Effects of Dispensing Pressure and Nozzle Diameter on Cell Survival from Solid Freeform Fabrication–Based Direct Cell Writing

Advances in current in vitro models on neurodegenerative diseases

Many neurodegenerative diseases are identified but their causes and cure are far from being well-known. The problem resides in the complexity of the neural tissue and its location which hinders its easy evaluation. Although necessary in the drug discovery process, in vivo animal models need to be reduced and show relevant differences with the human tissues that guide scientists to inquire about other possible options which lead to in vitro models being explored. From organoids to organ-on-a-chips, 3D models are considered the cutting-edge technology in cell culture. Cell choice is a big parameter to take into consideration when planning an in vitro model and cells capable of mimicking both healthy and diseased tissue, such as induced pluripotent stem cells (iPSC), are recognized as good candidates. Hence, we present a critical review of the latest models used to study neurodegenerative disease, how these models have evolved introducing microfluidics platforms, 3D cell cultures, and the use of induced pluripotent cells to better mimic the neural tissue environment in pathological conditions.

Global hotspots and emerging trends in 3D bioprinting research

Three-dimensional (3D) bioprinting is an advanced tissue engineering technique that has received a lot of interest in the past years. We aimed to highlight the characteristics of articles on 3D bioprinting, especially in terms of research hotspots and focus. Publications related to 3D bioprinting from 2007 to 2022 were acquired from the Web of Science Core Collection database. We have used VOSviewer, CiteSpace, and R-bibliometrix to perform various analyses on 3,327 published articles. The number of annual publications is increasing globally, a trend expected to continue. The United States and China were the most productive countries with the closest cooperation and the most research and development investment funds in this field. Harvard Medical School and Tsinghua University are the top-ranked institutions in the United States and China, respectively. Dr. Anthony Atala and Dr. Ali Khademhosseini, the most productive researchers in 3D bioprinting, may provide cooperation opportunities for interested researchers. Tissue Engineering Part A contributed the largest publication number, while Frontiers in Bioengineering and Biotechnology was the most attractive journal with the most potential. As for the keywords in 3D bioprinting, Bio-ink, Hydrogels (especially GelMA and Gelatin), Scaffold (especially decellularized extracellular matrix), extrusion-based bioprinting, tissue engineering, and in vitro models (organoids particularly) are research hotspots analyzed in the current study. Specifically, the research topics "new bio-ink investigation," "modification of extrusion-based bioprinting for cell viability and vascularization," "application of 3D bioprinting in organoids and in vitro model" and "research in personalized and regenerative medicine" were predicted to be hotspots for future research.

Investigation of Cell Aggregation on the Printing Performance in Inkjet-Based Bioprinting of Cell-Laden Bioink

During 3D bioprinting, when the gravitational force exceeds the buoyant force, cell sedimentation will be induced, resulting in local cell concentration change and cell aggregation which affect the printing performance. This paper aims at studying and quantifying cell aggregation and its effects on the droplet formation process during inkjet-based bioprinting and cell distribution after inkjet-based bioprinting. The major conclusions of this study are as follows: (1) Cell aggregation is a significant challenge during inkjet-based bioprinting by observing the percentage of individual cells after different printing times. In addition, as polymer concentration increases, the cell aggregation is suppressed. (2) As printing time and cell aggregation increase, the ligament length and droplet velocity generally decrease first and then increase due to the initial increase and subsequent decrease of the viscous effect. (3) As the printing time increases, both the maximum number of cells within one microsphere and the mean cell number have a significant increase, especially for low polymer concentrations such as 0.5% (w/v). In addition, the increased rate is the highest using the lowest polymer concentration of 0.5% (w/v) because of its highest cell sedimentation velocity.

3D Bioprinting at the Frontier of Regenerative Medicine, Pharmaceutical, and Food Industries

3D printing technology has emerged as a key driver behind an ongoing paradigm shift in the production process of various industrial domains. The integration of 3D printing into tissue engineering, by utilizing life cells which are encapsulated in specific natural or synthetic biomaterials (e.g., hydrogels) as bioinks, is paving the way toward devising many innovating solutions for key biomedical and healthcare challenges and heralds' new frontiers in medicine, pharmaceutical, and food industries. Here, we present a synthesis of the available 3D bioprinting technology from what is found and what has been achieved in various applications and discussed the capabilities and limitations encountered in this technology.

Candidate Bioinks for Extrusion 3D Bioprinting-A Systematic Review of the Literature

Purpose: Bioprinting is becoming an increasingly popular platform technology for engineering a variety of tissue types. Our aim was to identify biomaterials that have been found to be suitable for extrusion 3D bioprinting, outline their biomechanical properties and biocompatibility towards their application for bioprinting specific tissue types. This systematic review provides an in-depth overview of current biomaterials suitable for extrusion to aid bioink selection for specific research purposes and facilitate design of novel tailored bioinks.

Methods: A systematic search was performed on EMBASE, PubMed, Scopus and Web of Science databases according to the PRISMA guidelines. References of relevant articles, between December 2006 to January 2018, on candidate bioinks used in extrusion 3D bioprinting were reviewed by two independent investigators against standardised inclusion and exclusion criteria. Data was extracted on bioprinter brand and model, printing technique and specifications (speed and resolution), bioink material and class of mechanical assessment, cell type, viability, and target tissue. Also noted were authors, study design (in vitro/in vivo), study duration and year of publication.

Results: A total of 9,720 studies were identified, 123 of which met inclusion criteria, consisting of a total of 58 reports using natural biomaterials, 26 using synthetic biomaterials and 39 using a combination of biomaterials as bioinks. Alginate (n = 50) and PCL (n = 33) were the most commonly used bioinks, followed by gelatin (n = 18) and methacrylated gelatin (GelMA) (n = 16). Pneumatic extrusion bioprinting techniques were the most common (n = 78), followed by piston (n = 28). The majority of studies focus on the target tissue, most commonly bone and cartilage, and investigate only one bioink rather than assessing a range to identify those with the most promising printability and biocompatibility characteristics. The Bioscaffolder (GeSiM, Germany), 3D Discovery (regenHU, Switzerland), and Bioplotter (EnvisionTEC, Germany) were the most commonly used commercial bioprinters (n = 35 in total), but groups most often opted to create their own in-house devices (n = 20). Many studies also failed to specify whether the mechanical data reflected pre-, during or post-printing, pre- or post-crosslinking and with or without cells.

Conclusions: Despite the continued increase in the variety of biocompatible synthetic materials available, there has been a shift change towards using natural rather than synthetic bioinks for extrusion bioprinting, dominated by alginate either alone or in combination with other biomaterials. On qualitative analysis, no link was demonstrated between the type of bioink or extrusion technique and the target tissue, indicating that bioprinting research is in its infancy with no established tissue specific bioinks or bioprinting techniques. Further research is needed on side-by-side characterisation of bioinks with standardisation of the type and timing of biomechanical assessment.

Bio-printing of aligned GelMa-based cell-laden structure for muscle tissue regeneration

Volumetric muscle loss (VML) is associated with a severe loss of muscle tissue that overwhelms the regenerative potential of skeletal muscles. Tissue engineering has shown promise for the treatment of VML injuries, as evidenced by various preclinical trials. The present study describes the fabrication of a cell-laden GelMa muscle construct using an in situ crosslinking (ISC) strategy to improve muscle functionality. To obtain optimal biophysical properties of the muscle construct, two UV exposure sources, UV exposure dose, and wall shear stress were evaluated using C2C12 myoblasts. Additionally, the ISC system showed a significantly higher degree of uniaxial alignment and myogenesis compared to the conventional crosslinking strategy (post-crosslinking). To evaluate the in vivo regenerative potential, muscle constructs laden with human adipose stem cells were used. The VML defect group implanted with the bio-printed muscle construct showed significant restoration of functionality and muscular volume. The data presented in this study suggest that stem cell-based therapies combined with the modified bioprinting process could potentially be effective against VML injuries.

Towards the Experimentally-Informed In Silico Nozzle Design Optimization for Extrusion-Based Bioprinting of Shear-Thinning Hydrogels

Research in bioprinting is booming due to its potential in addressing several manufacturing challenges in regenerative medicine. However, there are still many hurdles to overcome to guarantee cell survival and good printability. For the 3D extrusion-based bioprinting, cell viability is amongst one of the lowest of all the bioprinting techniques and is strongly influenced by various factors including the shear stress in the print nozzle. The goal of this study is to quantify, by means of in silico modeling, the mechanical environment experienced by the bioink during the printing process. Two ubiquitous nozzle shapes, conical and blunted, were considered, as well as three common hydrogels with material properties spanning from almost Newtonian to highly shear-thinning materials following the power-law behavior: Alginate-Gelatin, Alginate and PF127. Comprehensive in silico testing of all combinations of nozzle geometry variations and hydrogels was achieved by combining a design of experiments approach (DoE) with a computational fluid dynamics (CFD) of the printing process, analyzed through a machine learning approach named Gaussian Process. Available experimental results were used to validate the CFD model and justify the use of shear stress as a surrogate for cell survival in this study. The lower and middle nozzle radius, lower nozzle length and the material properties, alone and combined, were identified as the major influencing factors affecting shear stress, and therefore cell viability, during printing. These results were successfully compared with those of reported experiments testing viability for different nozzle geometry parameters under constant flow rate or constant pressure. The in silico 3D bioprinting platform developed in this study offers the potential to assist and accelerate further development of 3D bioprinting.

Biomechanical factors in three-dimensional tissue bioprinting

3D bioprinting techniques have shown great promise in various fields of tissue engineering and regenerative medicine. Yet, creating a tissue construct that faithfully represents the tightly regulated composition, microenvironment, and function of native tissues is still challenging. Among various factors, biomechanics of bioprinting processes play fundamental roles in determining the ultimate outcome of manufactured constructs. This review provides a comprehensive and detailed overview on various biomechanical factors involved in tissue bioprinting, including those involved in pre, during, and post printing procedures. In preprinting processes, factors including viscosity, osmotic pressure, and injectability are reviewed and their influence on cell behavior during the bioink preparation is discussed, providing a basic guidance for the selection and optimization of bioinks. In during bioprinting processes, we review the key characteristics that determine the success of tissue manufacturing, including the rheological properties and surface tension of the bioink, printing flow rate control, process-induced mechanical forces, and the in situ cross-linking mechanisms. Advanced bioprinting techniques, including embedded and multi-material printing, are explored. For post printing steps, general techniques and equipment that are used for characterizing the biomechanical properties of printed tissue constructs are reviewed. Furthermore, the biomechanical interactions between printed constructs and various tissue/cell types are elaborated for both in vitro and in vivo applications. The review is concluded with an outlook regarding the significance of biomechanical processes in tissue bioprinting, presenting future directions to address some of the key challenges faced by the bioprinting community.

Trends in 3D bioprinting for esophageal tissue repair and reconstruction

In esophageal pathologies, such as esophageal atresia, cancers, caustic burns, or post-operative stenosis, esophageal replacement is performed by using parts of the gastrointestinal tract to restore nutritional autonomy. However, this surgical procedure most often does not lead to complete functional recovery and is instead associated with many complications resulting in a decrease in the quality of life and survival rate. Esophageal tissue engineering (ETE) aims at repairing the defective esophagus and is considered as a promising therapeutic alternative. Noteworthy progress has recently been made in the ETE research area but strong challenges remain to replicate the structural and functional integrity of the esophagus with the approaches currently being developed. Within this context, 3D bioprinting is emerging as a new technology to facilitate the patterning of both cellular and acellular bioinks into well-organized 3D functional structures. Here, we present a comprehensive overview of the recent advances in tissue engineering for esophageal reconstruction with a specific focus on 3D bioprinting approaches in ETE. Current biofabrication techniques and bioink features are highlighted, and these are discussed in view of the complexity of the native esophagus that the designed substitute needs to replace. Finally, perspectives on recent strategies for fabricating other tubular organ substitutes via 3D bioprinting are discussed briefly for their potential in ETE applications.

Safety Considerations in 3D Bioprinting Using Mesenchymal Stromal Cells

Three-dimensional (3D) bioprinting has demonstrated great potential for the fabrication of biomimetic human tissues and complex graft materials. This technology utilizes bioinks composed of cellular elements placed within a biomaterial. Mesenchymal stromal cells (MSCs) are an attractive option for cell selection in 3D bioprinting. MSCs can be isolated from a variety of tissues, can pose vast proliferative capacity and can differentiate to multiple committed cell types. Despite their promising properties, the use of MSCs has been associated with several drawbacks. These concerns are related to the ex vivo manipulation throughout the process of 3D bioprinting. The herein manuscript aims to present the current evidence surrounding these events and propose ways to minimize the risks to the patients following widespread expansion of 3D bioprinting in the medical field.

Control of Direct Written Ink Droplets Using Electrowetting

Here, we investigate the feasibility and effectiveness of electrowetting in the motion control of droplets of different liquids, which are widely used as inks in direct writing (DW)-based three-dimensional (3D) printing processes for various applications. To control the movement of DW ink droplets on dielectric substrates, the electrodes were embedded in the substrate. It is demonstrated that droplets of pure liquid inks, aqueous polymer solution inks, and carbon fiber suspension inks can be moved on multi-angled surfaces. Also, experimental results reveal that droplets of a commercial hydrogel, agar-agar, alginate, xanthan gum, and gum arabic can be moved by electrowetting. Droplets of sizes 200 μm-3 mm were manipulated and moved by the electric field on different dielectric substrates accurately and repeatedly. Effective electrowetting-based control and movement of droplets were observed on horizontal, vertical, and even inverted substrates. These findings imply the feasibility and potential application of electrowetting as a flexible, rapid, and new method for ink droplet control in 3D printing processes.

Bioprinting Vasculature: Materials, Cells and Emergent Techniques

Despite the great advances that the tissue engineering field has experienced over the last two decades, the amount of in vitro engineered tissues that have reached a stage of clinical trial is limited. While many challenges are still to be overcome, the lack of vascularization represents a major milestone if tissues bigger than approximately 200 µm are to be transplanted. Cell survival and homeostasis is to a large extent conditioned by the oxygen and nutrient transport (as well as waste removal) by blood vessels on their proximity and spontaneous vascularization in vivo is a relatively slow process, leading all together to necrosis of implanted tissues. Thus, in vitro vascularization appears to be a requirement for the advancement of the field. One of the main approaches to this end is the formation of vascular templates that will develop in vitro together with the targeted engineered tissue. Bioprinting, a fast and reliable method for the deposition of cells and materials on a precise manner, appears as an excellent fabrication technique. In this review, we provide a comprehensive background to the fields of vascularization and bioprinting, providing details on the current strategies, cell sources, materials and outcomes of these studies.

Recent Strategies in Extrusion-Based Three-Dimensional Cell Printing toward Organ Biofabrication

Reconstructing human organs is one of the ultimate goals of the medical industry. Organ printing utilizing three-dimensional cell printing technology to fabricate artificial living organ equivalents has shed light on the advancement of this field into a new era. Among three currently applied techniques (inkjet, laser-assisted, and extrusion-based), extrusion-based cell printing (ECP) has evoked the majority of interest due to its low cost, wide range of applicable materials, and ease of spatial and depositional controllability. Major challenges in organ reconstruction include difficulties in precisely fabricating complex structural features, creating perfusable and functional vasculatures, and mimicking biophysical and biochemical characteristics in the printed constructs. In this review, we describe the merits and limitations of ECP for organ fabrication and discuss its recent advances aimed at overcoming these challenges. In addition, we delineate the expected future techniques for printing live tissue or organ substitutes.

3D human skin bioprinting: a view from the bio side

Based on the 3D printing technologies and the concepts developed in tissue engineering during the last decades, 3D bioprinting is emerging as the most innovative and promising technology for the generation of human tissues and organs. In the case of skin bioprinting, thanks to the research process carried out during the last years, interfollicular skin has been printed with a structural and functional quality that paves the way for clinical and industrial applications. This review analyzes the present achievements and the future improvements that this area must bring about if bioprinted skin is to become widely used. We have made an effort to integrate the technological and the biological/biomedical sides of the subject.

3D Bioprinting and Stem Cells

Three-dimensional (3D) in vitro modeling is increasingly relevant as two-dimensional (2D) cultures have been recognized with limits to recapitulate the complex endogenous conditions in the body. Additionally, fabrication technology is more accessible than ever. Bioprinting, in particular, is an additive manufacturing technique that expands the capabilities of in vitro studies by precisely depositing cells embedded within a 3D biomaterial scaffold that acts as temporary extracellular matrix (ECM). More importantly, bioprinting has vast potential for customization. This allows users to manipulate parameters such as scaffold design, biomaterial selection, and cell types, to create specialized biomimetic 3D systems.The development of a 3D system is important to recapitulate the bone marrow (BM) microenvironment since this particular organ cannot be mimicked with other methods such as organoids. The 3D system can be used to study the interactions between native BM cells and metastatic breast cancer cells (BCCs). Although not perfect, such a system can recapitulate the BM microenvironment. Mesenchymal stem cells (MSCs), a key population within the BM, are known to communicate with BCCs invading the BM and to aid in their transition into dormancy. Dormant BCCs are cycling quiescent and resistant to chemotherapy, which allows them to survive in the BM to resurge even after decades. These persisting BCCs have been identified as the stem cell subset. These BCCs exhibit self-renewal and can be induced to differentiate. More importantly, this BCC subset can initiate tumor formation, exert chemoresistance, and form gap junction with endogenous BM stroma, including MSCs. The bioprinted model detailed in this chapter creates a MSC-BC stem cell coculture system to study intercellular interactions in a model that is more representative of the endogenous 3D microenvironment than conventional 2D cultures. The method can reliably seed primary BM MSCs and BC stem cells within a bioprinted scaffold fabricated from CELLINK Bioink. Since bioprinting is a highly customizable technique, parameters described in this method (i.e., cell-cell ratio, scaffold dimensions) can easily be altered to serve other applications, including studies on hematopoietic regulation.

NUMERICAL SIMULATION OF PRESSURE-INDUCED CELL PRINTING

Nowadays, because of great biomedical applications of state-of-the art prototyping (bio-printing), many studies have been conducted in this field with focus on three-dimensional prototyping. There are several mechanisms for bio-printing of live cells such as piezoelectric and thermal and pneumatic inkjeting systems. Cell viability should be preserved during the bio-printing process. Lots of researches have been carried out to investigate and compare cell viability through different prototyping mechanisms. In order to quantify percentage of the cells that are killed during the proto-typing process, applied stresses on the cell and consequently its deformation should be calculated. A maximum strain energy density that the cell can tolerate is reported in the range of 25 Kj ⋅ m-3 to 100 Kj ⋅ m-3. This can be considered as a criteria to find the percentage of the damaged cells during the bio-printing processes. In this study, the bio-printing of the cell has been modeled and the cell viability have been investigated. Firstly, it is shown that in modeling of the bio-printing process, the effects of dynamic flow on calculating the applied stress on the cell is not negligible and must be considered. In the next step, the percentage of damaged endothelial cell aggregate under 80 kPa applied pressure (64 MPa/m) and 200 micron nozzle diameter is reported. Based on findings of this study, the percentage of endothelial cells viability under mentioned condition is reported 76%. The proposed method of this study can be utilized to examine the cell viability and performance of each prototyping systems.

Structural and vascular analysis of tissue engineering scaffolds, Part 1: Numerical fluid analysis

Rapid prototyping technologies were recently introduced in the medical field, being particularly viable to produce porous scaffolds for tissue engineering. These scaffolds should be biocompatible, biodegradable, with appropriate porosity, pore structure, and pore distribution on top of presenting both surface and structural compatibility. This chapter presents the state-of-the-art in tissue engineering and scaffold design using numerical fluid analysis for optimal vascular design. The vascularization of scaffolds is an important aspect due to its influence regarding the normal flow of biofluids within the human body. This computational tool also allows to design either a scaffold offering less resistance to the normal flow of biofluids or reducing the possibility for blood coagulation through forcing the flow toward a specific direction.

Microprinting of liver micro-organ for drug metabolism study

In their normal in vivo matrix milieu, tissues assume complex well-organized 3D architectures. Therefore, a primary aim in the tissue engineering design process is to fabricate an optimal analog of the in vivo scenario, in which the precise configuration and composition of cells and bioactive matrix components can establish the well-defined biomimetic microenvironments that promote cell-cell and cell-matrix interactions. With the advent and refinements in microfabricated systems which can present physical and chemical cues to cells in a controllable and reproducible fashion unrealizable with conventional tissue culture, high-fidelity, high-throughput in vitro models are achieved. The convergence of solid freeform fabrication (SFF) technologies, namely microprinting, along with microfabrication techniques, a 3D microprinted micro-organ, can serve as an in vitro platform for cell culture, drug screening, or to elicit further biological insights. This chapter firstly details the principles, methods, and applications that undergird the fabrication process development and adaptation of microfluidic devices for the creation of a drug screening model. This model involves the combinatorial setup of an automated syringe-based, layered direct cell writing microprinting process with soft lithographic micropatterning techniques to fabricate a microscale in vitro device housing a chamber of microprinted 3D micro-organ that biomimics the cell's natural microenvironment for enhanced performance and functionality. In order to assess the structural formability and biological feasibility of such a micro-organ, 3D cell-encapsulated hydrogel-based tissue constructs are microprinted reproducibly in defined design patterns and biologically characterized for both viability and cell-specific function. Another key facet of the in vivo microenvironment that is recapitulated with the in vitro system is the necessary dynamic perfusion of the 3D microscale liver analog with cells probed for their collective drug metabolic function and suitability as a drug metabolism model.

Biofabrication of a three-dimensional liver micro-organ as an in vitro drug metabolism model

In their normal in vivo matrix milieu, tissues assume complex well-organized three-dimensional architectures. Therefore, the primary aim in the tissue engineering design process is to fabricate an optimal analog of the in vivo scenario. This challenge can be addressed by applying emerging layered biofabrication approaches in which the precise configuration and composition of cells and bioactive matrix components can recapitulate the well-defined three-dimensional biomimetic microenvironments that promote cell-cell and cell-matrix interactions. Furthermore, the advent of and refinements in microfabricated systems can present physical and chemical cues to cells in a controllable and reproducible fashion unmatched with conventional cultures, resulting in the precise construction of engineered biomimetic microenvironments on the cellular length scale in geometries that are readily parallelized for high throughput in vitro models. As such, the convergence of layered solid freeform fabrication (SFF) technologies along with microfabrication techniques enables the creation of a three-dimensional micro-organ device to serve as an in vitro platform for cell culture, drug screening or to elicit further biological insights, particularly for NASA's interest in a flight-suitable high-fidelity microscale platform to study drug metabolism in space and planetary environments. The proposed model in this paper involves the combinatorial setup of an automated syringe-based, layered direct cell writing bioprinting process with micro-patterning techniques to fabricate a microscale in vitro device housing a chamber of bioprinted three-dimensional liver cell-encapsulated hydrogel-based tissue constructs in defined design patterns that biomimic the cell's natural microenvironment for enhanced biological functionality. In order to assess the structural formability and biological feasibility of such a micro-organ, reproducibly fabricated tissue constructs were biologically characterized for liver cell-specific function. Another key facet of the in vivo microenvironment that was recapitulated with the in vitro system included the necessary dynamic perfusion of the three-dimensional microscale liver analog with cells probed for their collective drug metabolic function and suitability as a drug metabolism model. This paper details the principles and methods that undergird the direct cell writing biofabrication process development and adaptation of microfluidic devices for the creation of a drug screening model, thereby establishing a novel drug metabolism study platform for NASA's interest to adopt a microfluidic microanalytical device with an embedded three-dimensional microscale liver tissue analog to assess drug pharmacokinetic profiles in planetary environments.

Modeling of Spatially Controlled Biomolecules in Three-Dimensional Porous Alginate Structures

This paper presents a computer-aided design (CAD) of 3D porous tissue scaffolds with spatial control of encapsulated biomolecule distributions. A localized control of encapsulated biomolecule distribution over 3D structures is proposed to control release kinetics spatially for tissue engineering and drug release. Imaging techniques are applied to explore distribution of microspheres over porous structures. Using microspheres in this study represents a framework for modeling the distribution characteristics of encapsulated proteins, growth factors, cells, and drugs. A quantification study is then performed to assure microsphere variation over various structures under imaging analysis. The obtained distribution characteristics are mimicked by the developed stochastic modeling study of microsphere distribution over 3D engineered freeform structures. Based on the stochastic approach, 3D porous structures are modeled and designed in CAD. Modeling of microsphere and encapsulating biomaterial distribution in this work helps develop comprehensive modeling of biomolecule release kinetics for further research. A novel multichamber single nozzle solid freeform fabrication technique is utilized to fabricate sample structures. The presented methods are implemented and illustrative examples are presented in this paper.

A droplet-based building block approach for bladder smooth muscle cell (SMC) proliferation

Tissue engineering based on building blocks is an emerging method to fabricate 3D tissue constructs. This method requires depositing and assembling building blocks (cell-laden microgels) at high throughput. The current technologies (e.g., molding and photolithography) to fabricate microgels have throughput challenges and provide limited control over building block properties (e.g., cell density). The cell-encapsulating droplet generation technique has potential to address these challenges. In this study, we monitored individual building blocks for viability, proliferation and cell density. The results showed that (i) SMCs can be encapsulated in collagen droplets with high viability (>94.2 +/- 3.2%) for four cases of initial number of cells per building block (i.e. 7 +/- 2, 16 +/- 2, 26 +/- 3 and 37 +/- 3 cells/building block). (ii) Encapsulated SMCs can proliferate in building blocks at rates that are consistent (1.49 +/- 0.29) across all four cases, compared to that of the controls. (iii) By assembling these building blocks, we created an SMC patch (5 mm x 5 mm x 20 microm), which was cultured for 51 days forming a 3D tissue-like construct. The histology of the cultured patch was compared to that of a native rat bladder. These results indicate the potential of creating 3D tissue models at high throughput in vitro using building blocks.

Synthesis and microfabrication of biomaterials for soft-tissue engineering

Biomaterials synthesis and scaffold fabrication will play an increasingly important role in the design of systems for regenerative medicine and tissue engineering. These rapidly growing fields are converging as scaffold design must begin to incorporate multidisciplinary aspects in order to effectively organize cell-seeded constructs into functional tissue. This review article examines the use of synthetic biomaterials and fabrication strategies across length scales with the ultimate goal of guiding cell function and directing tissue formation. This discussion is parsed into three subsections: (1) biomaterials synthesis, including elastomers and gels; (2) synthetic micro- and nanostructures for engineering the cell–biomaterial interface; and (3) complex biomaterials systems design for controlling aspects of the cellular microenvironment.