Generating vascular channels within hydrogel constructs using an economical open-source 3D bioprinter and thermoreversible gels

Integrating microfluidics, hydrogels, and 3D bioprinting for personalized vessel-on-a-chip platforms

Thrombosis, a major cause of morbidity and mortality worldwide, presents a complex challenge in cardiovascular medicine due to the intricacy of clotting mechanisms in living organisms. Traditional research approaches, including clinical studies and animal models, often yield conflicting results due to the inability to control variables in these complex systems, highlighting the need for more precise investigative tools. This review explores the evolution of in vitro thrombosis models, from conventional polydimethylsiloxane (PDMS)-based microfluidic devices to advanced hydrogel-based systems and cutting-edge 3D bioprinted vascular constructs. We discuss how these emerging technologies, particularly vessel-on-a-chip platforms, are enabling researchers to control previously unmanageable factors, thereby offering unprecedented opportunities to pinpoint specific clotting mechanisms. While PDMS-based devices offer optical transparency and fabrication ease, their inherent limitations, including non-physiological rigidity and surface properties, have driven the development of hydrogel-based systems that better mimic the extracellular matrix of blood vessels. The integration of microfluidics with biomimetic materials and tissue engineering approaches has led to the development of sophisticated models capable of simulating patient-specific vascular geometries, flow dynamics, and cellular interactions under highly controlled conditions. The advent of 3D bioprinting further enables the creation of complex, multi-layered vascular structures with precise spatial control over geometry and cellular composition. Despite significant progress, challenges remain in achieving long-term stability, incorporating immune components, and translating these models to clinical applications. By providing a comprehensive overview of current advancements and future prospects, this review aims to stimulate further innovation in thrombosis research and accelerate the development of more effective, personalized approaches to thrombosis prevention and treatment.

Leveraging printability and biocompatibility in materials for printing implantable vessel scaffolds

Vessel scaffolds are crucial for treating cardiovascular diseases (CVDs). It is currently feasible to fabricate vessel scaffolds from a variety of materials using traditional fabrication methods, but the risks of thrombus formation, chronic inflammation, and atherosclerosis associated with these scaffolds have led to significant limitations in the clinical usages. Bioprinting, as an emerging technology, has great potential in constructing implantable vessel scaffolds. During the fabrication of the constructs, the biomaterials used for bioprinting have offered significant contributions for the successful fabrications of the vessel scaffolds. Herein, we review recent advances in biomaterials for bioprinting implantable vessel scaffolds. First, we briefly introduce the requirements for implantable vessel scaffolds and its conventional manufacturing methods. Next, a brief overview of the classic methods for bioprinting vessel scaffolds is presented. Subsequently, we provide an in-depth analysis of the properties of the representative natural, synthetic, composite and hybrid biomaterials that can be used for bioprinting implantable vessel scaffolds. Ultimately, we underscore the necessity of leveraging biocompatibility and printability for biomaterials, and explore the unmet needs and potential applications of these biomaterials in the field of bioprinted implantable vessel scaffolds.

Design considerations for digital light processing bioprinters

With the rapid development and popularization of additive manufacturing, different technologies, including, but not limited to, extrusion-, droplet-, and vat-photopolymerization-based fabrication techniques, have emerged that have allowed tremendous progress in three-dimensional (3D) printing in the past decades. Bioprinting, typically using living cells and/or biomaterials conformed by different printing modalities, has produced functional tissues. As a subclass of vat-photopolymerization bioprinting, digital light processing (DLP) uses digitally controlled photomasks to selectively solidify liquid photocurable bioinks to construct complex physical objects in a layer-by-layer manner. DLP bioprinting presents unique advantages, including short printing times, relatively low manufacturing costs, and decently high resolutions, allowing users to achieve significant progress in the bioprinting of tissue-like complex structures. Nevertheless, the need to accommodate different materials while bioprinting and improve the printing performance has driven the rapid progress in DLP bioprinters, which requires multiple pieces of knowledge ranging from optics, electronics, software, and materials beyond the biological aspects. This raises the need for a comprehensive review to recapitulate the most important considerations in the design and assembly of DLP bioprinters. This review begins with analyzing unique considerations and specific examples in the hardware, including the resin vat, optical system, and electronics. In the software, the workflow is analyzed, including the parameters to be considered for the control of the bioprinter and the voxelizing/slicing algorithm. In addition, we briefly discuss the material requirements for DLP bioprinting. Then, we provide a section with best practices and maintenance of a do-it-yourself DLP bioprinter. Finally, we highlight the future outlooks of the DLP technology and their critical role in directing the future of bioprinting. The state-of-the-art progress in DLP bioprinter in this review will provide a set of knowledge for innovative DLP bioprinter designs.

Biomaterials for extrusion-based bioprinting and biomedical applications

Amongst the range of bioprinting technologies currently available, bioprinting by material extrusion is gaining increasing popularity due to accessibility, low cost, and the absence of energy sources, such as lasers, which may significantly damage the cells. New applications of extrusion-based bioprinting are systematically emerging in the biomedical field in relation to tissue and organ fabrication. Extrusion-based bioprinting presents a series of specific challenges in relation to achievable resolutions, accuracy and speed. Resolution and accuracy in particular are of paramount importance for the realization of microstructures (for example, vascularization) within tissues and organs. Another major theme of research is cell survival and functional preservation, as extruded bioinks have cells subjected to considerable shear stresses as they travel through the extrusion apparatus. Here, an overview of the main available extrusion-based printing technologies and related families of bioprinting materials (bioinks) is provided. The main challenges related to achieving resolution and accuracy whilst assuring cell viability and function are discussed in relation to specific application contexts in the field of tissue and organ fabrication.

The Enderstruder: An accessible open-source syringe extruder compatible with Ender series 3D printers

Bioprinting has enabled the precise spatiotemporal deposition of cells and biomaterials, opening new avenues of research in tissue engineering and regenerative medicine. Although several open-source syringe extruder adaptations for bioprinters have been published and adopted by end users, only one has been specifically adapted for the Ender series, an affordable and open-source line of thermoplastic 3D printers. Here, we introduce the Enderstruder, a cost-effective extruder attachment that uses a standard 10 mL BD syringe, positions the stepper motor at the level of the gantry, enhances x-axis stability with a linear rail, and uses the originally included stepper motor, resulting in reduced cost and simplified assembly. Furthermore, we present an iterative process to fine-tune printing profiles for high-viscosity biomaterial inks. To facilitate the implementation of our work by other researchers, we provide fully editable Cura profiles for five commonly used biomaterials. Using these five materials to validate and characterize our design, we employ the Enderstruder to print established calibration patterns and complex shapes. By presenting the Enderstruder and its iterative development process, this study contributes to the growing repository of open-source bioprinting solutions, fostering greater accessibility and affordability for researchers in tissue engineering.

Thermoresponsive Alginate-Graft-pNIPAM/Methyl Cellulose 3D-Printed Scaffolds Promote Osteogenesis In Vitro

In this work, a sodium alginate-based copolymer grafted by thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) chains was used as gelator (Alg-g-PNIPAM) in combination with methylcellulose (MC). It was found that the mechanical properties of the resulting gel could be enhanced by the addition of MC and calcium ions (Ca2+). The proposed network is formed via a dual crosslinking mechanism including ionic interactions among Ca2+ and carboxyl groups and secondary hydrophobic associations of PNIPAM chains. MC was found to further reinforce the dynamic moduli of the resulting gels (i.e., a storage modulus of ca. 1500 Pa at physiological body and post-printing temperature), rendering them suitable for 3D printing in biomedical applications. The polymer networks were stable and retained their printed fidelity with minimum erosion as low as 6% for up to seven days. Furthermore, adhered pre-osteoblastic cells on Alg-g-PNIPAM/MC printed scaffolds presented 80% viability compared to tissue culture polystyrene control, and more importantly, they promoted the osteogenic potential, as indicated by the increased alkaline phosphatase activity, calcium, and collagen production relative to the Alg-g-PNIPAM control scaffolds. Specifically, ALP activity and collagen secreted by cells were significantly enhanced in Alg-g-PNIPAM/MC scaffolds compared to the Alg-g-PNIPAM counterparts, demonstrating their potential in bone tissue engineering.

Changes in the Mechanical Properties of Alginate-Gelatin Hydrogels with the Addition of Pygeum africanum with Potential Application in Urology

New hydrogel materials developed to improve soft tissue healing are an alternative for medical applications, such as tissue regeneration or enhancing the biotolerance effect in the tissue-implant–body fluid system. The biggest advantages of hydrogel materials are the presence of a large amount of water and a polymeric structure that corresponds to the extracellular matrix, which allows to create healing conditions similar to physiological ones. The present work deals with the change in mechanical properties of sodium alginate mixed with gelatin containing Pygeum africanum. The work primarily concentrates on the evaluation of the mechanical properties of the hydrogel materials produced by the sol–gel method. The antimicrobial activity of the hydrogels was investigated based on the population growth dynamics of Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923, as well as the degree of degradation after contact with urine using an innovative method with a urine flow simulation stand. On the basis of mechanical tests, it was found that sodium alginate-based hydrogels with gelatin showed weaker mechanical properties than without the additive. In addition, gelatin accelerates the degradation process of the produced hydrogel materials. Antimicrobial studies have shown that the presence of African plum bark extract in the hydrogel enhances the inhibitory effect on Gram-positive and Gram-negative bacteria. The research topic was considered due to the increased demand from patients for medical devices to promote healing of urethral epithelial injuries in order to prevent the formation of urethral strictures.

Study of sacrificial ink-assisted embedded printing for 3D perfusable channel creation for biomedical applications

For an engineered thick tissue construct to be alive and sustainable, it should be perfusable with respect to nutrients and oxygen. Embedded printing and then removing sacrificial inks in a cross-linkable yield-stress hydrogel matrix bath can serve as a valuable tool for fabricating perfusable tissue constructs. The objective of this study is to investigate the printability of sacrificial inks and the creation of perfusable channels in a cross-linkable yield-stress hydrogel matrix during embedded printing. Pluronic F-127, methylcellulose, and polyvinyl alcohol are selected as three representative sacrificial inks for their different physical and rheological properties. Their printability and removability performances have been evaluated during embedded printing in a gelatin microgel-based gelatin composite matrix bath, which is a cross-linkable yield-stress bath. The ink printability during embedded printing is different from that during printing in air due to the constraining effect of the matrix bath. Sacrificial inks with a shear-thinning property are capable of printing channels with a broad range of filaments by simply tuning the extrusion pressure. Bi-directional diffusion may happen between the sacrificial ink and matrix bath, which affects the sacrificial ink removal process and final channel diameter. As such, sacrificial inks with a low diffusion coefficient for gelatin precursor are desirable to minimize the diffusion from the gelatin precursor solution to minimize the post-printing channel diameter variation. For feasibility demonstration, a multi-channel perfusable alveolar mimic has been successfully designed, printed, and evaluated. The study results in the knowledge of the channel diameter controllability and sacrificial ink removability during embedded printing.

Bioprinted microvasculature: progressing from structure to function

Three-dimensional (3D) bioprinting seeks to unlock the rapid generation of complex tissue constructs, but long-standing challenges with efficientin vitromicrovascularization must be solved before this can become a reality. Microvasculature is particularly challenging to biofabricate due to the presence of a hollow lumen, a hierarchically branched network topology, and a complex signaling milieu. All of these characteristics are required for proper microvascular-and, thus, tissue-function. While several techniques have been developed to address distinct portions of this microvascularization challenge, no single approach is capable of simultaneously recreating all three microvascular characteristics. In this review, we present a three-part framework that proposes integration of existing techniques to generate mature microvascular constructs. First, extrusion-based 3D bioprinting creates a mesoscale foundation of hollow, endothelialized channels. Second, biochemical and biophysical cues induce endothelial sprouting to create a capillary-mimetic network. Third, the construct is conditioned to enhance network maturity. Across all three of these stages, we highlight the potential for extrusion-based bioprinting to become a central technique for engineering hierarchical microvasculature. We envision that the successful biofabrication of functionally engineered microvasculature will address a critical need in tissue engineering, and propel further advances in regenerative medicine andex vivohuman tissue modeling.

Click Chemistry Hydrogels for Extrusion Bioprinting: Progress, Challenges, and Opportunities

The emergence of 3D bioprinting has allowed a variety of hydrogel-based "bioinks" to be printed in the presence of cells to create precisely defined cell-loaded 3D scaffolds in a single step for advancing tissue engineering and/or regenerative medicine. While existing bioinks based primarily on ionic cross-linking, photo-cross-linking, or thermogelation have significantly advanced the field, they offer technical limitations in terms of the mechanics, degradation rates, and the cell viabilities achievable with the printed scaffolds, particularly in terms of aiming to match the wide range of mechanics and cellular microenvironments. Click chemistry offers an appealing solution to this challenge given that proper selection of the chemistry can enable precise tuning of both the gelation rate and the degradation rate, both key to successful tissue regeneration; simultaneously, the often bio-orthogonal nature of click chemistry is beneficial to maintain high cell viabilities within the scaffolds. However, to date, relatively few examples of 3D-printed click chemistry hydrogels have been reported, mostly due to the technical challenges of controlling mixing during the printing process to generate high-fidelity prints without clogging the printer. This review aims to showcase existing cross-linking modalities, characterize the advantages and disadvantages of different click chemistries reported, highlight current examples of click chemistry hydrogel bioinks, and discuss the design of mixing strategies to enable effective 3D extrusion bioprinting of click hydrogels.

An open source extrusion bioprinter based on the E3D motion system and tool changer to enable FRESH and multimaterial bioprinting

Bioprinting is increasingly used to create complex tissue constructs for an array of research applications, and there are also increasing efforts to print tissues for transplantation. Bioprinting may also prove valuable in the context of drug screening for personalized medicine for treatment of diseases such as cancer. However, the rapidly expanding bioprinting research field is currently limited by access to bioprinters. To increase the availability of bioprinting technologies we present here an open source extrusion bioprinter based on the E3D motion system and tool changer to enable high-resolution multimaterial bioprinting. As proof of concept, the bioprinter is used to create collagen constructs using freeform reversible embedding of suspended hydrogels (FRESH) methodology, as well as multimaterial constructs composed of distinct sections of laminin and collagen. Data is presented demonstrating that the bioprinted constructs support growth of cells either seeded onto printed constructs or included in the bioink prior to bioprinting. This open source bioprinter is easily adapted for different bioprinting applications, and additional tools can be incorporated to increase the capabilities of the system.

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.

Self-Standing Photo-Crosslinked Hydrogel Construct: in vitro Microphysiological Vascular Model

Modeling of the human vascular microphysiological system (MPS) has gained attention due to precise prediction of drug response and toxicity during drug screening process. Developing a physiologically equivalent vascular MPS still remains complex as it demands the recapitulation of dynamic structural and biological microenvironment similar to native vasculature. Hence, an ideal MPS would involve developing perfusable 3D in vitro models with multilayered human vascular cells encapsulated in a matrix to regulate the vascular tone resembling the native. Several attempts to model such anatomically accurate physiological and pathological blood vessels often fail to harmonize the essential vascular microenvironment. For instance, conventional microfluidic-based approaches employed for vascular MPS, though offering creation of perfusable channel, do not replicate the vascular hierarchical cellular arrangement due to planar geometry and confluent monolayered cell seeding. Also, recent advances with 3D biofabrication strategies are still limited by fabrication of small-diameter constructs and scalability besides post-processing techniques that indirectly distort the structural integrity of the hydrogel tubular constructs. These existing limitations toward fabricating a relevant vascular MPS demand a facile and mechanically stable construct. Hence, the present study is aimed toward developing a stable viable self-standing perfusable hydrogel construct by a rapid and scalable strategy toward vascular MPS application. The fabricated tubular constructs were found to be structurally stable with end-to-end perfusability exhibiting their potential as self-standing perfusable structures. Also, the construct exhibited nonhemolytic behavior with perfusion of red blood cells inside the luminal channel. The present study evidences creation of a dual-crosslinked stable, viable self-standing hydrogel construct with multilayered homogenous distribution of viable smooth muscle cells throughout the construct, thereby demonstrating its applicability as a promising 3D in vitro vascular microphysiological system.

A high performance open-source syringe extruder optimized for extrusion and retraction during FRESH 3D bioprinting

Recent advances in embedded 3D bioprinting have significantly improved the resolution of individual filaments to below 100 μm; however, printing with such small filaments requires accurate extrusion of nanoliter volumes of bioink. Commercially available bioprinters and extruders are expensive and most utilize pneumatic control, which limits the minimum extrusion volume and prevents retraction (pulling bioink back into the reservoir), which is essential to printing high resolution features and complex internal geometry. Here we present a new generation of our open-source syringe pump designed for extrusion-based 3D bioprinting of soft materials: the Replistruder 4. The Replistruder 4 takes advantage of the geometry customizability and ease of 3D plastic printing while improving performance by integrating mass produced high-precision linear motion components. Simultaneously this new syringe pump remains compact and lightweight enough for several to be utilized on a 3D bioprinter for multimaterial bioprinting. To facilitate multiple use cases the Replistruder 4 is compatible with a range of syringes including disposable BD and Hamilton gastight syringes. In addition, we describe the process of designing clamps for other syringes. We demonstrate the performance of a Replistruder 4 with a 2.5 mL Hamilton gastight syringe by printing collagen type I constructs with individual filaments comprising 3.35 nL and patent channels down to 300 μm in width. With smaller volume Hamilton gastight syringes this performance can be further improved. Thus, the Replistruder 4 provides an open-source solution to print soft materials at the resolution limits of current embedded bioprinting platforms.

Design and implementation of a low cost bio-printer modification, allowing for switching between plastic and gel extrusion

Due to the high cost of bioprinters they are not feasible for proof of concept experiments or educational purposes. Furthermore, the more affordable DIY methods all disable the plastic printing capability of the original printer. Here we present an affordable bio-printing modification that is easy to install and maintains the original capabilities of the printer. The modification used mostly 3D printed parts and is based on the popular, open-source Prusa i3 3D printer. The modifications are kept as simple as possible and uses standard slicing software, allowing for installation by less experienced builders. By using disposable syringes and easily sterilizable parts, an aseptic bioprinting setup can be achieved, depending on the environment. It also allows for 2 component printing as well as UV curing. The bio-printing and curing capabilities were shown by printing and curing an artificial biofilm of an electro-active bacteria, Geobacter sulfurreducens, onto a carbon-cloth electrode which was used in a microbial fuel cell.

Digital readiness in 3D bioprinting: software, governance and hospitals' proto-clinical interfaces

Aim: To understand the process through which some hospitals have become ready to assimilate the digital technologies required for 3D bioprinting. By enhancing their digital readiness, hospitals will be able to develop the current proto-clinical potentialities of bioprinting. Materials & methods: We conducted interviews with bioprinting researchers, entrepreneurs and regulators in three countries (United Kingdom, Italy and Brazil). We analyzed bioprinting papers in which hospital-based researchers participated. We also analyzed the international bioprinting market. Result s: Digital readiness is more advanced in some hospitals and countries, which have noticed the strategic relevance of bioprinting. Furthermore, it is strengthened by the reformulation of the relations between hospitals and other institutions, a phenomenon that is here interpreted with the concept of interfaces.

3D-bioprinted all-inclusive bioanalytical platforms for cell studies

Innovative drug screening platforms should improve the discovery of novel and personalized cancer treatment. Common models such as animals and 2D cell cultures lack the proper recapitulation of organ structure and environment. Thus, a new generation of platforms must consist of cell models that accurately mimic the cells’ microenvironment, along with flexibly prototyped cell handling structures that represent the human environment. Here, we adapted the 3D-bioprinting technology to develop multiple all-inclusive high throughputs and customized organ-on-a-chip-like platforms along with printed 3D-cell structures. Such platforms are potentially capable of performing 3D cell model analysis and cell-therapeutic response studies. We illustrated spherical and rectangular geometries of bio-printed 3D human colon cancer cell constructs. We also demonstrated the utility of directly 3D-bioprinting and rapidly prototyping of PDMS-based microfluidic cell handling arrays in different geometries. Besides, we successfully monitored the post-viability of the 3D-cell constructs for seven days. Furthermore, to mimic the human environment more closely, we integrated a 3D-bioprinted perfused drug screening microfluidics platform. Platform’s channels subject cell constructs to physiological fluid flow, while its concave well array hold and perfused 3D-cell constructs. The bio-applicability of PDMS-based arrays was also demonstrated by performing cancer cell-therapeutic response studies.

An open-source robotic platform that enables automated monitoring of replicate biofilm cultivations using optical coherence tomography

The paper introduces a fully automated cultivation and monitoring tool to study biofilm development in replicate experiments operated in parallel. To gain a fundamental understanding of the relation between cultivation conditions and biofilm characteristics (e.g., structural, mechanical) a monitoring setup allowing for the standardization of methods is required. Optical coherence tomography (OCT) is an imaging modality ideal for biofilms since it allows for the monitoring of structure in real time. By integrating an OCT device into the open-source robotic platform EvoBot, a fully automated monitoring platform for investigating biofilm development in several flow cells at once was realized. Different positioning scenarios were tested and revealed that the positioning accuracy is within the optical resolution of the OCT. On that account, a reliable and accurate monitoring of biofilm development by means of OCT has become possible. With this robotic platform, reproducible biofilm experiments including a statistical analysis are achievable with only a small investment of operator time. Furthermore, a number of structural parameters calculated within this study confirmed the necessity to perform replicate biofilm cultivations.

Principles of open source bioinstrumentation applied to the poseidon syringe pump system

The poseidon syringe pump and microscope system is an open source alternative to commercial systems. It costs less than $400 and can be assembled in under an hour using the instructions and source files available at https://pachterlab.github.io/poseidon . We describe the poseidon system and use it to illustrate design principles that can facilitate the adoption and development of open source bioinstruments. The principles are functionality, robustness, safety, simplicity, modularity, benchmarking, and documentation.