Microtopographical cues promote peripheral nerve regeneration via transient mTORC2 activation

Dual-layer microneedles with NO/O2 releasing for diabetic wound healing via neurogenesis, angiogenesis, and immune modulation

Diabetic wounds present multiple functional impairments, including neurovascular dysregulation, oxidative imbalance, and immune dysfunction, making wound healing particularly challenging, while traditional therapeutical strategies fail to address these complex issues effectively. Herein, we propose a strategy utilizing dual-layer microneedles to deliver therapeutic gases by modulating neurovascular coupling and immune functions for diabetic wound treatment. The microneedle can respond to reactive oxygen species (ROS) in the diabetic microenvironment and subsequently generate oxygen (O2) and nitric oxide (NO). These gases comprehensively promote neuro-vascular regeneration, reduce oxidative stress levels, and attenuate inflammation. In vivo studies demonstrate that the microneedle can accelerate diabetic wound healing by modulating neurovascular regeneration and inflammatory processes. Transcriptomic analyses further validate the involvement of related advantageous signaling pathways. The potential mechanism involves the activation of the PI3K-AKT-mTOR pathway to facilitate autophagy, ultimately accelerating the healing process. Thus, our multifunctional dual-layer microneedles provide an effective strategy for treating diabetic wounds.

Static Magnetic Stimulation and Magnetic Microwires Synergistically Enhance and Guide Neurite Outgrowth

Axonal growth is heavily influenced by topography and biophysical stimuli including magnetic and electrical fields. Despite extensive investigation, the degree of influence and the underlying genetic mechanisms remain poorly understood. Here, a novel approach to guide neurite growth is undertaken using an innovative ferromagnetic composite material - glass-coated magnetic microwire - to furnish a synergistic combination of magnetic and topographical cues. Whole rat dorsal root ganglia (DRG) are cultured under five different conditions: control, static magnetic field, magnetic microwire, static magnetic field + glass fiber, and static magnetic field + magnetic microwire. DRG outgrowth responses under each condition, including total neurite outgrowth and directionality, are compared. The combination of both magnetic stimulation and topography significantly increases total neurite outgrowth compared to the controls. The combination of magnetic stimulation and magnetic microwire lead to a strong directional bias of growth along the microwire, double what is observed with the glass fiber. Next generation RNA sequencing of DRG exposed to static magnetic field + magnetic microwire reveals the downregulation of genes relating to the immune response, interleukin signaling, and signal transduction. These results set the stage for contemplating future biophysical stimulation for axonal guidance and improved understanding of material-tissue interactions.

The limelight of adipose-derived stem cells in the landscape of neural tissue engineering for peripheral nerve injury

BACKGROUND AND AIMS

Challenges in treating peripheral nerve injury include prolonged repair time and insufficient functional recovery. Stem cell therapy coupled with neural tissue engineering has been shown to induce nerve regeneration following peripheral nerve injury. Among these stem cells, adipose-derived stem cells (ADSCs) are preferred due to their accessibility, expansion, multidirectional differentiation, and production of essential nutrient factors for nerve growth. In recent years, ADSC-laden nerve guide conduit has been utilized to enhance the therapeutic effects of tissue-engineered nerve grafts. This review explores existing research that recognizes the roles played by ADSCs in inducing peripheral nerve regeneration following injury and summarizes the different methods of application of ADSC-laden nerve conduit in neural tissue engineering.

Biogelx-IKVAV Is An Innovative Human Platelet Lysate-Adipose-Derived Stem Cells Delivery Strategy to Improve Peripheral Nerve Repair

Adipose-derived stem cells (ADSC) are nowadays one of the most exploited cells in regenerative medicine. They are fast growing, capable of enhancing axonal elongation, support and locally stimulate Schwann cells (SCs), and protect de-innervated muscles from atrophy after a peripheral nerve injury. With the aim of developing a bio-safe, clinically translatable cell-therapy, we assessed the effect of ADSC pre-expanded with human platelet lysate in an in vivo rat model, delivering the cells into a 15 mm critical-size sciatic nerve defect embedded within a laminin-peptide-functionalized hydrogel (Biogelx-IKVAV) wrapped by a poly-ɛ-caprolactone (PCL) nerve conduit. ADSC retained their stemness, their immunophenotype and proliferative activity when tested in vitro. At 6 weeks post-implantation, robust regeneration was observed across the critical-size gap as evaluated by both the axonal elongation (anti-NF 200) and SC proliferation (anti-S100) within the human ADSC-IKVAV filled PCL conduit. All the other experimental groups manifested significantly lower levels of growth cone elongation. The histological gastrocnemius muscle analysis was comparable with no quantitative significant differences among the experimental groups. Taken together, these results suggest that ADSC encapsulated in Biogelx-IKVAV are a potential path to improve the efficacy of nerve regeneration. New perspectives can be pursued for the development of a fully synthetic bioengineered nerve graft for the treatment of peripheral nerve injury. Impact statement Human adipose-derived stem cells pre-expanded in vitro with human platelet lysate culture medium additive and encapsulated into BiogelX-IKVAV are a promising strategy to improve nerve regeneration through a critical nerve gap in rat model.

Recent research of peptide-based hydrogel in nervous regeneration

Neurological disorders exert significantly affect the quality of life for patients, necessitating effective strategies for nerve regeneration. Both traditional autologous nerve transplantation and emerging therapeutic approaches encounter scientific challenges due to the complex nature of the nervous system and the unsuitability of the surrounding environment for cell transplantation. Tissue engineering techniques offer a promising path for neurotherapy. Successful neural tissue engineering relies on modulating cell differentiation behavior and tissue repair by developing biomaterials that mimic the natural extracellular matrix (ECM) and establish a three-dimensional microenvironment. Peptide-based hydrogels have emerged as a potent option among these biomaterials due to their ability to replicate the structure and complexity of the ECM. This review aims to explore the diverse range of peptide-based hydrogels used in nerve regeneration with a specific focus on dipeptide hydrogels, tripeptide hydrogels, oligopeptide hydrogels, multidomain peptides (MDPs), and amphiphilic peptide hydrogels (PAs). Peptide-based hydrogels offer numerous advantages, including biocompatibility, structural diversity, adjustable mechanical properties, and degradation without adverse effects. Notably, hydrogels formed from self-assembled polypeptide nanofibers, derived from amino acids, show promising potential in engineering neural tissues, outperforming conventional materials like alginate, poly(ε-caprolactone), and polyaniline. Additionally, the simple design and cost-effectiveness of dipeptide-based hydrogels have enabled the creation of various functional supramolecular structures, with significant implications for nervous system regeneration. These hydrogels are expected to play a crucial role in future neural tissue engineering research. This review aims to highlight the benefits and potential applications of peptide-based hydrogels, contributing to the advancement of neural tissue engineering.

Enhancing Therapeutic Efficacy in Cancer Treatment: Integrating Nanomedicine with Autophagy Inhibition Strategies

The complicated stepwise lysosomal degradation process known as autophagy is in charge of destroying and eliminating damaged organelles and defective cytoplasmic components. This mechanism promotes metabolic adaptability and nutrition recycling. Autophagy functions as a quality control mechanism in cells that support homeostasis and redox balance under normal circumstances. However, the role of autophagy in cancer is controversial because, mostly depending on the stage of the tumor, it may either suppress or support the disease. While autophagy delays the onset of tumors and slows the dissemination of cancer in the early stages of tumorigenesis, numerous studies demonstrate that autophagy promotes the development and spread of tumors as well as the evolution and development of resistance to several anticancer drugs in advanced cancer stages. In this Review, we primarily emphasize the therapeutic role of autophagy inhibition in improving the treatment of multiple cancers and give a broad overview of how its inhibition modulates cancer responses. There have been various attempts to inhibit autophagy, including the use of autophagy inhibitor drugs, gene silencing therapy (RNA interference), and nanoparticles. In this Review, all these topics are thoroughly covered and illustrated by recent studies and field investigations.

Local problems need global solutions: The metabolic needs of regenerating organisms

The vast majority of species that belong to the plant or animal kingdom evolved with two main strategies to counter tissue damage-scar formation and regeneration. Whereas scar formation provides a fast and cost-effective repair to exit life-threatening conditions, complete tissue regeneration is time-consuming and requires vast resources to reinstall functionality of affected organs or structures. Local environments in wound healing are widely studied and findings have provided important biomedical applications. Less well understood are organismic physiological parameters and signalling circuits essential to maintain effective tissue repair. Here, we review accumulated evidence that positions the interplay of local and systemic changes in metabolism as essential variables modulating the injury response. We particularly emphasise the role of lipids and lipid-like molecules as significant components long overlooked.

A Review on the Technological Advances and Future Perspectives of Axon Guidance and Regeneration in Peripheral Nerve Repair

Despite a significant advance in the pathophysiological understanding of peripheral nerve damage, the successful treatment of large nerve defects remains an unmet medical need. In this article, axon growth guidance for peripheral nerve regeneration was systematically reviewed and discussed mainly from the engineering perspective. In addition, the common approaches to surgery, bioengineering approaches to emerging technologies such as optogenetic stimulation and magnetic stimulation for functional recovery were discussed, along with their pros and cons. Additionally, clear future perspectives of axon guidance and nerve regeneration were addressed.

Biocompatibility pathways and mechanisms for bioactive materials: The bioactivity zone

This essay analyzes the scientific evidence that forms the basis of bioactive materials, covering the fundamental understanding of bioactivity phenomena and correlation with the mechanisms of biocompatibility of biomaterials. This is a detailed assessment of performance in areas such as bone-induction, cell adhesion, immunomodulation, thrombogenicity and antimicrobial behavior. Bioactivity is the modulation of biological activity by characteristics of the interfacial region that incorporates the material surface and the immediate local host tissue. Although the term ‘bioactive material’ is widely used and has a well understood general meaning, it would be useful now to concentrate on this interfacial region, considered as ‘the bioactivity zone’. Bioactivity phenomena are either due to topographical/micromechanical characteristics, or to biologically active species that are presented in the bioactivity zone. Examples of topographical/micromechanical effects are the modulation of the osteoblast – osteoclast balance, nanotopographical regulation of cell adhesion, and bactericidal nanostructures. Regulation of bioactivity by biologically active species include their influence, especially of metal ions, on signaling pathways in bone formation, the role of cell adhesion molecules and bioactive peptides in cell attachment, macrophage polarization by immunoregulatory molecules and antimicrobial peptides. While much experimental data exists to demonstrate the potential of such phenomena, there are considerable barriers to their effective clinical translation. This essay shows that there is solid scientific evidence of the existence of bioactivity mechanisms that are associated with some types of biomaterials, especially when the material is modified in a manner designed to specifically induce that activity.

Anisotropic scaffolds for peripheral nerve and spinal cord regeneration

The treatment of long-gap (>10 mm) peripheral nerve injury (PNI) and spinal cord injury (SCI) remains a continuous challenge due to limited native tissue regeneration capabilities. The current clinical strategy of using autografts for PNI suffers from a source shortage, while the pharmacological treatment for SCI presents dissatisfactory results. Tissue engineering, as an alternative, is a promising approach for regenerating peripheral nerves and spinal cords. Through providing a beneficial environment, a scaffold is the primary element in tissue engineering. In particular, scaffolds with anisotropic structures resembling the native extracellular matrix (ECM) can effectively guide neural outgrowth and reconnection. In this review, the anatomy of peripheral nerves and spinal cords, as well as current clinical treatments for PNI and SCI, is first summarized. An overview of the critical components in peripheral nerve and spinal cord tissue engineering and the current status of regeneration approaches are also discussed. Recent advances in the fabrication of anisotropic surface patterns, aligned fibrous substrates, and 3D hydrogel scaffolds, as well as their in vitro and in vivo effects are highlighted. Finally, we summarize potential mechanisms underlying the anisotropic architectures in orienting axonal and glial cell growth, along with their challenges and prospects.

Biomimicry in 3D printing design: implications for peripheral nerve regeneration

Nerve guide conduits (NGCs) connect dissected nerve stumps and effectively repair short-range peripheral nerve defects. However, for long-range defects, autografts show better therapeutic effects, despite intrinsic limitations. Recent evidence shows that biomimetic design is essential for high-performance NGCs, and 3D printing is a promising fabricating technique. The current work includes a brief review of the challenges for peripheral nerve regeneration. The authors propose a potential solution using biomimetic 3D-printed NGCs as alternative therapies. The assessment of biomimetic designs includes microarchitecture, mechanical property, electrical conductivity and biologics inclusion. The applications of 3D printing in preparing NGCs and present strategies to improve therapeutic effects are also discussed.

Enhanced efficiency of nonviral direct neuronal reprogramming on topographical patterns

Nonviral direct neuronal reprogramming holds significant potential in the fields of tissue engineering and regenerative medicine. However, the issue of low reprogramming efficiency poses a major barrier to its application. We propose that topographical cues, which have been applied successfully to enhance lineage-directed differentiation and multipotent stem cell transdifferentiation, could improve nonviral direct neuronal reprogramming efficiency. To investigate, we used a polymer-BAM (Brn2, Ascl1, Myt1l) factor transfection polypex to reprogram primary mouse embryonic fibroblasts. Using a multiarchitecture chip, we screened for patterns that may improve transfection and/or subsequent induced neuron reprogramming efficiency. Selected patterns were then investigated further by analyzing β-tubulin III (TUJ1) and microtubule-associated protein 2 (MAP2) protein expression, cell morphology and electrophysiological function of induced neurons. Certain hierarchical topographies, with nanopatterns imprinted on micropatterns, significantly improved the percentage of TUJ1+ and MAP2+ cells. It is postulated that the microscale base pattern enhances initial BAM expression while the nanoscale sub-pattern promotes subsequent maturation. This is because the base pattern alone increased expression of TUJ1 and MAP2, while the nanoscale pattern was the only pattern yielding induced neurons capable of firing multiple action potentials. Nanoscale patterns also produced the highest fraction of cells showing spontaneous synaptic activity. Overall, reprogramming efficiency with one dose of polyplex on hierarchical patterns was comparable to that of five doses without topography. Thus, topography can enhance nonviral direct reprogramming of fibroblasts into induced neurons.

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.

Materials for peripheral nerve repair constructs: Natural proteins or synthetic polymers?

The efficacious repair of severe peripheral nerve injuries is currently an unmet clinical need, and biomaterial constructs offer a promising approach to help promote nerve regeneration. Current research focuses on the development of more sophisticated constructs with complex architecture and the addition of regenerative agents to encourage timely reinnervation and promote functional recovery. This review surveyed the present landscape of nerve repair construct literature with a focus on six selected materials that are frequently encountered in this application: the natural proteins collagen, chitosan, and silk, and the synthetic polymers poly-ε-caprolactone (PCL), poly-lactic-co-glycolic acid (PLGA) and poly-glycolic acid (PGA). This review also investigated the use of cell therapy in nerve repair constructs, and in all instances concentrated on publications reporting constructs developed and tested in vivo in the last five years (2015-2020). Across the selected literature, the popularity of natural proteins and synthetic polymers appears to be broadly equivalent, with a similar number of studies reporting successful outcomes in vivo. Both material types are also utilised as vehicles for cell therapy, which has much potential to improve the results of nerve bridging for treating longer gaps.

Human platelet lysate as a potential clinical-translatable supplement to support the neurotrophic properties of human adipose-derived stem cells

Background

The autologous nerve graft, despite its donor site morbidity and unpredictable functional recovery, continues to be the gold standard in peripheral nerve repair. Rodent research studies have shown promising results with cell transplantation of human adipose-derived stem cells (hADSC) in a bioengineered conduit, as an alternative strategy for nerve regeneration. To achieve meaningful clinical translation, cell therapy must comply with biosafety. Cell extraction and expansion methods that use animal-derived products, including enzymatic adipose tissue dissociation and the use of fetal bovine serum (FBS) as a culture medium supplement, have the potential for transmission of zoonotic infectious and immunogenicity. Human-platelet-lysate (hPL) serum has been used in recent years in human cell expansion, showing reliability in clinical applications.

Methods

We investigated whether hADSC can be routinely isolated and cultured in a completely xenogeneic-free way (using hPL culture medium supplement and avoiding collagenase digestion) without altering their physiology and stem properties. Outcomes in terms of stem marker expression (CD105, CD90, CD73) and the osteocyte/adipocyte differentiation capacity were compared with classical collagenase digestion and FBS-supplemented hADSC expansion.

Results

We found no significant differences between the two examined extraction and culture protocols in terms of cluster differentiation (CD) marker expression and stem cell plasticity, while hADSC in hPL showed a significantly higher proliferation rate when compared with the usual FBS-added medium. Considering the important key growth factors (particularly brain-derived growth factor (BDNF)) present in hPL, we investigated a possible neurogenic commitment of hADSC when cultured with hPL. Interestingly, hADSC cultured in hPL showed a statistically higher secretion of neurotrophic factors BDNF, glial cell-derived growth factor (GDNF), and nerve-derived growth factor (NFG) than FBS-cultured cells. When cocultured in the presence of primary neurons, hADSC which had been grown under hPL supplementation, showed significantly enhanced neurotrophic properties.

Conclusions

The hPL-supplement medium could improve cell proliferation and neurotropism while maintaining stable cell properties, showing effectiveness in clinical translation and significant potential in peripheral nerve research.

Modern Trends for Peripheral Nerve Repair and Regeneration: Beyond the Hollow Nerve Guidance Conduit

Peripheral nerve repair and regeneration remains among the greatest challenges in tissue engineering and regenerative medicine. Even though peripheral nerve injuries (PNIs) are capable of some degree of regeneration, frail recovery is seen even when the best microsurgical technique is applied. PNIs are known to be very incapacitating for the patient, due to the deprivation of motor and sensory abilities. Since there is no optimal solution for tackling this problem up to this day, the evolution in the field is constant, with innovative designs of advanced nerve guidance conduits (NGCs) being reported every day. As a basic concept, a NGC should act as a physical barrier from the external environment, concomitantly acting as physical guidance for the regenerative axons across the gap lesion. NGCs should also be able to retain the naturally released nerve growth factors secreted by the damaged nerve stumps, as well as reducing the invasion of scar tissue-forming fibroblasts to the injury site. Based on the neurobiological knowledge related to the events that succeed after a nerve injury, neuronal subsistence is subjected to the existence of an ideal environment of growth factors, hormones, cytokines, and extracellular matrix (ECM) factors. Therefore, it is known that multifunctional NGCs fabricated through combinatorial approaches are needed to improve the functional and clinical outcomes after PNIs. The present work overviews the current reports dealing with the several features that can be used to improve peripheral nerve regeneration (PNR), ranging from the simple use of hollow NGCs to tissue engineered intraluminal fillers, or to even more advanced strategies, comprising the molecular and gene therapies as well as cell-based therapies.

Roles of mTOR Signaling in Tissue Regeneration

The mammalian target of rapamycin (mTOR), is a serine/threonine protein kinase and belongs to the phosphatidylinositol 3-kinase (PI3K)-related kinase (PIKK) family. mTOR interacts with other subunits to form two distinct complexes, mTORC1 and mTORC2. mTORC1 coordinates cell growth and metabolism in response to environmental input, including growth factors, amino acid, energy and stress. mTORC2 mainly controls cell survival and migration through phosphorylating glucocorticoid-regulated kinase (SGK), protein kinase B (Akt), and protein kinase C (PKC) kinase families. The dysregulation of mTOR is involved in human diseases including cancer, cardiovascular diseases, neurodegenerative diseases, and epilepsy. Tissue damage caused by trauma, diseases or aging disrupt the tissue functions. Tissue regeneration after injuries is of significance for recovering the tissue homeostasis and functions. Mammals have very limited regenerative capacity in multiple tissues and organs, such as the heart and central nervous system (CNS). Thereby, understanding the mechanisms underlying tissue regeneration is crucial for tissue repair and regenerative medicine. mTOR is activated in multiple tissue injuries. In this review, we summarize the roles of mTOR signaling in tissue regeneration such as neurons, muscles, the liver and the intestine.

Cell Morphology on Poly(methyl methacrylate) Microstructures as Function of Surface Energy

Whilst the significance of substrate topography as a regulator of cell function is well established, a systematic analysis of the principles underlying this is still unavailable. Here we evaluate the hypothesis that surface energy plays a decisive role in substrate-mediated modulation of cell phenotype by evaluation of cell behaviour on synthetic microstructures exhibiting pronounced differences in surface energy. These microstructures, specifically cubes and walls, were fabricated from a biocompatible base polymer, poly(methyl methacrylate), by variotherm injection molding. The dimensions of the cubes were 1 μm x 1 μm x 1 μm (height x width x length) with a periodicity of 1:1 and 1:5 and the dimensions of the walls 1 μm x 1 μm x 15 mm (height x width x length) with a periodicity of 1:1 and 1:5. Mold inserts were made by lithography and electroplating. The surface energy of the resultant microstructures was determined by static contact angle measurements. Light scanning microscopy of the morphology of NT2/D1 and MC3T3-E1 preosteoblast cells cultured on structured PMMA samples in both cases revealed a profound surface energy dependence. “Walls” appeared to promote significant cell elongation, whilst a lack of cell adhesion was observed on “cubes” with the lowest periodicity. Contact angle measurements on walls revealed enhanced surface energy anisotropy (55 mN/m max., 10 mN/m min.) causing a lengthwise spreading of the test liquid droplet, similar to cell elongation. Surface energy measurements for cubes revealed increased isotropic hydrophobicity (87° max., H₂O). A critical water contact angle of ≤ 80° appears to be necessary for adequate cell adhesion. A “switch” for cell adhesion and subsequently cell growth could therefore be applied by, for example, adjusting the periodicity of hydrophobic structures. In summary cell elongation on walls and a critical surface energy level for cell adhesion could be produced for NT2/D1 and MC3T3-E1 cells by symmetrical and asymmetrical energy barrier levels. We, furthermore, propose a water-drop model providing a common physicochemical cause regarding similar cell/droplet geometries and cell adhesion on the investigated microstructures.

Rapid 3D printing of functional nanoparticle-enhanced conduits for effective nerve repair

Nerve conduits provide an advanced tool for repairing the injured peripheral nerve that often causes disability and mortality. Currently, the efficiency of conduits in repairing peripheral nerve is unsatisfying. Here, we show a functional nanoparticle-enhanced nerve conduit for promoting the regeneration of peripheral nerves. This conduit, which consists of gelatin-methacryloyl (GelMA) hydrogels with drug loaded poly(ethylene glycol)- poly(3-caprolactone) (MPEG-PCL) nanoparticles dispersed in the hydrogel matrix, is rapidly fabricated by a continuous three-dimensional (3D) printing process. While the 3D-printed hydrogel conduit with customized size, shape and structure provides a physical microenvironment for axonal elongation, the nanoparticles sustained release the drug to facilitate the nerve regeneration. The drug, 4-((5,10-dimethyl-6-oxo-6,10-dihydro-5H-pyrimido[5,4-b]thieno[3,2-e][1,4]diazepin-2-yl)amino) benzenesulfonamide, is a Hippo pathway inhibitor with multiple functions including improving the proliferation and migration of Schwann cells and up-regulating neurotrophic factors genes. The descried functional nerve conduit efficiently induced the recovery of sciatic injuries in morphology, histopathology and functions in vivo, showing the potential clinical application in peripheral nerve repair. STATEMENTS OF SIGNIFICANCE: Functional nerve conduit provides a promising strategy alternative to autografts. In this work, we rapidly customized a nanoparticle-enhanced conduit by the continuous bioprinting process. This nanoparticle in the conduit can release a Hippo pathway inhibitor to facilitate the nerve regeneration and function restoration. The efficacy of the conduits is comparable to that of autograft, suggesting the potential clinical applications.

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

The technologies related to ex vivo models and lab-on-a-chip devices for studying the regeneration of brain, spinal cord, and peripheral nerve tissues are essential tools for neural tissue engineering and regenerative medicine research. The need for ex vivo systems, lab-on-a-chip technologies and disease models for neural tissue engineering applications are emerging to overcome the shortages and drawbacks of traditional in vitro systems and animal models. Ex vivo models have evolved from traditional 2D cell culture models to 3D tissue-engineered scaffold systems, bioreactors, and recently organoid test beds. In addition to ex vivo model systems, we discuss lab-on-a-chip devices and technologies specifically for neural tissue engineering applications. Finally, we review current commercial products that mimic diseased and normal neural tissues, and discuss the future directions in this field.

Age-dependent migratory behavior of human endothelial cells revealed by substrate microtopography

Cell migration is part of many important in vivo biological processes and is influenced by chemical and physical factors such as substrate topography. Although the migratory behavior of different cell types on structured substrates has already been investigated, up to date it is largely unknown if specimen's age affects cell migration on structures. In this work, we investigated age-dependent migratory behavior of human endothelial cells from young (≤ 31 years old) and old (≥ 60 years old) donors on poly(dimethylsiloxane) microstructured substrates consisting of well-defined parallel grooves. We observed a decrease in cell migration velocity in all substrate conditions and in persistence length perpendicular to the grooves in cells from old donors. Nevertheless, in comparison to young cells, old cells exhibited a higher cell directionality along grooves of certain depths and a higher persistence time. We also found a systematic decrease of donor age-dependent responses of cell protrusions in orientation, velocity and length, all of them decreased in old cells. These observations lead us to hypothesize a possible impairment of actin cytoskeleton network and affected actin polymerization and steering systems, caused by aging.

Lipid-modified cell-penetrating peptide-based self-assembly micelles for co-delivery of narciclasine and siULK1 in hepatocellular carcinoma therapy

Hepatocellular carcinoma (HCC) is the most frequent type of primary liver cancer, and one therapeutic approach is to target both the AMPK and autophagy pathways in order to synergistically promote programmed cell death. Here, a series of amphiphilic, lipid-modified cell-penetrating peptides were synthesized and allowed to self-assemble into micelles loaded with the AMPK activator narciclasine (Narc) and short interfering RNA targeting the unc-51-like kinase 1 (siULK1). The size of these micelles, their efficiency of transfection into cells, and their ability to release drug or siRNA cargo in vitro were pH-sensitive, such that drug release was facilitated in the acidic microenvironment of the tumor. Transfecting the micelles into HCC cells significantly inhibited protective autophagy within tumor cells, and delivering the micelles into mice carrying HCC xenografts induced apoptosis, slowed tumor growth, and inhibited autophagy. Our results indicate that co-delivering Narc and siULK1 in biocompatible micelles can safely inhibit tumor growth and protective autophagy, justifying further studies into this promising therapeutic approach against HCC.

STATEMENT OF SIGNIFICANCE

We have focused on the targeted therapy of HCC via synergistically inhibiting the autophagy and inducing apoptosis. The lipid-modified cell-penetrating peptide can not only aggregate into micelles to load natural product narciclasine and ULK1 siRNA simultaneously, but also facilitate uptake and endosome escape with a pH-sensitive manner in HepG2 cells. HepG2 cell treated with siULK1-M-Narc has increased apoptotic levels and declined autophagy via the targeted regulation of AMPK-ULK1 signaling axis. The in vivo studies have confirmed that siULK1-M-Narc efficiently reduce the growth of tumor on HCC xenograft models with good safety. Thus, we suppose the lipid-modified cell-penetrating peptide has good application prospects in the targeted combinational therapy of HCC.

Proteomic Dissection of Nanotopography-Sensitive Mechanotransductive Signaling Hubs that Foster Neuronal Differentiation in PC12 Cells

Neuronal cells are competent in precisely sensing nanotopographical features of their microenvironment. The perceived microenvironmental information will be “interpreted” by mechanotransductive processes and impacts on neuronal functioning and differentiation. Attempts to influence neuronal differentiation by engineering substrates that mimic appropriate extracellular matrix (ECM) topographies are hampered by the fact that profound details of mechanosensing/-transduction complexity remain elusive. Introducing omics methods into these biomaterial approaches has the potential to provide a deeper insight into the molecular processes and signaling cascades underlying mechanosensing/-transduction but their exigence in cellular material is often opposed by technical limitations of major substrate top-down fabrication methods. Supersonic cluster beam deposition (SCBD) allows instead the bottom-up fabrication of nanostructured substrates over large areas characterized by a quantitatively controllable ECM-like nanoroughness that has been recently shown to foster neuron differentiation and maturation. Exploiting this capacity of SCBD, we challenged mechanosensing/-transduction and differentiative behavior of neuron-like PC12 cells with diverse nanotopographies and/or changes of their biomechanical status, and analyzed their phosphoproteomic profiles in these settings. Versatile proteins that can be associated to significant processes along the mechanotransductive signal sequence, i.e., cell/cell interaction, glycocalyx and ECM, membrane/f-actin linkage and integrin activation, cell/substrate interaction, integrin adhesion complex, actomyosin organization/cellular mechanics, nuclear organization, and transcriptional regulation, were affected. The phosphoproteomic data suggested furthermore an involvement of ILK, mTOR, Wnt, and calcium signaling in these nanotopography- and/or cell mechanics-related processes. Altogether, potential nanotopography-sensitive mechanotransductive signaling hubs participating in neuronal differentiation were dissected.