On-Demand Picoliter-Level-Droplet Inkjet Printing for Micro Fabrication and Functional Applications

With the advent of Internet of Things (IoTs) and wearable devices, manufacturing requirements have shifted toward miniaturization, flexibility, environmentalization, and customization. Inkjet printing, as a non-contact picoliter-level droplet printing technology, can achieve material deposition at the microscopic level, helping to achieve high resolution and high precision patterned design. Meanwhile, inkjet printing has the advantages of simple process, high printing efficiency, mask-free digital printing, and direct pattern deposition, and is gradually emerging as a promising technology to meet such new requirements. However, there is a long way to go in constructing functional materials and emerging devices due to the uncommercialized ink materials, complicated film-forming process, and geometrically/functionally mismatched interface, limiting film quality and device applications. Herein, recent developments in working mechanisms, functional ink systems, droplet ejection and flight process, droplet drying process, as well as emerging multifunctional and intelligence applications including optics, electronics, sensors, and energy storage and conversion devices is reviewed. Finally, it is also highlight some of the critical challenges and research opportunities. The review is anticipated to provide a systematic comprehension and valuable insights for inkjet printing, thereby facilitating the advancement of their emerging applications.

Engineered bacterial therapeutics with material solutions

Recent advances in engineered bacterial therapeutics underscore their potential in treating diseases via targeted, live interventions. Despite their promising performance in early clinical phases, no engineered therapeutic bacteria have yet received approval, primarily due to challenges in proving efficacy while ensuring biosafety. Material science innovations, particularly the encapsulation of bacteria within hydrogels, present a promising avenue to enhance bacterial survival, efficacy, and safety in therapeutic applications. This review discusses this interdisciplinary approach to develop living therapeutic materials. Hydrogels not only safeguard the bacteria from harsh physiological conditions but also enable controlled therapeutic release and prevent unintended bacterial dissemination. The strategic use of encapsulation materials could redefine the delivery and functionality of engineered bacterial therapeutics, facilitating their clinical translation.

Rational construction of synthetic consortia: Key considerations and model-based methods for guiding the development of a novel biosynthesis platform

The rapid development of synthetic biology has significantly improved the capabilities of mono-culture systems in converting different substrates into various value-added bio-chemicals through metabolic engineering. However, overexpression of biosynthetic pathways in recombinant strains can impose a heavy metabolic burden on the host, resulting in imbalanced energy distribution and negatively affecting both cell growth and biosynthesis capacity. Synthetic consortia, consisting of two or more microbial species or strains with complementary functions, have emerged as a promising and efficient platform to alleviate the metabolic burden and increase product yield. However, research on synthetic consortia is still in its infancy, with numerous challenges regarding the design and construction of stable synthetic consortia. This review provides a comprehensive comparison of the advantages and disadvantages of mono-culture systems and synthetic consortia. Key considerations for engineering synthetic consortia based on recent advances are summarized, and simulation and computational tools for guiding the advancement of synthetic consortia are discussed. Moreover, further development of more efficient and cost-effective synthetic consortia with emerging technologies such as artificial intelligence and machine learning is highlighted.

Microbe-loaded bioink designed to support therapeutic yeast growth

Live biotherapeutic products (LBPs) are an emerging class of therapeutics comprised of engineered living organisms such as bacteria or yeast. Bioprinting with living materials has now become possible using modern three-dimensional (3D) printing strategies. While there has been significant progress in bioprinting cells, bioprinting LBPs, specifically yeast, remains in its infancy and has not been optimized. Yeasts are a promising platform to develop into protein biofactories because they (1) grow rapidly, (2) are easy to engineer and manufacture, and (3) are inexpensive to produce. Here we developed an optimized method for loading yeast into hydrogel patches using digital light processing (DLP) 3D printing. We assessed the effects of patch geometry, bioink composition, and yeast concentration on yeast viability, patch stability, and protein release, and in doing so developed a patch formulation capable of supporting yeast growth and sustained protein release for at least ten days.

Methods for numerical simulation of soft actively contractile materials

Soft materials that can demonstrate on demand reconfigurability and changing compliance are highly sought after as actuator materials in many fields such as soft robotics and biotechnology. Whilst there are numerous proof of concept materials and devices, rigorous predictive models of deformation have not been well-established or widely adopted. In this paper, we discuss programming complex three-dimensional deformations of a soft intrinsically anisotropic material by controlling the orientation of the contractile units and/or direction of the applied electric field. Programming is achieved by patterning contractile units and/or selectively activating spatial regions. A new constitutive model is derived to describe the soft intrinsic anisotropy of soft materials. The model is developed within a continuum mechanics framework using an invariant-based formulation. Computational implementation allows us to simulate the complex three-dimensional shape response when activated by electric field. Several examples of the achievable Gauss-curved surfaces are demonstrated. Our computational analysis introduces a mechanics-based framework for design when considering soft morphing materials with intrinsic anisotropy, and is meant to inspire the development of new soft active materials.

Gene expression dynamics in input-responsive engineered living materials programmed for bioproduction

Engineered living materials (ELMs) fabricated by encapsulating microbes in hydrogels have great potential as bioreactors for sustained bioproduction. While long-term metabolic activity has been demonstrated in these systems, the capacity and dynamics of gene expression over time is not well understood. Thus, we investigate the long-term gene expression dynamics in microbial ELMs constructed using different microbes and hydrogel matrices. Through direct gene expression measurements of engineered E. coli in F127-bisurethane methacrylate (F127-BUM) hydrogels, we show that inducible, input-responsive genetic programs in ELMs can be activated multiple times and maintained for multiple weeks. Interestingly, the encapsulated bacteria sustain inducible gene expression almost 10 times longer than free-floating, planktonic cells. These ELMs exhibit dynamic responsiveness to repeated induction cycles, with up to 97% of the initial gene expression capacity retained following a subsequent induction event. We demonstrate multi-week bioproduction cycling by implementing inducible CRISPR transcriptional activation (CRISPRa) programs that regulate the expression of enzymes in a pteridine biosynthesis pathway. ELMs fabricated from engineered S. cerevisiae in bovine serum albumin (BSA) - polyethylene glycol diacrylate (PEGDA) hydrogels were programmed to express two different proteins, each under the control of a different chemical inducer. We observed scheduled bioproduction switching between betaxanthin pigment molecules and proteinase A in S. cerevisiae ELMs over the course of 27 days under continuous cultivation. Overall, these results suggest that the capacity for long-term genetic expression may be a general property of microbial ELMs. This work establishes approaches for implementing dynamic, input-responsive genetic programs to tailor ELM functions for a wide range of advanced applications.

The Next Frontier of 3D Bioprinting: Bioactive Materials Functionalized by Bacteria

3D bioprinting has become a flexible technical means used in many fields. Currently, research on 3D bioprinting is mainly focused on the use of mammalian cells to print organ and tissue models, which has greatly promoted progress in the fields of tissue engineering, regenerative medicine, and pharmaceuticals. In recent years, bacterial bioprinting has gradually become a rapidly developing research fields, with a wide range of potential applications in basic research, biomedicine, bioremediation, and other field. Here, this works reviews new research on bacterial bioprinting, and discuss its future research direction.

Tailored Polypeptide Star Copolymers for 3D Printing of Bacterial Composites Via Direct Ink Writing

Hydrogels hold much promise for 3D printing of functional living materials; however, challenges remain in tailoring mechanical robustness as well as biological performance. In addressing this challenge, the modular synthesis of functional hydrogels from 3-arm diblock copolypeptide stars composed of an inner poly(l-glutamate) domain and outer poly(l-tyrosine) or poly(l-valine) blocks is described. Physical crosslinking due to ß-sheet assembly of these star block copolymers gives mechanical stability during extrusion printing and the selective incorporation of methacrylate units allows for subsequent photocrosslinking to occur under biocompatible conditions. This permits direct ink writing (DIW) printing of bacteria-based mixtures leading to 3D objects with high fidelity and excellent bacterial viability. The tunable stiffness of different copolypeptide networks enables control over proliferation and colony formation for embedded Escherichia coli bacteria as demonstrated via isopropyl ß-d-1-thiogalactopyranoside (IPTG) induction of green fluorescent protein (GFP) expression. This translation of molecular structure to network properties highlights the versatility of these polypeptide hydrogel systems with the combination of writable structures and biological activity illustrating the future potential of these 3D-printed biocomposites.

Design and biofabrication of bacterial living materials with robust and multiplexed biosensing capabilities

The intertwined adoption of synthetic biology and 3D bioprinting has the potential to improve different application fields by fabricating engineered living materials (ELMs) with unnatural genetically-encoded sense & response capabilities. However, efforts are still needed to streamline the fabrication of sensing ELMs compatible with field use and improving their functional complexity. To investigate these two unmet needs, we adopted a workflow to reproducibly construct bacterial ELMs with synthetic biosensing circuits that provide red pigmentation as visible readout in response to different proof-of-concept chemical inducers. We first fabricated single-input/single-output ELMs and we demonstrated their robust performance in terms of longevity (cell viability and evolutionary stability >15 days, and long-term storage >1 month), sensing in harsh, non-sterile or nutrient-free conditions compatible with field use (soil, water, and clinical samples, including real samples from Pseudomonas aeruginosa infected patients). Then, we fabricated ELMs including multiple spatially-separated biosensor strains to engineer: level-bar materials detecting molecule concentration ranges, multi-input/multi-output devices with multiplexed sensing and information processing capabilities, and materials with cell-cell communication enabling on-demand pattern formation. Overall, we showed successful field use and multiplexed functioning of reproducibly fabricated ELMs, paving the way to a future automation of the prototyping process and boosting applications of such devices as in-situ monitoring tools or easy-to-use sensing kits.

Confocal imaging of biomarkers at a single-cell resolution: quantifying 'living' in 3D-printable engineered living material based on Pluronic F-127 and yeast Saccharomyces cerevisiae

BACKGROUND

Engineered living materials (ELMs) combine living cells with non-living scaffolds to obtain life-like characteristics, such as biosensing, growth, and self-repair. Some ELMs can be 3D-printed and are called bioinks, and their scaffolds are mostly hydrogel-based. One such scaffold is polymer Pluronic F127, a liquid at 4 °C but a biocompatible hydrogel at room temperature. In such thermally-reversible hydrogel, the microorganism-hydrogel interactions remain uncharacterized, making truly durable 3D-bioprinted ELMs elusive.

METHODS

We demonstrate the methodology to assess cell-scaffold interactions by characterizing intact alive yeast cells in cross-linked F127-based hydrogels, using genetically encoded ratiometric biosensors to measure intracellular ATP and cytosolic pH at a single-cell level through confocal imaging.

RESULTS

When embedded in hydrogel, cells were ATP-rich, in exponential or stationary phase, and assembled into microcolonies, which sometimes merged into larger superstructures. The hydrogels supported (micro)aerobic conditions and induced a nutrient gradient that limited microcolony size. External compounds could diffuse at least 2.7 mm into the hydrogels, although for optimal yeast growth bioprinted structures should be thinner than 0.6 mm. Moreover, the hydrogels could carry whole-cell copper biosensors, shielding them from contaminations and providing them with nutrients.

CONCLUSIONS

F127-based hydrogels are promising scaffolds for 3D-bioprinted ELMs, supporting a heterogeneous cell population primarily shaped by nutrient availability.

Cocultivation of White-Rot Fungi and Microalgae in the Presence of Nanocellulose

Cocultivation of fungi and algae can result in a mutualistic or antagonistic interaction depending on the species involved and the cultivation conditions. In this study, we investigated the growth behavior and enzymatic activity of two filamentous white-rot fungi (Trametes versicolor and Trametes pubescens) and two freshwater algae (Chlorella vulgaris and Scenedesmus vacuolatus) cocultured in the presence of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidized cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC). The growth of fungi and algae was studied in liquid, agar medium, and 3D-printed nanocellulose hydrogels. The results showed that cocultures grew faster under nutrient-rich conditions than in nutrient-depleted conditions. Key cellulose-degrading enzymes, including endoglucanase and laccase activities, were higher in liquid cocultures of T. versicolor and S. vacuolatus in the presence of cellulose compared to single cultures of fungi or algae. Although similar results were observed for cocultures of T. pubescens and C. vulgaris, laccase production diminished over time in these cultures. Fungi and algae were capable of growth in 3D-printed cellulose hydrogels. These results showed that cellulase enzyme production could be enhanced by cocultivating white-rot fungi with freshwater algae under nutrient-rich conditions with TEMPO-CNF and CNC. Additionally, the growth of white-rot fungi and freshwater algae in printed cellulose hydrogels demonstrates the potential use of fungi and algae in hydrogel systems for biotechnological applications, including biofuel production and bio-based fuel cell components. IMPORTANCE Depending on the conditions used to grow fungi and algae in the lab, they can interact in a mutually beneficial or negative way. These interactions could stimulate the organisms to produce enzymes in response to the interaction. We studied how wood decay fungi and freshwater algae grew in the presence and absence of cellulose, one of the basic building blocks of wood. How fungi and algae grew in 3D-printed cellulose hydrogels was also tested. Our results showed that fungi and algae partners produced significantly larger amounts of enzymes that degraded cellulose when grown with cellulose than when grown alone. In addition, fungi and algae were shown to grow in dense nanocellulose hydrogels and could survive the shear conditions during gel structuring while 3D-printing. These cultures could potentially be applied in the biotech industry for applications like energy production from cellulose, biofuel production, and bioremediation of cellulose material.

Three-dimensional bioprinting: A cutting-edge tool for designing and fabricating engineered living materials

The design of engineered living materials (ELMs) is an emerging field developed from synthetic biology and materials science principles. ELMs are multi-scale bulk materials that combine the properties of self-healing and organism adaptability with the designed physicochemical or mechanical properties for functional applications in various fields, including therapy, electronics, and architecture. Among the many ELM design and manufacturing methods, three-dimensional (3D) bioprinting stands out for its precise control over the structure of the fabricated constructs and the spatial distribution of cells. In this review, we summarize the progress in the field, cell type and material selection, and the latest applications of 3D bioprinting to manufacture ELMs, as well as their advantages and limitations, hoping to deepen our understanding and provide new insights into ELM design. We believe that 3D bioprinting will become an important development direction and provide more contributions to this field.

Emergent Biological Endurance Depends on Extracellular Matrix Composition of Three-Dimensionally Printed Escherichia coli Biofilms

Biofilms are three-dimensional (3D) bacterial communities that exhibit a highly self-organized nature in terms of their composition and complex architecture. Bacteria in biofilms display emergent biological properties, such as resistance to antimicrobials and disinfectants that the individual planktonic cells lack. Bacterial biofilms possess specialized architectural features including unique extracellular matrix compositions and a distinct spatially patterned arrangement of cells and matrix components within the biofilm. It is unclear which of these architectural elements of bacterial biofilms lead to the development of their emergent biological properties. Here, we report a 3D printing-based technique for studying the emergent resistance behaviors of Escherichia coli biofilms as a function of their architecture. Cellulose and curli are the major extracellular-matrix components in E. coli biofilms. We show that 3D-printed biofilms expressing either curli alone or both curli and cellulose in their extracellular matrices show higher resistance to exposure against disinfectants than 3D prints expressing either cellulose alone or no biofilm-matrix components. The 3D-printed biofilms expressing cellulose and/or curli also show thicker anaerobic zones than nonbiofilm-forming E. coli 3D prints. Thus, the matrix composition plays a crucial role in the emergent spatial patterning and biological endurance of 3D-printed biofilms. In contrast, initial spatial distribution of bacterial density or curli-producing cells does not have an effect on biofilm resistance phenotypes. Further, these 3D-printed biofilms could be reversibly attached to different surfaces (bacterial cellulose, glass, and polystyrene) and display resistance to physical distortions by retaining their shape and structure. This physical robustness highlights their potential in applications including bioremediation, protective coatings against pathogens on medical devices, or wastewater treatment, among many others. This new understanding of the emergent behavior of bacterial biofilms could aid in the development of novel engineered living materials using synthetic biology and materials science approaches.

Metabolism Control in 3D-Printed Living Materials Improves Fermentation

The three-dimensional (3D) printing of cell-containing polymeric hydrogels creates living materials (LMs), offering a platform for developing innovative technologies in areas like biosensors and biomanufacturing. The polymer material properties of cross-linkable F127-bis-urethane methacrylate (F127-BUM) allow reproducible 3D printing and stability in physiological conditions, making it suitable for fabricating LMs. Though F127-BUM-based LMs permit diffusion of solute molecules like glucose and ethanol, it remains unknown whether these are permissible for oxygen, essential for respiration. To determine oxygen permissibility, we quantified dissolved oxygen consumption by the budding yeast-laden F127-BUM-based LMs. Moreover, we obtained data on cell-retaining LMs, which allowed a direct comparison between LMs and suspension cultures. We further developed a highly reliable method to isolate cells from LMs for flow cytometry analysis, cell viability evaluation, and the purification of macromolecules. We found oxygen consumption heavily impaired inside LMs, indicating that yeast metabolism relies primarily on fermentation instead of respiration. Applying this finding to brewing, we observed a higher (3.7%) ethanol production using LMs than the traditional brewing process, indicating improved fermentation. Our study concludes that the present F127-BUM-based LMs are useful for microaerobic processes but developing aerobic bioprocesses will require further research.

Emerging Applications of 3D Printing in Biomanufacturing

The combination of 3D printing and synthetic biology is a sustainable strategy to fabricate biological objects and systems that behave in a preprogrammed manner. Many microorganisms have been genetically engineered as cell factories for the biosynthesis of chemicals using fermentation, and 3D printing of living materials using these cells could lead to a new paradigm for biomanufacturing.

Recent Advances on Bioprinted Gelatin Methacrylate-Based Hydrogels for Tissue Repair

Bioprinting of body tissues has gained great attention in recent years due to its unique advantages, including the creation of complex geometries and printing the patient-specific tissues with various drug and cell types. The most momentous part of the bioprinting process is bioink, defined as a mixture of living cells and biomaterials (especially hydrogels). Among different biomaterials, natural polymers are the best choices for hydrogel-based bioinks due to their intrinsic biocompatibility and minimal inflammatory response in body condition. Gelatin methacryloyl (GelMA) hydrogel is one of the high-potential hydrogel-based bioinks due to its easy synthesis with low cost, great biocompatibility, transparent structure that is useful for cell monitoring, photocrosslinkability, and cell viability. Furthermore, the potential of adjusting properties of GelMA due to the synthesis protocol makes it a suitable choice for soft or hard tissues. In this review, different methods for the bioprinting of GelMA-based bioinks, as well as various effective process parameters, are reviewed. Also, several solutions for challenges in the printing of GelMA-based bioinks are discussed, and applications of GelMA-based bioprinted tissues argued as well. Impact statement Bioprinting has been demonstrated as a promising and alternative approach for organ transplantation to develop various types of living tissue. Bioinks, with great biological characteristics similar to the host tissues and rheological/flow features, are the first requirements for the successful bioprinting approach. Gelatin methacryloyl (GelMA) hydrogel is one of the high-potential hydrogel-based bioinks. This review provides a comprehensive look at different methods for the bioprinting of GelMA-based bioinks and applications of GelMA-based bioprinted tissues for tissue repair.

Stimuli-responsive engineered living materials

Stimuli-responsive materials are able to undergo controllable changes in materials properties in response to external cues. Increasing efforts have been directed towards building materials that mimic the responsive nature of biological systems. Nevertheless, limitations remain surrounding the way these synthetic materials interact and respond to their environment. In particular, it is difficult to synthesize synthetic materials that respond with specificity to poorly differentiated (bio)chemical and weak physical stimuli. The emerging area of engineered living materials (ELMs) includes composites that combine living cells and synthetic materials. ELMs have yielded promising advances in the creation of stimuli-responsive materials that respond with diverse outputs in response to a broad array of biochemical and physical stimuli. This review describes advances made in the genetic engineering of the living component and the processing-property relationships of stimuli-responsive ELMs. Finally, the implementation of stimuli-responsive ELMs as environmental sensors, biomedical sensors, drug delivery vehicles, and soft robots is discussed.