iPS cell therapy 2.0: Preparing for next-generation regenerative medicine

This year marks the tenth anniversary of the world's first transplantation of tissue generated from induced pluripotent stem cells (iPSCs). There is now a growing number of clinical trials worldwide examining the efficacy and safety of autologous and allogeneic iPSC-derived products for treating various pathologic conditions. As we patiently wait for the results from these and future clinical trials, it is imperative to strategize for the next generation of iPSC-based therapies. This review examines the lessons learned from the development of another advanced cell therapy, chimeric antigen receptor (CAR) T cells, and the possibility of incorporating various new bioengineering technologies in development, from RNA engineering to tissue fabrication, to apply iPSCs not only as a means to achieve personalized medicine but also as designer medical applications.

Enhancing Therapeutic Insulin Transport from Macroencapsulated Islets Using Sub-Minute Pressure at Physiological Levels

Cadaveric islet and stem cell-derived transplantations hold promise as treatments for type 1 diabetes. To tackle the issue of immunocompatibility, numerous cellular macroencapsulation techniques have been developed that utilize diffusion to transport insulin across an immunoisolating barrier. However, despite several devices progressing to human clinical trials, none have successfully managed to attain physiologic glucose control or insulin independence. Based on empirical evidence, macroencapsulation methods with multilayered, high islet surface density are incompatible with homeostatic, on-demand insulin delivery and physiologic glucose regulation, when reliant solely on diffusion. An additional driving force is essential to overcome the distance limit of diffusion. In this study, we present both theoretical proof and experimental validation that applying pressure at levels comparable to physiological diastolic blood pressure significantly enhances insulin flux across immunoisolation membranes-increasing it by nearly three orders of magnitude. This significant enhancement in transport rate allows for precise, sub-minute regulation of both bolus and basal insulin delivery. By incorporating this technique with a pump-based extravascular system, we demonstrate the ability to rapidly reduce glucose levels in diabetic rodent models, effectively replicating the timescale and therapeutic effect of subcutaneous insulin injection or infusion. This advance provides a potential path towards achieving insulin independence with islet macroencapsulation.

One Sentence Summary

Towards improved glucose control, applying sub-minute pressure at physiological levels enhances therapeutic insulin transport from macroencapsulated islets.

Robotic Actuation-Mediated Quantitative Mechanogenetics for Noninvasive and On-Demand Cancer Therapy

Cell mechanotransduction signals are important targets for physical therapy. However, current physiotherapy heavily relies on ultrasound, which is generated by high-power equipment or amplified by auxiliary drugs, potentially causing undesired side effects. To address current limitations, a robotic actuation-mediated therapy is developed that utilizes gentle mechanical loads to activate mechanosensitive ion channels. The resulting calcium influx precisely regulated the expression of recombinant tumor suppressor protein and death-associated protein kinase, leading to programmed apoptosis of cancer cell line through caspase-dependent pathway. In stark contrast to traditional gene therapy, the complete elimination of early- and middle-stage tumors (volume ≤ 100 mm3) and significant growth inhibition of late-stage tumor (500 mm3) are realized in tumor-bearing mice by transfecting mechanogenetic circuits and treating daily with quantitative robotic actuation in a form of 5 min treatment over the course of 14 days. Thus, this massage-derived therapy represents a quantitative strategy for cancer treatment.

Ultrashort-Peptide-Responsive Gene Switches for Regulation of Therapeutic Protein Expression in Mammalian Cells

Despite the array of mammalian transgene switches available for regulating therapeutic protein expression in response to small molecules or physical stimuli, issues remain, including cytotoxicity of chemical inducers and limited biocompatibility of physical cues. This study introduces gene switches driven by short peptides comprising eight or fewer amino acid residues. Utilizing a competence regulator (ComR) and sigma factor X-inducing peptide (XIP) from Streptococcus vestibularis as the receptor and inducer, respectively, this study develops two strategies for a peptide-activated transgene control system. The first strategy involves fusing ComR with a transactivation domain and utilizes ComR-dependent synthetic promoters to drive expression of the gene-of-interest, activated by XIP, thereby confirming its membrane penetrability and intracellular functionality. The second strategy features an orthogonal synthetic receptor exposing ComR extracellularly (ComREXTRA), greatly increasing sensitivity with exceptional responsiveness to short peptides. In a proof-of-concept study, peptides are administered to type-1 diabetic mice with microencapsulated engineered human cells expressing ComREXTRA for control of insulin expression, restoring normoglycemia. It is envisioned that this system will encourage the development of short peptide drugs and promote the introduction of non-toxic, orthogonal, and highly biocompatible personalized biopharmaceuticals for gene- and cell-based therapies.

Applications of genetic code expansion technology in eukaryotes

Unnatural amino acids (UAAs) have gained significant attention in protein engineering and drug development owing to their ability to introduce new chemical functionalities to proteins. In eukaryotes, genetic code expansion (GCE) enables the incorporation of UAAs and facilitates posttranscriptional modification (PTM), which is not feasible in prokaryotic systems. GCE is also a powerful tool for cell or animal imaging, the monitoring of protein interactions in target cells, drug development, and switch regulation. Therefore, there is keen interest in utilizing GCE in eukaryotic systems. This review provides an overview of the application of GCE in eukaryotic systems and discusses current challenges that need to be addressed.

A Gene-Switch Platform Interfacing with Reactive Oxygen Species Enables Transcription Fine-Tuning by Soluble and Volatile Pharmacologics and Food Additives

Synthetic biology aims to engineer transgene switches for precise therapeutic protein control in cell-based gene therapies. However, off-the-shelf trigger-inducible gene circuits are usually switched on by single or structurally similar molecules. This study presents a mammalian gene-switch platform that controls therapeutic gene expression by a wide range of molecules generating low, non-toxic levels of reactive oxygen species (ROS). In this system, KEAP1 (Kelch-like ECH-associated protein 1) serves as ROS sensor, regulating the translocation of NRF2 (nuclear factor erythroid 2-related factor 2) to the nucleus, where NRF2 binds to  antioxidant response elements (ARE) to activate the expression of a gene of interest. It is found that a promoter containing eight-tandem ARE repeats is highly sensitive to the low ROS levels generated by the soluble and volatile molecules, which include food preservatives, food additives, pharmaceuticals, and signal transduction inducers. In a proof-of-concept study, it is shown that many of these compounds can independently trigger microencapsulated engineered cells to produce sufficient insulin to restore normoglycemia in experimental type-1 diabetic mice. It is believed that this system greatly extends the variety of small-molecule inducers available to drive therapeutic gene switches.

External Electrons Directly Stimulate Escherichia coli for Enhancing Biological Hydrogen Production

External electric field has the potential to influence metabolic processes such as biological hydrogen production in microorganisms. Based on this concept, we designed and constructed an electroactive hybrid system for microbial biohydrogen production under an electric field comprised of polydopamine (PDA)-modified Escherichia coli (E. coli) and Ni foam (NF). In this system, electrons generated from NF directly migrate into E. coli cells to promote highly efficient biocatalytic hydrogen production. Compared to that generated in the absence of electric field stimulation, biohydrogen production by the PDA-modified E. coli-based system is significantly enhanced. This investigation has demonstrated the mechanism for electron transfer in a biohybrid system and gives insight into precise basis for the enhancement of hydrogen production by using the multifield coupling technology.

Alternating magnetic fields drive stimulation of gene expression via generation of reactive oxygen species

Magnetogenetics represents a method for remote control of cellular function. Previous work suggests that generation of reactive oxygen species (ROS) initiates downstream signaling. Herein, a chemical biology approach was used to elucidate further the mechanism of radio frequency-alternating magnetic field (RF-AMF) stimulation of a TRPV1-ferritin magnetogenetics platform that leads to Ca2+ flux. RF-AMF stimulation of HEK293T cells expressing TRPV1-ferritin resulted in ∼30% and ∼140% increase in intra- and extracellular ROS levels, respectively. Mutations to specific cysteine residues in TRPV1 responsible for ROS sensitivity eliminated RF-AMF driven Ca2+-dependent transcription of secreted embryonic alkaline phosphatase (SEAP). Using a non-tethered (to TRPV1) ferritin also eliminated RF-AMF driven SEAP production, and using specific inhibitors, ROS-activated TRPV1 signaling involves protein kinase C, NADPH oxidase, and the endoplasmic reticulum. These results suggest ferritin-dependent ROS activation of TRPV1 plays a key role in the initiation of magnetogenetics, and provides relevance for potential applications in medicine and biotechnology.

Synthetic Gene Circuits for Regulation of Next-Generation Cell-Based Therapeutics

Arming human cells with synthetic gene circuits enables to expand their capacity to execute superior sensing and response actions, offering tremendous potential for innovative cellular therapeutics. This can be achieved by assembling components from an ever-expanding molecular toolkit, incorporating switches based on transcriptional, translational, or post-translational control mechanisms. This review provides examples from the three classes of switches, and discusses their advantages and limitations to regulate the activity of therapeutic cells in vivo. Genetic switches designed to recognize internal disease-associated signals often encode intricate actuation programs that orchestrate a reduction in the sensed signal, establishing a closed-loop architecture. Conversely, switches engineered to detect external molecular or physical cues operate in an open-loop fashion, switching on or off upon signal exposure. The integration of such synthetic gene circuits into the next generation of chimeric antigen receptor T-cells is already enabling precise calibration of immune responses in terms of magnitude and timing, thereby improving the potency and safety of therapeutic cells. Furthermore, pre-clinical engineered cells targeting other chronic diseases are gathering increasing attention, and this review discusses the path forward for achieving clinical success. With synthetic biology at the forefront, cellular therapeutics holds great promise for groundbreaking treatments.

Excite the unexcitable: engineering cells and redox signaling for targeted bioelectronic control

The ever-growing influence of technology in our lives has led to an increasing interest in the development of smart electronic devices to interrogate and control biological systems. Recently, redox-mediated electrogenetics introduced a novel avenue that enables direct bioelectronic control at the genetic level. In this review, we discuss recent advances in methodologies for bioelectronic control, ranging from electrical stimulation to engineering efforts that allow traditionally unexcitable cells to be electrically 'programmable.' Alongside ion-transport signaling, we suggest redox as a route for rational engineering because it is a native form of electronic communication in biology. Using redox as a common language allows the interfacing of electronics and biology. This newfound connection opens a gateway of possibilities for next-generation bioelectronic tools.

Microneedle-Mediated Cell Therapy

Microneedles have emerged as a promising platform for transdermal drug delivery with prominent advantages, such as enhanced permeability, mitigated pain, and improved patient adherence. While microneedles have primarily been employed for delivering small molecules, nucleic acids, peptides, and proteins, recent researches have demonstrated their prospect in combination with cell therapy. Cell therapy involving administration or transplantation of living cells (e.g. T cells, stem cells, and pancreatic cells) has gained significant attention in preclinical and clinical applications for various disease treatments. However, the effectiveness of systemic cell delivery may be restricted in localized conditions like solid tumors and skin disorders due to limited penetration and accumulation into the lesions. In this perspective, an overview of recent advances in microneedle-assisted cell delivery for immunotherapy, tissue regeneration, and hormone modulation, with respect to their mechanical property, cell loading capacity, as well as viability and bioactivity of the loaded cells is provided. Potential challenges and future perspectives with microneedle-mediated cell therapy are also discussed.

Posttranslational Remote Control Mediated by Physical Inducers for Rapid Protein Release in Engineered Mammalian Cells

Physical cues such as light, heat, or an electrical field can be utilized for traceless, on-demand activation of the expression of a desired therapeutic gene in appropriately engineered cells with excellent spatiotemporal resolution, good inducibility, and simple reversibility. A similar approach can be applied to build a depolarization-based protein secretion system that enables rapid release of a therapeutic protein pre-stored in intracellular vesicles in mammalian cells. Here, we present a protocol to create designer β-cells that exhibit light-controllable rapid release (within 15 min) of a pre-synthesized proinsulin-nanoluciferase construct from vesicular stores. The construct is cleaved extracellularly to afford secreted insulin as a therapeutic protein and nanoluciferase as a reporter molecule. Such posttranslational remote control offers a much faster response than expression-based systems.

Redox-enabled electronic interrogation and feedback control of hierarchical and networked biological systems

Microelectronic devices can directly communicate with biology, as electronic information can be transmitted via redox reactions within biological systems. By engineering biology's native redox networks, we enable electronic interrogation and control of biological systems at several hierarchical levels: proteins, cells, and cell consortia. First, electro-biofabrication facilitates on-device biological component assembly. Then, electrode-actuated redox data transmission and redox-linked synthetic biology allows programming of enzyme activity and closed-loop electrogenetic control of cellular function. Specifically, horseradish peroxidase is assembled onto interdigitated electrodes where electrode-generated hydrogen peroxide controls its activity. E. coli's stress response regulon, oxyRS, is rewired to enable algorithm-based feedback control of gene expression, including an eCRISPR module that switches cell-cell quorum sensing communication from one autoinducer to another-creating an electronically controlled 'bilingual' cell. Then, these disparate redox-guided devices are wirelessly connected, enabling real-time communication and user-based control. We suggest these methodologies will help us to better understand and develop sophisticated control for biology.

Scheduled dosage regimen by irreversible electroporation of loaded erythrocytes for cancer treatment

Precise control of cargo release is essential but still a great challenge for any drug delivery system. Irreversible electroporation (IRE), utilizing short high-voltage pulsed electric fields to destabilize the biological membrane, has been recently approved as a non-thermal technique for tumor ablation without destroying the integrity of adjacent collagenous structures. Due to the electro-permeating membrane ability, IRE might also have great potential to realize the controlled drug release in response to various input IRE parameters, which were tested in a red blood cell (RBC) model in this work. According to the mathematical simulation model of a round biconcave disc-like cell based on RBC shape and dielectric characteristics, the permeability and the pore density of the RBC membrane were found to quantitatively depend on the pulse parameters. To further provide solid experimental evidence, indocyanine green (ICG) and doxorubicin (DOX) were both loaded inside RBCs (RBC@DOX&ICG) and the drug release rates were found to be tailorable by microsecond pulsed electric field (μsPEF). In addition, μsPEF could effectively modulate the tumor stroma to augment therapy efficacy by increasing micro-vessel density and permeability, softening extracellular matrix, and alleviating tumor hypoxia. Benefiting from these advantages, this IRE-responsive RBC@DOX&ICG achieved a remarkably synergistic anti-cancer effect by the combination of μsPEF and chemotherapy in the tumor-bearing mice model, with the survival time increasing above 90 days without tumor burden. Given that IRE is easily adaptable to different plasma membrane-based vehicles for delivering diverse drugs, this approach could offer a general applicability for cancer treatment.

A monolithically integrated in-textile wristband for wireless epidermal biosensing

Textile bioelectronics that allow comfortable epidermal contact hold great promise in noninvasive biosensing. However, their applications are limited mainly because of the large intrinsic electrical resistance and low compatibility for electronics integration. We report an integrated wristband that consists of multifunctional modules in a single piece of textile to realize wireless epidermal biosensing. The in-textile metallic patterning and reliable interconnect encapsulation contribute to the excellent electrical conductivity, mechanical robustness, and waterproofness that are competitive with conventional flexible devices. Moreover, the well-maintained porous textile architectures deliver air permeability of 79 mm s-1 and moisture permeability of 270 g m-2 day-1, which are more than one order of magnitude higher than medical tapes, thus ensuring superior wearing comfort. The integrated in-textile wristband performed continuous sweat potassium monitoring in the range of 0.3 to 40 mM with long-term stability, demonstrating its great potential for wearable fitness monitoring and point-of-care testing.

Electrocatalytic on-site oxygenation for transplanted cell-based-therapies

Implantable cell therapies and tissue transplants require sufficient oxygen supply to function and are limited by a delay or lack of vascularization from the transplant host. Previous exogenous oxygenation strategies have been bulky and had limited oxygen production or regulation. Here, we show an electrocatalytic approach that enables bioelectronic control of oxygen generation in complex cellular environments to sustain engineered cell viability and therapy under hypoxic stress and at high cell densities. We find that nanostructured sputtered iridium oxide serves as an ideal catalyst for oxygen evolution reaction at neutral pH. We demonstrate that this approach exhibits a lower oxygenation onset and selective oxygen production without evolution of toxic byproducts. We show that this electrocatalytic on site oxygenator can sustain high cell loadings (>60k cells/mm3) in hypoxic conditions in vitro and in vivo. Our results showcase that exogenous oxygen production devices can be readily integrated into bioelectronic platforms, enabling high cell loadings in smaller devices with broad applicability.

A wireless, battery-free device enables oxygen generation and immune protection of therapeutic xenotransplants in vivo

The immune isolation of cells within devices has the potential to enable long-term protein replacement and functional cures for a range of diseases, without requiring immune suppressive therapy. However, a lack of vasculature and the formation of fibrotic capsules around cell immune-isolating devices limits oxygen availability, leading to hypoxia and cell death in vivo. This is particularly problematic for pancreatic islet cells that have high O2 requirements. Here, we combine bioelectronics with encapsulated cell therapies to develop the first wireless, battery-free oxygen-generating immune-isolating device (O2-Macrodevice) for the oxygenation and immune isolation of cells in vivo. The system relies on electrochemical water splitting based on a water-vapor reactant feed, sustained by wireless power harvesting based on a flexible resonant inductive coupling circuit. As such, the device does not require pumping, refilling, or ports for recharging and does not generate potentially toxic side products. Through systematic in vitro studies with primary cell lines and cell lines engineered to secrete protein, we demonstrate device performance in preventing hypoxia in ambient oxygen concentrations as low as 0.5%. Importantly, this device has shown the potential to enable subcutaneous (SC) survival of encapsulated islet cells, in vivo in awake, freely moving, immune-competent animals. Islet transplantation in Type I Diabetes represents an important application space, and 1-mo studies in immune-competent animals with SC implants show that the O2-Macrodevice allows for survival and function of islets at high densities (~1,000 islets/cm2) in vivo without immune suppression and induces normoglycemia in diabetic animals.

Tissue-Matchable and Implantable Batteries Toward Biomedical Applications

Implantable electronic devices can realize real-time and reliable health monitoring, diagnosis, and treatment of human body, which are expected to overcome important bottlenecks in the biomedical field. However, the commonly used energy supply devices for them are implantable batteries based on conventional rigid device design with toxic components, which both mechanically and biologically mismatch soft biological tissues. Therefore, the development of highly soft, safe, and implantable tissue-matchable flexible batteries is of great significance and urgency for implantable bioelectronics. In this work, the recent advances of tissue-matchable and implantable flexible batteries are overviewed, focusing on the design strategies of electrodes/batteries and their biomedical applications. The mechanical flexibility, biocompatibility, and electrochemical performance in vitro and in vivo of these flexible electrodes/batteries are then discussed. Finally, perspectives are provided on the current challenges and possible directions of this field in the future.

Correcting instructive electric potential patterns in multicellular systems: External actions and endogenous processes

BACKGROUND

Transmembrane electrical potential differences in cells modulate the spatio-temporal distribution of signaling ions and molecules that are instructive for downstream signaling pathways in multicellular systems. The local coupling between bioelectricity and protein transcription patterns allows dynamic subsystems (modules) of cells that share the same bioelectrical state to show similar biochemical downstream processes.

METHODS

We simulate theoretically how the integration-segregation pattern formed by the different multicellular modules that define a biosystem can be controlled by multicellular potentials. To this end, we couple together the model equations of the bioelectrical network to those of the genetic network.

RESULTS

The coupling provided by the intercellular junctions and the external microenvironment allows the restoration of the target bioelectrical pattern by changing the transcription rate of specific ion channels, the post-translational blocking of these channels, and changes in the environmental ionic concentrations.

CONCLUSIONS

The simulations show that the single-cell feedback between bioelectrical and transcriptional processes, together with the coupling provided by the intercellular junctions and the environment, can correct large-scale patterns by means of suitable external actions.

GENERAL SIGNIFICANCE

This study provides a theoretical advancement in the understanding of how the multicellular bioelectric coupling may guide repolarizing interventions for regenerating a tissue, with potential implications in biomedicine.

Soft Bioelectronics for Therapeutics

Soft bioelectronics play an increasingly crucial role in high-precision therapeutics due to their softness, biocompatibility, clinical accuracy, long-term stability, and patient-friendliness. In this review, we provide a comprehensive overview of the latest representative therapeutic applications of advanced soft bioelectronics, ranging from wearable therapeutics for skin wounds, diabetes, ophthalmic diseases, muscle disorders, and other diseases to implantable therapeutics against complex diseases, such as cardiac arrhythmias, cancer, neurological diseases, and others. We also highlight key challenges and opportunities for future clinical translation and commercialization of soft therapeutic bioelectronics toward personalized medicine.

Shaping Synthetic Multicellular and Complex Multimaterial Tissues via Embedded Extrusion-Volumetric Printing of Microgels

In living tissues, cells express their functions following complex signals from their surrounding microenvironment. Capturing both hierarchical architectures at the micro- and macroscale, and anisotropic cell patterning remains a major challenge in bioprinting, and a bottleneck toward creating physiologically-relevant models. Addressing this limitation, a novel technique is introduced, termed Embedded Extrusion-Volumetric Printing (EmVP), converging extrusion-bioprinting and layer-less, ultra-fast volumetric bioprinting, allowing spatially pattern multiple inks/cell types. Light-responsive microgels are developed for the first time as bioresins (µResins) for light-based volumetric bioprinting, providing a microporous environment permissive for cell homing and self-organization. Tuning the mechanical and optical properties of gelatin-based microparticles enables their use as support bath for suspended extrusion printing, in which features containing high cell densities can be easily introduced. µResins can be sculpted within seconds with tomographic light projections into centimeter-scale, granular hydrogel-based, convoluted constructs. Interstitial microvoids enhanced differentiation of multiple stem/progenitor cells (vascular, mesenchymal, neural), otherwise not possible with conventional bulk hydrogels. As proof-of-concept, EmVP is applied to create complex synthetic biology-inspired intercellular communication models, where adipocyte differentiation is regulated by optogenetic-engineered pancreatic cells. Overall, EmVP offers new avenues for producing regenerative grafts with biological functionality, and for developing engineered living systems and (metabolic) disease models.

Evolution of molecular switches for regulation of transgene expression by clinically licensed gluconate

Synthetic biology holds great promise to improve the safety and efficacy of future gene and engineered cell therapies by providing new means of endogenous or exogenous control of the embedded therapeutic programs. Here, we focused on gluconate as a clinically licensed small-molecule inducer and engineered gluconate-sensitive molecular switches to regulate transgene expression in human cell cultures and in mice. Several switch designs were assembled based on the gluconate-responsive transcriptional repressor GntR from Escherichia coli. Initially we assembled OFF- and ON-type switches by rewiring the native gluconate-dependent binding of GntR to target DNA sequences in mammalian cells. Then, we utilized the ability of GntR to dimerize in the presence of gluconate to activate gene expression from a split transcriptional activator. By means of random mutagenesis of GntR combined with phenotypic screening, we identified variants that significantly enhanced the functionality of the genetic devices, enabling the construction of robust two-input logic gates. We also demonstrated the potential utility of the synthetic switch in two in vivo settings, one employing implantation of alginate-encapsulated engineered cells and the other involving modification of host cells by DNA delivery. Then, as proof-of-concept, the gluconate-actuated genetic switch was connected to insulin secretion, and the components encoding gluconate-induced insulin production were introduced into type-1 diabetic mice as naked DNA via hydrodynamic tail vein injection. Normoglycemia was restored, thereby showcasing the suitability of oral gluconate to regulate in situ production of a therapeutic protein.

Sub-1.4 cm3 capsule for detecting labile inflammatory biomarkers in situ

Transient molecules in the gastrointestinal tract such as nitric oxide and hydrogen sulfide are key signals and mediators of inflammation. Owing to their highly reactive nature and extremely short lifetime in the body, these molecules are difficult to detect. Here we develop a miniaturized device that integrates genetically engineered probiotic biosensors with a custom-designed photodetector and readout chip to track these molecules in the gastrointestinal tract. Leveraging the molecular specificity of living sensors1, we genetically encoded bacteria to respond to inflammation-associated molecules by producing luminescence. Low-power electronic readout circuits2 integrated into the device convert the light emitted by the encapsulated bacteria to a wireless signal. We demonstrate in vivo biosensor monitoring in the gastrointestinal tract of small and large animal models and the integration of all components into a sub-1.4 cm3 form factor that is compatible with ingestion and capable of supporting wireless communication. With this device, diseases such as inflammatory bowel disease could be diagnosed earlier than is currently possible, and disease progression could be more accurately tracked. The wireless detection of short-lived, disease-associated molecules with our device could also support timely communication between patients and caregivers, as well as remote personalized care.

An electrogenetic interface to program mammalian gene expression by direct current

Wearable electronic devices are playing a rapidly expanding role in the acquisition of individuals' health data for personalized medical interventions; however, wearables cannot yet directly program gene-based therapies because of the lack of a direct electrogenetic interface. Here we provide the missing link by developing an electrogenetic interface that we call direct current (DC)-actuated regulation technology (DART), which enables electrode-mediated, time- and voltage-dependent transgene expression in human cells using DC from batteries. DART utilizes a DC supply to generate non-toxic levels of reactive oxygen species that act via a biosensor to reversibly fine-tune synthetic promoters. In a proof-of-concept study in a type 1 diabetic male mouse model, a once-daily transdermal stimulation of subcutaneously implanted microencapsulated engineered human cells by energized acupuncture needles (4.5 V DC for 10 s) stimulated insulin release and restored normoglycemia. We believe this technology will enable wearable electronic devices to directly program metabolic interventions.

Reprogramming cellular metabolism to increase the efficiency of microbial cell factories

Recent studies are increasingly focusing on advanced biotechnological tools, self-adjusting smart microorganisms, and artificial intelligent networks, to engineer microorganisms with various functions. Microbial cell factories are a vital platform for improving the bioproduction of medicines, biofuels, and biomaterials from renewable carbon sources. However, these processes are significantly affected by cellular metabolism, and boosting the efficiency of microbial cell factories remains a challenge. In this review, we present a strategy for reprogramming cellular metabolism to enhance the efficiency of microbial cell factories for chemical biosynthesis, which improves our understanding of microbial physiology and metabolic control. Current methods are mainly focused on synthetic pathways, metabolic resources, and cell performance. This review highlights the potential biotechnological strategy to reprogram cellular metabolism and provide novel guidance for designing more intelligent industrial microbes with broader applications in this growing field.

A versatile bioelectronic interface programmed for hormone sensing

Precision medicine requires smart, ultrasensitive, real-time profiling of bio-analytes using interconnected miniaturized devices to achieve individually optimized healthcare. Here, we report a versatile bioelectronic interface (VIBE) that senses signaling-cascade-guided receptor-ligand interactions via an electronic interface. We show that VIBE offers a low detection limit down to sub-nanomolar range characterised by an output current that decreases significantly, leading to precise profiling of these peptide hormones throughout the physiologically relevant concentration ranges. In a proof-of-concept application, we demonstrate that the VIBE platform differentiates insulin and GLP-1 levels in serum samples of wild-type mice from type-1 and type-2 diabetic mice. Evaluation of human serum samples shows that the bioelectronic device can differentiate between samples from different individuals and report differences in their metabolic states. As the target analyte can be changed simply by introducing engineered cells overexpressing the appropriate receptor, the VIBE interface has many potential applications for point-of-care diagnostics and personalized medicine via the internet of things.

Applications of synthetic biology in medical and pharmaceutical fields

Synthetic biology aims to design or assemble existing bioparts or bio-components for useful bioproperties. During the past decades, progresses have been made to build delicate biocircuits, standardized biological building blocks and to develop various genomic/metabolic engineering tools and approaches. Medical and pharmaceutical demands have also pushed the development of synthetic biology, including integration of heterologous pathways into designer cells to efficiently produce medical agents, enhanced yields of natural products in cell growth media to equal or higher than that of the extracts from plants or fungi, constructions of novel genetic circuits for tumor targeting, controllable releases of therapeutic agents in response to specific biomarkers to fight diseases such as diabetes and cancers. Besides, new strategies are developed to treat complex immune diseases, infectious diseases and metabolic disorders that are hard to cure via traditional approaches. In general, synthetic biology brings new capabilities to medical and pharmaceutical researches. This review summarizes the timeline of synthetic biology developments, the past and present of synthetic biology for microbial productions of pharmaceutics, engineered cells equipped with synthetic DNA circuits for diagnosis and therapies, live and auto-assemblied biomaterials for medical treatments, cell-free synthetic biology in medical and pharmaceutical fields, and DNA engineering approaches with potentials for biomedical applications.

Electro-Biofabrication. Coupling Electrochemical and Biomolecular Methods to Create Functional Bio-Based Hydrogels

Twenty years ago, this journal published a review entitled "Biofabrication with Chitosan" based on the observations that (i) chitosan could be electrodeposited using low voltage electrical inputs (typically less than 5 V) and (ii) the enzyme tyrosinase could be used to graft proteins (via accessible tyrosine residues) to chitosan. Here, we provide a progress report on the coupling of electronic inputs with advanced biological methods for the fabrication of biopolymer-based hydrogel films. In many cases, the initial observations of chitosan's electrodeposition have been extended and generalized: mechanisms have been established for the electrodeposition of various other biological polymers (proteins and polysaccharides), and electrodeposition has been shown to allow the precise control of the hydrogel's emergent microstructure. In addition, the use of biotechnological methods to confer function has been extended from tyrosinase conjugation to the use of protein engineering to create genetically fused assembly tags (short sequences of accessible amino acid residues) that facilitate the attachment of function-conferring proteins to electrodeposited films using alternative enzymes (e.g., transglutaminase), metal chelation, and electrochemically induced oxidative mechanisms. Over these 20 years, the contributions from numerous groups have also identified exciting opportunities. First, electrochemistry provides unique capabilities to impose chemical and electrical cues that can induce assembly while controlling the emergent microstructure. Second, it is clear that the detailed mechanisms of biopolymer self-assembly (i.e., chitosan gel formation) are far more complex than anticipated, and this provides a rich opportunity both for fundamental inquiry and for the creation of high performance and sustainable material systems. Third, the mild conditions used for electrodeposition allow cells to be co-deposited for the fabrication of living materials. Finally, the applications have been expanded from biosensing and lab-on-a-chip systems to bioelectronic and medical materials. We suggest that electro-biofabrication is poised to emerge as an enabling additive manufacturing method especially suited for life science applications and to bridge communication between our biological and technological worlds.

Blood-Glucose-Powered Metabolic Fuel Cell for Self-Sufficient Bioelectronics

Currently available bioelectronic devices consume too much power to be continuously operated on rechargeable batteries, and are often powered wirelessly, with attendant issues regarding reliability, convenience, and mobility. Thus, the availability of a robust, self-sufficient, implantable electrical power generator that works under physiological conditions would be transformative for many applications, from driving bioelectronic implants and prostheses to programing cellular behavior and patients' metabolism. Here, capitalizing on a new copper-containing, conductively tuned 3D carbon nanotube composite, an implantable blood-glucose-powered metabolic fuel cell is designed that continuously monitors blood-glucose levels, converts excess glucose into electrical power during hyperglycemia, and produces sufficient energy (0.7 mW cm^-2 , 0.9 V, 50 mm glucose) to drive opto- and electro-genetic regulation of vesicular insulin release from engineered beta cells. It is shown that this integration of blood-glucose monitoring with elimination of excessive blood glucose by combined electro-metabolic conversion and insulin-release-mediated cellular consumption enables the metabolic fuel cell to restore blood-glucose homeostasis in an automatic, self-sufficient, and closed-loop manner in an experimental model of type-1 diabetes.

Cation pumping against a concentration gradient in conical nanopores characterized by load capacitors

We study the cation transport against an external concentration gradient (cation pumping) that occurs in conical nanopores when zero-average oscillatory and white noise potentials are externally applied. This pumping, based on the electrically asymmetric nanostructure, is characterized here by a load capacitor arrangement. In the case of white noise signals, the conical nanopore acts as an electrical valve that allows extraction of order from chaos. No molecular carriers, specific ion pumps, and competitive ion-binding phenomena are required. The nanopore conductance on/off states mimic those of the voltage-gated ion channels in the cell membrane. These channels allow modulating membrane potentials and ionic concentration gradients along oscillatory pulses in circadian rhythms and the cell cycle. We show that the combination of asymmetric nanostructures with load capacitors can be useful for the understanding of nanofluidic processes based on bioelectrochemical gradients.

Recent advances, opportunities and challenges in cybergenetic identification and control of biomolecular networks

Cybergenetics is a new area of research aimed at developing digital and biological controllers for living systems. Synthetic biologists have begun exploiting cybergenetic tools and platforms to both accelerate the development of mathematical models and develop control strategies for complex biological phenomena. Here, we review the state of the art in cybergenetic identification and control. Our aim is to lower the entry barrier to this field and foster the adoption of methods and technologies that will accelerate the pace at which Synthetic Biology progresses toward applications.

Controlling therapeutic protein expression via inhalation of a butter flavor molecule

Precise control of the delivery of therapeutic proteins is critical for gene- and cell-based therapies, and expression should only be switched on in the presence of a specific trigger signal of appropriate magnitude. Focusing on the advantages of delivering the trigger by inhalation, we have developed a mammalian synthetic gene switch that enables regulation of transgene expression by exposure to the semi-volatile small molecule acetoin, a widely used, FDA-approved food flavor additive. The gene switch capitalizes on the bacterial regulatory protein AcoR fused to a mammalian transactivation domain, which binds to promoter regions with specific DNA sequences in the presence of acetoin and dose-dependently activates expression of downstream transgenes. Wild-type mice implanted with alginate-encapsulated cells transgenic for the acetoin gene switch showed a dose-dependent increase in blood levels of reporter protein in response to either administration of acetoin solution via oral gavage or longer exposure to acetoin aerosol generated by a commercial portable inhaler. Intake of typical acetoin-containing foods, such as butter, lychees and cheese, did not activate transgene expression. As a proof of concept, we show that blood glucose levels were normalized by acetoin aerosol inhalation in type-I diabetic mice implanted with acetoin-responsive insulin-producing cells. Delivery of trigger molecules using portable inhalers may facilitate regular administration of therapeutic proteins via next-generation cell-based therapies to treat chronic diseases for which frequent dosing is required.

Engineered Living Materials For Sustainability

Recent advances in synthetic biology and materials science have given rise to a new form of materials, namely engineered living materials (ELMs), which are composed of living matter or cell communities embedded in self-regenerating matrices of their own or artificial scaffolds. Like natural materials such as bone, wood, and skin, ELMs, which possess the functional capabilities of living organisms, can grow, self-organize, and self-repair when needed. They also spontaneously perform programmed biological functions upon sensing external cues. Currently, ELMs show promise for green energy production, bioremediation, disease treatment, and fabricating advanced smart materials. This review first introduces the dynamic features of natural living systems and their potential for developing novel materials. We then summarize the recent research progress on living materials and emerging design strategies from both synthetic biology and materials science perspectives. Finally, we discuss the positive impacts of living materials on promoting sustainability and key future research directions.

Electrically regulated cell-based intervention for viral infections

This work reports on an engineered cell that-when electrically stimulated-synthesizes a desired protein, that is, ES-Biofactory. The platform has been used to express interferon (IFN)-β as a universal antiviral protein. Compelling evidence indicates the inevitability of new pandemics and drives the need for a pan-viral intervention that may be quickly deployed while more specific vaccines are in development. Toward this goal, a fast-growing mammalian cell (Chassis) has been engineered with multiple synthetic elements. These include-(1) a voltage-gated Ca²⁺ channel (Voltage-Sensor) that, upon sensing the electric field, activates the (2) Ca²⁺-mediated signaling pathway (Actuator) to upregulate (3) IFN-β, via an engineered antiviral transgene (Effector), that is, ES-Biofactory➔IFN-β. The antiviral effects of the ES-Biofactory➔IFN-β have been validated on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected cells. The irradiated ES-Biofactory, that does not exhibit oncogenic capacity, continues to exert antiviral effect. The resulting ES-Biofactory➔IFN-β uses a novel signaling pathway that, unlike the natural IFN synthesis pathway, is not subject to viral interference. Once clinically validated, the ES-Biofactory will be a universal antiviral cell therapy that can be immediately deployed in the event of an outbreak. The platform may also be useful in treating other diseases including cancer and autoimmune disorders.

A glucose-blue light AND gate-controlled chemi-optogenetic cell-implanted therapy for treating type-1 diabetes in mice

Exogenous insulin therapy is the mainstay treatment for Type-1 diabetes (T1D) caused by insulin deficiency. A fine-tuned insulin supply system is important to maintain the glucose homeostasis. In this study, we present a designed cell system that produces insulin under an AND gate control, which is triggered only in the presence of both high glucose and blue light illumination. The glucose-sensitive GIP promoter induces the expression of GI-Gal4 protein, which forms a complex with LOV-VP16 in the presence of blue light. The GI-Gal4:LOV-VP16 complex then promotes the expression of UAS-promoter-driven insulin. We transfected these components into HEK293T cells, and demonstrated the insulin was secreted under the AND gate control. Furthermore, we showed the capacity of the engineered cells to improve the blood glucose homeostasis through implantation subcutaneously into Type-1 diabetes mice.

Bioelectronic cell-based device provides a strategy for the treatment of the experimental model of multiple sclerosis

Wireless powered optogenetic cell-based implant provides a strategy to deliver subcutaneously therapeutic proteins. Immortalize Human Mesenchymal Stem Cells (hMSC-TERT) expressing the bacteriophytochrome diguanylate cyclase (DGCL) were validated for optogenetic controlled interferon-β delivery (Optoferon cells) in a bioelectronic cell-based implant. Optoferon cells transcriptomic profiling was used to elaborate an in-silico model of the recombinant interferon-β production. Wireless optoelectronic device integration was developed using additive manufacturing and injection molding. Implant cell-based optoelectronic interface manufacturing was established to integrate industrial flexible compact low-resistance screen-printed Near Field Communication (NFC) coil antenna. Optogenetic cell-based implant biocompatibility, and device performances were evaluated in the Experimental Autoimmune Encephalomyelitis (EAE) mouse model of multiple sclerosis.

Electronically powered drug delivery devices: considerations and challenges

INTRODUCTION

Electronically powered drug delivery devices enable a controlled drug release route for a more convenient and painless way with reduced side effects. The current advances in microfabrication and microelectronics have facilitated miniaturization and intelligence with the integration of sensors and wireless communication modules. These devices have become an essential component of commercialized on-demand drug delivery.

AREAS COVERED

This review aims to provide a concise overview of current progress in electronically powered drug devices, focusing on delivery strategies, manufacturing techniques, and control circuit design with specific examples.

EXPERT OPINION

The application of electronically powered drug delivery systems is now considered a feasible therapeutic approach with improved drug release efficiency and increased patient comfort. It is anticipated that these technologies will gradually fulfill clinical needs and resolve commercialization challenges in the future. This review discusses the current advances in electronic drug delivery devices, especially focusing on designing strategies to achieve an effective drug release, as well as the perspectives and challenges for future applications in clinical therapy.

Bio-hybrid electronic and photonic devices

Bio-hybrid devices, combining electronic and photonic components with cells, tissues, and organs, hold potential for advancing our understanding of biology, physiology, and pathologies and for treating a wide range of conditions and diseases. In this review, I describe the devices, materials, and technologies that enable bio-hybrid devices and provide examples of their utilization at multiple biological scales ranging from the subcellular to whole organs. Finally, I describe the outcomes of a National Science Foundation (NSF)-funded workshop envisioning potential applications of these technologies to improve health outcomes and quality of life.

Tumor-associated macrophages are shaped by intratumoral high potassium via Kir2.1

The tumor microenvironment (TME) is a unique niche governed by constant crosstalk within and across all intratumoral cellular compartments. In particular, intratumoral high potassium (K⁺) has shown immune-suppressive potency on T cells. However, as a pan-cancer characteristic associated with local necrosis, the impact of this ionic disturbance on innate immunity is unknown. Here, we reveal that intratumoral high K⁺ suppresses the anti-tumor capacity of tumor-associated macrophages (TAMs). We identify the inwardly rectifying K⁺ channel Kir2.1 as a central modulator of TAM functional polarization in high K⁺ TME, and its conditional depletion repolarizes TAMs toward an anti-tumor state, sequentially boosting local anti-tumor immunity. Kir2.1 deficiency disturbs the electrochemically dependent glutamine uptake, engendering TAM metabolic reprogramming from oxidative phosphorylation toward glycolysis. Kir2.1 blockade attenuates both murine tumor- and patient-derived xenograft growth. Collectively, our findings reveal Kir2.1 as a determinant and potential therapeutic target for regaining the anti-tumor capacity of TAMs within ionic-imbalanced TME.

Design of programmable post-translational switch control platform for on-demand protein secretion in mammalian cells

The development of novel strategies to program cellular behaviors is a central goal in synthetic biology, and post-translational control mediated by engineered protein circuits is a particularly attractive approach to achieve rapid protein secretion on demand. We have developed a programmable protease-mediated post-translational switch (POSH) control platform composed of a chimeric protein unit that consists of a protein of interest fused via a transmembrane domain to a cleavable ER-retention signal, together with two cytosolic inducer-sensitive split protease components. The protease components combine in the presence of the specific inducer to generate active protease, which cleaves the ER-retention signal, releasing the transmembrane-domain-linked protein for trafficking to the trans-Golgi region. A furin site placed downstream of the protein ensures cleavage and subsequent secretion of the desired protein. We show that stimuli ranging from plant-derived, clinically compatible chemicals to remotely controllable inducers such as light and electrostimulation can program protein secretion in various POSH-engineered designer mammalian cells. As proof-of-concept, an all-in-one POSH control plasmid encoding insulin and abscisic acid-activatable split protease units was hydrodynamically transfected into the liver of type-1 diabetic mice. Induction with abscisic acid attenuated glycemic excursions in glucose-tolerance tests. Increased blood levels of insulin were maintained for 12 days.

Sunlight-Controllable Biopharmaceutical Production for Remote Emergency Supply of Directly Injectable Therapeutic Proteins

Biopharmaceutical manufacturing requires specialized facilities and a long-range cold supply chain for the delivery of the therapeutics to patients. In order to produce biopharmaceuticals in locations lacking such infrastructure, a production process is designed that utilizes the trigger-inducible release of large quantities of a stored therapeutic protein from engineered endocrine cells within minutes to generate a directly injectable saline solution of the protein. To illustrate the versatility of this approach, it is shown that not only insulin, but also glucagon-like peptide 1 (GLP-1), nanoluciferase (NLuc), and the model biopharmaceutical erythropoietin (EPO) can be trigger-inducibly released, even when using biologically inactive insulin as a carrier. The facilitating beta cells are engineered with a controllable TRPV1-mediated Ca²⁺ influx that induces the fusion of cytoplasmic storage vesicles with the membrane, leading to the release of the stored protein. When required, the growth medium is exchanged for saline solution, and the system is stimulated with the small molecule capsaicin, with a hand-warming pack, or simply by using sunlight. Injection of insulin saline solution obtained in this way into a type-1 diabetes mouse model results in the regulation of blood glucose levels. It is believed that this system will be readily adaptable to deliver various biopharmaceutical proteins at remote locations.

Programmable Electrochemical Stimulation on a Large-Scale CMOS Microelectrode Array

In this paper we present spatio-temporally controlled electrochemical stimulation of aqueous samples using an integrated CMOS microelectrode array with 131,072 pixels. We demonstrate programmable gold electrodeposition in arbitrary spatial patterns, controllable electrolysis to produce microscale hydrogen bubbles, and spatially targeted electrochemical pH modulation. Dense spatially-addressable electrochemical stimulation is important for a wide range of bioelectronics applications.

Biomarker-driven feedback control of synthetic biology systems for next-generation personalized medicine

Many current clinical therapies for chronic diseases involve administration of drugs using dosage and bioavailability parameters estimated for a generalized population. This standard approach carries the risk of under dosing, which may result in ineffective treatment, or overdosing, which may cause undesirable side effects. Consequently, maintaining a drug concentration in the therapeutic window often requires frequent monitoring, adversely affecting the patient’s quality of life. In contrast, endogenous biosystems have evolved finely tuned feedback control loops that govern the physiological functions of the body based on multiple input parameters. To provide personalized treatment for chronic diseases, therefore, we require synthetic systems that can similarly generate a calibrated therapeutic response. Such engineered autonomous closed-loop devices should incorporate a sensor that actively tracks and evaluates the disease severity based on one or more biomarkers, as well as components that utilize these molecular inputs to bio compute and deliver the appropriate level of therapeutic output. Here, we review recent advances in applications of the closed-loop design principle in biomedical implants for treating severe and chronic diseases, highlighting translational studies of cellular therapies. We describe the engineering principles and components of closed-loop therapeutic devices, and discuss their potential to become a key pillar of personalized medicine.

A de novo matrix for macroscopic living materials from bacteria

Engineered living materials (ELMs) embed living cells in a biopolymer matrix to create materials with tailored functions. While bottom-up assembly of macroscopic ELMs with a de novo matrix would offer the greatest control over material properties, we lack the ability to genetically encode a protein matrix that leads to collective self-organization. Here we report growth of ELMs from Caulobacter crescentus cells that display and secrete a self-interacting protein. This protein formed a de novo matrix and assembled cells into centimeter-scale ELMs. Discovery of design and assembly principles allowed us to tune the composition, mechanical properties, and catalytic function of these ELMs. This work provides genetic tools, design and assembly rules, and a platform for growing ELMs with control over both matrix and cellular structure and function.

Engineered living materials (ELMs) embed living cells in a biopolymer matrix to create novel materials with tailored functions. In this work, the authors engineered bacteria to grow novel macroscopic materials that can be reshaped, functionalized, and used to filter contaminated water while also showing that the stiffness of these materials can be tuned through genetic changes.

Bioresorbable thin-film silicon diodes for the optoelectronic excitation and inhibition of neural activities

Neural activities can be modulated by leveraging light-responsive nanomaterials as interfaces for exerting photothermal, photoelectrochemical or photocapacitive effects on neurons or neural tissues. Here we show that bioresorbable thin-film monocrystalline silicon pn diodes can be used to optoelectronically excite or inhibit neural activities by establishing polarity-dependent positive or negative photovoltages at the semiconductor/solution interface. Under laser illumination, the silicon-diode optoelectronic interfaces allowed for the deterministic depolarization or hyperpolarization of cultured neurons as well as the upregulated or downregulated intracellular calcium dynamics. The optoelectronic interfaces can also be mounted on nerve tissue to activate or silence neural activities in peripheral and central nervous tissues, as we show in mice with exposed sciatic nerves and somatosensory cortices. Bioresorbable silicon-based optoelectronic thin films that selectively excite or inhibit neural tissue may find advantageous biomedical applicability.

Engineering the next generation of cell-based therapeutics

Cell-based therapeutics are an emerging modality with the potential to treat many currently intractable diseases through uniquely powerful modes of action. Despite notable recent clinical and commercial successes, cell-based therapies continue to face numerous challenges that limit their widespread translation and commercialization, including identification of the appropriate cell source, generation of a sufficiently viable, potent and safe product that meets patient- and disease-specific needs, and the development of scalable manufacturing processes. These hurdles are being addressed through the use of cutting-edge basic research driven by next-generation engineering approaches, including genome and epigenome editing, synthetic biology and the use of biomaterials.

Engineered living materials (ELMs) design: From function allocation to dynamic behavior modulation

Natural materials possess many distinctive "living" attributes, such as self-growth, self-healing, environmental responsiveness, and evolvability, that are beyond the reach of many existing synthetic materials. The emerging field of engineered living materials (ELMs) takes inspiration from nature and harnesses engineered living systems to produce dynamic and responsive materials with genetically programmable functionalities. Here, we identify and review two main directions for the rational design of ELMs: first, engineering of living materials with enhanced performances by incorporating functional material modules, including engineered biological building blocks (proteins, polysaccharides, and nucleic acids) or well-defined artificial materials; second, engineering of smart ELMs that can sense and respond to their surroundings by programming dynamic cellular behaviors regulated via cell-cell or cell-environment interactions. We next discuss the strengths and challenges of current ELMs and conclude by providing a perspective of future directions in this promising area.

Recent Advances in Intelligent Wearable Medical Devices Integrating Biosensing and Drug Delivery

The primary roles of precision medicine are to perform real-time examination, administer on-demand medication, and apply instruments continuously. However, most current therapeutic systems implement these processes separately, leading to treatment interruption and limited recovery in patients. Personalized healthcare and smart medical treatment have greatly promoted research on and development of biosensing and drug-delivery integrated systems, with intelligent wearable medical devices (IWMDs) as typical systems, which have received increasing attention because of their non-invasive and customizable nature. Here, the latest progress in research on IWMDs is reviewed, including their mechanisms of integrating biosensing and on-demand drug delivery. The current challenges and future development directions of IWMDs are also discussed.

Therapeutic cell engineering: designing programmable synthetic genetic circuits in mammalian cells

Cell therapy approaches that employ engineered mammalian cells for on-demand production of therapeutic agents in the patient's body are moving beyond proof-of-concept in translational medicine. The therapeutic cells can be customized to sense user-defined signals, process them, and respond in a programmable and predictable way. In this paper, we introduce the available tools and strategies employed to design therapeutic cells. Then, various approaches to control cell behaviors, including open-loop and closed-loop systems, are discussed. We also highlight therapeutic applications of engineered cells for early diagnosis and treatment of various diseases in the clinic and in experimental disease models. Finally, we consider emerging technologies such as digital devices and their potential for incorporation into future cell-based therapies.