Facile fabrication of poly(ε-caprolactone)/graphene oxide membranes for bioreactors in tissue engineering

Resveratrol-loaded PCL-PEG/GO/HAP biocomposite bone membranes: Evaluation of mechanical properties, release kinetics, and cellular response

In this study, biocomposite membranes were developed by incorporating resveratrol (RSV)-loaded PCL-PEG composites, modified with graphene oxide (GO) and hydroxyapatite (HAP). The aim was to enhance hydrophilicity with GO and improve bioactivity with HAP. The release kinetics of RSV was evaluated by using Franz diffusion cells and compared with various kinetic models, including Korsmeyer-Peppas, Higuchi, and Baker, all of which showed high correlation coefficients (R²) close to 0.99. Mechanical tests was performed to determine the suitability of these membranes for tissue engineering applications. The composite membrane modified with GO and HAP exhibited tensile strength of 105.2 ± 5.8 MPa, tensile modulus of 3895 ± 159 MPa, elongation at break of 8.4 ± 0.9%, and toughness of 5.88 ± 0.46 MJ/m³. In vitro cell adhesion studies, visualized using DAPI fluorescence staining, demonstrated increased cell adhesion to the composite membranes over periods of 1, 3, 5, 7, and 14 days. These findings highlight the potential of the RSV-loaded PCL-PEG membranes, enhanced with GO and HAP, for applications in bone tissue engineering.

Current Advances in 3D Dynamic Cell Culture Systems

The traditional two-dimensional (2D) cell culture methods have a long history of mimicking in vivo cell growth. However, these methods cannot fully represent physiological conditions, which lack two major indexes of the in vivo environment; one is a three-dimensional 3D cell environment, and the other is mechanical stimulation; therefore, they are incapable of replicating the essential cellular communications between cell to cell, cell to the extracellular matrix, and cellular responses to dynamic mechanical stimulation in a physiological condition of body movement and blood flow. To solve these problems and challenges, 3D cell carriers have been gradually developed to provide a 3D matrix-like structure for cell attachment, proliferation, differentiation, and communication in static and dynamic culture conditions. 3D cell carriers in dynamic culture systems could primarily provide different mechanical stimulations which further mimic the real in vivo microenvironment. In this review, the current advances in 3D dynamic cell culture approaches have been introduced, with their advantages and disadvantages being discussed in comparison to traditional 2D cell culture in static conditions.

On the quest of reliable 3D dynamic in vitro blood-brain barrier models using polymer hollow fiber membranes: Pitfalls, progress, and future perspectives

With the increasing concern of neurodegenerative diseases, the development of new therapies and effective pharmaceuticals targeted to central nervous system (CNS) illnesses is crucial for ensuring social and economic sustainability in an ageing world. Unfortunately, many promising treatments at the initial stages of the pharmaceutical development process, that is at the in vitro screening stages, do not finally show the expected results at the clinical level due to their inability to cross the human blood-brain barrier (BBB), highlighting the inefficiency of in vitro BBB models to recapitulate the real functionality of the human BBB. In the last decades research has focused on the development of in vitro BBB models from basic 2D monolayer cultures to 3D cell co-cultures employing different system configurations. Particularly, the use of polymeric hollow fiber membranes (HFs) as scaffolds plays a key role in perfusing 3D dynamic in vitro BBB (DIV-BBB) models. Their incorporation into a perfusion bioreactor system may potentially enhance the vascularization and oxygenation of 3D cell cultures improving cell communication and the exchange of nutrients and metabolites through the microporous membranes. The quest for developing a benchmark 3D dynamic in vitro blood brain barrier model requires the critical assessment of the different aspects that limits the technology. This article will focus on identifying the advantages and main limitations of the HFs in terms of polymer materials, microscopic porous morphology, and other practical issues that play an important role to adequately mimic the physiological environment and recapitulate BBB architecture. Based on this study, we consider that future strategic advances of this technology to become fully implemented as a gold standard DIV-BBB model will require the exploration of novel polymers and/or composite materials, and the optimization of the morphology of the membranes towards thinner HFs (<50 μm) with higher porosities and surface pore sizes of 1-2 µm to facilitate the intercommunication via regulatory factors between the cell co-culture models of the BBB.

Graphene Incorporated Electrospun Nanofiber for Electrochemical Sensing and Biomedical Applications: A Critical Review

The extraordinary material graphene arrived in the fields of engineering and science to instigate a material revolution in 2004. Graphene has promptly risen as the super star due to its outstanding properties. Graphene is an allotrope of carbon and is made up of sp²-bonded carbon atoms placed in a two-dimensional honeycomb lattice. Graphite consists of stacked layers of graphene. Due to the distinctive structural features as well as excellent physico-chemical and electrical conductivity, graphene allows remarkable improvement in the performance of electrospun nanofibers (NFs), which results in the enhancement of promising applications in NF-based sensor and biomedical technologies. Electrospinning is an easy, economical, and versatile technology depending on electrostatic repulsion between the surface charges to generate fibers from the extensive list of polymeric and ceramic materials with diameters down to a few nanometers. NFs have emerged as important and attractive platform with outstanding properties for biosensing and biomedical applications, because of their excellent functional features, that include high porosity, high surface area to volume ratio, high catalytic and charge transfer, much better electrical conductivity, controllable nanofiber mat configuration, biocompatibility, and bioresorbability. The inclusion of graphene nanomaterials (GNMs) into NFs is highly desirable. Pre-processing techniques and post-processing techniques to incorporate GNMs into electrospun polymer NFs are precisely discussed. The accomplishment and the utilization of NFs containing GNMs in the electrochemical biosensing pathway for the detection of a broad range biological analytes are discussed. Graphene oxide (GO) has great importance and potential in the biomedical field and can imitate the composition of the extracellular matrix. The oxygen-rich GO is hydrophilic in nature and easily disperses in water, and assists in cell growth, drug delivery, and antimicrobial properties of electrospun nanofiber matrices. NFs containing GO for tissue engineering, drug and gene delivery, wound healing applications, and medical equipment are discussed. NFs containing GO have importance in biomedical applications, which include engineered cardiac patches, instrument coatings, and triboelectric nanogenerators (TENGs) for motion sensing applications. This review deals with graphene-based nanomaterials (GNMs) such as GO incorporated electrospun polymeric NFs for biosensing and biomedical applications, that can bridge the gap between the laboratory facility and industry.

Influence of the properties of different graphene-based nanomaterials dispersed in polycaprolactone membranes on astrocytic differentiation

Composites of polymer and graphene-based nanomaterials (GBNs) combine easy processing onto porous 3D membrane geometries due to the polymer and cellular differentiation stimuli due to GBNs fillers. Aiming to step forward to the clinical application of polymer/GBNs composites, this study performs a systematic and detailed comparative analysis of the influence of the properties of four different GBNs: (i) graphene oxide obtained from graphite chemically processes (GO); (ii) reduced graphene oxide (rGO); (iii) multilayered graphene produced by mechanical exfoliation method (Gmec); and (iv) low-oxidized graphene via anodic exfoliation (Ganodic); dispersed in polycaprolactone (PCL) porous membranes to induce astrocytic differentiation. PCL/GBN flat membranes were fabricated by phase inversion technique and broadly characterized in morphology and topography, chemical structure, hydrophilicity, protein adsorption, and electrical properties. Cellular assays with rat C6 glioma cells, as model for cell-specific astrocytes, were performed. Remarkably, low GBN loading (0.67 wt%) caused an important difference in the response of the C6 differentiation among PCL/GBN membranes. PCL/rGO and PCL/GO membranes presented the highest biomolecule markers for astrocyte differentiation. Our results pointed to the chemical structural defects in rGO and GO nanomaterials and the protein adsorption mechanisms as the most plausible cause conferring distinctive properties to PCL/GBN membranes for the promotion of astrocytic differentiation. Overall, our systematic comparative study provides generalizable conclusions and new evidences to discern the role of GBNs features for future research on 3D PCL/graphene composite hollow fiber membranes for in vitro neural models.

Non-homogeneous dispersion of graphene in polyacrylonitrile substrates induces a migrastatic response and epithelial-like differentiation in MCF7 breast cancer cells

Background

Recent advances from studies of graphene and graphene-based derivatives have highlighted the great potential of these nanomaterials as migrastatic agents with the ability to modulate tumor microenvironments. Nevertheless, the administration of graphene nanomaterials in suspensions in vivo is controversial. As an alternative approach, herein, we report the immobilization of high concentrations of graphene nanoplatelets in polyacrylonitrile film substrates (named PAN/G10) and evaluate their potential use as migrastatic agents on cancer cells.

Results

Breast cancer MCF7 cells cultured on PAN/G10 substrates presented features resembling mesenchymal-to-epithelial transition, e.g., (i) inhibition of migratory activity; (ii) activation of the expression of E-cadherin, cytokeratin 18, ZO-1 and EpCAM, four key molecular markers of epithelial differentiation; (iii) formation of adherens junctions with clustering and adhesion of cancer cells in aggregates or islets, and (iv) reorganization of the actin cytoskeleton resulting in a polygonal cell shape. Remarkably, assessment with Raman spectroscopy revealed that the above-mentioned events were produced when MCF7 cells were preferentially located on top of graphene-rich regions of the PAN/G10 substrates.

Conclusions

The present data demonstrate the capacity of these composite substrates to induce an epithelial-like differentiation in MCF7 breast cancer cells, resulting in a migrastatic effect without any chemical agent-mediated signaling. Future works will aim to thoroughly evaluate the mechanisms of how PAN/G10 substrates trigger these responses in cancer cells and their potential use as antimetastatics for the treatment of solid cancers.

Graphical Abstract

Graphene-Based Materials Prove to Be a Promising Candidate for Nerve Regeneration Following Peripheral Nerve Injury

Peripheral nerve injury is a common medical condition that has a great impact on patient quality of life. Currently, surgical management is considered to be a gold standard first-line treatment; however, is often not successful and requires further surgical procedures. Commercially available FDA- and CE-approved decellularized nerve conduits offer considerable benefits to patients suffering from a completely transected nerve but they fail to support neural regeneration in gaps > 30 mm. To address this unmet clinical need, current research is focused on biomaterial-based therapies to regenerate dysfunctional neural tissues, specifically damaged peripheral nerve, and spinal cord. Recently, attention has been paid to the capability of graphene-based materials (GBMs) to develop bifunctional scaffolds for promoting nerve regeneration, often via supporting enhanced neural differentiation. The unique features of GBMs have been applied to fabricate an electroactive conductive surface in order to direct stem cells and improve neural proliferation and differentiation. The use of GBMs for nerve tissue engineering (NTE) is considered an emerging technology bringing hope to peripheral nerve injury repair, with some products already in preclinical stages. This review assesses the last six years of research in the field of GBMs application in NTE, focusing on the fabrication and effects of GBMs for neurogenesis in various scaffold forms, including electrospun fibres, films, hydrogels, foams, 3D printing, and bioprinting.

Biomedical Applications of Electrospun Graphene Oxide

Graphene oxide (GO) has broad potential in the biomedical sector. The oxygen-abundant nature of GO means the material is hydrophilic and readily dispersible in water. GO has also been known to improve cell proliferation, drug loading, and antimicrobial properties of composites. Electrospun composites likewise have great potential for biomedical applications because they are generally biocompatible and bioresorbable, possess low immune rejection risk, and can mimic the structure of the extracellular matrix. In the current review, GO-containing electrospun composites for tissue engineering applications are described in detail. In addition, electrospun GO-containing materials for their use in drug and gene delivery, wound healing, and biomaterials/medical devices have been examined. Good biocompatibility and anionic-exchange properties of GO make it an ideal candidate for drug and gene delivery systems. Drug/gene delivery applications for electrospun GO composites are described with a number of examples. Various systems using electrospun GO-containing therapeutics have been compared for their potential uses in cancer therapy. Micro- to nanosized electrospun fibers for wound healing applications and antimicrobial applications are explained in detail. Applications of various GO-containing electrospun composite materials for medical device applications are listed. It is concluded that the electrospun GO materials will find a broad range of biomedical applications such as cardiac patches, medical device coatings, sensors, and triboelectric nanogenerators for motion sensing and biosensing.

3D-printed cryomilled poly(ε-caprolactone)/graphene composite scaffolds for bone tissue regeneration

In this study, composite scaffolds based on poly(caprolactone) (PCL) and non-covalently functionalized few-layer graphene (FLG) were manufactured by an extrusion-based system for the first time. For that, functionalized FLG powder was obtained through the evaporation of a functionalized FLG aqueous suspension prepared from a graphite precursor. Cryomilling was shown to be an efficient mixing method, producing a homogeneous dispersion of FLG particles onto the PCL polymeric matrix. Thereafter, fused deposition modeling (FDM) was used to print 3D scaffolds and their morphology, thermal, biodegradability, mechanical, and cytotoxicity properties were analysed. The presence of functionalized FLG demonstrated to induce slight changes in the microstructure of the scaffold, did not affect the thermal stability and enhanced significantly the compressive modulus. The composite scaffolds presented a porosity of around 40% and a mean pore size in the range of 300 μm. The cell viability and proliferation of SaOs-2 cells were assessed and the results showed good cell viability and long-term proliferation onto produced composite scaffolds. Therefore, these new FLG/PCL scaffolds comprised adequate morphological, thermal, mechanical, and biological properties to be used in bone tissue regeneration.

Hollow Fiber Membranes of PCL and PCL/Graphene as Scaffolds with Potential to Develop In Vitro Blood-Brain Barrier Models

There is a huge interest in developing novel hollow fiber (HF) membranes able to modulate neural differentiation to produce in vitro blood-brain barrier (BBB) models for biomedical and pharmaceutical research, due to the low cell-inductive properties of the polymer HFs used in current BBB models. In this work, poly(ε-caprolactone) (PCL) and composite PCL/graphene (PCL/G) HF membranes were prepared by phase inversion and were characterized in terms of mechanical, electrical, morphological, chemical, and mass transport properties. The presence of graphene in PCL/G membranes enlarged the pore size and the water flux and presented significantly higher electrical conductivity than PCL HFs. A biocompatibility assay showed that PCL/G HFs significantly increased C6 cells adhesion and differentiation towards astrocytes, which may be attributed to their higher electrical conductivity in comparison to PCL HFs. On the other hand, PCL/G membranes produced a cytotoxic effect on the endothelial cell line HUVEC presumably related with a higher production of intracellular reactive oxygen species induced by the nanomaterial in this particular cell line. These results prove the potential of PCL HF membranes to grow endothelial cells and PCL/G HF membranes to differentiate astrocytes, the two characteristic cell types that could develop in vitro BBB models in future 3D co-culture systems.

Graphene nanosheets as reinforcement and cell-instructive material in soft tissue scaffolds

Mechanical strength of polymeric scaffolds deteriorates quickly in the physiological mileu. This can be minimized by reinforcing the polymeric matrix with graphene, a planar two-dimensional material with unique physicochemical and biological properties. Association between the sheet and polymer chains offers a range of porosity commensurate with tissue requirements. Besides, studies suggest that corrugated structure of graphene offers desirable bio-mechanical cues for tissue regeneration. This review covers three important aspects of graphene-polymer composites, (a) the opportunity on reinforcing the polymer matrix with graphene, (b) challenges associated with limited aqueous processability of graphene, and (c) physiological signaling in the presence of graphene. Among numerous graphene materials, our discussion is limited to graphene oxide (GO) and reduced graphene oxide (rGO) nanosheets. Challenges associated with limited dispersity of hydrophobic sheets within the polymeric matrix have been discussed at molecular level.

First Report on a Solvent-Free Preparation of Polymer Inclusion Membranes with an Ionic Liquid

A novel and environmentally-friendly procedure for the preparation of polymer inclusion membranes (PIMs) containing an ionic liquid is presented for the first time. Traditionally, PIMs are prepared by a solvent casting method with the use of harmful organic solvents. Here we report a new solvent-free procedure based on a thermal-compression technique which involve the melting of the components of the PIM and the application of a high pressure to the melted specimen to form a flat-sheet film. In our study, we have tested different polymers, such as two cellulose derivatives as well as two thermoplastic polymers, polyurethane (TPU) and poli ε-caprolactone (PCL). The ionic liquid (IL) trioctylmethylammonium chloride (Aliquat 336) has been used to produce PIMs with a fixed composition of 70% polymer–30% IL (w/w). Both TPU and PCL polymers provide successful membranes, which have been thoroughly characterized. PIMs based on the polymer PCL showed a high stability. To test whether the properties of the IL were affected by the preparation conditions, the extraction ability of Aliquat 336 was investigated for both PCL and TPU membranes in terms of Cr(VI) extraction. Satisfactory values (90% extraction) were obtained for both membranes tested, showing this novel procedure as a green alternative for the preparation of PIMs with ILs.

In vitro osteogenic differentiation potential of the human induced pluripotent stem cells augments when grown on Graphene oxide-modified nanofibers

Due to the several limitations that surgeons are faced during bone tissue implantation there are daily increases in introducing new cell-co-polymer composites for use in bone tissue engineering approaches. In this study tried to develop a suitable nanostructured bio-composite for enhancing osteogenic differentiation of the human induced pluripotent stem cells (iPSCs). Polyvinylidene fluoride-Graphene oxide (PVDF-GO) nanofibers was fabricated by electrospinning and then characterized using scanning electron microscope, tensile and viability assays. After that osteogenic differentiation of the iPSCs was investigated in three groups, including PVDF, PVDF-GO and tissue culture plate as a control group. Alkaline phosphatase activity and calcium content of the iPSCs cultured on PVDF-GO were significantly higher than those cultured on other groups. In addition, Runx2, osteocalcin and osteonectin genes were up regulated in iPSCs cultured on PVDF-GO significantly higher than those cells cultured on PVDF and control. Finally, osteocalcin and osteopontin proteins expression evaluated and the results confirmed higher osteoinductivity of the PVDF-GO nanofibers in comparison with the PVDF nanofibers. According to the results, it was demonstrated that PVDF-GO nanofibers have a great osteoinductive potential and taking together iPSCs-PVDF-GO nanofibrous construct can be an appropriate bio-implant to use for bone tissue engineering applications.

Evidences of the Effect of GO and rGO in PCL Membranes on the Differentiation and Maturation of Human Neural Progenitor Cells

The effect of doping graphene oxide (GO) and reduced graphene oxide (rGO) into poly(ε-caprolactone) (PCL) membranes prepared by solvent induced phase separation is evaluated in terms of nanomaterial distribution and compatibility with neural stem cell growth and functional differentiation. Raman spectra analyses demonstrate the homogeneous distribution of GO on the membrane surface while rGO concentration increases gradually toward the center of the membrane thickness. This behavior is associated with electrostatic repulsion that PCL exerted toward the polar GO and its affinity for the non-polar rGO. In vitro cell studies using human induced pluripotent cell derived neural progenitor cells (NPCs) show that rGO increases marker expression of NPCs differentiation with respect to GO (significantly to tissue culture plate (TCP)). Moreover, the distinctive nanomaterials distribution defines the cell-to-nanomaterial interaction on the PCL membranes: GO nanomaterials on the membrane surface favor higher number of active matured neurons, while PCL/rGO membranes present cells with significantly higher magnitude of neural activity compared to TCP and PCL/GO despite there being no direct contact of rGO with the cells on the membrane surface. Overall, this work evidences the important role of rGO electrical properties on the stimulation of neural cell electro-activity on PCL membrane scaffolds.

Trinity of Three-Dimensional (3D) Scaffold, Vibration, and 3D Printing on Cell Culture Application: A Systematic Review and Indicating Future Direction

Cell culture and cell scaffold engineering have previously developed in two directions. First can be 'static into dynamic', with proven effects that dynamic cultures have benefits over static ones. Researches in this direction have used several mechanical means, like external vibrators or shakers, to approximate the dynamic environments in real tissue, though such approaches could only partly address the issue. Second, can be '2D into 3D', that is, artificially created three-dimensional (3D) passive (also called 'static') scaffolds have been utilized for 3D cell culture, helping external culturing conditions mimic real tissue 3D environments in a better way as compared with traditional two-dimensional (2D) culturing. In terms of the fabrication of 3D scaffolds, 3D printing (3DP) has witnessed its high popularity in recent years with ascending applicability, and this tendency might continue to grow along with the rapid development in scaffold engineering. In this review, we first introduce cell culturing, then focus 3D cell culture scaffold, vibration stimulation for dynamic culture, and 3DP technologies fabricating 3D scaffold. Potential interconnection of these realms will be analyzed, as well as the limitations of current 3D scaffold and vibration mechanisms. In the recommendation part, further discussion on future scaffold engineering regarding 3D vibratory scaffold will be addressed, indicating 3DP as a positive bridging technology for future scaffold with integrated and localized vibratory functions.

Strategic Design and Fabrication of Biomimetic 3D Scaffolds: Unique Architectures of Extracellular Matrices for Enhanced Adipogenesis and Soft Tissue Reconstruction

The higher rate of soft tissue impairment due to lumpectomy or other trauma greatly requires the restoration of the irreversibly lost subcutaneous adipose tissues. The nanofibers fabricated by conventional electrospinning provide only a superficial porous structure due to its sheet like 2D structure and thereby hinder the cell infiltration and differentiation throughout the scaffolds. Thus we developed a novel electrospun 3D membrane using the zwitterionic poly (carboxybetaine-co-methyl methacrylate) co-polymer (CMMA) through electrostatic repulsion based electrospinning for soft tissue engineering. The inherent charges in the CMMA will aid the nanofiber to directly transform into a semiconductor and thereby transfer the immense static electricity from the grounded collector and will impart greater fluffiness to the scaffolds. The results suggest that the fabricated 3D nanofiber (CMMA 3NF) scaffolds possess nanofibers with larger inter connected pores and less dense structure compared to the conventional 2D scaffolds. The CMMA 3NF exhibits significant cues of soft tissue engineering such as enhanced biocompatibility as well as the faster regeneration of cells. Moreover the fabricated 3D scaffolds greatly assist the cells to develop into its stereoscopic topographies with an enhanced adipogenic property.

Hydrolytic Degradation and Mechanical Stability of Poly(ε-Caprolactone)/Reduced Graphene Oxide Membranes as Scaffolds for In Vitro Neural Tissue Regeneration

The present work studies the functional behavior of novel poly(ε-caprolactone) (PCL) membranes functionalized with reduced graphene oxide (rGO) nanoplatelets under simulated in vitro culture conditions (phosphate buffer solution (PBS) at 37 °C) during 1 year, in order to elucidate their applicability as scaffolds for in vitro neural regeneration. The morphological, chemical, and DSC results demonstrated that high internal porosity of the membranes facilitated water permeation and procured an accelerated hydrolytic degradation throughout the bulk pathway. Therefore, similar molecular weight reduction, from 80 kDa to 33 kDa for the control PCL, and to 27 kDa for PCL/rGO membranes, at the end of the study, was observed. After 1 year of hydrolytic degradation, though monomers coming from the hydrolytic cleavage of PCL diffused towards the PBS medium, the pH was barely affected, and the rGO nanoplatelets mainly remained in the membranes which envisaged low cytotoxic effect. On the other hand, the presence of rGO nanomaterials accelerated the loss of mechanical stability of the membranes. However, it is envisioned that the gradual degradation of the PCL/rGO membranes could facilitate cells infiltration, interconnectivity, and tissue formation.

Improving Antibacterial Activity and Biocompatibility of Bioinspired Electrospinning Silk Fibroin Nanofibers Modified by Graphene Oxide

In this article, the silk fibroin (SF)/graphene oxide (GO)-blended nanofibers with one bioinspired nanostructure are fabricated via electrospinning. The morphology, chemical structure, antibacterial activity, and biocompatibility of the blending nanofibers are investigated. The results indicate that GO plays an important role in preparing the distinctive bioinspired structure. The antibacterial activity and in vivo cell culture test demonstrate that blending of GO could improve the antibacterial activity and biocompatibility of SF nanofibers. The blended nanofibers developed in this study may have considerable potential for wound dressing applications.

Porous nanocomposite membranes based on functional GO with selective function for lithium adsorption

An inorganic–organic composite membrane based on functional GO nanosheet for selective lithium adsorption from compound has great potential.