulations for the prevention of post-operative adhesion. Finally, by virtue of their ability to mimic various body tissues, they have been explored as scaffolds and bio-inks for tissue engineering of a wide variety of organs. These applications have been described in detail, in this review.

Photocuring 3D printing technology as an advanced tool for promoting angiogenesis in hypoxia-related diseases

Three-dimensional (3D) bioprinting has emerged as a promising strategy for fabricating complex tissue analogs with intricate architectures, such as vascular networks. Achieving this necessitates bioink formulations that possess highly printable properties and provide a cell-friendly microenvironment mimicking the native extracellular matrix. Rapid advancements in printing techniques continue to expand the capabilities of researchers, enabling them to overcome existing biological barriers. This review offers a comprehensive examination of ultraviolet-based 3D bioprinting, renowned for its exceptional precision compared to other techniques, and explores its applications in inducing angiogenesis across diverse tissue models related to hypoxia. The high-precision and rapid photocuring capabilities of 3D bioprinting are essential for accurately replicating the intricate complexity of vascular networks and extending the diffusion limits for nutrients and gases. Addressing the lack of vascular structure is crucial in hypoxia-related diseases, as it can significantly improve oxygen delivery and overall tissue health. Consequently, high-resolution 3D bioprinting facilitates the creation of vascular structures within three-dimensional engineered tissues, offering a potential solution for addressing hypoxia-related diseases. Emphasis is placed on fundamental components essential for successful 3D bioprinting, including cell types, bioink compositions, and growth factors highlighted in recent studies. The insights provided in this review underscore the promising prospects of leveraging 3D printing technologies for addressing hypoxia-related diseases through the stimulation of angiogenesis, complementing the therapeutic efficacy of cell therapy.

Three Dimensional Bioprinting for Hepatic Tissue Engineering: From In Vitro Models to Clinical Applications

Fabrication of functional organs is the holy grail of tissue engineering and the possibilities of repairing a partial or complete liver to treat chronic liver disorders are discussed in this review. Liver is the largest gland in the human body and plays a responsible role in majority of metabolic function and processes. Chronic liver disease is one of the leading causes of death globally and the current treatment strategy of organ transplantation holds its own demerits. Hence there is a need to develop an in vitro liver model that mimics the native microenvironment. The developed model should be a reliable to understand the pathogenesis, screen drugs and assist to repair and replace the damaged liver. The three-dimensional bioprinting is a promising technology that recreates in vivo alike in vitro model for transplantation, which is the goal of tissue engineers. The technology has great potential due to its precise control and its ability to homogeneously distribute cells on all layers in a complex structure. This review gives an overview of liver tissue engineering with a special focus on 3D bioprinting and bioinks for liver disease modelling and drug screening.

Three dimensional printed biofilms: Fabrication, design and future biomedical and environmental applications

Three dimensional printing has emerged as a widely acceptable strategy for the fabrication of mammalian cell laden constructs with complex microenvironments for tissue engineering and regenerative medicine. More recently 3D printed living materials containing microorganisms have been developed and matured into living biofilms. The potential for engineered 3D biofilms as in vitro models for biomedical applications, such as antimicrobial susceptibility testing, and environmental applications, such as bioleaching, bioremediation, and wastewater purification, is extensive but the need for an in-depth understanding of the structure-function relationship between the complex construct and the microorganism response still exists. This review discusses 3D printing fabrication methods for engineered biofilms with specific structural features. Next, it highlights the importance of bioink compositions and 3D bioarchitecture design. Finally, a brief overview of current and potential applications of 3D printed biofilms in environmental and biomedical fields is discussed.

Decellularized extracellular matrix and silk fibroin-based hybrid biomaterials: A comprehensive review on fabrication techniques and tissue-specific applications

Biomaterials play a fundamental role in tissue engineering by providing biochemical and physical cues that influence cellular fate and matrix development. Decellularized extracellular matrix (dECM) as a biomaterial is distinguished by its abundant composition of matrix proteins, such as collagen, elastin, fibronectin, and laminin, as well as glycosaminoglycans and proteoglycans. However, the mechanical properties of only dECM-based constructs may not always meet tissue-specific requirements. Recent advancements address this challenge by utilizing hybrid biomaterials that harness the strengths of silk fibroin (SF), which contributes the necessary mechanical properties, while dECM provides essential cellular cues for in vitro studies and tissue regeneration. This review discusses emerging trends in developing such biopolymer blends, aiming to synergistically combine the advantages of SF and dECM through optimal concentrations and desired cross-linking density. We focus on different fabrication techniques and cross-linking methods that have been utilized to fabricate various tissue-engineered hybrid constructs. Furthermore, we survey recent applications of such biomaterials for the regeneration of various tissues, including bone, cartilage, trachea, bladder, vascular graft, heart, skin, liver, and other soft tissues. Finally, the trajectory and prospects of the constructs derived from this blend in the tissue engineering field have been summarized, highlighting their potential for clinical translation.

Exploring the Three-Dimensional Frontier: Advancements in MSC Spheroids and Their Implications for Breast Cancer and Personalized Regenerative Therapies

To more accurately replicate the in vivo three-dimensional (3D) mesenchymal stem cell (MSC) niche and enhance cellular phenotypes for superior in vivo treatments, MSC functionalization through in vitro 3D culture approaches has gained attention. The organization of MSCs in 3D spheroids results in altered cell shape, cytoskeleton rearrangement, and polarization. Investigations have revealed that the survival and secretory capability of MSCs are positively impacted by moderate hypoxia within the inner zones of MSC spheroids. The spheroid hypoxic microenvironment enhances the production of angiogenic and anti-apoptotic molecules, including HGF, VEGF, and FGF-2. Furthermore, it upregulates the expression of hypoxia-adaptive molecules such as CXCL12 and HIF-1, inhibiting MSC death. The current review focuses on the latest developments in fundamental and translational research concerning three-dimensional MSC systems. This emphasis extends to the primary benefits and potential applications of MSC spheroids, particularly in the context of breast cancer and customized regenerative therapies.

Advanced 3D Printing Strategies for the Controlled Delivery of Growth Factors

The controlled delivery of growth factors (GFs) from tissue engineered constructs represents a promising strategy to improve tissue repair and regeneration. However, despite their established key role in tissue regeneration, the use of GFs is limited by their short half-life in the in vivo environment, their dose-dependent effectiveness, and their space- and time-dependent activity. Promising results have been obtained both in vitro and in vivo in animal models. Nevertheless, the clinical application of tissue engineered constructs releasing GFs is still challenging due to the several limitations and risks associated with their use. 3D printing and bioprinting, by allowing the microprecise spatial deposition of multiple materials and the fabrication of complex geometries with high resolution, offer advanced strategies for an optimal release of GFs from tissue engineered constructs. This review summarizes the strategies that have been employed to include GFs and their delivery system into biomaterials used for 3D printing applications to optimize their controlled release and to improve both the in vitro and in vivo regeneration processes. The approaches adopted to overcome the above-mentioned limitations are presented, showing the potential of the technology of 3D printing to get one step closer to clinical applications.

Synergistic coupling between 3D bioprinting and vascularization strategies

Three-dimensional (3D) bioprinting offers promising solutions to the complex challenge of vascularization in biofabrication, thereby enhancing the prospects for clinical translation of engineered tissues and organs. While existing reviews have touched upon 3D bioprinting in vascularized tissue contexts, the current review offers a more holistic perspective, encompassing recent technical advancements and spanning the entire multistage bioprinting process, with a particular emphasis on vascularization. The synergy between 3D bioprinting and vascularization strategies is crucial, as 3D bioprinting can enable the creation of personalized, tissue-specific vascular network while the vascularization enhances tissue viability and function. The review starts by providing a comprehensive overview of the entire bioprinting process, spanning from pre-bioprinting stages to post-printing processing, including perfusion and maturation. Next, recent advancements in vascularization strategies that can be seamlessly integrated with bioprinting are discussed. Further, tissue-specific examples illustrating how these vascularization approaches are customized for diverse anatomical tissues towards enhancing clinical relevance are discussed. Finally, the underexplored intraoperative bioprinting (IOB) was highlighted, which enables the direct reconstruction of tissues within defect sites, stressing on the possible synergy shaped by combining IOB with vascularization strategies for improved regeneration.

Mending a broken heart by biomimetic 3D printed natural biomaterial-based cardiac patches: a review

Myocardial infarction is one of the major causes of mortality as well as morbidity around the world. Currently available treatment options face a number of drawbacks, hence cardiac tissue engineering, which aims to bioengineer functional cardiac tissue, for application in tissue repair, patient specific drug screening and disease modeling, is being explored as a viable alternative. To achieve this, an appropriate combination of cells, biomimetic scaffolds mimicking the structure and function of the native tissue, and signals, is necessary. Among scaffold fabrication techniques, three-dimensional printing, which is an additive manufacturing technique that enables to translate computer-aided designs into 3D objects, has emerged as a promising technique to develop cardiac patches with a highly defined architecture. As a further step toward the replication of complex tissues, such as cardiac tissue, more recently 3D bioprinting has emerged as a cutting-edge technology to print not only biomaterials, but also multiple cell types simultaneously. In terms of bioinks, biomaterials isolated from natural sources are advantageous, as they can provide exceptional biocompatibility and bioactivity, thus promoting desired cell responses. An ideal biomimetic cardiac patch should incorporate additional functional properties, which can be achieved by means of appropriate functionalization strategies. These are essential to replicate the native tissue, such as the release of biochemical signals, immunomodulatory properties, conductivity, enhanced vascularization and shape memory effects. The aim of the review is to present an overview of the current state of the art regarding the development of biomimetic 3D printed natural biomaterial-based cardiac patches, describing the 3D printing fabrication methods, the natural-biomaterial based bioinks, the functionalization strategies, as well as the in vitro and in vivo applications.

Three-Dimensional Printer-Assisted Electrospinning for Fabricating Intricate Biological Tissue Mimics

Although regenerative medicine necessitates advanced three-dimensional (3D) scaffolds for organ and tissue applications, creating intricate structures across scales, from nano- to meso-like biological tissues, remains a challenge. Electrospinning of nanofibers offers promise due to its capacity to craft not only the dimensions and surfaces of individual fibers but also intricate attributes, such as anisotropy and porosity, across various materials. In this study, we used a 3D printer to design a mold with polylactic acid for gel modeling. This gel template, which was mounted on a metal wire, facilitated microfiber electrospinning. After spinning, these structures were treated with EDTA to remove the template and were then cleansed and dried, resulting in 3D microfibrous (3DMF) structures, with average fiber diameters of approximately 1 µm on the outer and inner surfaces. Notably, these structures matched their intended design dimensions without distortion or shrinkage, demonstrating the adaptability of this method for various template sizes. The cylindrical structures showed high elasticity and stretchability with an elastic modulus of 6.23 MPa. Furthermore, our method successfully mimicked complex biological tissue structures, such as the inner architecture of the voice box and the hollow partitioned structure of the heart's tricuspid valve. Achieving specific intricate shapes required multiple spinning sessions and subsequent assemblies. In essence, our approach holds potential for crafting artificial organs and forming the foundational materials for cell culture scaffolds, addressing the challenges of crafting intricate multiscale structures.

Enhancement of properties of a cell-laden GelMA hydrogel-based bioink via calcium phosphate phase transition

To improve the properties of the hydrogel-based bioinks, a calcium phosphate phase transition was applied, and the products were examined. We successfully enhanced the mechanical properties of the hydrogels by adding small amounts (< 0.5 wt%) of alpha-tricalcium phosphate (α-TCP) to photo-crosslinkable gelatin methacrylate (GelMA). As a result of the hydrolyzing calcium phosphate phase transition involvingα-TCP, which proceeded for 36 h in the cell culture medium, calcium-deficient hydroxyapatite was produced. Approximately 18 times the compressive modulus was achieved for GelMA with 0.5 wt%α-TCP (20.96 kPa) compared with pure GelMA (1.18 kPa). Although cell proliferation decreased during the early stages of cultivation, both osteogenic differentiation and mineralization activities increased dramatically when the calcium phosphate phase transition was performed with 0.25 wt%α-TCP. The addition ofα-TCP improved the printability and fidelity of GelMA, as well as the structural stability and compressive modulus (approximately six times higher) after three weeks of culturing. Therefore, we anticipate that the application of calcium phosphate phase transition to hydrogels may have the potential for hard tissue regeneration.