Culture of neural stem cells on conductive and microgrooved polymeric scaffolds fabricated via electrospun fiber-template lithography

From innovation to clinic: Emerging strategies harnessing electrically conductive polymers to enhance electrically stimulated peripheral nerve repair

Peripheral nerve repair (PNR) is a major healthcare challenge due to the limited regenerative capacity of the nervous system, often leading to severe functional impairments. While nerve autografts are the gold standard, their implications are constrained by issues such as donor site morbidity and limited availability, necessitating innovative alternatives like nerve guidance conduits (NGCs). However, the inherently slow nerve growth rate (∼1 mm/day) and prolonged neuroinflammation, delay recovery even with the use of passive (no-conductive) NGCs, resulting in muscle atrophy and loss of locomotor function. Electrical stimulation (ES) has the ability to enhance nerve regeneration rate by modulating the innate bioelectrical microenvironment of nerve tissue while simultaneously fostering a reparative environment through immunoregulation. In this context, electrically conductive polymer (ECP)-based biomaterials offer unique advantages for nerve repair combining their flexibility, akin to traditional plastics, and mixed ionic-electronic conductivity, similar to ionically conductive nerve tissue, as well as their biocompatibility and ease of fabrication. This review focuses on the progress, challenges, and emerging techniques for integrating ECP based NGCs with ES for functional nerve regeneration. It critically evaluates the various approaches using ECP based scaffolds, identifying gaps that have hindered clinical translation. Key challenges discussed include designing effective 3D NGCs with high electroactivity, optimizing ES modules, and better understanding of immunoregulation during nerve repair. The review also explores innovative strategies in material development and wireless, self-powered ES methods. Furthermore, it emphasizes the need for non-invasive ES delivery methods combined with hybrid ECP based neural scaffolds, highlighting future directions for advancing preclinical and clinical translation. Together, ECP based NGCs combined with ES represent a promising avenue for advancing PNR and improving patient outcomes.

Neural Tissue-Like, not Supraphysiological, Electrical Conductivity Stimulates Neuronal Lineage Specification through Calcium Signaling and Epigenetic Modification

Electrical conductivity is a pivotal biophysical factor for neural interfaces, though optimal values remain controversial due to challenges isolating this cue. To address this issue, conductive substrates made of carbon nanotubes and graphene oxide nanoribbons, exhibiting a spectrum of conductivities from 0.02 to 3.2 S m-1, while controlling other surface properties is designed. The focus is to ascertain whether varying conductivity in isolation has any discernable impact on neural lineage specification. Remarkably, neural-tissue-like low conductivity (0.02-0.1 S m-1) prompted neural stem/progenitor cells to exhibit a greater propensity toward neuronal lineage specification (neurons and oligodendrocytes, not astrocytes) compared to high supraphysiological conductivity (3.2 S m-1). High conductivity instigated the apoptotic process, characterized by increased apoptotic fraction and decreased neurogenic morphological features, primarily due to calcium overload. Conversely, cells exposed to physiological conductivity displayed epigenetic changes, specifically increased chromatin openness with H3acetylation (H3ac) and neurogenic-transcription-factor activation, along with a more balanced intracellular calcium response. The pharmacological inhibition of H3ac further supported the idea that such epigenetic changes might play a key role in driving neuronal specification in response to neural-tissue-like, not supraphysiological, conductive cues. These findings underscore the necessity of optimal conductivity when designing neural interfaces and scaffolds to stimulate neuronal differentiation and facilitate the repair process.

Polypyrrole-based structures for activation of cellular functions under electrical stimulation

Polypyrrole (Ppy) is an electroconductive polymer used in various applications, including in vitro experiments with cell cultures under electrical stimulation (ES). Ppy can be applied in various forms and most importantly, it is biocompatible with cells. Ppy specifically directs ES to cells, which makes Ppy a potential polymer for the development of novel technologies for targeted tissue regeneration. The high potential of ES in combination with different Ppy-based systems, such as hydrogels, scaffolds, or Ppy-layers is advantageous to stimulate cellular differentiation towards neurogenic, cardiac, muscle, and osteogenic lineages. Different in-house devices and the principles of ES application used to stimulate cellular functions are reviewed and summarized. The focus of this review is to observe the most relevant studies and their in-house techniques regarding the application of Ppy-based materials for the use of bone, neural, cardiac, and muscle tissue regeneration under ES. Different types of Ppy materials, such as Ppy particles, layers/films, membranes, and 3D-shaped synthetic and natural scaffolds, as well as combining Ppy with different active molecules are reviewed.

The Recent Applications of PLGA-Based Nanostructures for Ischemic Stroke

With the accelerated development of nanotechnology in recent years, nanomaterials have become increasingly prevalent in the medical field. The poly (lactic acid-glycolic acid) copolymer (PLGA) is one of the most commonly used biodegradable polymers. It is biocompatible and can be fabricated into various nanostructures, depending on requirements. Ischemic stroke is a common, disabling, and fatal illness that burdens society. There is a need for further improvement in the diagnosis and treatment of this disease. PLGA-based nanostructures can facilitate therapeutic compounds' passage through the physicochemical barrier. They further provide both sustained and controlled release of therapeutic compounds when loaded with drugs for the treatment of ischemic stroke. The clinical significance and potential of PLGA-based nanostructures can also be seen in their applications in cell transplantation and imaging diagnostics of ischemic stroke. This paper summarizes the synthesis and properties of PLGA and reviews in detail the recent applications of PLGA-based nanostructures for drug delivery, disease therapy, cell transplantation, and the imaging diagnosis of ischemic stroke.

Facile fabrication of micropattern surfaces with controlled wettability on PDMS-modified fiber membranes for cell patterning

Various cell culture substrates have been developed for cell patterning to control cell distributions and orientations in tissue engineering, drug screening and regenerative medicine. In this study, a preparation method of modified fiber membranes was applied in the field of cell patterning, and the obtained fiber membranes guided the cell distributions and orientations flexibly. The aligned electrospinning fiber membranes were dip-coated with polydimethylsiloxane (PDMS) to improve the stability of wettability, and then it was treated with oxygen plasma with a photomask to obtain a hydrophilic-hydrophobic surface micropattern. The morphologies, wettabilities and chemical structures of the membranes were analyzed by using a scanning electron microscope (SEM), drop shape analysis instrument, energy dispersive spectrometer (EDS) and Fourier transform infrared (FTIR) spectrometer. The L929 cells were cultured on the obtained membranes to observe the controlled cell distributions and orientations by using a SEM and fluorescence microscope. The results indicate that the treated membranes have the ability to control both cell distributions and orientations simultaneously. This method offers a novel approach to develop cell culture substrates for cell patterning in tissue engineering.

Biomaterial-based strategies for in vitro neural models

In vitro models have been used as a complementary tool to animal studies in understanding the nervous system's physiological mechanisms and pathological disorders, while also serving as platforms to evaluate the safety and efficiency of therapeutic candidates. Following recent advances in materials science, micro- and nanofabrication techniques and cell culture systems, in vitro technologies have been rapidly gaining the potential to bridge the gap between animal and clinical studies by providing more sophisticated models that recapitulate key aspects of the structure, biochemistry, biomechanics, and functions of human tissues. This was made possible, in large part, by the development of biomaterials that provide cells with physicochemical features that closely mimic the cellular microenvironment of native tissues. Due to the well-known material-driven cellular response and the importance of mimicking the environment of the target tissue, the selection of optimal biomaterials represents an important early step in the design of biomimetic systems to investigate brain structures and functions. This review provides a comprehensive compendium of commonly used biomaterials as well as the different fabrication techniques employed for the design of neural tissue models. Furthermore, the authors discuss the main parameters that need to be considered to develop functional platforms not only for the study of brain physiological functions and pathological processes but also for drug discovery/development and the optimization of biomaterials for neural tissue engineering.

The Potential Contribution of Biopolymeric Particles in Lung Tissue Regeneration of COVID-19 Patients

The lung is a vital organ that houses the alveoli, which is where gas exchange takes place. The COVID-19 illness attacks lung cells directly, creating significant inflammation and resulting in their inability to function. To return to the nature of their job, it may be essential to rejuvenate the afflicted lung cells. This is difficult because lung cells need a long time to rebuild and resume their function. Biopolymeric particles are the most effective means to transfer developing treatments to airway epithelial cells and then regenerate infected lung cells, which is one of the most significant symptoms connected with COVID-19. Delivering biocompatible and degradable natural biological materials, chemotherapeutic drugs, vaccines, proteins, antibodies, nucleic acids, and diagnostic agents are all examples of these molecules' usage. Furthermore, they are created by using several structural components, which allows them to effectively connect with these cells. We highlight their most recent uses in lung tissue regeneration in this review. These particles are classified into three groups: biopolymeric nanoparticles, biopolymeric stem cell materials, and biopolymeric scaffolds. The techniques and processes for regenerating lung tissue will be thoroughly explored.

Regulation of stem cell fate using nanostructure-mediated physical signals

One of the major issues in tissue engineering is regulation of stem cell differentiation toward specific lineages. Unlike biological and chemical signals, physical signals with adjustable properties can be applied to stem cells in a timely and localized manner, thus making them a hot topic for research in the fields of biomaterials, tissue engineering, and cell biology. According to the signals sensed by cells, physical signals used for regulating stem cell fate can be classified into six categories: mechanical, light, thermal, electrical, acoustic, and magnetic. In most cases, external macroscopic physical fields cannot be used to modulate stem cell fate, as only the localized physical signals accepted by the surface receptors can regulate stem cell differentiation via nanoscale fibrin polysaccharide fibers. However, surface receptors related to certain kinds of physical signals are still unknown. Recently, significant progress has been made in the development of functional materials for energy conversion. Consequently, localized physical fields can be produced by absorbing energy from an external physical field and subsequently releasing another type of localized energy through functional nanostructures. Based on the above concepts, we propose a methodology that can be utilized for stem cell engineering and for the regulation of stem cell fate via nanostructure-mediated physical signals. In this review, the combined effect of various approaches and mechanisms of physical signals provides a perspective on stem cell fate promotion by nanostructure-mediated physical signals. We expect that this review will aid the development of remote-controlled and wireless platforms to physically guide stem cell differentiation both in vitro and in vivo, using optimized stimulation parameters and mechanistic investigations while driving the progress of research in the fields of materials science, cell biology, and clinical research.

Polymeric Nanocomposite Structures Based on Functionalized Graphene with Tunable Properties for Nervous Tissue Replacement

Electroconductive scaffolds can be a promising approach to repair conductive tissues when natural healing fails. Recently, nerve tissue engineering constructs have been widely investigated due to the challenges in creating a structure with optimized physiochemical and mechanical properties close to the native tissue. The goal of the current study was to fabricate graphene-containing polycaprolactone/gelatin/polypyrrole (PCL/gelatin/PPy) and polycaprolactone/polyglycerol-sebacate/polypyrrole (PCL/PGS/PPy) with intrinsic electrical properties through an electrospinning process. The effect of graphene on the properties of PCL/gelatin/PPy and PCL/PGS/PPy were investigated. Results demonstrated that graphene incorporation remarkably modulated the physical and mechanical properties of the scaffolds such that the electrical conductivity increased from 0.1 to 3.9 ± 0.3 S m^-1 (from 0 to 3 wt % graphene) and toughness was found to be 76 MPa (PCL/gelatin/PPy 3 wt % graphene) and 143.4 MPa (PCL/PGS/PPy 3 wt % graphene). Also, the elastic moduli of the scaffolds with 0, 1, and 2 wt % graphene were reported as 210, 300, and 340 kPa in the PCL/gelatin/PPy system and 72, 85, and 92 kPa for the PCL/PGS/PPy system. A cell viability study demonstrated the noncytotoxic nature of the resultant scaffolds. The sum of the results presented in this study suggests that both PCL/gelatin/PPy/graphene and PCL/PGS/PPy/graphene compositions could be promising biomaterials for a range of conductive tissue replacement or regeneration applications.

Regulation of Myogenic Differentiation by Topologically Microgrooved Surfaces for Skeletal Muscle Tissue Engineering

Inspired by the natural topological structure of skeletal muscle tissue, the topological surface construction of bionic scaffolds for skeletal muscle repair has attracted great interest. Many previous studies have focused on the effects of the topological structure on myoblasts. However, these studies used only specific repeating sizes and shapes to achieve the myoblast alignment and myotube formation; moreover, the regulatory effects of the size of a topological structure on myogenic differentiation are often neglected, leading to a lack of guidance for the design of scaffolds for skeletal muscle tissue engineering. In this study, we fabricated a series of microgroove topographies with various widths and depths via a combination of soft lithography and melt-casting and studied their effects on the behaviors of skeletal muscle cells, especially myogenic differentiation, in detail. Microgrooved poly(lactic-co-glycolic acid) substrates were found to effectively regulate the proliferation, myogenic differentiation, and myotube formation of C2C12 cells, and the degree of myogenic differentiation was significantly dependent on signals in response to the size of the microgroove structure. Compared with their depth, the width of the microgroove structures can more strongly affect the myogenic differentiation of C2C12 cells, and the degree of myoblast differentiation was enhanced with increasing groove width. Microgroove structures with relatively large groove widths and small groove depths promoted the myogenic differentiation of C2C12 cells. In addition, the integrin-mediated focal adhesion kinase signaling pathway and MAPK signaling pathway were activated in cells in response to the external topological structure, and the size of the topological structure of the material surface effectively regulated the degree of the cellular response to the external topological structure. These results can guide the design of scaffolds for skeletal muscle tissue engineering and the construction of effective bionic scaffold surfaces for skeletal muscle regeneration.

Conductive Biomaterials as Substrates for Neural Stem Cells Differentiation towards Neuronal Lineage Cells

The injuries and defects in the central nervous system are the causes of disability and death of an affected person. As of now, there are no clinically available methods to enhance neural structural regeneration and functional recovery of nerve injuries. Recently, some experimental studies claimed that the injuries in brain can be repaired by progenitor or neural stem cells located in the neurogenic sites of adult mammalian brain. Various attempts have been made to construct biomimetic physiological microenvironment for neural stem cells to control their ultimate fate. Conductive materials have been considered as one the best choices for nerve regeneration due to the capacity to mimic the microenvironment of stem cells and regulate the alignment, growth, and differentiation of neural stem cells. The review highlights the use of conductive biomaterials, e.g., polypyrrole, polyaniline, poly(3,4-ethylenedioxythiophene), multi-walled carbon nanotubes, single-wall carbon nanotubes, graphene, and graphite oxide, for controlling the neural stem cells activities in terms of proliferation and neuronal differentiation. The effects of conductive biomaterials in axon elongation and synapse formation for optimal repair of central nervous system injuries are also discussed.

Polypyrrole-Incorporated Conducting Constructs for Tissue Engineering Applications: A Review

Conductive polymers have recently attracted interest in biomedical applications because of their excellent intrinsic electrical conductivity and satisfactory biocompatibility. Polypyrrole (PPy) is one of the most popular among these conductive polymers due to its high conductivity under physiological conditions, and it can be chemically modified to allow biomolecules conjugation. PPy has been used in fabricating biocompatible stimulus-responsive scaffolds for tissue engineering applications, especially for repair and regeneration of electroactive tissues, such as the bone, neuron, and heart. This review provides a comprehensive overview of the basic properties and synthesis methods of PPy, as well as a summary of the materials that have been integrated with PPy. These composite scaffolds are comparatively evaluated with regard to their mechanical properties, biocompatibility, and usage in tissue engineering.