Synthesis and characterization of new electroactive polypyrrole–chondroitin sulphate A substrates

A review of glycosaminoglycan-modified electrically conductive polymers for biomedical applications

The application areas of electrically conductive polymers have been steadily growing since their discovery in the late 1970s. Recently, electrically conductive polymers have found their way into biomedicine, allowing the realization of many relevant applications ranging from bioelectronics to scaffolds for tissue engineering. Extracellular matrix components, such as glycosaminoglycans, build an important class of biomaterials that are heavily researched for biomedical applications due to their favorable properties. Due to their highly anionic character and the presence of sulfate groups in glycosaminoglycans, these biomolecules can be employed to functionalize conductive polymers, which enables the tailorability and improvement of cell-material interactions of conductive polymers. This review paper gives an overview of recent research on glycosaminoglycan-modified conductive polymers intended for biomedical applications and discusses the effect of different biological dopants on material characteristics, such as surface roughness, stiffness, and electrochemical properties. Moreover, the key findings of the biological characterization in vitro and in vivo are summarized, and remaining challenges in the field, particularly related to the modification of electrically conductive polymers with glycosaminoglycans to achieve improved functional and biological outcomes, are discussed. STATEMENT OF SIGNIFICANCE: The development of functional biomaterials based on electrically conductive polymers (CPs) for various biomedical applications, such as neural regeneration, drug delivery, or bioelectronics, has been increasingly investigated over the last decades. Recent literature has shown that changes in the synthesis procedure or the chosen dopant could adjust the resulting material characteristics. Hence, an interesting approach lies in using natural biomolecules as dopants for CPs to tailor the biological outcome. This review comprehensively summarizes the state of the art in the field of glycosaminoglycan-modified electrically conductive polymers for the first time, particularly highlighting the effect of the chosen dopant on material characteristics, such as surface morphology or stiffness, electrochemical properties, and consequently, cell-material interactions.

Chondroitin sulfate zinc with antibacterial properties and anti-inflammatory effects for skin wound healing

A chondroitin sulfate zinc (CSZn) complex was prepared by an ion-exchange method. The purified product was characterized by energy-dispersive X-ray spectroscopy, high-performance chromatography, elemental analysis, Fourier transform infrared spectroscopy, inductively coupled mass spectrometry, and nuclear magnetic resonance spectroscopy. The CSZn demonstrated antibacterial activity against Escherichia coli and Staphylococcus aureus and satisfied MTT cell viability (NIH3T3 fibroblasts) at ≤50 μg/mL. RT-PCR demonstrated significant promotion by CSZn of fibroblast growth factor beta (β-FGF), collagen III (COLIIIα1), vascular endothelial growth factor (VEGF) and reduction of cytokines IL-6, IL-1β & TNF-alpha. An in vivo rat full-thickness wound healing model demonstrated significant wound healing of CSZn relative to controls of saline treatment, zinc chloride treatment and chondroitin treatment. CSZn has demonstrated promising antibacterial and wound healing properties making it deserving of consideration for more advanced wound healing applications.

Electrically Conductive Materials: Opportunities and Challenges in Tissue Engineering

Tissue engineering endeavors to regenerate tissues and organs through appropriate cellular and molecular interactions at biological interfaces. To this aim, bio-mimicking scaffolds have been designed and practiced to regenerate and repair dysfunctional tissues by modifying cellular activity. Cellular activity and intracellular signaling are performances given to a tissue as a result of the function of elaborated electrically conductive materials. In some cases, conductive materials have exhibited antibacterial properties; moreover, such materials can be utilized for on-demand drug release. Various types of materials ranging from polymers to ceramics and metals have been utilized as parts of conductive tissue engineering scaffolds, having conductivity assortments from a range of semi-conductive to conductive. The cellular and molecular activity can also be affected by the microstructure; therefore, the fabrication methods should be evaluated along with an appropriate selection of conductive materials. This review aims to address the research progress toward the use of electrically conductive materials for the modulation of cellular response at the material-tissue interface for tissue engineering applications.

Physicochemical, antioxidant and biocompatible properties of chondroitin sulphate isolated from chicken keel bone for potential biomedical applications

Chicken keel bone cartilage was explored for cheaper and sustainable source for isolation of chondroitin sulphate (CS) for its future use in tissue engineering and pharmaceutical industry. HPSEC analysis displayed two peaks of 100kDa for CS-keel polysaccharide and 1kDa for protein. DLS analysis of CS-keel displayed polydispersity. CS-keel yield was 15% and 53±5% uronic acid content. The quantified percentages of UA-GalNAc4S and UA-GalNAc6S disaccharide in CS-keel were 58% and 42%, respectively. FT-IR identified CS-keel to be chondroitin 4-sulphate. ¹H NMR of CS-keel confirmed the presence of N-acetylgalactosamine and Glucuronic acid. FESEM demonstrated layer structure and AFM displayed the size of CS-keel fibres. DSC, TGA and DTG studies of CS-keel showed T_d at 243°C. In vitro cell proliferation assay and morphological analysis of mouse fibroblast L929 cell lines confirmed the biocompatibility of CS-keel. CS-keel (5mg/ml) exhibited ∼49% antioxidant activity against DPPH and 22% against superoxide radical protecting from oxidative damage. CS-keel demonstrated better (70.3%) emulsifying activity than commercial sodium alginate (60.2%).

Fabrication and characterization of conductive poly (3,4-ethylenedioxythiophene) doped with hyaluronic acid/poly (l-lactic acid) composite film for biomedical application

Poly 3,4-ethylenedioxythiophene (PEDOT), a polythiophene derivative, has been proved to be modified by chemical process as biocompatible conductive polymer for biomedical applications. In this study, novel hyaluronic acid (HA)-doped PEDOT nanoparticles were synthesized by the method of chemical oxidative polymerization, then conductive PEDOT-HA/poly(l-lactic acid) (PLLA) composite films were prepared. The physicochemical characteristics and biocompatibility of films were further investigated. FTIR, Raman and EDX analysis demonstrated that HA was successfully doped into PEDOT particles. Cyclic voltammograms indicated PEDOT-HA particles had favorable electrochemical stability. PEDOT-HA/PLLA films showed lower surface contact angle and faster degradation degree compared with PLLA films. Moreover, the cytotoxicity test of PEDOT-HA/PLLA films showed that neuron-like pheochromocytoma (PC12) cells adhered and spread well on the surface of PEDOT-HA/PLLA films and cell viability denoted by MTT assay had a significant increase. PEDOT-HA/PLLA films modified with laminin (LN) also exhibited an efficiently elongated cell morphology observed by fluorescent microscope and metallographic microscope. Furthermore, PEDOT-HA/PLLA films were subjected to different current intensity to elucidate the effect of electrical stimulation (ES) on neurite outgrowth of PC12 cells. ES (0.5 mA, 2 h) significantly promoted neurite outgrowth with an average value length of 122 ± 5 μm and enhanced the mRNA expression of growth-associated protein (GAP43) and synaptophysin (SYP) in PC12 cells when compared with other ES groups. These results suggest that PEDOT-HA/PLLA film combined with ES are conducive to cell growth and neurite outgrowth, indicating the conductive PEDOT-HA/PLLA film may be an attractive candidate with ES for enhancing nerve regeneration in nerve tissue engineering.

Optimisation of conductive polymer biomaterials for cardiac progenitor cells

The characterisation of biomaterials for cardiac tissue engineering applications is vital for the development of effective treatments for the repair of cardiac function.

Modification of surface/neuron interfaces for neural cell-type specific responses: a review

Surface/neuron interfaces have played an important role in neural repair including neural prostheses and tissue engineered scaffolds. This comprehensive literature review covers recent studies on the modification of surface/neuron interfaces. These interfaces are identified in cases both where the surfaces of substrates or scaffolds were in direct contact with cells and where the surfaces were modified to facilitate cell adhesion and controlling cell-type specific responses. Different sources of cells for neural repair are described, such as pheochromocytoma neuronal-like cell, neural stem cell (NSC), embryonic stem cell (ESC), mesenchymal stem cell (MSC) and induced pluripotent stem cell (iPS). Commonly modified methods are discussed including patterned surfaces at micro- or nano-scale, surface modification with conducting coatings, and functionalized surfaces with immobilized bioactive molecules. These approaches to control cell-type specific responses have enormous potential implications in neural repair.

Poly(3,4-ethylenedioxythiophene) Bearing Phosphorylcholine Groups for Metal-Free, Antibody-Free, and Low-Impedance Biosensors Specific for C-Reactive Protein

Conducting polymers possessing biorecognition elements are essential for developing electrical biosensors sensitive and specific to clinically relevant biomolecules. We developed a new 3,4-ethylenedioxythiophene (EDOT) derivative bearing a zwitterionic phosphorylcholine group via a facile synthesis through the Michael-type addition thiol-ene "click" reaction for the detection of an acute-phase biomarker human C-reactive protein (CRP). The phosphorylcholine group, a major headgroup in phospholipid, which is the main constituent of plasma membrane, was also expected to resist nonspecific adsorption of other proteins at the electrode/solution interface. The biomimetic EDOT derivative was randomly copolymerized with EDOT, via an electropolymerization technique with a dopant sodium perchlorate, onto a glassy carbon electrode to make the synthesized polymer film both conductive and target-responsive. The conducting copolymer films were characterized by cyclic voltammetry, scanning electron microscopy, attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. The specific interaction of CRP with phosphorylcholine in a calcium-containing buffer solution was determined by differential pulse voltammetry, which measures the altered redox reaction between the indicators ferricyanide/ferrocyanide as a result of the binding event. The conducting polymer-based protein sensor achieved a limit of detection of 37 nM with a dynamic range of 10-160 nM, covering the dynamically changing CRP levels in circulation during the acute phase. The results will enable the development of metal-free, antibody-free, and low-impedance electrochemical biosensors for the screening of nonspecific biomarkers of inflammation and infection.

A simple approach for protein covalent grafting on conducting polymer films

By mixing a PEDOT:PSS suspension with the modified biopolymer carboxymethylated dextran (CMD), we obtain conductive films displaying carboxyl (–COOH) groups allowing for covalent grafting of proteins via amide bonds.

Chondroitin sulphate-guided construction of polypyrrole nanoarchitectures

Nanospheres, nanocones, and nanowires are three typical polypyrrole (PPy) nanoarchitectures and electrochemically polymerized with the dope of chondroitin sulphate (CS) in this study. CS, a functional biomacromolecule, guides the formation of PPy nanoarchitectures as the dopant and morphology-directing agent. Combined with our previous reported other PPy nanoarchitectures (such as nanotube arrays and nanowires), this work further proposed the novel mechanism of the construction of PPy/CS nanoarchitectures with the synergistic effect of CS molecular chains structure and the steric hindrance. Compared to the undoped PPy, MC3T3-E1 cells with PPy/CS nanoarchitectures possessed stronger proliferation and osteogenic differentiation capability. This suggests that PPy/CS nanoarchitectures have appropriate biocompatibility. Altogether, the nanoarchitectured PPy/CS may find application in the regeneration of bone defect.

Conductive polymers: towards a smart biomaterial for tissue engineering

Developing stimulus-responsive biomaterials with easy-to-tailor properties is a highly desired goal of the tissue engineering community. A novel type of electroactive biomaterial, the conductive polymer, promises to become one such material. Conductive polymers are already used in fuel cells, computer displays and microsurgical tools, and are now finding applications in the field of biomaterials. These versatile polymers can be synthesised alone, as hydrogels, combined into composites or electrospun into microfibres. They can be created to be biocompatible and biodegradable. Their physical properties can easily be optimized for a specific application through binding biologically important molecules into the polymer using one of the many available methods for their functionalization. Their conductive nature allows cells or tissue cultured upon them to be stimulated, the polymers' own physical properties to be influenced post-synthesis and the drugs bound in them released, through the application of an electrical signal. It is thus little wonder that these polymers are becoming very important materials for biosensors, neural implants, drug delivery devices and tissue engineering scaffolds. Focusing mainly on polypyrrole, polyaniline and poly(3,4-ethylenedioxythiophene), we review conductive polymers from the perspective of tissue engineering. The basic properties of conductive polymers, their chemical and electrochemical synthesis, the phenomena underlying their conductivity and the ways to tailor their properties (functionalization, composites, etc.) are discussed.

Influence of conductive polymer doping on the viability of cardiac progenitor cells

Investigating the influence of conductive polymer dopants on surface properties and chemistry, and how they may modify cardiac progenitor cell interactions.

Resolving sub-molecular binding and electrical switching mechanisms of single proteins at electroactive conducting polymers

Polymer-based electrodes for interfacing biological tissues are becoming increasingly sophisticated. Their many functions place them at the cross-roads of electromaterials, biomaterials, and drug-delivery systems. For conducting polymers, the mechanism of conductivity requires doping with anionic molecules such as extracellular matrix molecules, a process that distinguishes them as biomaterials and provides a means to control interactions at the cellular-electrode interface. However, due to their complex structure, directly observing the selective binding of target molecules or proteins has so far eluded researchers. This situation is compounded by the polymer's ability to adopt different electronic states that alter the polymer-dopant interactions. Here, the ability to resolve sub-molecular binding specificity between sulfate and carboxyl groups of dopants and heparin binding domains of human plasma fibronectin is demonstrated. The interaction exploits a form of biological 'charge complementarity' to enable specificity. When an electrical signal is applied to the polymer, the specific interaction is switched to a non-specific, high-affinity binding state that can be reversibly controlled using electrochemical processes. Both the specific and non-specific interactions are integral for controlling protein conformation and dynamics. These details, which represent the first direct measurement of biomolecular recognition between a single protein and any type of organic conductor, give new molecular insight into controlling cellular interactions on these polymer surfaces.

Review paper: Progress in the Field of Conducting Polymers for Tissue Engineering Applications

This review focuses on one of the most exciting applications area of conjugated conducting polymers, which is tissue engineering. Strategies used for the biocompatibility improvement of this class of polymers (including biomolecules’ entrapment or covalent grafting) and also the integrated novel technologies for smart scaffolds generation such as micropatterning, electrospinning, self-assembling are emphasized. These processing alternatives afford the electroconducting polymers nanostructures, the most appropriate forms of the materials that closely mimic the critical features of the natural extracellular matrix. Due to their capability to electronically control a range of physical and chemical properties, conducting polymers such as polyaniline, polypyrrole, and polythiophene and/or their derivatives and composites provide compatible substrates which promote cell growth, adhesion, and proliferation at the polymer—tissue interface through electrical stimulation. The activities of different types of cells on these materials are also presented in detail. Specific cell responses depend on polymers surface characteristics like roughness, surface free energy, topography, chemistry, charge, and other properties as electrical conductivity or mechanical actuation, which depend on the employed synthesis conditions. The biological functions of cells can be dramatically enhanced by biomaterials with controlled organizations at the nanometer scale and in the case of conducting polymers, by the electrical stimulation. The advantages of using biocompatible nanostructures of conducting polymers (nanofibers, nanotubes, nanoparticles, and nanofilaments) in tissue engineering are also highlighted.

Electroactivity and biocompatibility of polypyrrole-hyaluronic acid multi-walled carbon nanotube composite

Electroactivity of polypyrrole hyaluronic acid, electropolymerized in the presence of oxidized carbon nanotubes (PPyHA-CNT) was studied in situ by electrochemical atomic force microscopy (EC-AFM) in physiological electrolyte solution. In situ Raman spectroscopic and quartz crystal microbalance (QCM) studies were conducted on layers of the polymer grown on AT-cut 5 MHz quartz crystals. Human adipose stem cell (ASC) attachment and viability were studied by Live/Dead staining, and the proliferation was evaluated by WST-1 Cell proliferation assay for polypyrrole samples electropolymerized on titanium. According to cyclic voltammetry, the measured specific capacitance of the material on gold is roughly 20% of the reference polypyrrole dodecylbenzene sulfonate (PPyDBS). Electrochemical-QCM (EC-QCM) analysis of a 210-nm thick film reveals that the material is very soft G' approximately 100 kPa and swells upon reduction. EC-AFM of samples polymerized on microelectrodes show that there are areas of varying electroactivity, especially for samples without a hydrophopic backing PPyDBS layer. AFM line scans show typically 20-25% thickness change during electrochemical reduction. Raman spectroscopic analysis suggests that the material supports noticeable polaron conduction. Biocompatibility study of the PPyHA-CNT on titanium with adipose stem cells showed equal or better cell attachment, viability, and proliferation compared with the reference polylactide.

Biocompatibility implications of polypyrrole synthesis techniques

Polypyrrole (PPy) is an inherently conducting polymer that has shown great promise for biomedical applications within the nervous system. However, to effectively use PPy as a biomaterial implant, it is important to understand and reproducibly control the electrical properties, physical topography and surface chemistry of the polymer. Although there is much research published on the use of PPy in various applications, there is no systematic study linking the methodologies used for PPy synthesis to PPy's basic polymeric properties (e.g., hydrophilicity, surface roughness), and to the biological effects these properties have on cells. Electrochemically synthesized PPy films differ greatly in their characteristics depending on synthesis parameters such as dopant, substrate and thickness, among other parameters. In these studies, we have used three dopants (chloride (Cl), tosylate (ToS), polystyrene sulfonate (PSS)), two substrates (gold and indium tin oxide-coated glass), and a range of thicknesses, to measure and compare the biomedically important characteristics of surface roughness, contact angle, conductivity, dopant stability and cell adhesion (using PC-12 cells and Schwann cells). As predicted, we discovered large differences in roughness depending on the dopant used and the thickness of the film, while substrate choice had little effect. From contact angle measurements, PSS was found to yield the most hydrophilic material, most likely because of free charges from the long PSS chains exposed on the surface of the PPy. ToS-doped PPy films were tenfold more conductive than Cl- or PSS-doped films. X-ray photoelectron spectroscopy studies were used to evaluate dopant concentrations of PPy films stored in water and phosphate buffered saline over 14 days, and conductance studies over the same timeframe measured electrical stability. PSS proved to be the most stable dopant, though all films experienced significant decay in conductivity and dopant concentration. Cell adhesion studies demonstrated the dependence of cell outcome on film thickness and dopant choice. The strengths and weaknesses of different synthesis parameters, as demonstrated by these experiments, are critical design factors that must be leveraged when designing biomedical implants. The results of these studies should provide practical insight to researchers working with conducting polymers, and particularly PPy, on the relationships between synthesis parameters, polymeric properties and biological compatibility.