Laser-induced Forward Transfer Hydrogel Printing: A Defined Route for Highly Controlled Process

Spheroids from Epithelial and Mesenchymal Cell Phenotypes as Building Blocks in Bioprinting (Review)

Most tissues and organs are based on cells of the epithelial and mesenchymal phenotypes. Epithelial cells build protective barriers, have a key role in absorption and secretion, and participate in metabolism. Characterized by high plasticity and ability to migrate, mesenchymal cells ensure structural support, promote tissue restoration and are important for matrix remodeling. Interaction between these two cell types is critical for maintaining the body integrity and functioning. Modern tissue engineering is aimed at creation of artificial tissues and organs that have the required cellular composition, mechanical properties and functional potential for medical usage. One of the most popular methods of tissue engineering is 3D bioprinting, which allows creating complex three-dimensional structures with specified characteristics. Recently, special attention has been paid to bioprinting with spheroids being three-dimensional cellular aggregates that can be used as building blocks for tissue-engineered structures. Due to numerous cell-to-cell contacts and accumulation of extracellular matrix, spheroids ensure conditions allowing to form anatomical tissues and organs. To optimize bioprinting conditions, one shall precisely understand the mechanical properties of spheroids, as they directly affect the ability of cells to migrate and fuse, and thus the rate of construct formation and its overall morphology. This review summarizes the available data on the differences in mechanical properties of epithelial and mesenchymal spheroids, examines methods for their co-culturing in various applications of regenerative medicine, as well as analyzes the peculiarities of their use in different bioprinting methods to obtain high-quality tissue constructs.

Integrating microfluidic and bioprinting technologies: advanced strategies for tissue vascularization

Tissue engineering offers immense potential for addressing the unmet needs in repairing tissue damage and organ failure. Vascularization, the development of intricate blood vessel networks, is crucial for the survival and functions of engineered tissues. Nevertheless, the persistent challenge of ensuring an ample nutrient supply within implanted tissues remains, primarily due to the inadequate formation of blood vessels. This issue underscores the vital role of the human vascular system in sustaining cellular functions, facilitating nutrient exchange, and removing metabolic waste products. In response to this challenge, new approaches have been explored. Microfluidic devices, emulating natural blood vessels, serve as valuable tools for investigating angiogenesis and allowing the formation of microvascular networks. In parallel, bioprinting technologies enable precise placement of cells and biomaterials, culminating in vascular structures that closely resemble the native vessels. To this end, the synergy of microfluidics and bioprinting has further opened up exciting possibilities in vascularization, encompassing innovations such as microfluidic bioprinting. These advancements hold great promise in regenerative medicine, facilitating the creation of functional tissues for applications ranging from transplantation to disease modeling and drug testing. This review explores the potentially transformative impact of microfluidic and bioprinting technologies on vascularization strategies within the scope of tissue engineering.

3D bioprinting approaches for enhancing stem cell-based neural tissue regeneration

Three-dimensional (3D) bioprinting holds immense promise for advancing stem cell research and developing novel therapeutic strategies in the field of neural tissue engineering and disease modeling. This paper critically analyzes recent breakthroughs in 3D bioprinting, specifically focusing on its application in these areas. We comprehensively explore the advantages and limitations of various 3D printing methods, the selection and formulation of bioink materials tailored for neural stem cells, and the incorporation of nanomaterials with dual functionality, enhancing the bioprinting process and promoting neurogenesis pathways. Furthermore, the paper reviews the diverse range of stem cells employed in neural bioprinting research, discussing their potential applications and associated challenges. We also introduce the emerging field of 4D bioprinting, highlighting current efforts to develop time-responsive constructs that improve the integration and functionality of bioprinted neural tissues. In short, this manuscript aims to provide a comprehensive understanding of this rapidly evolving field. It underscores the transformative potential of 3D and 4D bioprinting technologies in revolutionizing stem cell research and paving the way for novel therapeutic solutions for neurological disorders and injuries, ultimately contributing significantly to the advancement of regenerative medicine. STATEMENT OF SIGNIFICANCE: This comprehensive review critically examines the current bioprinting research landscape, highlighting efforts to overcome key limitations in printing technologies-improving cell viability post-printing, enhancing resolution, and optimizing cross-linking efficiencies. The continuous refinement of material compositions aims to control the spatiotemporal delivery of therapeutic agents, ensuring better integration of transplanted cells with host tissues. Specifically, the review focuses on groundbreaking advancements in neural tissue engineering. The development of next-generation bioinks, hydrogels, and scaffolds specifically designed for neural regeneration complexities holds the potential to revolutionize treatments for debilitating neural conditions, especially when nanotechnologies are being incorporated. This review offers the readers both a comprehensive analysis of current breakthroughs and an insightful perspective on the future trajectory of neural tissue engineering.

Dynamics of Blister Actuation in Laser-Induced Forward Transfer for Contactless Microchip Transfer

The rapid evolution of microelectronics and display technologies has driven the demand for advanced manufacturing techniques capable of precise, high-speed microchip transfer. As devices shrink in size and increase in complexity, scalable and contactless methods for microscale placement are essential. Laser-induced forward transfer (LIFT) has emerged as a transformative solution, offering the precision and adaptability required for next-generation applications such as micro-light-emitting diodes (μ-LEDs). This study optimizes the LIFT process for the precise transfer of silicon microchips designed to mimic μ-LEDs. Critical parameters, including laser energy density, laser pulse width, and dynamic release layer (DRL) thickness are systematically adjusted to ensure controlled blister formation, a key factor for successful material transfer. The DRL, a polyimide-based photoreactive layer, undergoes photothermal decomposition under 355 nm laser irradiation, creating localized pressure that propels microchips onto the receiver substrate in a contactless manner. Using advanced techniques such as three-dimensional profilometry, X-ray photoelectron spectroscopy, and ultrafast imaging, this study evaluates the rupture dynamics of the DRL and the velocity of microchips during transfer. Optimization of the DRL thickness to 1 µm and a transfer velocity of 20 m s⁻1 achieves a transfer yield of up to 97%, showcasing LIFT's potential in μ-LED manufacturing and semiconductor production.

Bioprinting of Cells, Organoids and Organs-on-a-Chip Together with Hydrogels Improves Structural and Mechanical Cues

The 3D bioprinting technique has made enormous progress in tissue engineering, regenerative medicine and research into diseases such as cancer. Apart from individual cells, a collection of cells, such as organoids, can be printed in combination with various hydrogels. It can be hypothesized that 3D bioprinting will even become a promising tool for mechanobiological analyses of cells, organoids and their matrix environments in highly defined and precisely structured 3D environments, in which the mechanical properties of the cell environment can be individually adjusted. Mechanical obstacles or bead markers can be integrated into bioprinted samples to analyze mechanical deformations and forces within these bioprinted constructs, such as 3D organoids, and to perform biophysical analysis in complex 3D systems, which are still not standard techniques. The review highlights the advances of 3D and 4D printing technologies in integrating mechanobiological cues so that the next step will be a detailed analysis of key future biophysical research directions in organoid generation for the development of disease model systems, tissue regeneration and drug testing from a biophysical perspective. Finally, the review highlights the combination of bioprinted hydrogels, such as pure natural or synthetic hydrogels and mixtures, with organoids, organoid-cell co-cultures, organ-on-a-chip systems and organoid-organ-on-a chip combinations and introduces the use of assembloids to determine the mutual interactions of different cell types and cell-matrix interferences in specific biological and mechanical environments.

Bioprinted research models of urological malignancy

Urological malignancy (UM) is among the leading threats to health care worldwide. Recent years have seen much investment in fundamental UM research, including mechanistic investigation, early diagnosis, immunotherapy, and nanomedicine. However, the results are not fully satisfactory. Bioprinted research models (BRMs) with programmed spatial structures and functions can serve as powerful research tools and are likely to disrupt traditional UM research paradigms. Herein, a comprehensive review of BRMs of UM is presented. It begins with a brief introduction and comparison of existing UM research models, emphasizing the advantages of BRMs, such as modeling real tissues and organs. Six kinds of mainstream bioprinting techniques used to fabricate such BRMs are summarized with examples. Thereafter, research advances in the applications of UM BRMs, such as culturing tumor spheroids and organoids, modeling cancer metastasis, mimicking the tumor microenvironment, constructing organ chips for drug screening, and isolating circulating tumor cells, are comprehensively discussed. At the end of this review, current challenges and future development directions of BRMs and UM are highlighted from the perspective of interdisciplinary science.

Towards single-cell bioprinting: micropatterning tools for organ-on-chip development

Organs-on-chips (OoCs) hold promise to engineer progressively more human-relevant in vitro models for pharmaceutical purposes. Recent developments have delivered increasingly sophisticated designs, yet OoCs still lack in reproducing the inner tissue physiology required to fully resemble the native human body. This review emphasizes the need to include microarchitectural and microstructural features, and discusses promising avenues to incorporate well-defined microarchitectures down to the single-cell level. We highlight how their integration will significantly contribute to the advancement of the field towards highly organized structural and hierarchical tissues-on-chip. We discuss the combination of state-of-the-art micropatterning technologies to achieve OoCs resembling human-intrinsic complexity. It is anticipated that these innovations will yield significant advances in realization of the next generation of OoC models.

The influence of viscosity of hydrogels on the spreading and migration of cells in 3D bioprinted skin cancer models

Various in vitro three-dimensional (3D) tissue culture models of human and diseased skin exist. Nevertheless, there is still room for the development and improvement of 3D bioprinted skin cancer models. The need for reproducible bioprinting methods, cell samples, biomaterial inks, and bioinks is becoming increasingly important. The influence of the viscosity of hydrogels on the spreading and migration of most types of cancer cells is well studied. There are however limited studies on the influence of viscosity on the spreading and migration of cells in 3D bioprinted skin cancer models. In this review, we will outline the importance of studying the various types of skin cancers by using 3D cell culture models. We will provide an overview of the advantages and disadvantages of the various 3D bioprinting technologies. We will emphasize how the viscosity of hydrogels relates to the spreading and migration of cancer cells. Lastly, we will give an overview of the specific studies on cell migration and spreading in 3D bioprinted skin cancer models.

Advanced 3D imaging and organoid bioprinting for biomedical research and therapeutic applications

Organoid cultures offer a valuable platform for studying organ-level biology, allowing for a closer mimicry of human physiology compared to traditional two-dimensional cell culture systems or non-primate animal models. While many organoid cultures use cell aggregates or decellularized extracellular matrices as scaffolds, they often lack precise biochemical and biophysical microenvironments. In contrast, three-dimensional (3D) bioprinting allows precise placement of organoids or spheroids, providing enhanced spatial control and facilitating the direct fusion for the formation of large-scale functional tissues in vitro. In addition, 3D bioprinting enables fine tuning of biochemical and biophysical cues to support organoid development and maturation. With advances in the organoid technology and its potential applications across diverse research fields such as cell biology, developmental biology, disease pathology, precision medicine, drug toxicology, and tissue engineering, organoid imaging has become a crucial aspect of physiological and pathological studies. This review highlights the recent advancements in imaging technologies that have significantly contributed to organoid research. Additionally, we discuss various bioprinting techniques, emphasizing their applications in organoid bioprinting. Integrating 3D imaging tools into a bioprinting platform allows real-time visualization while facilitating quality control, optimization, and comprehensive bioprinting assessment. Similarly, combining imaging technologies with organoid bioprinting can provide valuable insights into tissue formation, maturation, functions, and therapeutic responses. This approach not only improves the reproducibility of physiologically relevant tissues but also enhances understanding of complex biological processes. Thus, careful selection of bioprinting modalities, coupled with appropriate imaging techniques, holds the potential to create a versatile platform capable of addressing existing challenges and harnessing opportunities in these rapidly evolving fields.

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.

Laser-induced forward transfer based laser bioprinting in biomedical applications

Bioprinting is an emerging field that utilizes 3D printing technology to fabricate intricate biological structures, including tissues and organs. Among the various promising bioprinting techniques, laser-induced forward transfer (LIFT) stands out by employing a laser to precisely transfer cells or bioinks onto a substrate, enabling the creation of complex 3D architectures with characteristics of high printing precision, enhanced cell viability, and excellent technical adaptability. This technology has found extensive applications in the production of biomolecular microarrays and biological structures, demonstrating significant potential in tissue engineering. This review briefly introduces the experimental setup, bioink ejection mechanisms, and parameters relevant to LIFT bioprinting. Furthermore, it presents a detailed summary of both conventional and cutting-edge applications of LIFT in fabricating biomolecule microarrays and various tissues, such as skin, blood vessels and bone. Additionally, the review addresses the existing challenges in this field and provides corresponding suggestions. By contributing to the ongoing development of this field, this review aims to inspire further research on the utilization of LIFT-based bioprinting in biomedical applications.

Laser Bioprinting with Cell Spheroids: Accurate and Gentle

Laser printing with cell spheroids can become a promising approach in tissue engineering and regenerative medicine. However, the use of standard laser bioprinters for this purpose is not optimal as they are optimized for transferring smaller objects, such as cells and microorganisms. The use of standard laser systems and protocols for the transfer of cell spheroids leads either to their destruction or to a significant deterioration in the quality of bioprinting. The possibilities of cell spheroids printing by laser-induced forward transfer in a gentle mode, which ensures good cell survival ~80% without damage and burns, were demonstrated. The proposed method showed a high spatial resolution of laser printing of cell spheroid geometric structures at the level of 62 ± 33 µm, which is significantly less than the size of the cell spheroid itself. The experiments were performed on a laboratory laser bioprinter with a sterile zone, which was supplemented with a new optical part based on the Pi-Shaper element, which allows for forming laser spots with different non-Gaussian intensity distributions. It is shown that laser spots with an intensity distribution profile of the "Two rings" type (close to Π-shaped) and a size comparable to a spheroid are optimal. To select the operating parameters of laser exposure, spheroid phantoms made of a photocurable resin and spheroids made from human umbilical cord mesenchymal stromal cells were used.

Recent Developments of Silk-Based Scaffolds for Tissue Engineering and Regenerative Medicine Applications: A Special Focus on the Advancement of 3D Printing

Regenerative medicine has received potential attention around the globe, with improving cell performances, one of the necessary ideas for the advancements of regenerative medicine. It is crucial to enhance cell performances in the physiological system for drug release studies because the variation in cell environments between in vitro and in vivo develops a loop in drug estimation. On the other hand, tissue engineering is a potential path to integrate cells with scaffold biomaterials and produce growth factors to regenerate organs. Scaffold biomaterials are a prototype for tissue production and perform vital functions in tissue engineering. Silk fibroin is a natural fibrous polymer with significant usage in regenerative medicine because of the growing interest in leftovers for silk biomaterials in tissue engineering. Among various natural biopolymer-based biomaterials, silk fibroin-based biomaterials have attracted significant attention due to their outstanding mechanical properties, biocompatibility, hemocompatibility, and biodegradability for regenerative medicine and scaffold applications. This review article focused on highlighting the recent advancements of 3D printing in silk fibroin scaffold technologies for regenerative medicine and tissue engineering.

Laser-assisted bioprinting of microorganisms with hydrogel microdroplets: peculiarities of Ascomycota and Basidiomycota yeast transfer

Laser-assisted bioprinting of microbial cells by hydrogel microdroplets is a rapidly developing and promising field that can contribute to solving a number of issues in microbiology and biotechnology. To date, most research on the use of laser bioprinting for microorganism manipulation and sorting has focused on prokaryotes; the bioprinting of eukaryotic microorganisms is much less understood. The use of hydrogel allows solving two fundamental problems: creating comfortable environments for living microorganisms and imparting the necessary rheological properties of the gel for the stable transfer of microdroplets of a preset size. Two main problems were solved in this article. First, the parameters of the hydrogel based on hyaluronic acid and laser fluence to ensure stable transfer of single drops are selected. Second, possible differences in the bioprinting by hyaluronic acid hydrogel microdroplets with yeasts of various taxonomy (Ascomycota vs Basidiomycota), which form and do not form polysaccharide capsules and evaluated. We have performed laser induced forward transfer of 8 yeast species (Goffeauzyma gilvescens, Lipomyces lipofer, Lipomyces starkey, Pichia manshurica, Saitozyma podzolica, Schwanniomyces occidentalis var. occidentalis, Sterigmatosporidium polymorphum, Vanrija humicola) and assessed its viability based on colony formation on the nutrient medium. It is shown that after laser-induced transfer in hydrogel microdroplets the mean viability rate was 77% with some strains showing relatively high viability rates exceeding 90%. Effect of capsules presence on colony formation after laser bioprinting was not revealed. Differences in laser transfer of the yeast of various phyla were found-basidiomycetes formed a greater number of colonies than ascomycetes. The causes and mechanisms of these effects require detailed studies. The data obtained contributes to the knowledge about the bioprinting of eukaryotic microorganisms and can be useful in the studies of single microbial cells and inter-organism interactions.

Hybrid biomanufacturing systems applied in tissue regeneration

Scaffold-based approach is a developed strategy in biomanufacturing, which is based on the use of temporary scaffold that performs as a house of implanted cells for their attachment, proliferation, and differentiation. This strategy strongly depends on both materials and manufacturing processes. However, it is very difficult to meet all the requirements, such as biocompatibility, biodegradability, mechanical strength, and promotion of cell-adhesion, using only single material. At present, no single bioprinting technique can meet the requirements for tissue regeneration of all scales. Thus, multi-material and mixing-material scaffolds have been widely investigated. Challenges in terms of resolution, uniform cell distribution, and tissue formation are still the obstacles in the development of bioprinting technique. Hybrid bioprinting techniques have been developed to print scaffolds with improved properties in both mechanical and biological aspects for broad biomedical engineering applications. In this review, we introduce the basic multi-head bioprinters, semi-hybrid and fully-hybrid biomanufacturing systems, highlighting the modifications, the improved properties and the effect on the complex tissue regeneration applications.

A Review on Stimuli-Actuated 3D Micro/Nanostructures for Tissue Engineering and the Potential of Laser-Direct Writing via Two-Photon Polymerization for Structure Fabrication

In this review, we present the most recent and relevant research that has been done regarding the fabrication of 3D micro/nanostructures for tissue engineering applications. First, we make an overview of 3D micro/nanostructures that act as backbone constructs where the seeded cells can attach, proliferate and differentiate towards the formation of new tissue. Then, we describe the fabrication of 3D micro/nanostructures that are able to control the cellular processes leading to faster tissue regeneration, by actuation using topographical, mechanical, chemical, electric or magnetic stimuli. An in-depth analysis of the actuation of the 3D micro/nanostructures using each of the above-mentioned stimuli for controlling the behavior of the seeded cells is provided. For each type of stimulus, a particular recent application is presented and discussed, such as controlling the cell proliferation and avoiding the formation of a necrotic core (topographic stimulation), controlling the cell adhesion (nanostructuring), supporting the cell differentiation via nuclei deformation (mechanical stimulation), improving the osteogenesis (chemical and magnetic stimulation), controlled drug-delivery systems (electric stimulation) and fastening tissue formation (magnetic stimulation). The existing techniques used for the fabrication of such stimuli-actuated 3D micro/nanostructures, are briefly summarized. Special attention is dedicated to structures' fabrication using laser-assisted technologies. The performances of stimuli-actuated 3D micro/nanostructures fabricated by laser-direct writing via two-photon polymerization are particularly emphasized.

Theoretical and Experimental Assay of Shock Experienced by Yeast Cells during Laser Bioprinting

Laser-induced forward transfer (LIFT) is a useful technique for bioprinting using gel-embedded cells. However, little is known about the stresses experienced by cells during LIFT. This paper theoretically and experimentally explores the levels of laser pulse irradiation and pulsed heating experienced by yeast cells during LIFT. It has been found that only 5% of the cells in the gel layer adjacent to the absorbing Ti film should be significantly heated for fractions of microseconds, which was confirmed by the fact that a corresponding population of cells died during LIFT. This was accompanied by the near-complete dimming of intracellular green fluorescent protein, also observed in response to heat shock. It is shown that microorganisms in the gel layer experience laser irradiation with an energy density of ~0.1-6 J/cm2. This level of irradiation had no effect on yeast on its own. We conclude that in a wide range of laser fluences, bioprinting kills only a minority of the cell population. Importantly, we detected a previously unobserved change in membrane permeability in viable cells. Our data provide a wider perspective on the effects of LIFT-based bioprinting on living organisms and might provide new uses for the procedure based on its effects on cell permeability.

Laser Bioprinting of Cells Using UV and Visible Wavelengths: A Comparative DNA Damage Study

Laser-based techniques for printing cells onto different substrates with high precision and resolution present unique opportunities for contributing to a wide range of biomedical applications, including tissue engineering. In this study, laser-induced forward transfer (LIFT) printing was employed to rapidly and accurately deposit patterns of cancer cells in a non-contact manner, using two different wavelengths, 532 and 355 nm. To evaluate the effect of LIFT on the printed cells, their growth and DNA damage profiles were assessed and evaluated quantitatively over several days. The damaging effect of LIFT-printing was thoroughly investigated, for the first time at a single cell level, by counting individual double strand breaks (DSB). Overall, we found that LIFT was able to safely print patterns of breast cancer cells with high viability with little or no heat or shear damage to the cells, as indicated by unperturbed growth and negligible gross DNA damage.

Improving printability of hydrogel-based bio-inks for thermal inkjet bioprinting applications via saponification and heat treatment processes

Material jetting bioprinting is a highly promising three-dimensional (3D) bioprinting technique that facilitates drop-on-demand (DOD) deposition of biomaterials and cells at pre-defined positions with high precision and resolution. A major challenge that hinders the prevalent use of the material jetting bioprinting technique is due to its limited range of printable hydrogel-based bio-inks. As a proof-of-concept, further modifications were made to gelatin methacrylate (GelMA), a gold-standard bio-ink, to improve its printability in a thermal inkjet bioprinter (HP Inc. D300e Digital Dispenser). A two-step modification process comprising saponification and heat treatment was performed; the GelMA bio-ink was first modified via a saponification process under highly alkali conditions to obtain saponified GelMA (SP-GelMA), followed by heat treatment via an autoclaving process to obtain heat-treated SP-GelMA (HSP-GelMA). The bio-ink modification process was optimized by evaluating the material properties of the GelMA bio-inks via rheological characterization, the bio-ink crosslinking test, nuclear magnetic resonance (NMR) spectroscopy and the material swelling ratio after different numbers of heat treatment cycles (0, 1, 2 and 3 cycles). Lastly, size-exclusion chromatography with multi-angle light scattering (SEC-MALS) was performed to determine the effect of heat treatment on the molecular weight of the bio-inks. In this work, the 4% H2SP-GelMA bio-inks (after 2 heat treatment cycles) demonstrated good printability and biocompatibility (in terms of cell viability and proliferation profile). Furthermore, thermal inkjet bioprinting of the modified hydrogel-based bio-ink (a two-step modification process comprising saponification and heat treatment) via direct/indirect cell patterning is a facile approach for potential fundamental cell-cell and cell-material interaction studies.

Silk Fibroin as a Bioink - A Thematic Review of Functionalization Strategies for Bioprinting Applications

Bioprinting is an emerging tissue engineering technique that has attracted the attention of researchers around the world, for its ability to create tissue constructs that recapitulate physiological function. While the technique has been receiving hype, there are still limitations to the use of bioprinting in practical applications, much of which is due to inappropriate bioink design that is unable to recapitulate complex tissue architecture. Silk fibroin (SF) is an exciting and promising bioink candidate that has been increasingly popular in bioprinting applications because of its processability, biodegradability, and biocompatibility properties. However, due to its lack of optimum gelation properties, functionalization strategies need to be employed so that SF can be effectively used in bioprinting applications. These functionalization strategies are processing methods which allow SF to be compatible with specific bioprinting techniques. Previous literature reviews of SF as a bioink mainly focus on discussing different methods to functionalize SF as a bioink, while a comprehensive review on categorizing SF functional methods according to their potential applications is missing. This paper seeks to discuss and compartmentalize the different strategies used to functionalize SF for bioprinting and categorize the strategies for each bioprinting method (namely, inkjet, extrusion, and light-based bioprinting). By compartmentalizing the various strategies for each printing method, the paper illustrates how each strategy is better suited for a target tissue application. The paper will also discuss applications of SF bioinks in regenerating various tissue types and the challenges and future trends that SF can take in its role as a bioink material.

Infiltration from Suspension Systems Enables Effective Modulation of 3D Scaffold Properties in Suspension Bioprinting

Bioprinting is a biofabrication technology which allows efficient and large-scale manufacture of 3D cell culture systems. However, the available biomaterials for bioinks used in bioprinting are limited by their printability and biological functionality. Fabricated constructs are often homogeneous and have limited complexity in terms of current 3D cell culture systems comprising multiple cell types. Inspired by the phenomenon that hydrogels can exchange liquids under the infiltration action, infiltration-induced suspension bioprinting (IISBP), a novel printing technique based on a hyaluronic acid (HA) suspension system to modulate the properties of the printed scaffolds by infiltration action, was described in this study. HA served as a suspension system due to its shear-thinning and self-healing rheological properties, simplicity of preparation, reusability, and ease of adjustment to osmotic pressure. Changes in osmotic pressure were able to direct the swelling or shrinkage of 3D printed gelatin methacryloyl (GelMA)-based bioinks, enabling the regulation of physical properties such as fiber diameter, micromorphology, mechanical strength, and water absorption of 3D printed scaffolds. Human umbilical vein endothelial cells (HUVEC) were applied as a cell culture model and printed within cell-laden scaffolds at high resolution and cell viability with the IISBP technique. Herein, the IISBP technique had been realized as a reliable hydrogel-based bioprinting technique, which enabled facile modulation of 3D printed hydrogel scaffolds properties, being expected to meet the scaffolds requirements of a wide range of cell culture conditions to be utilized in bioprinting applications.

Polymeric Coatings and Antimicrobial Peptides as Efficient Systems for Treating Implantable Medical Devices Associated-Infections

Many infections are associated with the use of implantable medical devices. The excessive utilization of antibiotic treatment has resulted in the development of antimicrobial resistance. Consequently, scientists have recently focused on conceiving new ways for treating infections with a longer duration of action and minimum environmental toxicity. One approach in infection control is based on the development of antimicrobial coatings based on polymers and antimicrobial peptides, also termed as “natural antibiotics”.

Metal Nanoparticles in Laser Bioprinting

Laser bioprinting is a promising method for applications in biotechnology, tissue engineering, and regenerative medicine. It is based on a microdroplet transfer from a donor slide induced by laser pulse heating of a thin metal absorption film covered with a layer of hydrogel containing living cells (bioink). Due to the presence of the metal absorption layer, some debris in the form of metal nanoparticles is printed together with bioink microdroplets. In this article, experimental investigations of the amount of metal nanoparticles formed during the laser bioprinting process and transported in bioink microdroplets are performed. As metal absorption layers, Ti films with the thickness in the range of 25-400 nm, produced by magnetron spattering, were applied. Dependences of the volume of bioink microdroplets and the amount of Ti nanoparticles within them on the laser pulse fluence were obtained. It has been experimentally found that practically all nanoparticles remain in the hydrogel layer on the donor slide during bioprinting, with only a small fraction of them transferred within the microdroplet (0.5% to 2.5%). These results are very important for applications of laser bioprinting since the transferred metal nanoparticles can potentially affect living systems. The good news is that the amount of such nanoparticles is very low to produce any negative effect on the printed cells.

Evolution of Shock-Induced Pressure in Laser Bioprinting

Laser bioprinting with gel microdroplets that contain living cells is a promising method for use in microbiology, biotechnology, and medicine. Laser engineering of microbial systems (LEMS) technology by laser-induced forward transfer (LIFT) is highly effective in isolating difficult-to-cultivate and uncultured microorganisms, which are essential for modern bioscience. In LEMS the transfer of a microdroplet of a gel substrate containing living cell occurs due to the rapid heating under the tight focusing of a nanosecond infrared laser pulse onto thin metal film with the substrate layer. During laser transfer, living organisms are affected by temperature and pressure jumps, high dynamic loads, and several others. The study of these factors’ role is important both for improving laser printing technology itself and from a purely theoretical point of view in relation to understanding the mechanisms of LEMS action. This article presents the results of an experimental study of bubbles, gel jets, and shock waves arising in liquid media during nanosecond laser heating of a Ti film obtained using time-resolving shadow microscopy. Estimates of the pressure jumps experienced by microorganisms in the process of laser transfer are performed: in the operating range of laser energies for bioprinting LEMS technology, pressure jumps near the absorbing film of the donor plate is about 30 MPa. The efficiency of laser pulse energy conversion to mechanical post-effects is about 10%. The estimates obtained are of great importance for microbiology, biotechnology, and medicine, particularly for improving the technologies related to laser bioprinting and the laser engineering of microbial systems.

Laser-based bioprinting for multilayer cell patterning in tissue engineering and cancer research

3D printing, or additive manufacturing, is a process for patterning functional materials based on the digital 3D model. A bioink that contains cells, growth factors, and biomaterials are utilized for assisting cells to develop into tissues and organs. As a promising technique in regenerative medicine, many kinds of bioprinting platforms have been utilized, including extrusion-based bioprinting, inkjet bioprinting, and laser-based bioprinting. Laser-based bioprinting, a kind of bioprinting technology using the laser as the energy source, has advantages over other methods. Compared with inkjet bioprinting and extrusion-based bioprinting, laser-based bioprinting is nozzle-free, which makes it a valid tool that can adapt to the viscosity of the bioink; the cell viability is also improved because of elimination of nozzle, which could cause cell damage when the bioinks flow through a nozzle. Accurate tuning of the laser source and bioink may provide a higher resolution for reconstruction of tissue that may be transplanted used as an in vitro disease model. Here, we introduce the mechanism of this technology and the essential factors in the process of laser-based bioprinting. Then, the most potential applications are listed, including tissue engineering and cancer models. Finally, we present the challenges and opportunities faced by laser-based bioprinting.

Triblock Copolymer Bioinks in Hydrogel Three-Dimensional Printing for Regenerative Medicine: A Focus on Pluronic F127

Three-dimensional (3D) bioprinting is a novel technique applied to manufacture semisolid or solid objects via deposition of successive thin layers. The widespread implementation of the 3D bioprinting technology encouraged scientists to evaluate its feasibility for applications in human regenerative medicine. 3D bioprinting gained much interest as a new strategy to prepare implantable 3D tissues or organs, tissue and organ evaluation models to test drugs, and cell/material interaction systems. The present work summarizes recent and relevant progress based on the use of hydrogels for the technology of 3D bioprinting and their emerging biomedical applications. An overview of different 3D printing techniques in addition to the nature and properties of bioinks used will be described with a focus on hydrogels as suitable bioinks for 3D printing. A comprehensive overview of triblock copolymers with emphasis on Pluronic F127 (PF127) as a bioink in 3D printing for regenerative medicine will be provided. Several biomedical applications of PF127 in tissue engineering, particularly in bone and cartilage regeneration and in vascular reconstruction, will be also discussed.

3D Bioprinting of Vascularized Tissues for in vitro and in vivo Applications

With a limited supply of organ donors and available organs for transplantation, the aim of tissue engineering with three-dimensional (3D) bioprinting technology is to construct fully functional and viable tissue and organ replacements for various clinical applications. 3D bioprinting allows for the customization of complex tissue architecture with numerous combinations of materials and printing methods to build different tissue types, and eventually fully functional replacement organs. The main challenge of maintaining 3D printed tissue viability is the inclusion of complex vascular networks for nutrient transport and waste disposal. Rapid development and discoveries in recent years have taken huge strides toward perfecting the incorporation of vascular networks in 3D printed tissue and organs. In this review, we will discuss the latest advancements in fabricating vascularized tissue and organs including novel strategies and materials, and their applications. Our discussion will begin with the exploration of printing vasculature, progress through the current statuses of bioprinting tissue/organoids from bone to muscles to organs, and conclude with relevant applications for in vitro models and drug testing. We will also explore and discuss the current limitations of vascularized tissue engineering and some of the promising future directions this technology may bring.