Influence of oriented nanofibrous PCL scaffolds on quantitative gene expression during neural differentiation of mouse embryonic stem cells

Micro- and Nanostructured Fibrous Composites via Electro-Fluid Dynamics: Design and Applications for Brain

The brain consists of an interconnected network of neurons tightly packed in the extracellular matrix (ECM) to form complex and heterogeneous composite tissue. According to recent biomimicry approaches that consider biological features as active components of biomaterials, designing a highly reproducible microenvironment for brain cells can represent a key tool for tissue repair and regeneration. Indeed, this is crucial to support cell growth, mitigate inflammation phenomena and provide adequate structural properties needed to support the damaged tissue, corroborating the activity of the vascular network and ultimately the functionality of neurons. In this context, electro-fluid dynamic techniques (EFDTs), i.e., electrospinning, electrospraying and related techniques, offer the opportunity to engineer a wide variety of composite substrates by integrating fibers, particles, and hydrogels at different scales-from several hundred microns down to tens of nanometers-for the generation of countless patterns of physical and biochemical cues suitable for influencing the in vitro response of coexistent brain cell populations mediated by the surrounding microenvironment. In this review, an overview of the different technological approaches-based on EFDTs-for engineering fibrous and/or particle-loaded composite substrates will be proposed. The second section of this review will primarily focus on describing current and future approaches to the use of composites for brain applications, ranging from therapeutic to diagnostic/theranostic use and from repair to regeneration, with the ultimate goal of providing insightful information to guide future research efforts toward the development of more efficient and reliable solutions.

Overview of Tissue Engineering and Drug Delivery Applications of Reactive Electrospinning and Crosslinking Techniques of Polymeric Nanofibers with Highlights on Their Biocompatibility Testing and Regulatory Aspects

Traditional electrospinning is a promising technique for fabricating nanofibers for tissue engineering and drug delivery applications. The method is highly efficient in producing nanofibers with morphology and porosity similar to the extracellular matrix. Nonetheless, and in many instances, the process has faced several limitations, including weak mechanical strength, large diameter distributions, and scaling-up difficulties of its fabricated electrospun nanofibers. The constraints of the polymer solution's intrinsic properties are primarily responsible for these limitations. Reactive electrospinning constitutes a novel and modified electrospinning techniques developed to overcome those challenges and improve the properties of the fabricated fibers intended for various biomedical applications. This review mainly addresses reactive electrospinning techniques, a relatively new approach for making in situ or post-crosslinked nanofibers. It provides an overview of and discusses the recent literature about chemical and photoreactive electrospinning, their various techniques, their biomedical applications, and FDA regulatory aspects related to their approval and marketing. Another aspect highlighted in this review is the use of crosslinking and reactive electrospinning techniques to enhance the fabricated nanofibers' physicochemical and mechanical properties and make them more biocompatible and tailored for advanced intelligent drug delivery and tissue engineering applications.

The effect of nanomaterials on embryonic stem cell neural differentiation: a systematic review

BACKGROUND

Humans' nervous system has a limited ability to repair nerve cells, which poses substantial challenges in treating injuries and diseases. Stem cells are identified by the potential to renew their selves and develop into several cell types, making them ideal candidates for cell replacement in injured neurons. Neuronal differentiation of embryonic stem cells in modern medicine is significant. Nanomaterials have distinct advantages in directing stem cell function and tissue regeneration in this field. We attempted in this systematic review to collect data, analyze them, and report results on the effect of nanomaterials on neuronal differentiation of embryonic stem cells.

METHODS

International databases such as PubMed, Scopus, ISI Web of Science, and EMBASE were searched for available articles on the effect of nanomaterials on neuronal differentiation of embryonic stem cells (up to OCTOBER 2023). After that, screening (by title, abstract, and full text), selection, and data extraction were performed. Also, quality assessment was conducted based on the STROBE checklist.

RESULTS

In total, 1507 articles were identified and assessed, and then only 29 articles were found eligible to be included. Nine studies used 0D nanomaterials, ten used 1D nanomaterials, two reported 2D nanomaterials, and eight demonstrated the application of 3D nanomaterials. The main biomaterial in studies was polymer-based composites. Three studies reported the negative effect of nanomaterials on neural differentiation.

CONCLUSION

Neural differentiation is crucial in neurological regenerative medicine. Nanomaterials with different characteristics, particularly those cellular regulating activities and stem cell fate, have much potential in neural tissue engineering. These findings indicate a new understanding of potential applications of physicochemical cues in nerve tissue engineering.

Gene Therapy for Regenerative Medicine

The development of biological methods over the past decade has stimulated great interest in the possibility to regenerate human tissues. Advances in stem cell research, gene therapy, and tissue engineering have accelerated the technology in tissue and organ regeneration. However, despite significant progress in this area, there are still several technical issues that must be addressed, especially in the clinical use of gene therapy. The aims of gene therapy include utilising cells to produce a suitable protein, silencing over-producing proteins, and genetically modifying and repairing cell functions that may affect disease conditions. While most current gene therapy clinical trials are based on cell- and viral-mediated approaches, non-viral gene transfection agents are emerging as potentially safe and effective in the treatment of a wide variety of genetic and acquired diseases. Gene therapy based on viral vectors may induce pathogenicity and immunogenicity. Therefore, significant efforts are being invested in non-viral vectors to enhance their efficiency to a level comparable to the viral vector. Non-viral technologies consist of plasmid-based expression systems containing a gene encoding, a therapeutic protein, and synthetic gene delivery systems. One possible approach to enhance non-viral vector ability or to be an alternative to viral vectors would be to use tissue engineering technology for regenerative medicine therapy. This review provides a critical view of gene therapy with a major focus on the development of regenerative medicine technologies to control the in vivo location and function of administered genes.

Recent Advances in Cell and Functional Biomaterial Treatment for Spinal Cord Injury

Spinal cord injury (SCI) is a devastating central nervous system disease caused by accidental events, resulting in loss of sensory and motor function. Considering the multiple effects of primary and secondary injuries after spinal cord injury, including oxidative stress, tissue apoptosis, inflammatory response, and neuronal autophagy, it is crucial to understand the underlying pathophysiological mechanisms, local microenvironment changes, and neural tissue functional recovery for preparing novel treatment strategies. Treatment based on cell transplantation has become the forefront of spinal cord injury therapy. The transplanted cells provide physical and nutritional support for the damaged tissue. At the same time, the implantation of biomaterials with specific biological functions at the site of the SCI has also been proved to improve the local inhibitory microenvironment and promote axonal regeneration, etc. The combined transplantation of cells and functional biomaterials for SCI treatment can result in greater neuroprotective and regenerative effects by regulating cell differentiation, enhancing cell survival, and providing physical and directional support for axon regeneration and neural circuit remodeling. This article reviews the pathophysiology of the spinal cord, changes in the microenvironment after injury, and the mechanisms and strategies for spinal cord regeneration and repair. The article will focus on summarizing and discussing the latest intervention models based on cell and functional biomaterial transplantation and the latest progress in combinational therapies in SCI repair. Finally, we propose the future prospects and challenges of current treatment regimens for SCI repair, to provide references for scientists and clinicians to seek better SCI repair strategies in the future.

Differentiation of the mesenchymal stem cells to pancreatic β-like cells in alginate/trimethyl chitosan/alginate microcapsules

Cell therapy is one of the proposed treatments for diabetes. Cell encapsulation and differentiation inside the biodegradable polymers overcome the limitations such as islet deficiency and the host immune responses. This study was set to encapsulate the mesenchymal stem cells (MSCs) and differentiate them into insulin-producing cells (IPCs). Human bone marrow-mesenchymal stem cells (hBM-MSCs) were encapsulated in alginate/trimethyl chitosan/alginate (Alg/TMC/Alg) coating. At first, morphology and swelling properties of the cell-free microcapsules were investigated. Next, a three-step protocol was used in the presence of exendin-4 and nicotinamide to differentiate hBM-MSCs into IPCs. Viability of the encapsulated cells was investigated using MTT assay. The differentiated cells were analyzed using a real-time RT-PCR to investigate Glut-2, Insulin, Pdx-1, Ngn-3, nestin, and Isl-1 gene expression. The results revealed that differentiation of the encapsulated cells was higher than non-encapsulated cells. Also, dithizone staining in  two-dimensional (2D) environment showed the differentiated cell clusters. In summary, here, hBM-MSCs after encapsulation in Alg/TMC/Alg microcapsules, as a new design, were differentiated properly in the presence of exendin-4 and nicotinamide as main inducers. A three-dimensional (3D) matrix is more similar to the native ECM in the body and prepares higher cell-cell contacts.

Recreating Tissue Structures Representative of Teratomas In Vitro Using a Combination of 3D Cell Culture Technology and Human Embryonic Stem Cells

In vitro studies using human embryonic stem cells (hESCs) are a valuable method to study aspects of embryogenesis, avoiding ethical issues when using embryonic materials and species dissimilarities. The xenograft teratoma assay is often traditionally used to establish pluripotency in putative PSC populations, but also has additional applications, including the study of tissue differentiation. The stem cell field has long sought an alternative due to various well-established issues with the in vivo technique, including significant protocol variability and animal usage. We have established a two-step culture method which combines PSC-derived embryoid bodies (EBs) with porous scaffolds to enhance their viability, prolonging the time these structures can be maintained, and therefore, permitting more complex, mature differentiation. Here, we have utilised human embryonic stem cell-derived EBs, demonstrating the formation of tissue rudiments of increasing complexity over time and the ability to manipulate their differentiation through the application of exogenous morphogens to achieve specific lineages. Crucially, these EB-derived tissues are highly reminiscent of xenograft teratoma samples derived from the same cell line. We believe this in vitro approach represents a reproducible, animal-free alternative to the teratoma assay, which can be used to study human tissue development.

Gold nanorods decorated polycaprolactone/cellulose acetate hybrid scaffold for PC12 cells proliferation

Synthetic and natural polymers have recently received considerable attention due to the exclusive potential for supporting the regenerative cellular processes in peripheral nerve injuries (PNIs). Gold nanorods (GNRs) decorated polycaprolactone (PCL)/cellulose acetate (CA) nanocomposite (PCL/CA/GNR) were fabricated via electrospinning to improve PC12 cells attachment and growth or scaffold cues. Transmission electron microscopy (TEM) corroborated the GNR distribution (23 ± 2 nm length and 3/1 Aspect ratio) and suitable average dimension of 800 nm for the fibers; also, scanning electron microscopy (SEM) represented block-free and smooth fibers without perturbation. Because of gold nanorods incorporation, electrical conductivity of PCL/CA/GNR increased ~21%. Water contact angle data emphasized PCL/CA/GNR surface is more wettable that PCL/CA (<90° at 62 s). Real-time PCR technique (RT-PCR) demonstrated overexpression of β-tubulin and microtubule-associated protein 2 (MAP2) on PCL/CA/GNR compared to PCL/CA composite. Additionally, evaluated of the maturation and neurogenic differentiation of PC12 cells emphasized overexpression of nestin and β-tubulin by Immunocytochemistry staining onto PCL/CA/GNR in comparison to PCL/CA composite. Notably, these recently developed hybrid scaffolds could be considered for peripheral nerve injury (PNI) regeneration.

Current hydrogel advances in physicochemical and biological response-driven biomedical application diversity

Hydrogel is a type of versatile platform with various biomedical applications after rational structure and functional design that leverages on material engineering to modulate its physicochemical properties (e.g., stiffness, pore size, viscoelasticity, microarchitecture, degradability, ligand presentation, stimulus-responsive properties, etc.) and influence cell signaling cascades and fate. In the past few decades, a plethora of pioneering studies have been implemented to explore the cell-hydrogel matrix interactions and figure out the underlying mechanisms, paving the way to the lab-to-clinic translation of hydrogel-based therapies. In this review, we first introduced the physicochemical properties of hydrogels and their fabrication approaches concisely. Subsequently, the comprehensive description and deep discussion were elucidated, wherein the influences of different hydrogels properties on cell behaviors and cellular signaling events were highlighted. These behaviors or events included integrin clustering, focal adhesion (FA) complex accumulation and activation, cytoskeleton rearrangement, protein cyto-nuclei shuttling and activation (e.g., Yes-associated protein (YAP), catenin, etc.), cellular compartment reorganization, gene expression, and further cell biology modulation (e.g., spreading, migration, proliferation, lineage commitment, etc.). Based on them, current in vitro and in vivo hydrogel applications that mainly covered diseases models, various cell delivery protocols for tissue regeneration and disease therapy, smart drug carrier, bioimaging, biosensor, and conductive wearable/implantable biodevices, etc. were further summarized and discussed. More significantly, the clinical translation potential and trials of hydrogels were presented, accompanied with which the remaining challenges and future perspectives in this field were emphasized. Collectively, the comprehensive and deep insights in this review will shed light on the design principles of new biomedical hydrogels to understand and modulate cellular processes, which are available for providing significant indications for future hydrogel design and serving for a broad range of biomedical applications.

Fabrication of dual layered biocompatible herbal biopatch from biological waste for skin - tissue regenerative applications

A dual layered herbal biopolymeric patch (biopatch) with enhanced wound healing efficiency and skin mimicking functions was fabricated for skin-tissue regenerative applications. In this study, hoof keratin (KE) extracted from biological waste and gelatin (GE) was employed for KE-GE biosheet fabrication using a simple casting method. Further, the top layer of the fabricated KE-GE biosheet was coated with bioactive Matricaria recutita (Chamomile flower) extract (CH) with gelatin through an electrospraying method. The optimized dual layered herbal biopatch (KE-GE/GE-CH) exhibits strong physiochemical (FTIR, XRD TG-DTA), mechanical (tensile strength) and biological (in vitro and in vivo) studies. Moreover, the morphology (SEM) of soft mimetic biopatch possesses excellent cell-material interaction and cell proliferation which accelerates the wound healing process. Biopatch demonstrates a proven degradation profile with good swelling features to achieve more than 80% herbal drug release in 96 h. Antimicrobial properties also reveal the potential activity of biopatch against bacterial microbes. In addition, in vitro cell viability using NIH 3T3 fibroblast cell lines and in vivo investigations revealed that the biopatch is non-cytotoxic, increases collagen deposition and shows rapid reepithelialization at the wound site as a potential wound dressing. We anticipated that the biological hoof keratin and bioactive herbal extract coated biopatch could serve as a desirable wound dressing candidate to suit various skin tissue regenerative applications.

Glutamatergic Neurons Differentiated from Embryonic Stem Cells: An Investigation of Differentiation and Associated Diseases

Neurons that have been derived from various types of stem cells have recently undergone significant study due to their potential for use in various aspects of biomedicine. In particular, glutamatergic neurons differentiated from embryonic stem cells (ESCs) potentially have many applications in both basic research and regenerative medicine. This review summarized the literatures published thus far and focused on two areas related to these applications. Firstly, these neurons can be used to investigate neuronal signal transduction during differentiation and this means that the genes/proteins/markers involved in this process can be identified. In this way, the dynamic spatial and temporal changes associated with neuronal morphology can be investigated relatively easily. Such an in vitro system can also be used to study how neurons during neurogenesis integrate into normal tissue. At the same time, the integration, regulation and functions of extracellular matrix secretion, various molecular interactions, various ion channels, the neuronal microenvironment, etc., can be easily traced. Secondly, the disease-related aspects of ESC-derived glutamatergic neurons can also be studied and then applied therapeutically. In the future, greater efforts are needed to explore how ESC-differentiated glutamatergic neurons can be used as a neuronal model for the study of Alzheimer’s disease (AD) mechanistically, to identify possible therapeutic strategies for treating AD, including tissue replacement, and to screen for drugs that can be used to treat AD patients. With all of the modern technology that is available, translational medicine should begin to benefit patients soon.

Next generation human brain models: engineered flat brain organoids featuring gyrification

Brain organoids are considered to be a highly promising in vitro model for the study of the human brain and, despite their various shortcomings, have already been used widely in neurobiological studies. Especially for drug screening applications, a highly reproducible protocol with simple tissue culture steps and consistent output, is required. Here we present an engineering approach that addresses several existing shortcomings of brain organoids. By culturing brain organoids with a polycaprolactone scaffold, we were able to modify their shape into a flat morphology. Engineered flat brain organoids (efBOs) possess advantageous diffusion conditions and thus their tissue is better supplied with oxygen and nutrients, preventing the formation of a necrotic tissue core. Moreover, the efBO protocol is highly simplified and allows to customize the organoid size directly from the start. By seeding cells onto 12 by 12 mm scaffolds, the brain organoid size can be significantly increased. In addition, we were able to observe folding reminiscent of gyrification around day 20, which was self-generated by the tissue. To our knowledge, this is the first study that reports intrinsically caused gyrification of neuronal tissue in vitro. We consider our efBO protocol as a next step towards the generation of a stable and reliable human brain model for drug screening applications and spatial patterning experiments.

The effect of electrospun scaffolds on the glycosaminoglycan profile of differentiating neural stem cells

The use of electrospun scaffolds for neural tissue engineering applications allows a closer mimicry of the native tissue extracellular matrix (ECM), important for the transplantation of cells in vivo. Moreover, the role of the electrospun fiber mat topography on neural stem cell (NSC) differentiation remains to be completely understood. In this work REN-VM cells (NSC model) were differentiated on polycaprolactone (PCL) nanofibers, obtained by wet/wet electrospinning, and on flat glass lamellas. The obtained differentiation profile of NSCs was evaluated using immunofluorescence and qPCR analysis. Glycosaminoglycan (GAG) analysis was successfully emplyed to evaluate changes in the GAG profile of differentiating cells through the use of the highly sensitive liquid chromatography-tandem mass/mass spectrometry (LC-MS/MS) method. Our results show that both culture platforms allow the differentiation of REN-VM cells into neural cells (neurons and astrocytes) similarly. Moreover, LC-MS/MS analysis shows changes in the production of GAGs present both in cell cultures and conditioned media samples. In the media, hyaluronic acid (HA) was detected and correlated with cellular activity and the production of a more plastic extracellular matrix. The cell samples evidence changes in chondroitin sulfate (CS4S, CS6S, CS4S6S) and heparan sulfate (HS6S, HS0S), similar to those previously described in vivo studies and possibly associated with the creation of complex structures, such as perineural networks. The GAG profile of differentiating REN-VM cells on electrospun scaffolds was analyzed for the first time. Our results highlight the advantage of using platforms obtain more reliable and robust neural tissue-engineered transplants.

Development of Inula graveolens (L.) Plant Extract Electrospun/Polycaprolactone Nanofibers: A Novel Material for Biomedical Application

Recently, there has been a growing interest in research on nanofibrous scaffolds developed by electrospinning bioactive plant extracts. In this study, the extract material obtained from the medicinal plant Inula graveolens (L.) was loaded on polycaprolactone (PCL) electrospun polymeric nanofibers. The combined mixture was prepared by 5% of I. graveolens at 8% (PCL) concentration and electrospun under optimal conditions. The chemical analysis, morphology, and crystallization of polymeric nanofibers were carried out by (FT-IR) spectrometer, scanning electron microscopy (SEM), and XRD diffraction. Hydrophilicity was determined by a contact angle experiment. The strength was characterized, and the toxicity of scaffolds on the cell line of fibroblasts was finally investigated. The efficiency of nanofibers to enhance the proliferation of fibroblasts was evaluated in vitro using the optimal I. graveolens/PCL solutions. The results show that I. graveolens/PCL polymeric scaffolds exhibited dispersion in homogeneous nanofibers around 72 ± 963 nm in the ratio 70/30 (V:V), with no toxicity for cells, meaning that they can be used for biomedical applications.

Cellular and Subcellular Contact Guidance on Microfabricated Substrates

Topography of the extracellular environment is now recognized as a major biophysical regulator of cell behavior and function. The study of the influence of patterned substrates on cells, named contact guidance, has greatly benefited from the development of micro and nano-fabrication techniques, allowing the emergence of increasingly diverse and elaborate engineered platforms. The purpose of this review is to provide a comprehensive view of the process of contact guidance from cellular to subcellular scales. We first classify and illustrate the large diversity of topographies reported in the literature by focusing on generic cellular responses to diverse topographical cues. Subsequently, and in a complementary fashion, we adopt the opposite approach and highlight cell type-specific responses to classically used topographies (arrays of pillars or grooves). Finally, we discuss recent advances on the key subcellular and molecular players involved in topographical sensing. Throughout the review, we focus particularly on neuronal cells, whose unique morphology and behavior have inspired a large body of studies in the field of topographical sensing and revealed fascinating cellular mechanisms. We conclude by using the current understanding of the cell-topography interactions at different scales as a springboard for identifying future challenges in the field of contact guidance.

Design of hydrogel-based scaffolds for the treatment of spinal cord injuries

Hydrogel-based scaffold design approaches for the treatment of spinal cord injuries.

Extracellular matrix and biomimetic engineering microenvironment for neuronal differentiation

Extracellular matrix (ECM) influences cell differentiation through its structural and biochemical properties. In nervous system, neuronal behavior is influenced by these ECMs structures which are present in a meshwork, fibrous, or tubular forms encompassing specific molecular compositions. In addition to contact guidance, ECM composition and structures also exert its effect on neuronal differentiation. This short report reviewed the native ECM structure and composition in central nervous system and peripheral nervous system, and their impact on neural regeneration and neuronal differentiation. Using topographies, stem cells have been differentiated to neurons. Further, focussing on engineered biomimicking topographies, we highlighted the role of anisotropic topographies in stem cell differentiation to neurons and its recent temporal application for efficient neuronal differentiation.

Effect of Ethylene Oxide and Gamma (γ-) Sterilization on the Properties of a PLCL Polymer Material in Balloon Implants

Poly-l-lactide-co-ε-caprolactone (PLCL) is a unique polymer containing both polylactic acid and poly-ε-caprolactone (PCL) chain units, and thus it has better flexible and biodegradable properties. Based on these unique properties of PLCL, we have developed balloons that are now widely used in treating major medical problems [Biomaterials 2016, 105, 109-116]. One of the most important considerations needed for balloons is to ensure that the material properties remain similar after undergoing ethylene oxide (EtO) or gamma (γ-) sterilization treatments. From the biotechnological point of view, we focused on analyzing the vital molecular properties of the PLCL material after sterilization, such as changes in crystallinity, molecular weight distributions (M _w, M _n, and polydispersity index), and inherent viscosity (η). Analysis of the data reveals that EtO sterilization does not engender any change in crystallinity, melting temperature (T _m), molecular weights, and η of the polymer. On the contrary, γ-radiations induce chain scission and consequential decrease of ∼33 and ∼15% in molecular weights and η values, respectively. Based on our observations, we recommend EtO sterilization instead of γ-radiation for PLCL. This ensures prolonged stability of the polymer against degradation in a biological environment, long-shelf life, and absolute assurance that balloon failures do not occur after implantation.

Neurogenesis-on-Chip: Electric field modulated transdifferentiation of human mesenchymal stem cell and mouse muscle precursor cell coculture

A number of bioengineering strategies, using biophysical stimulation, are being explored to guide the human mesenchymal stem cells (hMScs) into different lineages. In this context, we have limited understanding on the transdifferentiation of matured cells to another functional-cell type, when grown with stem cells, in a constrained cellular microenvironment under biophysical stimulation. While addressing such aspects, the present work reports the influence of the electric field (EF) stimulation on the phenotypic and functionality modulation of the coculture of murine myoblasts (C2C12) with hMScs [hMSc:C2C12=1:10] in a custom designed polymethylmethacrylate (PMMA) based microfluidic device with in-built metal electrodes. The quantitative and qualitative analysis of the immunofluorescence study confirms that the cocultured cells in the conditioned medium with astrocytic feed, exhibit differentiation towards neural-committed cells under biophysical stimulation in the range of the endogenous physiological electric field strength (8 ± 0.06  mV/mm). The control experiments using similar culture protocols revealed that while C2C12 monoculture exhibited myotube-like fused structures, the hMScs exhibited the neurosphere-like clusters with SOX2, nestin, βIII-tubulin expression. The electrophysiological study indicates the significant role of intercellular calcium signalling among the differentiated cells towards transdifferentiation. Furthermore, the depolarization induced calcium influx strongly supports neural-like behaviour for the electric field stimulated cells in coculture. The intriguing results are explained in terms of the paracrine signalling among the transdifferentiated cells in the electric field stimulated cellular microenvironment. In summary, the present study establishes the potential for neurogenesis on-chip for the coculture of hMSc and C2C12 cells under tailored electric field stimulation, in vitro.

Synthetic scaffolds for musculoskeletal tissue engineering: cellular responses to fiber parameters

Tissue engineering often uses synthetic scaffolds to direct cell responses during engineered tissue development. Since cells reside within specific niches of the extracellular matrix, it is important to understand how the matrix guides cell response and then incorporate this knowledge into scaffold design. The goal of this review is to review elements of cell-matrix interactions that are critical to informing and evaluating cellular response on synthetic scaffolds. Therefore, this review examines fibrous proteins of the extracellular matrix and their effects on cell behavior, followed by a discussion of the cellular responses elicited by fiber diameter, alignment, and scaffold porosity of two dimensional (2D) and three dimensional (3D) synthetic scaffolds. Variations in fiber diameter, alignment, and scaffold porosity guide stem cells toward different lineages. Cells generally exhibit rounded morphology on nanofibers, randomly oriented fibers, and low-porosity scaffolds. Conversely, cells exhibit elongated, spindle-shaped morphology on microfibers, aligned fibers, and high-porosity scaffolds. Cells migrate with higher velocities on nanofibers, aligned fibers, and high-porosity scaffolds but migrate greater distances on microfibers, aligned fibers, and highly porous scaffolds. Incorporating relevant biomimetic factors into synthetic scaffolds destined for specific tissue application could take advantage of and further enhance these responses.

Guggulsterone-releasing microspheres direct the differentiation of human induced pluripotent stem cells into neural phenotypes

Parkinson's disease (PD), a common neurodegenerative disorder, results from the loss of motor function when dopaminergic neurons (DNs) in the brain selectively degenerate. While pluripotent stem cells (PSCs) show promise for generating replacement neurons, current protocols for generating terminally differentiated DNs require a complicated cocktail of factors. Recent work demonstrated that a naturally occurring steroid called guggulsterone effectively differentiated PSCs into DNs, simplifying this process. In this study, we encapsulated guggulsterone into novel poly-ε-caprolactone-based microspheres and characterized its release profile over 44 d in vitro, demonstrating we can control its release over time. These guggulsterone-releasing microspheres were also successfully incorporated in human induced pluripotent stem cell-derived cellular aggregates under feeder-free and xeno-free conditions and cultured for 20 d to determine their effect on differentiation. All cultures stained positive for the early neuronal marker TUJ1 and guggulsterone microsphere-incorporated aggregates did not adversely affect neurite length and branching. Guggulsterone microsphere incorporated aggregates exhibited the highest levels of TUJ1 expression as well as high Olig 2 expression, an inhibitor of the STAT3 astrogenesis pathway previously known as a target for guggulsterone in cancer treatment. Together, this study represents an important first step towards engineered neural tissues consisting of guggulsterone microspheres and PSCs for generating DNs that could eventually be evaluated in a pre-clinical model of PD.

Harnessing Nanotopography of Electrospun Nanofibrous Nerve Guide Conduits (NGCs) for Neural Tissue Engineering

The anatomical recovery of nerve defects with their neurological functions after an injury caused by diseases or accidents is an important clinical issue. The most efficient surgical technique so far to the nerve defects, which are unrepairable by direct end-to-end suture, can be autograft transplantation. The autograft transplantation, however, has disadvantages including multiple rounds of surgery, a shortage of nerve donor, and function loss at the donor site. Tissue-engineered nerve guide conduits (TENGCs) have emerged as a potential alternative to autologous nerve grafts for nerve regeneration and functional recovery. Various TENGCs researches are being carried out to improve characteristics and enhance functionality such as material selection, biomimetic, topography, and enhancement by the biomolecules additions. Among them, the customizable surface nanotopography of aligned fibrous TENGCs foster neural repair by providing a cell-friendly environment, permissiveness, guidance cues, and directional growth of the cells. Fibrous nerve guide conduits (NGCs) made of longitudinally ordered fibers is a promising candidate for nerve tissue engineering.

Novel Biomimetic Microphysiological Systems for Tissue Regeneration and Disease Modeling

Biomaterials engineered to closely mimic morphology, architecture, and nanofeatures of naturally occurring in vivo extracellular matrices (ECM) have gained much interest in regenerative medicine and in vitro biomimetic platforms. Similarly, microphysiological systems (MPS), such as lab-chip, have drummed up momentum for recapitulating precise biomechanical conditions to model the in vivo microtissue environment. However, porosity of in vivo scaffolds regulating barrier and interface functions is generally absent in lab-chip systems, or otherwise introduces considerable cost, complexity, and an unrealistic uniformity in pore geometry. We address this by integrating electrospun nanofibrous porous scaffolds in MPS to develop the lab-on-a-brane (LOB) MPS for more effectively modeling transport, air-liquid interface, and tumor progression and for personalized medicine applications.

Embryonic Stem Cells in Development and Regenerative Medicine

After progressive improvement in embryonic stem (ES) cell field, several studies have been conducted to explore the usage of ES cells in regenerative medicine. Unlimited self renewal and pluripoteny properties, combined with encouraging preclinical trials, remark that ES cell technology might be promising for clinical practice. ES cells, which can form three germ layers in vitro, are potential candidates to study development at the cellular and molecular level. Understanding the cell fate decision and differentiation processes during development might enable generating functional progenitor cells for tissue restoration. Progression in gene modifications and tissue engineering technology has facilitated the derivation of desired cells for therapy. Success in differentiation protocols and identification the regulatory pathways simplify the research for clinical applications. Although there are established protocols for cell differentiation in vitro and promising preclinical studies in vivo, many challenges need to be adressed before clinical translation. In this review, ES cells are discussed as a model of development in vitro and as a potential candidate for regenerative medicine. This review also dissusses current challenges for ES cell based therapy.

Microfibrous Scaffolds Enhance Endothelial Differentiation and Organization of Induced Pluripotent Stem Cells

INTRODUCTION

Human induced pluripotent stem cells (iPSCs) are a promising source of endothelial cells (iPSC-ECs) for engineering three-dimensional (3D) vascularized cardiac tissues. To mimic cardiac microvasculature, in which capillaries are oriented in parallel, we hypothesized that endothelial differentiation of iPSCs within topographically aligned 3D scaffolds would be a facile one-step approach to generate iPSC-ECs as well as induce aligned vascular organization.

METHODS

Human iPSCs underwent endothelial differentiation within electrospun 3D polycaprolactone (PCL) scaffolds having either randomly oriented or parallel-aligned microfibers. Using transcriptional, protein, and endothelial functional assays, endothelial differentiation was compared between conventional two-dimensional (2D) films and 3D scaffolds having either randomly oriented or aligned microfibers. Furthermore, the role of parallel-aligned microfiber patterning on the organization of vessel-like networks was assessed.

RESULTS

The cells in both the randomly oriented and aligned 3D scaffolds demonstrated an 11-fold upregulation in gene expression of the endothelial phenotypic marker, CD31, compared to cells on 2D films. This upregulation corresponded to >3-fold increase in CD31 protein expression in 3D scaffolds, compared to 2D films. Concomitantly, other endothelial phenotypic markers including CD144 and endothelial nitric oxide synthase also showed significant transcriptional upregulation in 3D scaffolds by >7-fold, compared to 2D films. Nitric oxide production, which is characteristic of endothelial function, was produced 4-fold more abundantly in 3D scaffolds, compared to on 2D PCL films. Within aligned scaffolds, the iPSC-ECs displayed parallel-aligned vascular-like networks with 70% longer branch length, compared to cells in randomly oriented scaffolds, suggesting that fiber topography modulates vascular network-like formation and patterning.

CONCLUSION

Together, these results demonstrate that 3D scaffold structure promotes endothelial differentiation, compared to 2D substrates, and that aligned topographical patterning induces anisotropic vascular network organization.

Three-Dimensional Stiff Graphene Scaffold on Neural Stem Cells Behavior

Physical cues of the scaffolds, elasticity, and stiffness significantly guide adhesion, proliferation, and differentiation of stem cells. In addressable microenvironments constructed by three-dimensional graphene foams (3D-GFs), neural stem cells (NSCs) interact with and respond to the structural geometry and mechanical properties of porous scaffolds. Our studies aim to investigate NSC behavior on the various stiffness of 3D-GFs. Two kinds of 3D-GFs scaffolds present soft and stiff properties with elasticity moduli of 30 and 64 kPa, respectively. Stiff scaffold enhanced NSC attachment and proliferation with vinculin and integrin gene expression were up-regulated by 2.3 and 1.5 folds, respectively, compared with the soft one. Meanwhile, up-regulated Ki67 expression and almost no variation of nestin expression in a group of the stiff scaffold were observed, implying that the stiff substrate fosters NSC growth and keeps the cells in an active stem state. Furthermore, NSCs grown on stiff scaffold exhibited enhanced differentiation to astrocytes. Interestingly, differentiated neurons on stiff scaffold are suppressed since growth associated protein-43 expression was significantly improved by 5.5 folds.

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.

Neural patterning of human induced pluripotent stem cells in 3-D cultures for studying biomolecule-directed differential cellular responses

INTRODUCTION

Appropriate neural patterning of human induced pluripotent stem cells (hiPSCs) is critical to generate specific neural cells/tissues and even mini-brains that are physiologically relevant to model neurological diseases. However, the capacity of signaling factors that regulate 3-D neural tissue patterning in vitro and differential responses of the resulting neural populations to various biomolecules have not yet been fully understood.

METHODS

By tuning neural patterning of hiPSCs with small molecules targeting sonic hedgehog (SHH) signaling, this study generated different 3-D neuronal cultures that were mainly comprised of either cortical glutamatergic neurons or motor neurons.

RESULTS

Abundant glutamatergic neurons were observed following the treatment with an antagonist of SHH signaling, cyclopamine, while Islet-1 and HB9-expressing motor neurons were enriched by an SHH agonist, purmorphamine. In neurons derived with different neural patterning factors, whole-cell patch clamp recordings showed similar voltage-gated Na(+)/K(+) currents, depolarization-evoked action potentials and spontaneous excitatory post-synaptic currents. Moreover, these different neuronal populations exhibited differential responses to three classes of biomolecules, including (1) matrix metalloproteinase inhibitors that affect extracellular matrix remodeling; (2) N-methyl-d-aspartate that induces general neurotoxicity; and (3) amyloid β (1-42) oligomers that cause neuronal subtype-specific neurotoxicity.

CONCLUSIONS

This study should advance our understanding of hiPSC self-organization and neural tissue development and provide a transformative approach to establish 3-D models for neurological disease modeling and drug discovery.

STATEMENT OF SIGNIFICANCE

Appropriate neural patterning of human induced pluripotent stem cells (hiPSCs) is critical to generate specific neural cells, tissues and even mini-brains that are physiologically relevant to model neurological diseases. However, the capability of sonic hedgehog-related small molecules to tune different neuronal subtypes in 3-D differentiation from hiPSCs and the differential cellular responses of region-specific neuronal subtypes to various biomolecules have not been fully investigated. By tuning neural patterning of hiPSCs with small molecules targeting sonic hedgehog signaling, this study provides knowledge on the differential susceptibility of region-specific neuronal subtypes derived from hiPSCs to different biomolecules in extracellular matrix remodeling and neurotoxicity. The findings are significant for understanding 3-D neural patterning of hiPSCs for the applications in brain organoid formation, neurological disease modeling, and drug discovery.