Designs of Biomaterials and Microenvironments for Neuroengineering

Mussel‐Inspired Biomaterials: From Chemistry to Clinic

After several billions of years, nature still makes decisions on its own to identify, develop, and direct the most effective material for phenomena/challenges faced. Likewise, and inspired by the nature, we learned how to take steps in developing new technologies and materials innovations. Wet and strong adhesion by Mytilidae mussels (among which Mytilus edulis—blue mussel and Mytilus californianus—California mussel are the most well‐known species) has been an inspiration in developing advanced adhesives for the moist condition. The wet adhesion phenomenon is significant in designing tissue adhesives and surgical sealants. However, a deep understanding of engaged chemical moieties, microenvironmental conditions of secreted proteins, and other contributing mechanisms for outstanding wet adhesion mussels are essential for the optimal design of wet glues. In this review, all aspects of wet adhesion of Mytilidae mussels, as well as different strategies needed for designing and fabricating wet adhesives are discussed from a chemistry point of view. Developed muscle‐inspired chemistry is a versatile technique when designing not only wet adhesive, but also, in several more applications, especially in the bioengineering area. The applications of muscle‐inspired biomaterials in various medical applications are summarized for future developments in the field.

Stem Cell-Based Therapies in Hearing Loss

In recent years, neural stem cell transplantation has received widespread attention as a new treatment method for supplementing specific cells damaged by disease, such as neurodegenerative diseases. A number of studies have proved that the transplantation of neural stem cells in multiple organs has an important therapeutic effect on activation and regeneration of cells, and restore damaged neurons. This article describes the methods for inducing the differentiation of endogenous and exogenous stem cells, the implantation operation and regulation of exogenous stem cells after implanted into the inner ear, and it elaborates the relevant signal pathways of stem cells in the inner ear, as well as the clinical application of various new materials. At present, stem cell therapy still has limitations, but the role of this technology in the treatment of hearing diseases has been widely recognized. With the development of related research, stem cell therapy will play a greater role in the treatment of diseases related to the inner ear.

Promising Applications of Nanoparticles in the Treatment of Hearing Loss

Hearing loss is one of the most common disabilities affecting both children and adults worldwide. However, traditional treatment of hearing loss has some limitations, particularly in terms of drug delivery system as well as diagnosis of ear imaging. The blood–labyrinth barrier (BLB), the barrier between the vasculature and fluids of the inner ear, restricts entry of most blood-borne compounds into inner ear tissues. Nanoparticles (NPs) have been demonstrated to have high biocompatibility, good degradation, and simple synthesis in the process of diagnosis and treatment, which are promising for medical applications in hearing loss. Although previous studies have shown that NPs have promising applications in the field of inner ear diseases, there is still a gap between biological research and clinical application. In this paper, we aim to summarize developments and challenges of NPs in diagnostics and treatment of hearing loss in recent years. This review may be useful to raise otology researchers’ awareness of effect of NPs on hearing diagnosis and treatment.

A facile approach for the development of high mechanical strength 3D neuronal network scaffold based on chitosan and graphite nanoplatelets

In this work, novel composite microparticles based on chitosan (CHI) and graphite nanoplatelets (GNP) were developed as 3D scaffolds for neuronal cells. The aim is to improve the scaffold strength while maintaining its ability to sustain cell adhesion and differentiation. An air-assisted jetting technique followed by physical crosslinking is employed to obtain CHI/GNP microparticles. Optical and Field Emission Scanning Electron Microscopy micrographs showed a uniform distribution of GNP within the CHI porous matrix. The presence of GNP turned out to improve the strength of the microparticles while conferring good electrical conductivity and ameliorating their stability in aqueous environment. The morphological and immunocytochemical characterization, combined with a preliminary electrophysiological analysis, evidenced the effectiveness of the developed composite microparticles as a scaffold for neuron growth. These scaffolds could be employed for the development of advanced 3D neuronal in vitro models for networks dynamics analysis and drug screening.

Systematic Analysis of Survival-Associated Alternative Splicing Signatures in Thyroid Carcinoma

Alternative splicing (AS) is a key mechanism involved in regulating gene expression and is closely related to tumorigenesis. The incidence of thyroid cancer (THCA) has increased during the past decade, and the role of AS in THCA is still unclear. Here, we used TCGA and to generate AS maps in patients with THCA. Univariate analysis revealed 825 AS events related to the survival of THCA. Five prognostic models of AA, AD, AT, ES, and ME events were obtained through lasso and multivariate analyses, and the final prediction model was established by integrating all the AS events in the five prediction models. Kaplan–Meier survival analysis revealed that the overall survival rate of patients in the high-risk group was significantly shorter than that of patients in the low-risk group. The ROC results revealed that the prognostic capabilities of each model at 3, 5, and 8 years were all greater than 0.7, and the final prognostic capabilities of the models were all greater than 0.9. By reviewing other databases and utilizing qPCR, we verified the established THCA gene model. In addition, gene set enrichment analysis showed that abnormal AS events might play key roles in tumor development and progression of THCA by participating in changes in molecular structure, homeostasis of the cell environment and in cell energy. Finally, a splicing correlation network was established to reveal the potential regulatory patterns between the predicted splicing factors and AS event candidates. In summary, AS should be considered an important prognostic indicator of THCA. Our results will help to elucidate the underlying mechanism of AS in the process of THCA tumorigenesis and broaden the prognostic and clinical application of molecular targeted therapy for THCA.

Development and validation of a RNA binding protein-associated prognostic model for head and neck squamous cell carcinoma

Evidence shows that defects in RNA-binding proteins (RBPs) are closely related to the occurrence and development of HNSCC. We obtained 502 tumors and 44 normal samples from the TCGA database, among which 190 differentially expressed RBPs were screened. Finally, a prognostic model containing nine RBPs (CELF2, CPEB1, DDX39B, EIF3L, EZH2, KHDRBS3, RNASE10, RNASE3 and SIDT1) was produced. Further analysis showed that the overall survival rate in the high-risk group was lower than that in the low-risk group. The area under the ROC curve (AUC) in the training and testing groups was significant (3-year AUC, 0.735 vs 0.796; 5-year AUC, 0.821 vs 0.804). In addition, a comprehensive analysis of nine identified RBPs showed that most of them were related to the OS of HNSCC patients, and three of them (CELF2, EZH2, and SIDT1) were differentially expressed in HNSCC and control tissues at the protein level. In addition, our data revealed that the identified RBPs are highly interconnected, with high frequency copy number changes in HNSCC samples. GSEA indicated that the abnormal biological processes related to RNA and the activation of some classical tumor signaling pathways were important driving forces for the development of HNSCC. Our results provide novel insights into the pathogenesis of HNSCC, among which nine RBP markers have potential application value in clinical decision-making and individualized treatment of HNSCC.

Microtopographical patterns promote different responses in fibroblasts and Schwann cells: A possible feature for neural implants

The chronic reliability of bioelectronic neural interfaces has been challenged by foreign body reactions (FBRs) resulting in fibrotic encapsulation and poor integration with neural tissue. Engineered microtopographies could alleviate these challenges by manipulating cellular responses to the implanted device. Parallel microchannels have been shown to modulate neuronal cell alignment and axonal growth, and Sharklet™ microtopographies of targeted feature sizes can modulate bio-adhesion of an array of bacteria, marine organisms, and epithelial cells due to their unique geometry. We hypothesized that a Sharklet™ micropattern could be identified that inhibited fibroblasts partially responsible for FBR while promoting Schwann cell proliferation and alignment. in vitro cell assays were used to screen the effect of Sharklet™ and channel micropatterns of varying dimensions from 2 to 20 μm on fibroblast and Schwann cell metrics (e.g., morphology/alignment, nuclei count, metabolic activity), and a hierarchical analysis of variance was used to compare treatments. In general, Schwann cells were found to be more metabolically active and aligned than fibroblasts when compared between the same pattern. 20 μm wide channels spaced 2 μm apart were found to promote Schwann cell attachment and alignment while simultaneously inhibiting fibroblasts and warrant further in vivo study on neural interface devices. No statistically significant trends between cellular responses and geometrical parameters were identified because mammalian cells can change their morphology dependent on their environment in a manner dissimilar to bacteria. Our results showed although surface patterning is a strong physical tool for modulating cell behavior, responses to micropatterns are highly dependent on the cell type.

Atrial Natriuretic Peptide Improves Neurite Outgrowth from Spiral Ganglion Neurons In Vitro through a cGMP-Dependent Manner

The spiral ganglion neurons (SGNs) are the primary afferent neurons in the spiral ganglion (SG), while their degeneration or loss would cause sensorineural hearing loss. As a cardiac-derived hormone, atrial natriuretic peptide (ANP) plays a critical role in cardiovascular homeostasis through binding to its functional receptors (NPR-A and NPR-C). ANP and its receptors are widely expressed in the mammalian nervous system where they could be implicated in the regulation of multiple neural functions. Although previous studies have provided direct evidence for the presence of ANP and its functional receptors in the inner ear, their presence within the cochlear SG and their regulatory roles during auditory neurotransmission and development remain largely unknown. Based on our previous findings, we investigated the expression patterns of ANP and its receptors in the cochlear SG and dissociated SGNs and determined the influence of ANP on neurite outgrowth in vitro by using organotypic SG explants and dissociated SGN cultures from postnatal rats. We have demonstrated that ANP and its receptors are expressed in neurons within the cochlear SG of postnatal rat, while ANP may promote neurite outgrowth of SGNs via the NPR-A/cGMP/PKG pathway in a dose-dependent manner. These results indicate that ANP would play a role in normal neuritogenesis of SGN during cochlear development and represents a potential therapeutic candidate to enhance regeneration and regrowth of SGN neurites.

Stem Cell-Based Therapeutic Approaches to Restore Sensorineural Hearing Loss in Mammals

The hair cells that reside in the cochlear sensory epithelium are the fundamental sensory structures responsible for understanding the mechanical sound waves evoked in the environment. The intense damage to these sensory structures may result in permanent hearing loss. The present strategies to rehabilitate the hearing function include either hearing aids or cochlear implants that may recover the hearing capability of deaf patients to a limited extent. Therefore, much attention has been paid on developing regenerative therapies to regenerate/replace the lost hair cells to treat the damaged cochlear sensory epithelium. The stem cell therapy is a promising approach to develop the functional hair cells and neuronal cells from endogenous and exogenous stem cell pool to recover hearing loss. In this review, we specifically discuss the potential of different kinds of stem cells that hold the potential to restore sensorineural hearing loss in mammals and comprehensively explain the current therapeutic applications of stem cells in both the human and mouse inner ear to regenerate/replace the lost hair cells and spiral ganglion neurons.

Oriented Neural Spheroid Formation and Differentiation of Neural Stem Cells Guided by Anisotropic Inverse Opals

Isotropic inverse opal structures have been extensively studied for the ability to manipulate cell behaviors such as attachment, migration, and spheroid formation. However, their use in regulate the behaviors of neural stem cells has not been fully explored, besides, the isotropic inverse opal structures usually lack the ability to induce the oriented cell growth which is fundamental in neural regeneration based on neural stem cell therapy. In this paper, the anisotropic inverse opal substrates were obtained by mechanically stretching the poly (vinylidene fluoride) (PVDF) inverse opal films. The anisotropic inverse opal substrates possessed good biocompatibility, optical properties and anisotropy, provided well guidance for the formation of neural spheroids, the alignment of neural stem cells, the differentiation of neural stem cells, the oriented growth of derived neurons and the dendritic complexity of the newborn neurons. Thus, we conclude that the anisotropic inverse opal substrates possess great potential in neural regeneration applications.

Grooved hydroxyapatite scaffold modulates mitochondria homeostasis and thus promotes osteogenesis in bone mesenchymal stromal cells

Hydroxyapatite scaffolds (HASs) are widely studied as suitable materials for bone replacement scaffolds due to their chemical similarities to organic materials. In our previous study, a novel HAS with a 25–30-µm groove structure (HAS-G) exhibited enhanced osteogenesis of bone mesenchymal stromal cells (BMSCs) compared with HAS, potentially by modulating the macrophage-induced immune microenvironment. However, the exact effects of different surface patterns on the physiological processes of attached cells is not known. The present study aimed to determine the effects of HAS-G on the osteogenesis and physiological processes in BMSCs. Cell counting kit-8 assays and propidium iodide staining followed by flow cytometry were performed, and the results demonstrated that both in normal medium and differentiating medium, HAS-G promoted cell proliferation by decreasing the proportion of G1/G0 cells and decreased reactive oxygen species (ROS) accumulation in BMSCs compared with HAS. Detection markers of osteogenesis revealed that compared with HAS, HAS-G increased runt-related transcription factor 2, osteocalcin and osteopontin protein levels and promoted osteogenesis, which was further confirmed by Alizarin Red S staining. Following JC-1 staining, it was observed that HAS-G maintained the mitochondrial membrane potential, similar to that achieved by N-acetylcysteine pretreatment. In addition, compared with those of HAS, HAS-G decreased mitochondrial ROS levels, which potentially contributed to the promotion of osteogenesis. The results also demonstrated that HAS-G inhibited mitophagy induced by ROS accumulation and ATP synthesis compared with HAS. In conclusion, HAS-G decreased ROS accumulation and mitophagy and thus promoted osteogenesis of BMSCs, indicating that ROS modulation of HAS-G may serve a key role in osteogenesis.

A Neurophysiological Study of Musical Pitch Identification in Mandarin-Speaking Cochlear Implant Users

Music perception in cochlear implant (CI) users is far from satisfactory, not only because of the technological limitations of current CI devices but also due to the neurophysiological alterations that generally accompany deafness. Early behavioral studies revealed that similar mechanisms underlie musical and lexical pitch perception in CI-based electric hearing. Although neurophysiological studies of the musical pitch perception of English-speaking CI users are actively ongoing, little such research has been conducted with Mandarin-speaking CI users; as Mandarin is a tonal language, these individuals require pitch information to understand speech. The aim of this work was to study the neurophysiological mechanisms accounting for the musical pitch identification abilities of Mandarin-speaking CI users and normal-hearing (NH) listeners. Behavioral and mismatch negativity (MMN) data were analyzed to examine musical pitch processing performance. Moreover, neurophysiological results from CI users with good and bad pitch discrimination performance (according to the just-noticeable differences (JND) and pitch-direction discrimination (PDD) tasks) were compared to identify cortical responses associated with musical pitch perception differences. The MMN experiment was conducted using a passive oddball paradigm, with musical tone C4 (262 Hz) presented as the standard and tones D4 (294 Hz), E4 (330 Hz), G#4 (415 Hz), and C5 (523 Hz) presented as deviants. CI users demonstrated worse musical pitch discrimination ability than did NH listeners, as reflected by larger JND and PDD thresholds for pitch identification, and significantly increased latencies and reduced amplitudes in MMN responses. Good CI performers had better MMN results than did bad performers. Consistent with findings for English-speaking CI users, the results of this work suggest that MMN is a viable marker of cortical pitch perception in Mandarin-speaking CI users.

A Polydopamine-Functionalized Carbon Microfibrous Scaffold Accelerates the Development of Neural Stem Cells

Neuroregenerative medicine has witnessed impressive technological breakthroughs in recent years, but the currently available scaffold materials still have limitations regarding the development of effective treatment strategies for neurological diseases. Electrically conductive micropatterned materials have gained popularity in recent years due to their significant effects on neural stem cell fate. Polydopamine (PDA)-modified materials can also enhance the differentiation of neurons. In this work, we show that PDA-modified carbon microfiber skeleton composites have the appropriate conductivity, three-dimensional structure, and microenvironment regulation that are crucial for the growth of neural stem cells. The design we present is low-cost and easy to make and shows great promise for studying the growth and development of mouse neural stem cells. Our results show that the PDA-mediated formation of electrically conductive and viscous nanofiber webs promoted the adhesion, organization, and intercellular coupling of neural stem cells relative to the control group. PDA induced massive proliferation of neural stem cells and promoted the expression of Ki-67. Together, our results suggest that the composite material can be used as a multifunctional neural scaffold for clinical treatment and in vitro research by improving the structure, conductivity, and mechanical integrity of the regenerated tissues.

Customizable Implant-specific and Tissue-Specific Extracellular Matrix Protein Coatings Fabricated Using Atmospheric Plasma

Progression in implant science has benefited from ample amount of technological contributions from various disciplines, including surface biotechnology. In this work, we successfully used atmospheric plasma to enhance the biological functions of surgical implants by coating them with extracellular matrix proteins. The developed collagen and laminin coatings demonstrate advantageous material properties. Chemical analysis by XPS and morphological investigation by SEM both suggested a robust coating. Contact angle goniometry and dissolution study in simulated body fluid (SBF) elicited increased hydrophilicity and physiological durability. Furthermore, these coatings exhibited improved biological interactions with human mesenchymal and neural stem cells (NSCs). Cell adhesion, proliferation, and differentiation proved markedly refined as shown by enzymatic detachment, flow cytometry, and ELISA data, respectively. Most importantly, using the pathway-specific PCR array, our study discovered dozens of deregulated genes during osteogenesis and neurogenesis on our newly fabricated ECM coatings. The coating-induced change in molecular profile serves as a promising clue for designing future implant-based therapy. Collectively, we present atmospheric plasma as a versatile tool for enhancing surgical implants, through customizable implant-specific and tissue-specific coatings.