Advances in ex vivo models and lab-on-a-chip devices for neural tissue engineering

Emerging Landscape of In Vitro Models for Assessing Rheumatoid Arthritis Management

Rheumatoid arthritis (RA) is a complex condition that is influenced by various causes, including immunological, genetic, and environmental factors. Several studies using animal models have documented immune system dysfunction and described the clinical characteristics of the disease. These studies have provided valuable insights into the pathogenesis of inflammatory arthritis and the identification of new targets for treatment. Nevertheless, none of these animal models successfully replicated all the characteristics of RA. Additionally, numerous experimental medications, which were developed based on our enhanced comprehension of the immune system's function in RA, have shown potential in animal research but ultimately proved ineffective during different stages of clinical trials. There have been several novel therapy alternatives, which do not achieve a consistently outstanding therapeutic outcome in all patients. This underscores the importance of employing the progress in in vitro models, particularly 3D models like tissue explants, and diverse multicomponent approaches such as coculture strategies, synovial membrane, articular cartilage, and subchondral bone models that accurately replicate the structural characteristics of RA pathophysiology. These methods are crucial for the advancement of potential therapeutic strategies. This review discusses the latest advancements in in vitro models and their potential to greatly impact research on managing RA.

The Glycocalyx: The Importance of Sugar Coating the Blood-Brain Barrier

The endothelial glycocalyx (GCX), located on the luminal surface of vascular endothelial cells, is composed of glycoproteins, proteoglycans, and glycosaminoglycans. It plays a pivotal role in maintaining blood-brain barrier (BBB) integrity and vascular health within the central nervous system (CNS), influencing critical processes such as blood flow regulation, inflammation modulation, and vascular permeability. While the GCX is ubiquitously expressed on the surface of every cell in the body, the GCX at the BBB is highly specialized, with a distinct composition of glycans, physical structure, and surface charge when compared to GCX elsewhere in the body. There is evidence that the GCX at the BBB is disrupted and partially shed in many diseases that impact the CNS. Despite this, the GCX has yet to be a major focus of therapeutic targeting for CNS diseases. This review examines diverse model systems used in cerebrovascular GCX-related research, emphasizing the importance of selecting appropriate models to ensure clinical relevance and translational potential. This review aims to highlight the importance of the GCX in disease and how targeting the GCX at the BBB specifically may be an effective approach for brain specific targeting for therapeutics.

Assessment of the Behaviors of an In Vitro Brain Model On-Chip under Shockwave Impacts

Herein we report the assessment of the effects of shockwave (SW) impacts on adult rat hippocampal progenitor cell (AHPC) neurospheres (NSs), which are used as in vitro brain models, for enhancing our understanding of the mechanisms of traumatic brain injury (TBI). The assessment has been achieved by using culture dishes and a new microchip. The microchip allows the chemicals released from the brain models cultured inside the cell culture chamber under SW impacts to diffuse to the nanosensors in adjacent sensor chambers through built-in diffusion barriers, which are used to prevent the cells from entering the sensor chambers, thereby mitigating the biofouling issues of the sensor surface. Experiments showed the negative impact of the SW on the viability, proliferation, and differentiation of the cells within the NSs. A qPCR gene expression analysis was performed and appeared to confirm some of the immunocytochemistry (ICC) results. Finally, we demonstrated that the microchip can be used to monitor lactate dehydrogenase (LDH) released from the AHPC-NSs subjected to SW impacts. As expected, LDH levels changed when AHPC-NSs were injured by SW impacts, verifying this chip can be used for assessing the degrees of injuries to AHPC-NSs by monitoring LDH levels. Taken together, these results suggest the feasibility of using the chip to better understand the interactions between SW impacts and in vitro brain models, paving the way for potentially establishing in vitro TBI models on a chip.

Brain stimulation-on-a-chip: a neuromodulation platform for brain slices

Electrical stimulation of ex vivo brain tissue slices has been a method used to understand mechanisms imparted by transcranial direct current stimulation (tDCS), but there are significant direct current electric field (dcEF) dosage and electrochemical by-product concerns in conventional experimental setups that may impact translational findings. Therefore, we developed an on-chip platform with fluidic, electrochemical, and magnetically-induced spatial control. Fluidically, the chamber geometrically confines precise dcEF delivery to the enclosed brain slice and allows for tissue recovery in order to monitor post-stimulation effects. Electrochemically, conducting hydrogel electrodes mitigate stimulation-induced faradaic reactions typical of commonly-used metal electrodes. Magnetically, we applied ferromagnetic substrates beneath the tissue and used an external permanent magnet to enable in situ rotational control in relation to the dcEF. By combining the microfluidic chamber with live-cell calcium imaging and electrophysiological recordings, we showcased the potential to study the acute and lasting effects of dcEFs with the potential of providing multi-session stimulation. This on-chip bioelectronic platform presents a modernized yet simple solution to electrically stimulate explanted tissue by offering more environmental control to users, which unlocks new opportunities to conduct thorough brain stimulation mechanistic investigations.

Long-termin vitroculture of 3D brain tissue model based on chitosan thermogel

Methods for studying brain function and disease heavily rely onin vivoanimal models,ex-vivotissue slices, and 2D cell culture platforms. These methods all have limitations that significantly impact the clinical translatability of results. Consequently, models able to better recapitulate some aspects ofin vivohuman brain are needed as additional preclinical tools. In this context, 3D hydrogel-basedin vitromodels of the brain are considered promising tools. To create a 3D brain-on-a-chip model, a hydrogel capable of sustaining neuronal maturation over extended culture periods is required. Among biopolymeric hydrogels, chitosan-β-glycerophosphate (CHITO-β-GP) thermogels have demonstrated their versatility and applicability in the biomedical field over the years. In this study, we investigated the ability of this thermogel to encapsulate neuronal cells and support the functional maturation of a 3D neuronal network in long-term cultures. To the best of our knowledge, we demonstrated for the first time that CHITO-β-GP thermogel possesses optimal characteristics for promoting neuronal growth and the development of an electrophysiologically functional neuronal network derived from both primary rat neurons and neurons differentiated from human induced pluripotent stem cells (h-iPSCs) co-cultured with astrocytes. Specifically, two different formulations were firstly characterized by rheological, mechanical and injectability tests. Primary nervous cells and neurons differentiated from h-iPSCs were embedded into the two thermogel formulations. The 3D cultures were then deeply characterized by immunocytochemistry, confocal microscopy, and electrophysiological recordings, employing both 2D and 3D micro-electrode arrays. The thermogels supported the long-term culture of neuronal networks for up to 100 d. In conclusion, CHITO-β-GP thermogels exhibit excellent mechanical properties, stability over time under culture conditions, and bioactivity toward nervous cells. Therefore, they are excellent candidates as artificial extracellular matrices in brain-on-a-chip models, with applications in neurodegenerative disease modeling, drug screening, and neurotoxicity evaluation.

Microfabrication and lab-on-a-chip devices promotein vitromodeling of neural interfaces for neuroscience researches and preclinical applications

Neural tissues react to injuries through the orchestration of cellular reprogramming, generating specialized cells and activating gene expression that helps with tissue remodeling and homeostasis. Simplified biomimetic models are encouraged to amplify the physiological and morphological changes during neural regeneration at cellular and molecular levels. Recent years have witnessed growing interest in lab-on-a-chip technologies for the fabrication of neural interfaces. Neural system-on-a-chip devices are promisingin vitromicrophysiological platforms that replicate the key structural and functional characteristics of neural tissues. Microfluidics and microelectrode arrays are two fundamental techniques that are leveraged to address the need for microfabricated neural devices. In this review, we explore the innovative fabrication, mechano-physiological parameters, spatiotemporal control of neural cell cultures and chip-based neurogenesis. Although the high variability in different constructs, and the restriction in experimental and analytical access limit the real-life applications of microphysiological models, neural system-on-a-chip devices have gained considerable translatability for modeling neuropathies, drug screening and personalized therapy.

Models and approaches to comprehend and address glial inflammation following spinal cord injury

Spinal cord injury (SCI) culminates in chronic inflammation and glial scar formation driven by the activation of microglia and astrocytes. Current anti-inflammatory strategies to treat glial activation associated with SCI have several limitations. Existing in vitro and ex vivo models studying molecular mechanisms associated with inflammation focus only on the acute phase. However, the progression of glial cell-derived inflammation over the acute-to-chronic phases has not been assessed. Understanding this progression will help establish a framework for evaluating therapeutic strategies. Additionally, new models could be useful as high-throughput screening (HTS) platforms. This review aims to highlight currently available models and future methods that could facilitate screening of novel therapeutics for SCI.

Engineered hydrogels for peripheral nerve repair

Peripheral nerve injury (PNI) is a complex disease that often appears in young adults. It is characterized by a high incidence, limited treatment options, and poor clinical outcomes. This disease not only causes dysfunction and psychological disorders in patients but also brings a heavy burden to the society. Currently, autologous nerve grafting is the gold standard in clinical treatment, but complications, such as the limited source of donor tissue and scar tissue formation, often further limit the therapeutic effect. Recently, a growing number of studies have used tissue-engineered materials to create a natural microenvironment similar to the nervous system and thus promote the regeneration of neural tissue and the recovery of impaired neural function with promising results. Hydrogels are often used as materials for the culture and differentiation of neurogenic cells due to their unique physical and chemical properties. Hydrogels can provide three-dimensional hydration networks that can be integrated into a variety of sizes and shapes to suit the morphology of neural tissues. In this review, we discuss the recent advances of engineered hydrogels for peripheral nerve repair and analyze the role of several different therapeutic strategies of hydrogels in PNI through the application characteristics of hydrogels in nerve tissue engineering (NTE). Furthermore, the prospects and challenges of the application of hydrogels in the treatment of PNI are also discussed.

Electrodeposition of chitosan/graphene oxide conduit to enhance peripheral nerve regeneration

Currently available commercial nerve guidance conduits have been applied in the repair of peripheral nerve defects. However, a conduit exhibiting good biocompatibility remains to be developed. In this work, a series of chitosan/graphene oxide (GO) films with concentrations of GO varying from 0–1 wt% (collectively referred to as CHGF-n) were prepared by an electrodeposition technique. The effects of CHGF-n on proliferation and adhesion abilities of Schwann cells were evaluated. The results showed that Schwann cells exhibited elongated spindle shapes and upregulated expression of nerve regeneration-related factors such as Krox20 (a key myelination factor), Zeb2 (essential for Schwann cell differentiation, myelination, and nerve repair), and transforming growth factor β (a cytokine with regenerative functions). In addition, a nerve guidance conduit with a GO content of 0.25% (CHGFC-0.25) was implanted to repair a 10-mm sciatic nerve defect in rats. The results indicated improvements in sciatic functional index, electrophysiology, and sciatic nerve and gastrocnemius muscle histology compared with the CHGFC-0 group, and similar outcomes to the autograft group. In conclusion, we provide a candidate method for the repair of peripheral nerve defects using free-standing chitosan/GO nerve conduits produced by electrodeposition.

Electrospun Carbon Nanotube-Based Scaffolds Exhibit High Conductivity and Cytocompatibility for Tissue Engineering Applications

Carbon nanotubes (CNTs) are known for their excellent conductive properties. Here, we present two novel methods, "sandwich" (sCNT) and dual deposition (DD CNT), for incorporating CNTs into electrospun polycaprolactone (PCL) and gelatin scaffolds to increase their conductance. Based on CNT percentage, the DD CNT scaffolds contain significantly higher quantities of CNTs than the sCNT scaffolds. The inclusion of CNTs increased the electrical conductance of scaffolds from 0.0 ± 0.00 kS (non-CNT) to 0.54 ± 0.10 kS (sCNT) and 5.22 ± 0.49 kS (DD CNT) when measured parallel to CNT arrays and to 0.25 ± 0.003 kS (sCNT) and 2.85 ± 1.12 (DD CNT) when measured orthogonally to CNT arrays. The inclusion of CNTs increased fiber diameter and pore size, promoting cellular migration into the scaffolds. CNT inclusion also decreased the degradation rate and increased hydrophobicity of scaffolds. Additionally, CNT inclusion increased Young's modulus and failure load of scaffolds, increasing their mechanical robustness. Murine fibroblasts were maintained on the scaffolds for 30 days, demonstrating high cytocompatibility. The increased conductivity and high cytocompatibility of the CNT-incorporated scaffolds make them appropriate candidates for future use in cardiac and neural tissue engineering.

Bioelectric Potential in Next-Generation Organoids: Electrical Stimulation to Enhance 3D Structures of the Central Nervous System

Pluripotent stem cell-derived organoid models of the central nervous system represent one of the most exciting areas in in vitro tissue engineering. Classically, organoids of the brain, retina and spinal cord have been generated via recapitulation of in vivo developmental cues, including biochemical and biomechanical. However, a lesser studied cue, bioelectricity, has been shown to regulate central nervous system development and function. In particular, electrical stimulation of neural cells has generated some important phenotypes relating to development and differentiation. Emerging techniques in bioengineering and biomaterials utilise electrical stimulation using conductive polymers. However, state-of-the-art pluripotent stem cell technology has not yet merged with this exciting area of bioelectricity. Here, we discuss recent findings in the field of bioelectricity relating to the central nervous system, possible mechanisms, and how electrical stimulation may be utilised as a novel technique to engineer “next-generation” organoids.

[Experimental study on the construction of telmisartan/collagen/polycaprolactone nerve conduit and its repair effect on rat sciatic nerve defect]

OBJECTIVE

To construction the telmisartan/collagen/polycaprolactone (PCL) nerve conduit and assess its effect on repairing sciatic nerve defect in rats.

METHODS

The 60% collagen/hexafluoroisopropanol (HFIP) solution and 40% PCL/HFIP solution were prepared and mixed (collagen/PCL solution). Then the 0, 5, 10, and 20 mg of telmisartan were mixed with the 10 mL collagen/PCL solution, respectively. Telmisartan/collagen/PCL nerve conduits were fabricated via high voltage electrospinning technology. The structure of nerve conduit before and after crosslinking was observed by using scanning electron microscope (SEM). The drug release efficiency was detected by in vitro sustained release method. RAW264.7 cells were cultured with lipopolysaccharide to induce inflammation, and then co-cultured with nerve conduits loaded with different concentrations of telmisartan for 24 hours. The mRNA expressions of inducible nitric oxide synthase (iNOS) and Arginase 1 (Arg-1) were detected by using real-time fluorescence quantitative PCR. Forty adult Wistar rats were randomly divided into 4 groups ( n=10). After preparing 15-mm-long sciatic nerve defect, the defect was repaired by cross-linked nerve conduits loaded with 0, 5, 10, and 20 mg telmisartan in groups A, B, C, and D, respectively. After operation, the general condition of rats was observed after operation; the sciatic function index (SFI) was tested; the bridging between the nerve conduit and sciatic nerve, and the integrity of nerve conduit were observed; the tissue growth in nerve conduit and material degradation were observed by HE staining; the expressions of CD86 (M1 macrophage marker), CD206 (M2 macrophage marker), myelin basic protein (MBP), and myelin protein 0 (P0) in new tissues were also observed by immunohistochemical staining; the expressions of neurofilament 200 (NF-200) and S-100β in new tissues were assessed by immunofluorescence staining.

RESULTS

The general observation showed that the inner diameter of the nerve conduit was 1.8 mm and the outer diameter was 2.0 mm. After cross-linking by genipin, the nanofiber became thicker and denser. The drug release test showed that the telmisartan loaded nerve conduit could be released gradually. With the increase of telmisartan content in nerve conduit, the iNOS mRNA expression decreased and the Arg-1 mRNA expression increased; and the differences between 20 mg group and other groups were significant ( P<0.05). In vivo experiment showed that all animals in each group survived until the completion of the experiment. The SFI was significantly higher in groups C and D than in groups A and B at different time points ( P<0.05) and in group D than in group C at 6 months after operation ( P<0.05). HE staining showed that there were significantly more new tissues in the middle of the nerve conduit in group D after operation than in other groups. Immunohistochemical staining showed that CD86 and CD206 stainings were positive in each group at 1 month after operation, among which group D had the lowest positive rate of CD86 and the highest positive rate of CD206, and there were significant differences in the positive rate of CD206 between group D and groups A, B, and C ( P<0.05); the MBP and P0 stainings were positive in groups C and D at 6 months, and the positive rate in group D was significantly higher than that in group C ( P<0.05). Immunofluorescence staining showed that the NF-200 and S-100β expressions in group D were significantly higher than those in other groups.

CONCLUSION

Telmisartan/collagen/PLC nerve conduit can promote the sciatic nerve defect repair in rats through promoting the polarization of M1 macrophages to M2 macrophages, and the nerve conduit loaded with20 mg telmisartan has the most significant effect.

Application of Hybrid Electrically Conductive Hydrogels Promotes Peripheral Nerve Regeneration

Peripheral nerve injury (PNI) occurs frequently, and the prognosis is unsatisfactory. As the gold standard of treatment, autologous nerve grafting has several disadvantages, such as lack of donors and complications. The use of functional biomaterials to simulate the natural microenvironment of the nervous system and the combination of different biomaterials are considered to be encouraging alternative methods for effective tissue regeneration and functional restoration of injured nerves. Considering the inherent presence of an electric field in the nervous system, electrically conductive biomaterials have been used to promote nerve regeneration. Due to their singular physical properties, hydrogels can provide a three-dimensional hydrated network that can be integrated into diverse sizes and shapes and stimulate the natural functions of nerve tissue. Therefore, conductive hydrogels have become the most effective biological material to simulate human nervous tissue's biological and electrical characteristics. The principal merits of conductive hydrogels include their physical properties and their electrical peculiarities sufficient to effectively transmit electrical signals to cells. This review summarizes the recent applications of conductive hydrogels to enhance peripheral nerve regeneration.

Advances in microfluidic 3D cell culture for preclinical drug development

Drug development is often a very long, costly, and risky process due to the lack of reliability in the preclinical studies. Traditional current preclinical models, mostly based on 2D cell culture and animal testing, are not full representatives of the complex in vivo microenvironments and often fail. In order to reduce the enormous costs, both financial and general well-being, a more predictive preclinical model is needed. In this chapter, we review recent advances in microfluidic 3D cell culture showing how its development has allowed the introduction of in vitro microphysiological systems, laying the foundation for organ-on-a-chip technology. These findings provide the basis for numerous preclinical drug discovery assays, which raise the possibility of using micro-engineered systems as emerging alternatives to traditional models, based on 2D cell culture and animals.

Pharmaceutical technologies with potential application to insecticide discovery†

Novel neuroactive insecticides are discovered/registered differently, have a lower value in use, and exert their physiological actions in manners distinct from neuroactive pharmaceuticals, but there are clear similarities in their biochemical modes of action. Insecticides are generally discovered using whole pest insect screens, and this eases difficulties in 'translational science' from laboratory to field, as opposed to pharmaceutical translation from biochemical or cell-based targets to animal models to human clinical trials to registered drug. This paper examines recent trends in pharmaceutical science and identifies some technologies which may represent complementary approaches to insecticide discovery screening and mode of action determination beyond the sound processes in common practice today. Examples will be drawn from nanoparticle delivery of neuroactives, unique ligand-polymer conjugates, proposed advances in insect cell culture following from pharmaceutical cell biology, and laboratory or organ-on-a-chip approaches. It is hoped that these concepts will stimulate novel thinking which may enable discovery of efficacious new neuroactive insecticides. © 2020 Society of Chemical Industry.

Design and Evaluation of an In Vitro Mild Traumatic Brain Injury Modeling System Using 3D Printed Mini Impact Device on the 3D Cultured Human iPSC Derived Neural Progenitor Cells

Despite significant progress in understanding the disease mechanism of traumatic brain injury (TBI), promising preclinical therapeutics have seldom been translated into successful clinical outcomes, partially because the model animals have physiological and functional differences in the central nervous system (CNS) compared to humans. Human relevant models are thus urgently required. Here, an in vitro mild TBI (mTBI) modeling system is reported based on 3D cultured human induced pluripotent stem cells (iPSC) derived neural progenitor cells (iPSC-NPCs) to evaluate consequences of single and repetitive mTBI using a 3D printed mini weight-drop impact device. Computational simulation is performed to understand the single/cumulative effects of weight-drop impact on the NPC differentiated neurospheres. Experimental results reveal that neurospheres show reactive astrogliosis and glial scar formation after repetitive (10 hits) mild impacts, while no astrocyte activation is found after one or two mild impacts. A 3D co-culture model of human microglia cells with neurospheres is further developed. It is found that astrocyte response is promoted even after two mild impacts, possibly caused by the chronic neuroinflammation after microglia activation. The in vitro mTBI modeling system recapitulates several hallmarks of the brain impact injury and might serve as a good platform for future drug screening.

Development of novel apoptosis-assisted lung tissue decellularization methods

Decellularized tissues hold great potential for both regenerative medicine and disease modeling applications. The acellular extracellular matrix (ECM)-enriched scaffolds can be recellularized with patient-derived cells prior to transplantation, or digested to create thermally-gelling ECM hydrogels for 3D cell culture. Current methods of decellularization clear cellular components using detergents, which can result in loss of ECM proteins and tissue architectural integrity. Recently, an alternative approach utilizing apoptosis to decellularize excised murine sciatic nerves resulted in superior ECM preservation, cell removal, and immune tolerance in vivo. However, this apoptosis-assisted decellularization approach has not been optimized for other tissues with a more complex geometry, such as lungs. To this end, we developed an apoptosis-assisted lung tissue decellularization method using a combination of camptothecin and sulfobetaine-10 (SB-10) to induce apoptosis and facilitate gentle and effective removal of cell debris, respectively. Importantly, combination of the two agents resulted in superior cell removal and ECM preservation compared to either of the treatments alone, presumably because of pulmonary surfactants. In addition, our method was superior in cell removal compared to a previously established detergent-based decellularization protocol. Furthermore, thermally-gelling lung ECM hydrogels supported high viability of rat lung epithelial cells for up to 2 weeks in culture. This work demonstrates that apoptosis-based lung tissue decellularization is a superior technique that warrants further utilization for both regenerative medicine and disease modeling purposes.

Microfluidic integration of regeneratable electrochemical affinity-based biosensors for continual monitoring of organ-on-a-chip devices

Organs-on-chips have emerged as viable platforms for drug screening and personalized medicine. While a wide variety of human organ-on-a-chip models have been developed, rarely have there been reports on the inclusion of sensors, which are critical in continually measuring the microenvironmental parameters and the dynamic responses of the microtissues to pharmaceutical compounds over extended periods of time. In addition, automation capacity is strongly desired for chronological monitoring. To overcome this major hurdle, in this protocol we detail the fabrication of electrochemical affinity-based biosensors and their integration with microfluidic chips to achieve in-line microelectrode functionalization, biomarker detection and sensor regeneration, allowing continual, in situ and noninvasive quantification of soluble biomarkers on organ-on-a-chip platforms. This platform is almost universal and can be applied to in-line detection of a majority of biomarkers, can be connected with existing organ-on-a-chip devices and can be multiplexed for simultaneous measurement of multiple biomarkers. Specifically, this protocol begins with fabrication of the electrochemically competent microelectrodes and the associated microfluidic devices (~3 d). The integration of electrochemical biosensors with the chips and their further combination with the rest of the platform takes ~3 h. The functionalization and regeneration of the microelectrodes are subsequently described, which require ~7 h in total. One cycle of sampling and detection of up to three biomarkers accounts for ~1 h.

Nanomedicine for Gene Delivery and Drug Repurposing in the Treatment of Muscular Dystrophies

Muscular Dystrophies (MDs) are a group of rare inherited genetic muscular pathologies encompassing a variety of clinical phenotypes, gene mutations and mechanisms of disease. MDs undergo progressive skeletal muscle degeneration causing severe health problems that lead to poor life quality, disability and premature death. There are no available therapies to counteract the causes of these diseases and conventional treatments are administered only to mitigate symptoms. Recent understanding on the pathogenetic mechanisms allowed the development of novel therapeutic strategies based on gene therapy, genome editing CRISPR/Cas9 and drug repurposing approaches. Despite the therapeutic potential of these treatments, once the actives are administered, their instability, susceptibility to degradation and toxicity limit their applications. In this frame, the design of delivery strategies based on nanomedicines holds great promise for MD treatments. This review focuses on nanomedicine approaches able to encapsulate therapeutic agents such as small chemical molecules and oligonucleotides to target the most common MDs such as Duchenne Muscular Dystrophy and the Myotonic Dystrophies. The challenge related to in vitro and in vivo testing of nanosystems in appropriate animal models is also addressed. Finally, the most promising nanomedicine-based strategies are highlighted and a critical view in future developments of nanomedicine for neuromuscular diseases is provided.

Characteristics of neural growth and cryopreservation of the dorsal root ganglion using three-dimensional collagen hydrogel culture versus conventional culture

In vertebrates, most somatosensory pathways begin with the activation of dorsal root ganglion (DRG) neurons. The development of an appropriate DRG culture method is a prerequisite for establishing in vitro peripheral nerve disease models and for screening therapeutic drugs. In this study, we compared the changes in morphology, molecular biology, and transcriptomics of chicken embryo DRG cultured on tissue culture plates (T-DRG) versus three-dimensional collagen hydrogels (C-DRG). Our results showed that after 7 days of culture, the transcriptomics of T-DRG and C-DRG were quite different. The upregulated genes in C-DRG were mainly related to neurogenesis, axon guidance, and synaptic plasticity, whereas the downregulated genes in C-DRG were mainly related to cell proliferation and cell division. In addition, the genes related to cycles/pathways such as the synaptic vesicle cycle, cyclic adenosine monophosphate signaling pathway, and calcium signaling pathway were activated, while those related to cell-cycle pathways were downregulated. Furthermore, neurogenesis- and myelination-related genes were highly expressed in C-DRG, while epithelial–mesenchymal transition-, apoptosis-, and cell division-related genes were suppressed. Morphological results indicated that the numbers of branches, junctions, and end-point voxels per C-DRG were significantly greater than those per T-DRG. Furthermore, cells were scattered in T-DRG and more concentrated in C-DRG, with a higher ratio of 5-ethynyl-2′-deoxyuridine (EdU)-positive cells in T-DRG compared with C-DRG. C-DRG also had higher S100 calcium-binding protein B (S100B) and lower α-smooth muscle actin (α-SMA) expression than T-DRG, and contained fewer terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive cells after 48 hours of serum starvation. After cryopreservation, C-DRG maintained more intact morphological characteristics, and had higher viability and less TUNEL-positive cells than T-DRG. Furthermore, newly formed nerve bundles were able to grow along the existing Schwann cells in C-DRG. These results suggest that C-DRG may be a promising in vitro culture model, with better nerve growth and anti-apoptotic ability, quiescent Schwann cells, and higher viability. Results from this study provide a reference for the construction, storage, and transportation of tissue-engineered nerves. The study was approved by the Ethics Committee of Aier School of Ophthalmology, Central South University, China (approval No. 2020-IRB16), on March 15, 2020.

Potential applications of microfluidics based blood brain barrier (BBB)-on-chips for in vitro drug development

The human blood-brain barrier (BBB) is a complex multi-dimensional reticular barrier system composed of cerebral microvascular endothelial cells, pericytes, astrocytes and a variety of neurons. The conventional in vitro cell culture model fails to truly present the dynamic hemodynamics of BBB and the interaction between neurons. And it is even more impossible to explore brain-related multi-organ diseases, which brings huge obstacles to explore diseases of the central nervous system and the interaction between brain-related multi-organs, and evaluate drug efficacy. Miniaturized microfluidics based BBB chips are being commonly used to co-culture a variety of cells on a small-sized chip to construct a three-dimensional (3D) BBB or BBB-related organ disease models. By combining with other electrophysiological, biochemical sensors or equipment and imaging systems, it can in real time and quickly screen disease-related markers and evaluate drug efficacy. This review systematically summarized the research progress of in vitro BBB and BBB-related organ chips, and analyzed the obstacles of BBB models in depth. Parallelly combined with the current research trends and hot spots, we give the further improvement measures of microfluidic BBB chips.

The biology and engineered modeling strategies of cancer-nerve crosstalk

A recent finding critical to cancer aggravation is the interaction between cancer cells and nerves. There exist two main modes of cancer-nerve interaction: perineural invasion (PNI) and tumor innervation. PNI occurs when cancer cells infiltrate the adjacent nerves, and its relative opposite, tumor innervation, occurs when axons extend into tumor bodies. Like most cancer studies, these crosstalk interactions have mostly been observed in patient samples and animal models at this point, making it difficult to understand the mechanisms in a controlled manner. As such, in recent years in vitro studies have emerged that have helped identify various microenvironmental factors responsible for cancer-nerve crosstalk, including but not limited to neurotrophic factors, neurotransmitters, chemokines, cancer-derived exosomes, and Schwann cells. The versatility of in vitro systems warrants continuous development to increase physiological relevance to study PNI and tumor innervation, for example by utilizing biomimetic three-dimensional (3D) culture systems. Despite the wealth of 3D in vitro cancer models, comparatively there exists a lack of 3D in vitro models of nerve, PNI, and tumor innervation. Native-like 3D in vitro models of cancer-nerve interactions may further help develop therapeutic strategies to curb nerve-mediated cancer aggravation. As such, we provide an overview of the key players of cancer-nerve crosstalk and current in vitro models of the crosstalk, as well as cancer and nerve models. We also discuss a few future directions in cancer-nerve crosstalk research.

Decellularized tissues as platforms for in vitro modeling of healthy and diseased tissues

Biomedical engineers are at the forefront of developing novel treatments to improve human health, however, many products fail to translate to clinical implementation. In vivo pre-clinical animal models, although the current best approximation of complex disease conditions, are limited by reproducibility, ethical concerns, and poor accurate prediction of human response. Hence, there is a need to develop physiologically relevant, low cost, scalable, and reproducible in vitro platforms to provide reliable means for testing drugs, biomaterials, and tissue engineered products for successful clinical translation. One emerging approach of developing physiologically relevant in vitro models utilizes decellularized tissues/organs as biomaterial platforms for 2D and 3D models of healthy and diseased tissue. Decellularization is a process that removes cellular content and produces tissue-specific extracellular matrix scaffolds that can more accurately recapitulate an organ/tissue's native microenvironment compared to other natural or synthetic materials. Decellularized tissues hold enormous potential for in vitro modeling of various disease phenotypes and tissue responses to drugs or external conditions such as aging, toxin exposure, or even implantation. In this review, we highlight the need for in vitro models, the advantages and limitations of implementing decellularized tissues, and considerations of the decellularization process. We discuss current research efforts towards applying decellularized tissues as platforms to generate in vitro models of healthy and diseased tissues, and where we foresee the field progressing. A variety of organs/tissues are discussed, including brain, heart, kidney, large intestine, liver, lung, skeletal muscle, skin, and tongue. STATEMENT OF SIGNIFICANCE: Many biomedical products fail to reach clinical translation due to animal model limitations. Development of physiologically relevant in vitro models can provide a more economic, scalable, and reproducible means of testing drugs/therapeutics for successful clinical translation. The use of decellularized tissues as platforms for in vitro models holds promise, as these scaffolds can effectively replicate native tissue complexity, but is not widely explored. This review discusses the need for in vitro models, the promise of decellularized tissues as biomaterial substrates, and the current research applying decellularized tissues towards the creation of in vitro models. Further, this review provides insights into the current limitations and future of such in vitro models.

Biofabrication Strategies and Engineered In Vitro Systems for Vascular Mechanobiology

The vascular system is integral for maintaining organ-specific functions and homeostasis. Dysregulation in vascular architecture and function can lead to various chronic or acute disorders. Investigation of the role of the vascular system in health and disease has been accelerated through the development of tissue-engineered constructs and microphysiological on-chip platforms. These in vitro systems permit studies of biochemical regulation of vascular networks and parenchymal tissue and provide mechanistic insights into the biophysical and hemodynamic forces acting in organ-specific niches. Detailed understanding of these forces and the mechanotransductory pathways involved is necessary to develop preventative and therapeutic strategies targeting the vascular system. This review describes vascular structure and function, the role of hemodynamic forces in maintaining vascular homeostasis, and measurement approaches for cell and tissue level mechanical properties influencing vascular phenomena. State-of-the-art techniques for fabricating in vitro microvascular systems, with varying degrees of biological and engineering complexity, are summarized. Finally, the role of vascular mechanobiology in organ-specific niches and pathophysiological states, and efforts to recapitulate these events using in vitro microphysiological systems, are explored. It is hoped that this review will help readers appreciate the important, but understudied, role of vascular-parenchymal mechanotransduction in health and disease toward developing mechanotherapeutics for treatment strategies.

Tissue Engineering and Regenerative Medicine: Achievements, Future, and Sustainability in Asia

Exploring innovative solutions to improve the healthcare of the aging and diseased population continues to be a global challenge. Among a number of strategies toward this goal, tissue engineering and regenerative medicine (TERM) has gradually evolved into a promising approach to meet future needs of patients. TERM has recently received increasing attention in Asia, as evidenced by the markedly increased number of researchers, publications, clinical trials, and translational products. This review aims to give a brief overview of TERM development in Asia over the last decade by highlighting some of the important advances in this field and featuring major achievements of representative research groups. The development of novel biomaterials and enabling technologies, identification of new cell sources, and applications of TERM in various tissues are briefly introduced. Finally, the achievement of TERM in Asia, including important publications, representative discoveries, clinical trials, and examples of commercial products will be introduced. Discussion on current limitations and future directions in this hot topic will also be provided.

Tunable methacrylated hyaluronic acid-based hydrogels as scaffolds for soft tissue engineering applications

Hyaluronic acid (HA)-based biomaterials have been explored for a number of applications in biomedical engineering, particularly as tissue regeneration scaffolds. Crosslinked forms of HA are more robust and provide tunable mechanical properties and degradation rates that are critical in regenerative medicine; however, crosslinking modalities reported in the literature vary and there are few comparisons of different scaffold properties for various crosslinking approaches. In this study, we offer direct comparison of two methacrylation techniques for HA (glycidyl methacrylate HA [GMHA] or methacrylic anhydride HA [MAHA]). The two methods for methacrylating HA provide degrees of methacrylation ranging from 2.4 to 86%, reflecting a wider range of properties than is possible using only a single methacrylation technique. We have also characterized mechanical properties for nine different tissues isolated from rat (ranging from lung at the softest to muscle at the stiffest) using indentation techniques and show that we can match the full range of mechanical properties (0.35-6.13 kPa) using either GMHA or MAHA. To illustrate utility for neural tissue engineering applications, functional hydrogels with adhesive proteins (either GMHA or MAHA base hydrogels with collagen I and laminin) were designed with effective moduli mechanically matched to rat sciatic nerve (2.47 ± 0.31 kPa). We demonstrated ability of these hydrogels to support three-dimensional axonal elongation from dorsal root ganglia cultures. Overall, we have shown that methacrylated HA provides a tunable platform with a wide range of properties for use in soft tissue engineering.

Fly-on-a-Chip: Microfluidics for Drosophila melanogaster Studies

The fruit fly or Drosophila melanogaster has been used as a promising model organism in genetics, developmental and behavioral studies as well as in the fields of neuroscience, pharmacology, and toxicology. Not only all the developmental stages of Drosophila, including embryonic, larval, and adulthood stages, have been used in experimental in vivo biology, but also the organs, tissues, and cells extracted from this model have found applications in in vitro assays. However, the manual manipulation, cellular investigation and behavioral phenotyping techniques utilized in conventional Drosophila-based in vivo and in vitro assays are mostly time-consuming, labor-intensive, and low in throughput. Moreover, stimulation of the organism with external biological, chemical, or physical signals requires precision in signal delivery, while quantification of neural and behavioral phenotypes necessitates optical and physical accessibility to Drosophila. Recently, microfluidic and lab-on-a-chip devices have emerged as powerful tools to overcome these challenges. This review paper demonstrates the role of microfluidic technology in Drosophila studies with a focus on both in vivo and in vitro investigations. The reviewed microfluidic devices are categorized based on their applications to various stages of Drosophila development. We have emphasized technologies that were utilized for tissue- and behavior-based investigations. Furthermore, the challenges and future directions in Drosophila-on-a-chip research, and its integration with other advanced technologies, will be discussed.

In vitro tissue-engineered adipose constructs for modeling disease

BACKGROUND

Adipose tissue is a vital tissue in mammals that functions to insulate our bodies, regulate our internal thermostat, protect our organs, store energy (and burn energy, in the case of beige and brown fat), and provide endocrine signals to other organs in the body. Tissue engineering of adipose and other soft tissues may prove essential for people who have lost this tissue from trauma or disease.

MAIN TEXT

In this review, we discuss the applications of tissue-engineered adipose tissue specifically for disease modeling applications. We provide a basic background to adipose depots and describe three-dimensional (3D) in vitro adipose models for obesity, diabetes, and cancer research applications.

CONCLUSIONS

The approaches to engineering 3D adipose models are diverse in terms of scaffold type (hydrogel-based, silk-based and scaffold-free), species of origin (H. sapiens and M. musculus) and cell types used, which allows researchers to choose a model that best fits their application, whether it is optimization of adipocyte differentiation or studying the interaction of adipocytes and other cell types like endothelial cells. In vitro 3D adipose tissue models support discoveries into the mechanisms of adipose-related diseases and thus support the development of novel anti-cancer or anti-obesity/diabetes therapies.

Optoelectrokinetics-based microfluidic platform for bioapplications: A review of recent advances

The introduction of optoelectrokinetics (OEK) into lab-on-a-chip systems has facilitated a new cutting-edge technique-the OEK-based micro/nanoscale manipulation, separation, and assembly processes-for the microfluidics community. This technique offers a variety of extraordinary advantages such as programmability, flexibility, high biocompatibility, low-cost mass production, ultralow optical power requirement, reconfigurability, rapidness, and ease of integration with other microfluidic units. This paper reviews the physical mechanisms that govern the manipulation of micro/nano-objects in microfluidic environments as well as applications related to OEK-based micro/nanoscale manipulation-applications that span from single-cell manipulation to single-molecular behavior determination. This paper wraps up with a discussion of the current challenges and future prospects for the OEK-based microfluidics technique. The conclusion is that this technique will allow more opportunities for biomedical and bioengineering researchers to improve lab-on-a-chip technologies and will have far-reaching implications for biorelated researches and applications in the future.

Functional Scaffolding for Brain Implants: Engineered Neuronal Network by Microfabrication and iPSC Technology

Neuroengineering methods can be effectively used in the design of new approaches to treat central nervous system and brain injury caused by neurotrauma, ischemia, or neurodegenerative disorders. During the last decade, significant results were achieved in the field of implant (scaffold) development using various biocompatible and biodegradable materials carrying neuronal cells for implantation into the injury site of the brain to repair its function. Neurons derived from animal or human induced pluripotent stem (iPS) cells are expected to be an ideal cell source, and induction methods for specific cell types have been actively studied to improve efficacy and specificity. A critical goal of neuro-regeneration is structural and functional restoration of the injury site. The target treatment area has heterogeneous and complex network topology with various types of cells that need to be restored with similar neuronal network structure to recover correct functionality. However, current scaffold-based technology for brain implants operates with homogeneous neuronal cell distribution, which limits recovery in the damaged area of the brain and prevents a return to fully functional biological tissue. In this study, we present a neuroengineering concept for designing a neural circuit with a pre-defined unidirectional network architecture that provides a balance of excitation/inhibition in the scaffold to form tissue similar to that in the injured area using various types of iPS cells. Such tissue will mimic the surrounding niche in the injured site and will morphologically and topologically integrate into the brain, recovering lost function.

Current Progress in 3D Bioprinting of Tissue Analogs

Tissue engineering has progressed tremendously over recent decades through the generation of functional tissue analogs. Traditional approaches based on seeding cells into scaffold are limited in their capacity to produce tissues with precise biomimetic properties. Three-dimensional (3D) bioprinting is one kind of fabrication technology used to precisely dispense cell-laden biomaterials for the construction of functional tissues or organs. In recent years, much research progress has been made in 3D bioprinting technology and its application in generating tissue analogs, including skin, heart valves, blood vessels, bone, and cardiac tissue. However, it still faces many technical challenges. In this review, we introduce the current progress in 3D bioprinting technology and focus on biomaterials and their potential applications in regenerative medicine and drug discovery. Current challenges are also discussed.