Electrospun gelatin-based scaffolds as a novel 3D platform to study the function of contractile smooth muscle cells in vitro

Artificial periosteum promotes bone regeneration through synergistic immune regulation of aligned fibers and BMSC-recruiting phages

Given the crucial role of periosteum in bone repair, the use of artificial periosteum to induce spontaneous bone healing instead of using bone substitutes has become a potential strategy. Also, the proper transition from pro-inflammatory signals to anti-inflammatory signals is pivotal for achieving optimal repair outcomes. Hence, we designed an artificial periosteum loaded with a filamentous bacteriophage clone named P11, featuring an aligned fiber morphology. P11 endowed the artificial periosteum with the capacity to recruit bone marrow mesenchymal stem cells (BMSCs). The artificial periosteum also regulated the immune microenvironment at the bone injury site through the synergistic effects of biochemical factors and topography. Specifically, the inclusion of P11 preserved inflammatory signaling in macrophages and additionally facilitated the migration of BMSCs. Subsequently, aligned fibers stimulated macrophages, inducing alterations in cytoskeletal and metabolic activities, resulting in the polarization into the M2 phenotype. This progression encouraged the osteogenic differentiation of BMSCs and promoted vascularization. In vivo experiments showed that the new bone generated in the AP group exhibited the most efficient healing pattern. Overall, the integration of biochemical factors with topographical considerations for sequential immunomodulation during bone repair indicates a promising approach for artificial periosteum development. STATEMENT OF SIGNIFICANCE: The appropriate transition of macrophages from a pro-inflammatory to an anti-inflammatory phenotype is pivotal for achieving optimal bone repair outcomes. Hence, we designed an artificial periosteum featuring an aligned fiber morphology and loaded with specific phage clones. The artificial periosteum not only fostered the recruitment of BMSCs but also achieved sequential regulation of the immune microenvironment through the synergistic effects of biochemical factors and topography, and improved the effect of bone repair. This study indicates that the integration of biochemical factors with topographical considerations for sequential immunomodulation during bone repair is a promising approach for artificial periosteum development.

From mesenchymal niches to engineered in vitro model systems: Exploring and exploiting biomechanical regulation of vertebrate hedgehog signalling

Tissue patterning is the result of complex interactions between transcriptional programs and various mechanical cues that modulate cell behaviour and drive morphogenesis. Vertebrate Hedgehog signalling plays key roles in embryogenesis and adult tissue homeostasis, and is central to skeletal development and the osteogenic differentiation of mesenchymal stem cells. The expression of several components of the Hedgehog signalling pathway have been reported to be mechanically regulated in mesodermal tissue patterning and osteogenic differentiation in response to external stimulation. Since a number of bone developmental defects and skeletal diseases, such as osteoporosis, are directly linked to aberrant Hedgehog signalling, a better knowledge of the regulation of Hedgehog signalling in the mechanosensitive bone marrow-residing mesenchymal stromal cells will present novel avenues for modelling these diseases and uncover novel opportunities for extracellular matrix-targeted therapies. In this review, we present a brief overview of the key molecular players involved in Hedgehog signalling and the basic concepts of mechanobiology, with a focus on bone development and regeneration. We also highlight the correlation between the activation of the Hedgehog signalling pathway in response to mechanical cues and osteogenesis in bone marrow-derived mesenchymal stromal cells. Finally, we propose different tissue engineering strategies to apply the expanding knowledge of 3D material-cell interactions in the modulation of Hedgehog signalling in vitro for fundamental and translational research applications.

Resveratrol Mitigates Oxygen and Glucose Deprivation-Induced Inflammation, NLRP3 Inflammasome, and Oxidative Stress in 3D Neuronal Culture

Oxygen glucose deprivation (OGD) can produce hypoxia-induced neurotoxicity and is a mature in vitro model of hypoxic cell damage. Activated AMP-activated protein kinase (AMPK) regulates a downstream pathway that substantially increases bioenergy production, which may be a key player in physiological energy and has also been shown to play a role in regulating neuroprotective processes. Resveratrol is an effective activator of AMPK, indicating that it may have therapeutic potential as a neuroprotective agent. However, the mechanism by which resveratrol achieves these beneficial effects in SH-SY5Y cells exposed to OGD-induced inflammation and oxidative stress in a 3D gelatin scaffold remains unclear. Therefore, in the present study, we investigated the effect of resveratrol in 3D gelatin scaffold cells to understand its neuroprotective effects on NF-κB signaling, NLRP3 inflammasome, and oxidative stress under OGD conditions. Here, we show that resveratrol improves the expression levels of cell viability, inflammatory cytokines (TNF-α, IL-1β, and IL-18), NF-κB signaling, and NLRP3 inflammasome, that OGD increases. In addition, resveratrol rescued oxidative stress, nuclear factor-erythroid 2 related factor 2 (Nrf2), and Nrf2 downstream antioxidant target genes (e.g., SOD, Gpx GSH, catalase, and HO-1). Treatment with resveratrol can significantly normalize OGD-induced changes in SH-SY5Y cell inflammation, oxidative stress, and oxidative defense gene expression; however, these resveratrol protective effects are affected by AMPK antagonists (Compounds C) blocking. These findings improve our understanding of the mechanism of the AMPK-dependent protective effect of resveratrol under 3D OGD-induced inflammation and oxidative stress-mediated cerebral ischemic stroke conditions.

Electrospun fibre diameter and its effects on vascular smooth muscle cells

Bypass grafting is a technique used in the treatment of vascular disease, which is currently the leading cause of mortality worldwide. While technology has moved forward over the years, synthetic grafts still show significantly lower rates of patency in small diameter bypass operations compared to the gold standard (autologous vessel grafts). Scaffold morphology plays an important role in vascular smooth muscle cell (VSMC) performance, with studies showing how fibre alignment and surface roughness can modulate phenotypic and genotypic changes. Herein, this study has looked at how the fibre diameter of electrospun polymer scaffolds can affect the performance of seeded VSMCs. Four different scaffolds were electrospun with increasing fibre sizes ranging from 0.75 to 6 µm. Culturing VSMCs on the smallest fibre diameter (0.75 µm) lead to a significant increase in cell viability after 12 days of culture. Furthermore, interesting trends were noted in the expression of two key phenotypic genes associated with mature smooth muscle cell contractility (myocardin and smooth muscle alpha-actin 1), whereby reducing the fibre diameter lead to relative upregulations compared to the larger fibre diameters. These results showed that the smallest (0.75 µm) fibre diameter may be best suited for the culture of VSMCs with the aim of increasing cell proliferation and aiding cell maturity.

Hybrid Gelatin Hydrogels in Nanomedicine Applications

Gelatin based hydrogels are often incorporated with supporting materials such as chitosan, poly(vinyl alcohol), alginate, carbon nanotubes, and hyaluronic acid. These hybrid materials are specifically of interest in diversified nanomedicine fields as they exhibit unique physicochemical properties, antimicrobial activity, biodegradability, and biocompatibility. The applications include drug delivery, wound healing, cell culture, and tissue engineering. This paper reviews the various up-to-date methods to fabricate gelatin-based hydrogels, including UV photo-cross-linking, electrospinning, and 3D bioprinting. This paper also includes physical, chemical, mechanical, and biocompatibility characterization studies of several hybrid gelatin hydrogels and discusses their relevance in nanomedicine based applications. Challenges associated with the fabrication of hybrid materials for nanotechnology implementation, specifically in nanomedicine development, are critically discussed, and some future recommendations are provided.

Enhanced Generation of Reactive Species by Cold Plasma in Gelatin Solutions for Selective Cancer Cell Death

Atmospheric pressure plasma jets generate reactive oxygen and nitrogen species (RONS) in liquids and biological media, which find application in the new area of plasma medicine. These plasma-treated liquids were demonstrated recently to possess selective properties on killing cancer cells and attracted attention toward new plasma-based cancer therapies. These allow for local delivery by injection in the tumor but can be quickly washed away by body fluids. By confining these RONS in a suitable biocompatible delivery system, great perspectives can be opened in the design of novel biomaterials aimed for cancer therapies. Gelatin solutions are evaluated here to store RONS generated by atmospheric pressure plasma jets, and their release properties are evaluated. The concentration of RONS was studied in 2% gelatin as a function of different plasma parameters (treatment time, nozzle distance, and gas flow) with two different plasma jets. Much higher production of reactive species (H₂O₂ and NO₂^-) was revealed in the polymer solution than in water after plasma treatment. The amount of RONS generated in gelatin is greatly improved with respect to water, with concentrations of H₂O₂ and NO₂^- between 2 and 12 times higher for the longest plasma treatments. Plasma-treated gelatin exhibited the release of these RONS to a liquid media, which induced an effective killing of bone cancer cells. Indeed, in vitro studies on the sarcoma osteogenic (SaOS-2) cell line exposed to plasma-treated gelatin led to time-dependent increasing cytotoxicity with the longer plasma treatment time of gelatin. While the SaOS-2 cell viability decreased to 12%-23% after 72 h for cells exposed to 3 min of treated gelatin, the viability of healthy cells (hMSC) was preserved (∼90%), establishing the selectivity of the plasma-treated gelatin on cancer cells. This sets the basis for designing improved hydrogels with high capacity to deliver RONS locally to tumors.

Gelatin Electrospun Mat as a Potential Co-culture System for In Vitro Production of Sperm Cells from Embryonic Stem Cells

Engineering of 3D substrates with maximum similarity to seminiferous tubules would help to produce functional sperm cells in vitro from stem cells. Here, we present a 3D electrospun gelatin (EG) substrate seeded with Sertoli cells and determine its potential for guided differentiation of embryonic stem cells (ESCs) toward germline cells. The EG was fabricated by electrospinning, and its morphology under SEM, as well as cytobiocompatibility for Sertoli cells and ESCs, was confirmed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and cell attachment assay. Embryoid bodies (EBs) were formed from ESCs and co-cultured with Sertoli cells, induced with BMP4 for 3 and 7 consecutive days to induce the differentiation of EBs toward germline cells. The differentiation was investigated by immunocytochemistry (ICC), flow cytometry, and RT-PCR in four experimental groups of EBs (EBs cultured in gelatin-coated cell culture plates); Scaffold/EB (EBs cultured on EG); ESCs/Ser (EBs and Sertoli cells co-cultured on gelatin-coated cell culture plates without EG); and Scaffold/EB/Ser (EBs and Sertoli cells co-cultured on EG). All experimental groups exhibited a significantly increased MVH (germline-specific marker) and decreased c-KIT (stemness marker) expression when compared with the EB group. ICC and flow cytometry revealed that Scaffold/EB/Ser had the highest level of MVH and the lowest c-KIT expression at both 3 and 7 days postdifferentiation compared with other groups. RT-PCR results showed a significant increase in the germline marker (Dazl) and a significant decrease in the ESC stemness marker (Nanog) in Scaffold/EB compared to the EB group. The germline markers Gcna, Stella, Mvh, Stra8, Piwil2, and Dazl were significantly increased in Scaffold/EB/Ser compared to the Scaffold/EB group. Our findings revealed that the EG scaffold can provide an excellent substrate biomimicking the micro/nanostructure of native seminiferous tubules and a platform for Sertoli cell-EB communication required for growth and differentiation of ESCs into germline cells.

Fabrication and Plasma Modification of Nanofibrous Tissue Engineering Scaffolds

This paper provides a comprehensive overview of nanofibrous structures for tissue engineering purposes and the role of non-thermal plasma technology (NTP) within this field. Special attention is first given to nanofiber fabrication strategies, including thermally-induced phase separation, molecular self-assembly, and electrospinning, highlighting their strengths, weaknesses, and potentials. The review then continues to discuss the biodegradable polyesters typically employed for nanofiber fabrication, while the primary focus lies on their applicability and limitations. From thereon, the reader is introduced to the concept of NTP and its application in plasma-assisted surface modification of nanofibrous scaffolds. The final part of the review discusses the available literature on NTP-modified nanofibers looking at the impact of plasma activation and polymerization treatments on nanofiber wettability, surface chemistry, cell adhesion/proliferation and protein grafting. As such, this review provides a complete introduction into NTP-modified nanofibers, while aiming to address the current unexplored potentials left within the field.

Muscle tissue engineering in fibrous gelatin: implications for meat analogs

Bioprocessing applications that derive meat products from animal cell cultures require food-safe culture substrates that support volumetric expansion and maturation of adherent muscle cells. Here we demonstrate scalable production of microfibrous gelatin that supports cultured adherent muscle cells derived from cow and rabbit. As gelatin is a natural component of meat, resulting from collagen denaturation during processing and cooking, our extruded gelatin microfibers recapitulated structural and biochemical features of natural muscle tissues. Using immersion rotary jet spinning, a dry-jet wet-spinning process, we produced gelatin fibers at high rates (~ 100 g/h, dry weight) and, depending on process conditions, we tuned fiber diameters between ~ 1.3 ± 0.1 μm (mean ± SEM) and 8.7 ± 1.4 μm (mean ± SEM), which are comparable to natural collagen fibers. To inhibit fiber degradation during cell culture, we crosslinked them either chemically or by co-spinning gelatin with a microbial crosslinking enzyme. To produce meat analogs, we cultured bovine aortic smooth muscle cells and rabbit skeletal muscle myoblasts in gelatin fiber scaffolds, then used immunohistochemical staining to verify that both cell types attached to gelatin fibers and proliferated in scaffold volumes. Short-length gelatin fibers promoted cell aggregation, whereas long fibers promoted aligned muscle tissue formation. Histology, scanning electron microscopy, and mechanical testing demonstrated that cultured muscle lacked the mature contractile architecture observed in natural muscle but recapitulated some of the structural and mechanical features measured in meat products.

Three-dimensional electrospun gelatin scaffold coseeded with embryonic stem cells and sertoli cells: A promising substrate for in vitro coculture system

In this study, we present an electrospun gelatin (EG) scaffold to mimic the extracellular matrix of the testis. The EG scaffold was synthesized by electrospinning and crosslinked with glutaraldehyde vapor to decrease its water solubility and degradation rate. The scanning electron microscope micrographs showed the homogenous morphology of randomly aligned gelatin fibers. The average diameter of gelatin fibers before and after crosslinking was approximately 180 and 220 nm, respectively. Modulus, tensile strength, and elongation at break values were as 161.8 ± 24.4 MPa, 4.21 ± 0.54 MPa, and 7.06 ± 2.12 MPa, respectively. The crosslinked EG showed 75.2% ± 4.5% weight loss after 14 days with no changes in the pH value of degradation solution. Cytobiocompatibility of the EG for sertoli cells and embryonic stem cells (ESCs) was determined in vitro. Sertoli cells were isolated from mouse testis and characterized by immunostaining and flow cytometry. The effects of EG on proliferation and attachment of both sertoli cells and ESCs were examined. The EG scaffolds exhibited no cytotoxicity for sertoli and ESCs. Both sertoli and ESCs were well attached and grown on EG. Coculture of sertoli and ESCs on EG showed better ESCs adhesion compared with ESCs alone. Our findings indicate the potential of EG as a substrate for proliferation, adhesion, and coculture of sertoli and ESCs and may be considered as a promising engineered microenvironment for in vitro coculture system with the aim of guiding stem cells differentiation toward sperm-producing cells.