Bioprinting functional neural networks

3D printing human tissue models derived from stem cells provides an increasingly popular tissue engineering strategy for probing biological questions. Here Yan et al.1 demonstrate how this technology can be used to model mature human neural tissues with functional neural networks in healthy and disease states.

Modeling the neuroimmune system in Alzheimer's and Parkinson's diseases

Parkinson's disease (PD) and Alzheimer's disease (AD) are neurodegenerative disorders caused by the interaction of genetic, environmental, and familial factors. These diseases have distinct pathologies and symptoms that are linked to specific cell populations in the brain. Notably, the immune system has been implicated in both diseases, with a particular focus on the dysfunction of microglia, the brain's resident immune cells, contributing to neuronal loss and exacerbating symptoms. Researchers use models of the neuroimmune system to gain a deeper understanding of the physiological and biological aspects of these neurodegenerative diseases and how they progress. Several in vitro and in vivo models, including 2D cultures and animal models, have been utilized. Recently, advancements have been made in optimizing these existing models and developing 3D models and organ-on-a-chip systems, holding tremendous promise in accurately mimicking the intricate intracellular environment. As a result, these models represent a crucial breakthrough in the transformation of current treatments for PD and AD by offering potential for conducting long-term disease-based modeling for therapeutic testing, reducing reliance on animal models, and significantly improving cell viability compared to conventional 2D models. The application of 3D and organ-on-a-chip models in neurodegenerative disease research marks a prosperous step forward, providing a more realistic representation of the complex interactions within the neuroimmune system. Ultimately, these refined models of the neuroimmune system aim to aid in the quest to combat and mitigate the impact of debilitating neuroimmune diseases on patients and their families.

The Impact of Biomaterial Surface Properties on Engineering Neural Tissue for Spinal Cord Regeneration

Tissue engineering for spinal cord injury (SCI) remains a complex and challenging task. Biomaterial scaffolds have been suggested as a potential solution for supporting cell survival and differentiation at the injury site. However, different biomaterials display multiple properties that significantly impact neural tissue at a cellular level. Here, we evaluated the behavior of different cell lines seeded on chitosan (CHI), poly (ε-caprolactone) (PCL), and poly (L-lactic acid) (PLLA) scaffolds. We demonstrated that the surface properties of a material play a crucial role in cell morphology and differentiation. While the direct contact of a polymer with the cells did not cause cytotoxicity or inhibit the spread of neural progenitor cells derived from neurospheres (NPCdn), neonatal rat spinal cord cells (SCC) and NPCdn only attached and matured on PCL and PLLA surfaces. Scanning electron microscopy and computational analysis suggested that cells attached to the material's surface emerged into distinct morphological populations. Flow cytometry revealed a higher differentiation of neural progenitor cells derived from human induced pluripotent stem cells (hiPSC-NPC) into glial cells on all biomaterials. Immunofluorescence assays demonstrated that PCL and PLLA guided neuronal differentiation and network development in SCC. Our data emphasize the importance of selecting appropriate biomaterials for tissue engineering in SCI treatment.

3D bioprinting for organ and organoid models and disease modeling

INTRODUCTION

3D printing, a versatile additive manufacturing technique, has diverse applications ranging from transportation, rapid prototyping, clean energy, and medical devices.

AREAS COVERED

The authors focus on how 3D printing technology can enhance the drug discovery process through automating tissue production that enables high-throughput screening of potential drug candidates. They also discuss how the 3D bioprinting process works and what considerations to address when using this technology to generate cell laden constructs for drug screening as well as the outputs from such assays necessary for determining the efficacy of potential drug candidates. They focus on how bioprinting how has been used to generate cardiac, neural, and testis tissue models, focusing on bio-printed 3D organoids.

EXPERT OPINION

The next generation of 3D bioprinted organ model holds great promises for the field of medicine. In terms of drug discovery, the incorporation of smart cell culture systems and biosensors into 3D bioprinted models could provide highly detailed and functional organ models for drug screening. By addressing current challenges of vascularization, electrophysiological control, and scalability, researchers can obtain more reliable and accurate data for drug development, reducing the risk of drug failures during clinical trials.

3D bioprinting patient-derived induced pluripotent stem cell models of Alzheimer's disease using a smart bioink

BACKGROUND

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is becoming increasingly prevalent as our population ages. It is characterized by the buildup of amyloid beta plaques and neurofibrillary tangles containing hyperphosphorylated-tau. The current treatments for AD do not prevent the long-term progression of the disease and pre-clinical models often do not accurately represent its complexity. Bioprinting combines cells and biomaterials to create 3D structures that replicate the native tissue environment and can be used as a tool in disease modeling or drug screening.

METHODS

This work differentiated both healthy and diseased patient-derived human induced pluripotent stems cells (hiPSCs) into neural progenitor cells (NPCs) that were bioprinted using the Aspect RX1 microfluidic printer into dome-shaped constructs. The combination of cells, bioink, and puromorphamine (puro)-releasing microspheres were used to mimic the in vivo environment and direct the differentiation of the NPCs into basal forebrain-resembling cholinergic neurons (BFCN). These tissue models were then characterized for cell viability, immunocytochemistry, and electrophysiology to evaluate their functionality and physiology for use as disease-specific neural models.

RESULTS

Tissue models were successfully bioprinted and the cells were viable for analysis after 30- and 45-day cultures. The neuronal and cholinergic markers β-tubulin III (Tuj1), forkhead box G1 (FOXG1), and choline acetyltransferase (ChAT) were identified as well as the AD markers amyloid beta and tau. Further, immature electrical activity was observed when the cells were excited with potassium chloride and acetylcholine.

CONCLUSIONS

This work shows the successful development of bioprinted tissue models incorporating patient derived hiPSCs. Such models can potentially be used as a tool to screen promising drug candidates for treating AD. Further, this model could be used to increase the understanding of AD progression. The use of patient derived cells also shows the potential of this model for use in personalized medicine applications.

Protocol for 3D Bioprinting Mesenchymal Stem Cell-derived Neural Tissues Using a Fibrin-based Bioink

Three-dimensional bioprinting utilizes additive manufacturing processes that combine cells and a bioink to create living tissue models that mimic tissues found in vivo. Stem cells can regenerate and differentiate into specialized cell types, making them valuable for research concerning degenerative diseases and their potential treatments. 3D bioprinting stem cell-derived tissues have an advantage over other cell types because they can be expanded in large quantities and then differentiated to multiple cell types. Using patient-derived stem cells also enables a personalized medicine approach to the study of disease progression. In particular, mesenchymal stem cells (MSC) are an attractive cell type for bioprinting because they are easier to obtain from patients in comparison to pluripotent stem cells, and their robust characteristics make them desirable for bioprinting. Currently, both MSC bioprinting protocols and cell culturing protocols exist separately, but there is a lack of literature that combines the culturing of the cells with the bioprinting process. This protocol aims to bridge that gap by describing the bioprinting process in detail, starting with how to culture cells pre-printing, to 3D bioprinting the cells, and finally to the culturing process post-printing. Here, we outline the process of culturing MSCs to produce cells for 3D bioprinting. We also describe the process of preparing Axolotl Biosciences TissuePrint - High Viscosity (HV) and Low Viscosity (LV) bioink, the incorporation of MSCs to the bioink, setting up the BIO X and the Aspect RX1 bioprinters, and necessary computer-aided design (CAD) files. We also detail the differentiation of 2D and 3D cell cultures of MSC to dopaminergic neurons, including media preparation. We have also included the protocols for viability, immunocytochemistry, electrophysiology, and performing a dopamine enzyme-linked immunosorbent assay (ELISA), along with the statistical analysis. Graphical overview.

hiPSC-derived GRN-deficient astrocytes delay spiking activity of developing neurons

Frontotemporal dementia (FTD) refers to a group of neurodegenerative disorders that are characterized by pathology predominantly localized to the frontal and temporal lobes. Approximately 40% of FTD cases are familial, and 25% of these are caused by heterozygous loss of function mutations in the gene encoding for progranulin (PGRN), GRN. The mechanisms by which loss of PGRN leads to FTD remain incompletely understood. While astrocytes and microglia have long been linked to the neuropathology of FTD due to mutations in GRN (FTD-GRN), a primary mechanistic role of these supporting cells have not been thoroughly addressed. In contrast, mutations in MAPT, another leading cause of familial FTD, greatly alters astrocyte gene expression leading to subsequent non-cell autonomous effects on neurons, suggesting similar mechanisms may be present in FTD-GRN. Here, we utilized human induced pluripotent stem cell (hiPSC)-derived neural tissue carrying a homozygous GRN R493X^-/- knock-in mutation to investigate in vitro whether GRN mutant astrocytes have a non-cell autonomous effect on neurons. Using microelectrode array (MEA) analysis, we demonstrate that the development of spiking activity of neurons cultured with GRN R493X^-/- astrocytes was significantly delayed compared to cultures with WT astrocytes. Histological analysis of synaptic markers in these cultures, showed an increase in GABAergic synaptic markers and a decrease in glutamatergic synaptic markers during this period when activity was delayed . We also demonstrate that this effect may be due in-part to soluble factors. Overall, this work represents the first study investigating astrocyte-induced neuronal pathology in GRN mutant hiPSCs, and supports the hypothesis of astrocyte involvement in the early pathophysiology of FTD.

Differentiation of Peritubular Myoid-Like Cells from Human Induced Pluripotent Stem Cells

Infertility affects 10-15% of couples, with half attributed to male factors. An improved understanding of the cell-type-specific dysfunction contributing to male infertility is needed to improve available therapies; however, human testicular tissues are difficult to obtain for research purposes. To overcome this, researchers have begun to use human induced pluripotent stem cells (hiPSCs) to generate various testis-specific cell types in vitro. Peritubular myoid cells (PTMs) are one such testicular cell type that serves a critical role in the human testis niche but, to date, have not been derived from hiPSCs. This study set forth to generate a molecular-based differentiation method for deriving PTMs from hiPSCs, mirroring in vivo patterning factors. Whole transcriptome profiling and quantitative polymerase chain reaction (qPCR) show that this differentiation method is sufficient to derive cells with PTM-like transcriptomes, including upregulation of hallmark PTM functional genes, secreted growth and matrix factors, smooth muscle, integrins, receptors, and antioxidants. Hierarchical clustering shows that they acquire transcriptomes similar to primary isolated PTMs, and immunostaining shows the acquisition of a smooth muscle phenotype. Overall, these hiPSC-PTMs will allow in vitro study of patient-specific PTM development and function in spermatogenesis and infertility.

3D bioprinting complex models of cancer

The cancer microenvironment contains a variety of cell types along with a heterogenous extracellular matrix (ECM). Current 2D culture methods for mimicking this microenvironment remain severely limited due to spatial...

Optimization of Precision Nanofiber Micelleplexes for DNA Delivery

As nucleic acid (NA) technologies continue to revolutionize medicine, new delivery vehicles are needed to effectively transport NA cargoes into cells. Uniform and length-tunable nanofiber micelleplexes have recently shown promise...

Length-Controlled Nanofiber Micelleplexes as Efficient Nucleic Acid Delivery Vehicles

Micelleplexes show great promise as effective polymeric delivery systems for nucleic acids. Although studies have shown that spherical micelleplexes can exhibit superior cellular transfection to polyplexes, to date there has been no report on the effects of micelleplex morphology on cellular transfection. In this work, we prepared precision, length-tunable poly(fluorenetrimethylenecarbonate)-b-poly(2-(dimethylamino)ethyl methacrylate) (PFTMC₁₆-b-PDMAEMA₁₃₁) nanofiber micelleplexes and compared their properties and transfection activity to those of the equivalent nanosphere micelleplexes and polyplexes. We studied the DNA complexation process in detail via a range of techniques including cryo-transmission electron microscopy, atomic force microscopy, dynamic light scattering, and ζ-potential measurements, thereby examining how nanofiber micelleplexes form, as well the key differences that exist compared to nanosphere micelleplexes and polyplexes in terms of DNA loading and colloidal stability. The effects of particle morphology and nanofiber length on the transfection and cell viability of U-87 MG glioblastoma cells with a luciferase plasmid were explored, revealing that short nanofiber micelleplexes (length < ca. 100 nm) were the most effective delivery vehicle examined, outperforming nanosphere micelleplexes, polyplexes, and longer nanofiber micelleplexes as well as the Lipofectamine 2000 control. This study highlights the potential importance of 1D micelleplex morphologies for achieving optimal transfection activity and provides a fundamental platform for the future development of more effective polymeric nucleic acid delivery vehicles.

Testing specificity and sensitivity of wastewater-based epidemiology for detecting SARS-CoV-2 in four communities on Vancouver Island, Canada

We report wastewater surveillance of the spread of SARS-CoV-2 based upon 24-h composite influent samples taken weekly from four wastewater treatment plants (WWTP) on Vancouver Island, BC, Canada between January 3, 2021 and July 10, 2021. Samples were analyzed by reverse transcription quantitative polymerase chain reaction targeting the N1 and N2 gene fragments of SARS-CoV-2 and a region of the replication associate protein of the pepper mottle mosaic virus (PMMoV) serving as endemic control. Only a small proportion of samples had quantifiable levels of N1 or N2. Overall case rates are weakly correlated with the concentration (gene copies/L) and with the flux of viral material influent to the WWTP (gene copies/day); the latter accounts for influent flow variations. Poisson multimodal rank correlation accounts for differences between the four WWTP and shows a significant correlation with a significant positive intercept. Receiver operator characteristics (ROC) analysis confirms a cut-off of cases based on amplified/not-amplified experimental data. At the optimal cut point of 19 (N1) or 17 (N2) cases/week/100,000 the sensitivity and specificity is about 75% for N1 and 67% for N2.

Protocol for printing 3D neural tissues using the BIO X equipped with a pneumatic printhead

3D bioprinting—a type of additive manufacturing—can create 3D tissue constructs resembling in vivo tissues. Here, we present a protocol for 3D printing neural tissues using Axolotl Biosciences’ fibrin-based bioink and the CELLINK BIO X bioprinter with a pneumatic printhead. This workflow can be applied to printing 3D tissue models using a variety of cell lines and any chemically crosslinked bioink. These 3D-printed tissue models can be used for applications such as drug screening and disease modeling in vitro.

•

Protocol to 3D bioprint neural tissues with an extrusion-based bioink and the BIO X

•

Prepares bioink and crosslinker that support many cell types including neural progenitors

•

Protocol compatible with other cell types and chemically crosslinked bioinks

Using clinically derived human tissue to 3-dimensionally bioprint personalized testicular tubules for in vitro culturing: first report

OBJECTIVE

To study the feasibility and spermatogenic potential of 3-dimensional (3D) bioprinting personalized human testicular cells derived from a patient with nonobstructive azoospermia (NOA).

DESIGN

A human testicular biopsy from a single donor with NOA was dissociated into single cells, expanded in vitro, and 3D bioprinted into tubular structures akin to the seminiferous tubule using AGC-10 bioink and an RX1 bioprinter with a CENTRA coaxial microfluidic printhead from Aspect Biosystems. Three-dimensional organoid cultures were used as a nonbioprinted in vitro control.

SETTING

Academic medical center.

PATIENT(S)

A 31-year-old man with NOA with testis biopsy demonstrating Sertoli cell-only syndrome.

INTERVENTION(S)

Three-dimensional bioprinting and in vitro culturing of patient-derived testis cells.

MAIN OUTCOME MEASURE(S)

Cellular viability after printing was determined, along with the expression of phenotypic and spermatogenic functional genetic markers after 12 days of in vitro culture.

RESULT(S)

Testicular cultures were expandable in vitro and generated sufficiently large numbers for 3D bioprinting at 35 million cells per mL of bioink. Viability 24 hours after printing was determined to be 93.4% ± 2.4%. Immunofluorescence staining for the phenotype markers SRY-Box transcription factor 9, insulin-like 3, actin alpha 2 smooth muscle, and synaptonemal complex protein 3 after 12 days was positive, confirming the presence of Sertoli, Leydig, peritubular myoid, and meiotic germ cells. Reverse transcription qualitative polymerase chain reaction analysis showed that after 12 days in spermatogenic media, the bioprints substantially up-regulated spermatogenic gene expression on par with nonbioprinted controls and showed a particularly significant improvement in genes involved in spermatogonial stem cell maintenance: inhibitor of deoxyribonucleic acid binding 4 by 365-fold; fibroblast growth factor 3 by 94,152-fold; stem cell growth factor receptor KIT by twofold; stimulated by retinoic acid 8 by 125-fold; deleted in azoospermia-like by 114-fold; synaptonemal complex protein 3 by sevenfold; zona pellucida binding protein by twofold; transition protein 1 by 2,908-fold; and protamine 2 by 11-fold.

CONCLUSION(S)

This study demonstrates for the first time the feasibility of 3D bioprinting adult human testicular cells. We show that the bioprinting process is compatible with high testicular cell viability and without loss of the main somatic phenotypes within the testis tissue. We demonstrate an increase in germ cell markers in the 3D bioprinted tubules after 12 days of in vitro culture. This platform may carry future potential for disease modeling and regenerative opportunities in a personalized medicine framework.

Drug-releasing Microspheres for Stem Cell Differentiation

The ability of stem cells to differentiate into specialized cells make them a valuable tool for therapeutic applications. 3D bioprinting, a subset of additive manufacturing, uses bioinks composed of cells and biomaterials to create living tissues. The use of bioactive factors like small molecules and proteins can promote stem cell differentiation into the desired cell phenotypes for tissue regeneration. Small molecules can accelerate the process of regeneration in tissue engineering, maintain bioactivity in a biological environment, and minimize the costs associated with this process. Additionally, they can be encapsulated in specialized drug-delivery devices called microspheres for controlled release. Microspheres are small (1-1000 μm) spherical particles usually made from biodegradable and biocompatible polymers that can be loaded with drugs and other bioactive components. They can then be integrated into stem-cell-laden bioinks used to form bioprinted tissues, where they will release the encapsulated drug and promote differentiation of stem cells into the desired mature cell type. Microspheres can be widely used to encapsulate a broad range of therapeutic agents, including hydrophilic and hydrophobic small molecule drugs, DNA, and proteins. The release of encapsulated molecules occurs through degradation and erosion of the polymer matrix. This article provides detailed protocols for fabricating and sterilizing drug-releasing microspheres made from poly-ε-caprolactone, a promising biodegradable polymer often used for controlled drug delivery due to its biocompatibility and biodegradation kinetics. Additional protocols describe characterization of the loading and size of microspheres as well as incorporation of microspheres into a fibrin-based bioink for 3D bioprinting. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Fabrication of drug-releasing PCL microspheres Support Protocol 1: Preparation of microspheres for determination of encapsulation efficiency by HPLC Support Protocol 2: Preparation of microspheres for SEM analysis Basic Protocol 2: Incorporation of microspheres into fibrin-based bioink.

Evaluation of 3D-printer settings for producing personal protective equipment

Aim: COVID-19 resulted in a shortage of personal protective equipment. Community members united to 3D-print face shield headbands to support local healthcare workers. This study examined factors altering print time and strength. Materials & methods: Combinations of infill density (50%, 100%), shell thickness (0.8, 1.2 mm), line width (0.2 mm, 0.4 mm), and layer height (0.1 mm, 0.2 mm) were evaluated through tensile testing, finite element analysis, and printing time. Results: Strength increased with increased infill (p < 0.001) and shell thickness (p < 0.001). Layer height had no effect on strength. Increasing line width increased strength (p < 0.001). Discussion: Increasing layer height and line width decreased print time by 50 and 39%, respectively. Increased shell thickness did not alter print time. These changes are recommended for printing.

The effect of SARS-CoV-2 on the nervous system: a review of neurological impacts caused by human coronaviruses

The COVID-19 pandemic has affected millions of people worldwide. While coronaviruses typically have low rates of neurotropic effects, the massive transmission of SARS-CoV-2 suggests that a substantial population will suffer from potential SARS-CoV-2-related neurological disorders. The rapid and recent emergence of SARS-CoV-2 means little research exists on its potential neurological effects. Here we analyze the effects of similar viruses to provide insight into the potential effects of SARS-CoV-2 on the nervous system and beyond. Seven coronavirus strains (HCoV-OC43, HCoV-HKU1, HCoV-229E, HCoV-NL63, SARS-CoV, MERS-CoV, SARS-CoV-2) can infect humans. Many of these strains cause neurological effects, such as headaches, dizziness, strokes, seizures, and critical illness polyneuropathy/myopathy. Certain studies have also linked coronaviruses with multiple sclerosis and extensive central nervous system injuries. Reviewing these studies provides insight into the anticipated effects for patients with SARS-CoV-2. This review will first describe the effects of other coronaviruses that have caused severe disease (SARS-CoV, MERS-CoV) on the nervous system, as well as their proposed origins, non-neurological effects, and neurological infection mechanisms. It will then discuss what is known about SARS-CoV-2 in these areas with reference to the aforementioned viruses, with the goal of providing a holistic picture of SARS-CoV-2.

Recent advances in the design of microfluidic technologies for the manufacture of drug releasing particles

Drug releasing particles are valued for their ability to deliver therapeutics to targeted locations and for their controllable release patterns. The development of microfluidic technologies, which are designed specifically to manipulate small amounts of fluids, to manufacture particles for drug delivery applications reflects a recent trend due to the advantages they confer in terms of control over particle size and material composition. This review takes a comprehensive look at the different types of microfluidic devices used to fabricate such particles from different types of biomaterials, and at how the on-chip features enable the production of particles with different types of properties. The review concludes by suggesting avenues for future work that will enable these technologies to fulfill their potential and be used in industrial settings for the manufacture of drug releasing particles with unique capabilities.

Natural Biomaterials and Their Use as Bioinks for Printing Tissues

The most prevalent form of bioprinting-extrusion bioprinting-can generate structures from a diverse range of materials and viscosities. It can create personalized tissues that aid in drug testing and cancer research when used in combination with natural bioinks. This paper reviews natural bioinks and their properties and functions in hard and soft tissue engineering applications. It discusses agarose, alginate, cellulose, chitosan, collagen, decellularized extracellular matrix, dextran, fibrin, gelatin, gellan gum, hyaluronic acid, Matrigel, and silk. Multi-component bioinks are considered as a way to address the shortfalls of individual biomaterials. The mechanical, rheological, and cross-linking properties along with the cytocompatibility, cell viability, and printability of the bioinks are detailed as well. Future avenues for research into natural bioinks are then presented.

Effect of bioactive Biosilicate® /F18 glass scaffolds on osteogenic differentiation of human adipose stem cells

This study evaluated the gene expression profile of the human adipose-derived stem cells (hASCs) grown on the Biosilicate^® /F18 glass (BioS-2P/F18) scaffolds. hASCs were cultured using the osteogenic medium (control), the scaffolds, and their ionic extract. We observed that ALP activity was higher in hASCs grown on the BioS-2P/F18 scaffolds than in hASCs cultured with the ionic extract or the osteogenic medium on day 14. Moreover, the dissolution product group and the control exhibited deposited calcium, which peaked on day 21. Gene expression profiles of cell cultured using the BioS-2P/F18 scaffolds and their extract were evaluated in vitro using the RT² Profiler polymerase chain reaction (PCR) microarray on day 21. Mineralizing tissue-associated proteins, differentiation factors, and extracellular matrix enzyme expressions were measured using quantitative PCR. The gene expression of different proteins involved in osteoblast differentiation was significantly up-regulated in hASCs grown on the scaffolds, especially BMP1, BMP2, SPP1, BMPR1B, ITGA1, ITGA2, ITGB1, SMAD1, and SMAD2, showing that both the composition and topographic features of the biomaterial could stimulate osteogenesis. This study demonstrated that gene expression of hASCs grown on the scaffold surface showed significantly increased gene expression related to hASCs cultured with the ionic extract or the osteogenic medium, evidencing that the BioS-2P/F18 scaffolds have a substantial effect on cellular behavior of hASCs.

3D Bioprinting Pluripotent Stem Cell Derived Neural Tissues Using a Novel Fibrin Bioink Containing Drug Releasing Microspheres

3D bioprinting combines cells with a supportive bioink to fabricate multiscale, multi-cellular structures that imitate native tissues. Here, we demonstrate how our novel fibrin-based bioink formulation combined with drug releasing microspheres can serve as a tool for bioprinting tissues using human induced pluripotent stem cell (hiPSC)-derived neural progenitor cells (NPCs). Microspheres, small spherical particles that generate controlled drug release, promote hiPSC differentiation into dopaminergic neurons when used to deliver small molecules like guggulsterone. We used the microfluidics based RX1 bioprinter to generate domes with a 1 cm diameter consisting of our novel fibrin-based bioink containing guggulsterone microspheres and hiPSC-derived NPCs. The resulting tissues exhibited over 90% cellular viability 1 day post printing that then increased to 95% 7 days post printing. The bioprinted tissues expressed the early neuronal marker, TUJ1 and the early midbrain marker, Forkhead Box A2 (FOXA2) after 15 days of culture. These bioprinted neural tissues expressed TUJ1 (15 ± 1.3%), the dopamine marker, tyrosine hydroxylase (TH) (8 ± 1%) and other glial markers such as glial fibrillary acidic protein (GFAP) (15 ± 4%) and oligodendrocyte progenitor marker (O4) (4 ± 1%) after 30 days. Also, quantitative polymerase chain reaction (qPCR) analysis showed these bioprinted tissues expressed TUJ1, NURR1 (gene expressed in midbrain dopaminergic neurons), LMX1B, TH, and PAX6 after 30 days. In conclusion, we have demonstrated that using a microsphere-laden bioink to bioprint hiPSC-derived NPCs can promote the differentiation of neural tissue.

A Visible Light-Cross-Linkable, Fibrin-Gelatin-Based Bioprinted Construct with Human Cardiomyocytes and Fibroblasts

In this study, fibrin was added to a photo-polymerizable gelatin-based bioink mixture to fabricate cardiac cell-laden constructs seeded with human induced pluripotent stem cell-derived cardiomyocytes (iPS-CM) or CM cell lines with cardiac fibroblasts (CF). The extensive use of platelet-rich fibrin, its capacity to offer patient specificity, and the similarity in composition to surgical glue prompted us to include fibrin in the existing bioink composition. The cell-laden bioprinted constructs were cross-linked to retain a herringbone pattern via a two-step procedure including the visible light cross-linking of furfuryl-gelatin followed by the chemical cross-linking of fibrinogen via thrombin and calcium chloride. The printed constructs revealed an extremely porous, networked structure that afforded long-term in vitro stability. Cardiomyocytes printed within the sheet structure showed excellent viability, proliferation, and expression of the troponin I cardiac marker. We extended the utility of this fibrin-gelatin bioink toward coculturing and coupling of CM and cardiac fibroblasts (CF), the interaction of which is extremely important for maintenance of normal physiology of the cardiac wall in vivo. This enhanced "cardiac construct" can be used for drug cytotoxicity screening or unraveling triggers for heart diseases in vitro.

3D Printing Breast Tissue Models: A Review of Past Work and Directions for Future Work

Breast cancer often results in the removal of the breast, creating a need for replacement tissue. Tissue engineering offers the promise of generating such replacements by combining cells with biomaterial scaffolds and serves as an attractive potential alternative to current surgical repair methods. Such engineered tissues can also serve as important tools for drug screening and provide in vitro models for analysis. 3D bioprinting serves as an exciting technology with significant implications and applications in the field of tissue engineering. Here we review the work that has been undertaken in hopes of generating the recognized in-demand replacement breast tissue using different types of bioprinting. We then offer suggestions for future work needed to advance this field for both in vitro and in vivo applications.

Modeling the Effects of Yoga on the Progression of Alzheimer's Disease in a Dish

Alzheimer's disease (AD) accounts for 80% of all dementia cases, making it the most common form of dementia. Aging serves as the main risk factor for AD, but early onset AD can also occur in individuals younger than 65 years. AD results from progressive neurodegeneration leading to dysfunctional synaptic transmission in the brain. The cascade hypothesis of AD states that amyloid precursor protein (APP) metabolism becomes impaired either by mutation or an interleukin-mediated stress response to injury, resulting in the splicing of harmful oligomeric forms of amyloid beta (Aβ). These oligomers disrupt extracellular receptor binding, intracellular function, and cellular membrane integrity. Yoga and meditative practices slow the progression of the cognitive decline associated with AD. However, the biological mechanisms underlying this therapeutic effect remain elusive. Here, we investigated the ability of neurotransmitters released during yoga and meditative practices to rescue neurons from synaptic dysfunction in an in vitro Alzheimer's model created by culturing basal forebrain cholinergic neurons with physiologically relevant levels of the I-42 isoform of oligomeric Aβ (OΑβI-42). We found that the neurotransmitters dopamine and histamine produce a cooperative action with serotonin to reverse the loss of choline acetyltransferase (CHaT) by OΑβI-42. The loss of ChaT, the enzyme responsible for processing the cholinergic neurotransmitter acetylcholine, contributes to the synaptic dysfunction experienced during AD. These neurotransmitters inhibit nitric oxide synthesis caused by OΑβI-42, preventing oxidative and nitrosative stress. Serotonin activates an alternate cleavage of APP to produce a fragment with known neurotrophic effects, giving it the unique ability to inhibit the OΑβI-42 production cycle. We hypothesize here that these concerted actions lead to the protection of cholinergic synaptic transmission in AD.

A Novel Toolkit for Characterizing the Mechanical and Electrical Properties of Engineered Neural Tissues

We have designed and validated a set of robust and non-toxic protocols for directly evaluating the properties of engineered neural tissue. These protocols characterize the mechanical properties of engineered neural tissues and measure their electrophysical activity. The protocols obtain elastic moduli of very soft fibrin hydrogel scaffolds and voltage readings from motor neuron cultures. Neurons require soft substrates to differentiate and mature, however measuring the elastic moduli of soft substrates remains difficult to accurately measure using standard protocols such as atomic force microscopy or shear rheology. Here we validate a direct method for acquiring elastic modulus of fibrin using a modified Hertz model for thin films. In this method, spherical indenters are positioned on top of the fibrin samples, generating an indentation depth that is then correlated with elastic modulus. Neurons function by transmitting electrical signals to one another and being able to assess the development of electrical signaling serves is an important verification step when engineering neural tissues. We then validated a protocol wherein the electrical activity of motor neural cultures is measured directly by a voltage sensitive dye and a microplate reader without causing damage to the cells. These protocols provide a non-destructive method for characterizing the mechanical and electrical properties of living spinal cord tissues using novel biosensing methods.

Combining Stem Cells and Biomaterial Scaffolds for Constructing Tissues and Cell Delivery

Combining stem cells with biomaterial scaffolds serves as a promising strategy for engineering tissues for both in vitro and in vivo applications. This updated review details commonly used biomaterial scaffolds for engineering tissues from stem cells. We first define the different types of stem cells and their relevant properties and commonly used scaffold formulations. Next, we discuss natural and synthetic scaffold materials typically used when engineering tissues, along with their associated advantages and drawbacks and gives examples of target applications. New approaches to engineering tissues, such as 3D bioprinting, are described as they provide exciting opportunities for future work along with current challenges that must be addressed. Thus, this review provides an overview of the available biomaterials for directing stem cell differentiation as a means of producing replacements for diseased or damaged tissues.

Direct Reprogramming of Glioblastoma Cells into Neurons Using Small Molecules

Glioblastoma multiforme, a type of deadly brain cancer, originates most commonly from astrocytes found in the brain. Current multimodal treatments for glioblastoma minimally increase life expectancy, but significant advancements in prognosis have not been made in the past few decades. Here we investigate cellular reprogramming for inhibiting the aggressive proliferation of glioblastoma cells. Cellular reprogramming converts one differentiated cell type into another type based on the principles of regenerative medicine. In this study, we used cellular reprogramming to investigate whether small molecule mediated reprogramming could convert glioblastoma cells into neurons. We investigated a novel method for reprogramming U87MG human glioblastoma cells into terminally differentiated neurons using a small molecule cocktail consisting of forskolin, ISX9, CHIR99021 I-BET 151, and DAPT. Treating U87MG glioblastoma cells with this cocktail successfully reprogrammed the malignant cells into early neurons over 13 days. The reprogrammed cells displayed morphological and immunofluorescent characteristics associated with neuronal phenotypes. Genetic analysis revealed that the chemical cocktail upregulates the Ngn2, Ascl1, Brn2, and MAP2 genes, resulting in neuronal reprogramming. Furthermore, these cells displayed decreased viability and lacked the ability to form high numbers of tumor-like spheroids. Overall, this study validates the use of a novel small molecule cocktail for reprogramming glioblastoma into nonproliferating neurons.

Transdifferentiating Astrocytes Into Neurons Using ASCL1 Functionalized With a Novel Intracellular Protein Delivery Technology

Cellular transdifferentiation changes mature cells from one phenotype into another by altering their gene expression patterns. Manipulating expression of transcription factors, proteins that bind to DNA promoter regions, regulates the levels of key developmental genes. Viral delivery of transcription factors can efficiently reprogram somatic cells, but this method possesses undesirable side effects, including mutations leading to oncogenesis. Using protein transduction domains (PTDs) fused to transcription factors to deliver exogenous transcription factors serves as an alternative strategy that avoids the issues associated with DNA integration into the host genome. However, lysosomal degradation and inefficient nuclear localization pose significant barriers when performing PTD-mediated reprogramming. Here, we investigate a novel PTD by placing a secretion signal sequence next to a cleavage inhibition sequence at the end of the target transcription factor–achaete scute homolog 1 (ASCL1), a powerful regulator of neurogenesis, resulting in superior stability and nuclear localization. A fusion protein consisting of the amino acid sequence of ASCL1 transcription factor with this novel PTD added can transdifferentiate cerebral cortex astrocytes into neurons. Additionally, we show that the synergistic action of certain small molecules improves the efficiency of the transdifferentiation process. This study serves as the first step toward developing a clinically relevant in vivo transdifferentiation strategy for converting astrocytes into neurons.

3D Bioprinting Stem Cell Derived Tissues

Stem cells offer tremendous promise for regenerative medicine as they can become a variety of cell types. They also continuously proliferate, providing a renewable source of cells. Recently, it has been found that 3D printing constructs using stem cells, can generate models representing healthy or diseased tissues, as well as substitutes for diseased and damaged tissues. Here, we review the current state of the field of 3D printing stem cell derived tissues. First, we cover 3D printing technologies and discuss the different types of stem cells used for tissue engineering applications. We then detail the properties required for the bioinks used when printing viable tissues from stem cells. We give relevant examples of such bioprinted tissues, including adipose tissue, blood vessels, bone, cardiac tissue, cartilage, heart valves, liver, muscle, neural tissue, and pancreas. Finally, we provide future directions for improving the current technologies, along with areas of focus for future work to translate these exciting technologies into clinical applications.

3-D Bioprinting of Neural Tissue for Applications in Cell Therapy and Drug Screening

Neurodegenerative diseases affect millions of individuals in North America and cost the health-care industry billions of dollars for treatment. Current treatment options for degenerative diseases focus on physical rehabilitation or drug therapies, which temporarily mask the effects of cell damage, but quickly lose their efficacy. Cell therapies for the central nervous system remain an untapped market due to the complexity involved in growing neural tissues, controlling their differentiation, and protecting them from the hostile environment they meet upon implantation. Designing tissue constructs for the discovery of better drug treatments are also limited due to the resolution needed for an accurate cellular representation of the brain, in addition to being expensive and difficult to translate to biocompatible materials. 3-D printing offers a streamlined solution for engineering brain tissue for drug discovery or, in the future, for implantation. New microfluidic and bioplotting devices offer increased resolution, little impact on cell viability and have been tested with several bioink materials including fibrin, collagen, hyaluronic acid, poly(caprolactone), and poly(ethylene glycol). This review details current efforts at bioprinting neural tissue and highlights promising avenues for future work.

Modeling the behavior of human induced pluripotent stem cells seeded on melt electrospun scaffolds

BACKGROUND

Human induced pluripotent stem cells (hiPSCs) can form any tissue found in the body, making them attractive for regenerative medicine applications. Seeding hiPSC aggregates into biomaterial scaffolds can control their differentiation into specific tissue types. Here we develop and analyze a mathematical model of hiPSC aggregate behavior when seeded on melt electrospun scaffolds with defined topography.

RESULTS

We used ordinary differential equations to model the different cellular populations (stem, progenitor, differentiated) present in our scaffolds based on experimental results and published literature. Our model successfully captures qualitative features of the cellular dynamics observed experimentally. We determined the optimal parameter sets to maximize specific cellular populations experimentally, showing that a physiologic oxygen level (∼ 5%) increases the number of neural progenitors and differentiated neurons compared to atmospheric oxygen levels (∼ 21%) and a scaffold porosity of ∼ 63% maximizes aggregate size.

CONCLUSIONS

Our mathematical model determined the key factors controlling hiPSC behavior on melt electrospun scaffolds, enabling optimization of experimental parameters.

An Affordable Microsphere-Based Device for Visual Assessment of Water Quality

This work developed a prototype of an affordable, long-term water quality detection device that provides a visual readout upon detecting bacterial contamination. This device prototype consists of: (1) enzyme-releasing microspheres that lyse bacteria present in a sample, (2) microspheres that release probes that bind the DNA of the lysed bacteria, and (3) a detector region consisting of gold nanoparticles. The probes bind bacterial DNA, forming complexes. These complexes induce aggregation of the gold nanoparticles located in the detector region. The nanoparticle aggregation process causes a red to blue color change, providing a visual indicator of contamination being detected. Our group fabricated and characterized microspheres made of poly (ε-caprolactone) that released lysozyme (an enzyme that degrades bacterial cell walls) and hairpin DNA probes that bind to regions of the Escherichiacoli genome over a 28-day time course. The released lysozyme retained its ability to lyse bacteria. We then showed that combining these components with gold nanoparticles followed by exposure to an E. coli-contaminated water sample (concentrations tested-10⁶ and 10⁸ cells/mL) resulted in a dramatic red to blue color change. Overall, this device represents a novel low-cost system for long term detection of bacteria in a water supply and other applications.

Emerging Biofabrication Strategies for Engineering Complex Tissue Constructs

The demand for organ transplantation and repair, coupled with a shortage of available donors, poses an urgent clinical need for the development of innovative treatment strategies for long-term repair and regeneration of injured or diseased tissues and organs. Bioengineering organs, by growing patient-derived cells in biomaterial scaffolds in the presence of pertinent physicochemical signals, provides a promising solution to meet this demand. However, recapitulating the structural and cytoarchitectural complexities of native tissues in vitro remains a significant challenge to be addressed. Through tremendous efforts over the past decade, several innovative biofabrication strategies have been developed to overcome these challenges. This review highlights recent work on emerging three-dimensional bioprinting and textile techniques, compares the advantages and shortcomings of these approaches, outlines the use of common biomaterials and advanced hybrid scaffolds, and describes several design considerations including the structural, physical, biological, and economical parameters that are crucial for the fabrication of functional, complex, engineered tissues. Finally, the applications of these biofabrication strategies in neural, skin, connective, and muscle tissue engineering are explored.

Biomaterial Strategies for Delivering Stem Cells as a Treatment for Spinal Cord Injury

Ongoing clinical trials are evaluating the use of stem cells as a way to treat traumatic spinal cord injury (SCI). However, the inhibitory environment present in the injured spinal cord makes it challenging to achieve the survival of these cells along with desired differentiation into the appropriate phenotypes necessary to regain function. Transplanting stem cells along with an instructive biomaterial scaffold can increase cell survival and improve differentiation efficiency. This study reviews the literature discussing different types of instructive biomaterial scaffolds developed for transplanting stem cells into the injured spinal cord. We have chosen to focus specifically on biomaterial scaffolds that direct the differentiation of neural stem cells and pluripotent stem cells since they offer the most promise for producing the cell phenotypes that could restore function after SCI. In terms of biomaterial scaffolds, this article reviews the literature associated with using hydrogels made from natural biomaterials and electrospun scaffolds for differentiating stem cells into neural phenotypes. It then presents new data showing how these different types of scaffolds can be combined for neural tissue engineering applications and provides directions for future studies.

Optimizing Differentiation Protocols for Producing Dopaminergic Neurons from Human Induced Pluripotent Stem Cells for Tissue Engineering Applications: Supplementary Issue: Stem Cell Biology

Parkinson's disease (PD) is a neurodegenerative disorder that results when the dopaminergic neurons (DNs) present in the substantia nigra necessary for voluntary motor control are depleted, making patients with this disorder ideal candidates for cell replacement therapy. Human induced pluripotent stem cells (hiPSCs), obtained by reprogramming adult cells, possess the properties of pluripotency and immortality while enabling the possibility of patient-specific therapies. An effective cell therapy for PD requires an efficient, defined method of DN generation, as well as protection from the neuroinflammatory environment upon engraftment. Although similar in pluripotency to human embryonic stem cells (hESCs), hiPSCs differentiate less efficiently into neuronal subtypes. Previous work has shown that treatment with guggulsterone can efficiently differentiate hESCs into DNs. Our work shows that guggulsterone is able to derive DNs from hiPSCs with comparable efficiency, and furthermore, this differentiation can be achieved inside three-dimensional fibrin scaffolds that could enhance cell survival upon engraftment.