A biofunctionalization scheme for neural interfaces using polydopamine polymer

Surface Modification Progress for PLGA-Based Cell Scaffolds

Poly(lactic-glycolic acid) (PLGA) is a biocompatible bio-scaffold material, but its own hydrophobic and electrically neutral surface limits its application as a cell scaffold. Polymer materials, mimics ECM materials, and organic material have often been used as coating materials for PLGA cell scaffolds to improve the poor cell adhesion of PLGA and enhance tissue adaptation. These coating materials can be modified on the PLGA surface via simple physical or chemical methods, and coating multiple materials can simultaneously confer different functions to the PLGA scaffold; not only does this ensure stronger cell adhesion but it also modulates cell behavior and function. This approach to coating could facilitate the production of more PLGA-based cell scaffolds. This review focuses on the PLGA surface-modified materials, methods, and applications, and will provide guidance for PLGA surface modification.

Fully Integrated 3D Microelectrode Arrays with Polydopamine-Mediated Silicon Dioxide Insulation for Electrophysiological Interrogation of a Novel 3D Human, Neural Microphysiological Construct

Advances within in vitro biological system complexity have enabled new possibilities for the "Organs-on-a-Chip" field. Microphysiological systems (MPS) as such incorporate sophisticated biological constructs with custom biological sensors. For microelectromechanical systems (MEMS) sensors, the dielectric layer is critical for device performance, where silicon dioxide (SiO2) represents an excellent candidate due to its biocompatibility and wide utility in MEMS devices. Yet, high temperatures traditionally preclude SiO2 from incorporation in polymer-based BioMEMS. Electron-beam deposition of SiO2 may provide a low-temperature, dielectric serving as a nanoporous MPS growth substrate. Herein, we enable improved adherence of nanoporous SiO2 to polycarbonate (PC) and 316L stainless steel (SS) via polydopamine (PDA)-mediated chemistry. The resulting stability of the combinatorial PDA-SiO2 film was interrogated, along with the nature of the intrafilm interactions. A custom polymer-metal three-dimensional (3D) microelectrode array (3D MEA) is then reported utilizing PDA-SiO2 insulation, for definition of novel dorsal root ganglion (DRG)/nociceptor and dorsal horn (DH) 3D neural constructs in excess of 6 months for the first time. Spontaneous/evoked compound action potentials (CAPs) are successfully reported. Finally, inhibitory drugs treatments showcase pharmacological responsiveness of the reported multipart biological activity. These results represent the initiation of a novel 3D MEA-integrated, 3D neural MPS for the long-term electrophysiological study.

Composite microgranular scaffolds with surface modifications for improved initial osteoblastic cell proliferation

Polyester-based granular scaffolds are a potent material for tissue engineering due to their porosity, controllable pore size, and potential to be molded into various shapes. Additionally, they can be produced as composite materials, e.g., mixed with osteoconductive β-tricalcium phosphate or hydroxyapatite. Such polymer-based composite materials often happen to be hydrophobic, which disrupts cell attachment and decreases cell growth on the scaffold, undermining its primary function. In this work, we propose the experimental comparison of three modification techniques for granular scaffolds to increase their hydrophilicity and cell attachment. Those techniques include atmospheric plasma treatment, polydopamine coating, and polynorepinephrine coating. Composite polymer/β-tricalcium phosphate granules have been produced in a solution-induced phase separation (SIPS) process using commercially available biomedical polymers: poly(lactic acid), poly(lactic-co-glycolic acid), and polycaprolactone. We used thermal assembly to prepare cylindrical scaffolds from composite microgranules. Atmospheric plasma treatment, polydopamine coating, and polynorepinephrine coating showed similar effects on polymer composites' hydrophilic and bioactive properties. All modifications significantly increased human osteosarcoma MG-63 cell adhesion and proliferation in vitro compared to cells cultured on unmodified materials. In the case of polycaprolactone/β-tricalcium phosphate scaffolds, modifications were the most necessary, as unmodified polycaprolactone-based material disrupted the cell attachment. Modified polylactide/β-tricalcium phosphate scaffold supported excellent cell growth and showed ultimate compressive strength exceeding this of human trabecular bone. This suggests that all investigated modification techniques can be used interchangeably for increasing wettability and cell attachment properties of various scaffolds for medical applications, especially those with high surface and volumetric porosity, like granular scaffolds.

A small-diameter vascular graft immobilized peptides for capturing endothelial colony-forming cells

Combining synthetic polymers and biomacromolecules prevents the occurrence of thrombogenicity and intimal hyperplasia in small-diameter vascular grafts (SDVGs). In the present study, an electrospinning poly (L)-lactic acid (PLLA) bilayered scaffold is developed to prevent thrombosis after implantation by promoting the capture and differentiation of endothelial colony-forming cells (ECFCs). The scaffold consists of an outer PLLA scaffold and an inner porous PLLA biomimetic membrane combined with heparin (Hep), peptide Gly-Gly-Gly-Arg-Glu-Asp-Val (GGG-REDV), and vascular endothelial growth factor (VEGF). Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle goniometry were performed to determine successful synthesis. The tensile strength of the outer layer was obtained using the recorded stress/strain curves, and hemocompatibility was evaluated using the blood clotting test. The proliferation, function, and differentiation properties of ECFCs were measured on various surfaces. Scanning electronic microscopy (SEM) was used to observe the morphology of ECFCs on the surface. The outer layer of scaffolds exhibited a similar strain and stress performance as the human saphenous vein via the tensile experiment. The contact angle decreased continuously until it reached 56° after REDV/VEGF modification, and SEM images of platelet adhesion showed a better hemocompatibility surface after modification. The ECFCs were captured using the REDV + VEGF + surface successfully under flow conditions. The expression of mature ECs was constantly increased with the culture of ECFCs on REDV + VEGF + surfaces. SEM images showed that the ECFCs captured by the REDV + VEGF + surface formed capillary-like structures after 4 weeks of culture. The SDVGs modified by REDV combined with VEGF promoted ECFC capture and rapid differentiation into ECs, forming capillary-like structures in vitro. The bilayered SDVGs could be used as vascular devices that achieved a high patency rate and rapid re-endothelialization.

Electrically Copolymerized Polydopamine Melanin/Poly(3,4-ethylenedioxythiophene) Applied for Bioactive Multimodal Neural Interfaces with Induced Pluripotent Stem Cell-Derived Neurons

Multimodal neural interfaces include combined functions of electrical neuromodulation and synchronic monitoring of neurochemical and physiological signals in one device. The remarkable biocompatibility and electrochemical performance of polystyrene sulfonate-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) have made it the most recommended conductive polymer neural electrode material. However, PEDOT:PSS formed by electrochemical deposition, called PEDOT/PSS, often need multiple doping to improve structural instability in moisture, resolve the difficulties of functionalization, and overcome the poor cellular affinity. In this work, inspired by the catechol-derived adhesion and semiconductive properties of polydopamine melanin (PDAM), we used electrochemical oxidation polymerization to develop PDAM-doped PEDOT (PEDOT/PDAM) as a bioactive multimodal neural interface that permits robust electrochemical performance, structural stability, analyte-trapping capacity, and neural stem cell affinity. The use of potentiodynamic scans resolved the problem of copolymerizing 3,4-ethylenedioxythiophene (EDOT) and dopamine (DA), enabling the formation of PEDOT/PDAM self-assembled nanodomains with an ideal doping state associated with remarkable current storage and charge transfer capacity. Owing to the richness of hydrogen bond donors/acceptors provided by the hydroxyl groups of PDAM, PEDOT/PDAM presented better electrochemical and mechanical stability than PEDOT/PSS. It has also enabled high sensitivity and selectivity in the electrochemical detection of DA. Different from PEDOT/PSS, which inhibited the survival of human induced pluripotent stem cell-derived neural progenitor cells, PEDOT/PDAM maintained cell proliferation and even promoted cell differentiation into neuronal networks. Finally, PEDOT/PDAM was modified on a commercialized microelectrode array system, which resulted in the reduction of impedance by more than one order of magnitude; this significantly improved the resolution and reduced the noise of neuronal signal recording. With these advantages, PEDOT/PDAM is anticipated to be an efficient bioactive multimodal neural electrode material with potential application to brain-machine interfaces.

Lubricant skin on diverse biomaterials with complex shapes via polydopamine-mediated surface functionalization for biomedical applications

Implantable biomedical devices require an anti-biofouling, mechanically robust, low friction surface for a prolonged lifespan and improved performance. However, there exist no methods that could provide uniform and effective coatings for medical devices with complex shapes and materials to prevent immune-related side effects and thrombosis when they encounter biological tissues. Here, we report a lubricant skin (L-skin), a coating method based on the application of thin layers of bio-adhesive and lubricant-swellable perfluoropolymer that impart anti-biofouling, frictionless, robust, and heat-mediated self-healing properties. We demonstrate biocompatible, mechanically robust, and sterilization-safe L-skin in applications of bioprinting, microfluidics, catheter, and long and narrow medical tubing. We envision that diverse applications of L-skin improve device longevity, as well as anti-biofouling attributes in biomedical devices with complex shapes and material compositions.

Mussel‐Inspired Biomaterials: From Chemistry to Clinic

After several billions of years, nature still makes decisions on its own to identify, develop, and direct the most effective material for phenomena/challenges faced. Likewise, and inspired by the nature, we learned how to take steps in developing new technologies and materials innovations. Wet and strong adhesion by Mytilidae mussels (among which Mytilus edulis—blue mussel and Mytilus californianus—California mussel are the most well‐known species) has been an inspiration in developing advanced adhesives for the moist condition. The wet adhesion phenomenon is significant in designing tissue adhesives and surgical sealants. However, a deep understanding of engaged chemical moieties, microenvironmental conditions of secreted proteins, and other contributing mechanisms for outstanding wet adhesion mussels are essential for the optimal design of wet glues. In this review, all aspects of wet adhesion of Mytilidae mussels, as well as different strategies needed for designing and fabricating wet adhesives are discussed from a chemistry point of view. Developed muscle‐inspired chemistry is a versatile technique when designing not only wet adhesive, but also, in several more applications, especially in the bioengineering area. The applications of muscle‐inspired biomaterials in various medical applications are summarized for future developments in the field.

Spatial barcoding-enabled highly multiplexed immunoassay with digital microfluidics

Digital microfluidics (DMF), facilitating independent manipulation of microliter samples, provides an ideal platform for immunoassay detection; however, suffering limited multiplexity. To address the need, herein we described a digital microfluidics (DMF) platform that realizes spatial barcoding on the Teflon-coated indium tin oxide (ITO) glass side to fulfill highly multiplexed immunoassay (10+) with low-volume samples (∼4 μL) in parallel, representing the highest multiplexing recorded to date for DMF-actuated immunoassay. Planar-based spatial immobilization of multiple capture antibodies was realized on a Teflon-coated ITO glass side, which was then used as the top plate of the DMF device. Droplets containing analytes, secondary antibodies, and fluorescent signaling reporters with low volume, which were electrically manipulated by our DMF control system, were shuttled sequentially along the working electrodes to complete the immuno-reaction. Evaluation of platform performance with recombinant proteins showed excellent sensitivity and reproducibility. To test the feasibility of our platform in analyzing multiplex biomarkers of the immune response, we used lipopolysaccharide-stimulated macrophages as a model system for protein secretion dynamics studies. As a result, temporal profiling of pro-inflammatory cytokine secretion dynamics was obtained. The spatial barcoding strategy presented here is easy-to-operate to enable a more comprehensive evaluation of protein abundance from biological samples, paving the way for new opportunities to realize multiplexity-associated applications with the DMF platform.

Nitric oxide-propelled nanomotors for bacterial biofilm elimination and endotoxin removal to treat infected burn wounds

Biofilm infection is regarded as a major contributing factor to the failure of burn treatment and a persistent inflammatory state delays healing and leads to the formation of chronic wounds. Herein, self-propelled nanomotors (NMs) are proposed to enhance biofilm infiltration, bacterial destruction, and endotoxin clearance to accelerate the healing of infected burn wounds. Janus nanoparticles (NPs) were prepared through partially coating Fe₃O₄ NPs with polydopamine (PDA) layers, and then polymyxin B (PMB) and thiolated nitric oxide (SNO) donors were separately grafted onto the Janus NPs to obtain IO@PMB-SNO NMs. In response to elevated glutathione (GSH) levels in biofilms, NO generation from one side of the Janus NPs leads to self-propelled motion and deep infiltration into biofilms. The local release of NO could destroy bacteria inside the biofilm, which provides a non-antibiotic antibiofilm approach without the development of drug resistance. In addition to intrinsic antibacterial effects, the PMB grafts preferentially bind with bacteria and the active motion enhances lipopolysaccharide (LPS) clearance and then significantly attenuates the production of inflammatory cytokines and reactive oxide species by macrophages. Partial-thickness burn wounds were established on mice and infected with P. aeruginosa, and NM treatment almost fully destroyed the bacteria in the wounds. IO@PMB-SNO NMs absorb LPS and remove it from the wounds under a magnetic field, which downregulates the interleukin-6 and tumor necrosis factor-α levels in tissues. The infected wounds were completely healed with the deposition and arrangement of collagen fibers and the generation of skin features similar to those of normal skin. Thus, IO@PMB-SNO NMs achieved multiple-mode effects, including GSH-triggered NO release and self-propelled motion, the NO-induced non-antibiotic elimination of biofilms and bacteria, and PMB-induced endotoxin removal. This study offers a feasible strategy, with integrated antibiofilm and anti-inflammatory effects, for accelerating the healing of infected burn wounds.

Functional Ultra-High Molecular Weight Polyethylene Composites for Ligament Reconstructions and Their Targeted Applications in the Restoration of the Anterior Cruciate Ligament

The selection of biomaterials as biomedical implants is a significant challenge. Ultra-high molecular weight polyethylene (UHMWPE) and composites of such kind have been extensively used in medical implants, notably in the bearings of the hip, knee, and other joint prostheses, owing to its biocompatibility and high wear resistance. For the Anterior Cruciate Ligament (ACL) graft, synthetic UHMWPE is an ideal candidate due to its biocompatibility and extremely high tensile strength. However, significant problems are observed in UHMWPE based implants, such as wear debris and oxidative degradation. To resolve the issue of wear and to enhance the life of UHMWPE as an implant, in recent years, this field has witnessed numerous innovative methodologies such as biofunctionalization or high temperature melting of UHMWPE to enhance its toughness and strength. The surface functionalization/modification/treatment of UHMWPE is very challenging as it requires optimizing many variables, such as surface tension and wettability, active functional groups on the surface, irradiation, and protein immobilization to successfully improve the mechanical properties of UHMWPE and reduce or eliminate the wear or osteolysis of the UHMWPE implant. Despite these difficulties, several surface roughening, functionalization, and irradiation processing technologies have been developed and applied in the recent past. The basic research and direct industrial applications of such material improvement technology are very significant, as evidenced by the significant number of published papers and patents. However, the available literature on research methodology and techniques related to material property enhancement and protection from wear of UHMWPE is disseminated, and there is a lack of a comprehensive source for the research community to access information on the subject matter. Here we provide an overview of recent developments and core challenges in the surface modification/functionalization/irradiation of UHMWPE and apply these findings to the case study of UHMWPE for ACL repair.

Engineering Tissues of the Central Nervous System: Interfacing Conductive Biomaterials with Neural Stem/Progenitor Cells

Conductive biomaterials provide an important control for engineering neural tissues, where electrical stimulation can potentially direct neural stem/progenitor cell (NS/PC) maturation into functional neuronal networks. It is anticipated that stem cell-based therapies to repair damaged central nervous system (CNS) tissues and ex vivo, "tissue chip" models of the CNS and its pathologies will each benefit from the development of biocompatible, biodegradable, and conductive biomaterials. Here, technological advances in conductive biomaterials are reviewed over the past two decades that may facilitate the development of engineered tissues with integrated physiological and electrical functionalities. First, one briefly introduces NS/PCs of the CNS. Then, the significance of incorporating microenvironmental cues, to which NS/PCs are naturally programmed to respond, into biomaterial scaffolds is discussed with a focus on electrical cues. Next, practical design considerations for conductive biomaterials are discussed followed by a review of studies evaluating how conductive biomaterials can be engineered to control NS/PC behavior by mimicking specific functionalities in the CNS microenvironment. Finally, steps researchers can take to move NS/PC-interfacing, conductive materials closer to clinical translation are discussed.

Hydroxyapatite gradient on poly (vinyl alcohol) hydrogels surface to mimic calcified cartilage zone for cartilage repair

Poly (vinyl alcohol) (PVA) hydrogels are considered promising artificial articular cartilage. However, the weak attachment between PVA hydrogels and subchondral bone limit its application in the biomedical field. In this article, we present a new method to improve the mineralization of PVA hydrogels, and fabricate PVA hydrogels with continuously graded hydroxyapatite coating. The surface of the hydrogels was modified by dopamine self-polymerization and alendronate conjugation subsequently. Based on these, we used simulated body fluids to mineralize the hydrogels to mimic calcified cartilage zone. The modified surface of the PVA hydrogels showed excellent mineralization ability with continuously graded hydroxyapatite (HA). As the main component of human bones, HA can be chemically bonded body tissue on the interface, showing great biological activity. With the content of HA increasing, the cell adhesion ability of the hydrogels was enhanced, which helped the hydrogels integrate tightly with subchondral bone. These results demonstrate that the modified hydrogels could be promising substitutes for articular cartilage.

Development of the micro-patterned 3D neuronal-hydrogel model using soft-lithography for study a 3D neural network on a microelectrode array. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2021;2021:1234-1237. [PMID: 34891510 DOI: 10.1109/embc46164.2021.9629822]

In vitro patterned neuronal models have been studied as one of the strategies to investigate the relationship between structural connectivity and functional activity of neural network. Despite the importance of three-dimensional (3D) cell models, most of these studies have been performed on two-dimensional models. In this study, we present a technique to construct the micro-pattern to 3D neuronal-hydrogel model using a micromolding in capillaries (MIMIC) technique on microelectrode array (MEA). Our technique was suitable to prevent the deformation of micro-patterned collagen model against the neuronal contracted tension during the network formation. The relationship between the growth directions of glial cells and micro-pattern direction was investigated. Lastly, we confirmed that our 3D model had synchronized activity among neurons in 3D. This model is expected to be used as a tool to study the relationship between structural connectivity and functional activity in the 3D environment.

Fabrication of Bacterial Cellulose-Based Dressings for Promoting Infected Wound Healing

Bacterial cellulose (BC) holds several unique properties such as high water retention capability, flexibility, biocompatibility, and high absorption capacity. All these features make it a potential material for wound healing applications. However, it lacks antibacterial properties, which hampers its applications for infectious wound healings. This study reported BC-based dressings containing ε-polylysine (ε-PL), cross-linked by a biocompatible and mussel-inspired polydopamine (PDA) for promoting infectious wound healing. BC membranes were coated with PDA by a simple self-polymerization process, followed by treating with different contents of ε-PL. The resulted membranes showed strong antibacterial properties against tested bacteria by both in vitro and in vivo evaluations. The membranes also exhibited hemocompatibility and cytocompatibility by in vitro investigations. Moreover, the functionalized membranes promoted infected wound healing using Sprague-Dawley rats as a model animal. A complete wound healing was observed in the group treated with functionalized membranes, while wounds were still open for control and pure BC groups in the same duration. Histological investigations indicated that the thickness of newborn skin was greater and smoother in the groups treated with modified membranes in comparison to neat BC or control groups. These results revealed that the functionalized membranes have great potential as a dressing material for infected wounds in future clinical applications.

Universal Surface Coating with a Non-Phenolic Molecule, Sulfonated Pyrene

Nature-inspired small molecules such as catecholamines and polyphenols have gained a great deal of attention because of the exceptional surface-coating property that is applicable to many diverse substrates. Many researchers have conducted studies to expand molecular pools with surface-coating properties, but previous reports have still been limited to phenolic molecules as surface-coating agents. In this study, we describe for the first time the material-independent coating properties of nonphenolic molecules, namely, sulfonated pyrenes with Zr^IV ions. Owing to the binding capability with several oxygen-containing ligands, Zr^IV can be used for the molecular assembly of sulfonated pyrenes. We also report on the mixing of multiple sulfonated pyrenes and Zr^IV results in cross-linked complexes that can coat diverse solid substrates. The resulting coating can serve as a platform for grafting functional polysaccharides.

Polydopamine-Based Nanoparticles for Photothermal Therapy/Chemotherapy and their Synergistic Therapy with Autophagy Inhibitor to Promote Antitumor Treatment

Polydopamine (PDA) has attracted much attention recently due to its strong adhesion capability to most substrates. After combining with organic (such as organic metal framework, micelles, hydrogel, polypeptide copolymer) or inorganic nanomaterials (such as gold, silicon, carbon), polydopamine-based nanoparticles (PDA NPs) exhibit the merging of characteristics. Until now, the preparation methods, polymerization mechanism, and photothermal therapy (PTT) or chemotherapy (CT) applications of PDA NPs have been reported detailly. Since the PTT or CT treatment process is often accompanied by exogenous stimuli, tumor cells usually induce pro-survival autophagy to protect the cells from further damage, which will weaken the therapeutic effect. Therefore, an in-depth understanding of PDA NPs modulated PTT, CT, and autophagy is required. However, this association is rarely reviewed. Herein, we briefly described the relationship between PTT/CT, autophagy, and tumor treatment. Then, the outstanding performances of PDA NPs in PTT/CT and their combination with autophagy inhibitors for tumor synergistic therapy have been summarized. This work is expected to shed light on the multi-strategy antitumor therapy applications of PDA NPs.

Applications of Polydopamine-Modified Scaffolds in the Peripheral Nerve Tissue Engineering

Peripheral nerve injury is a common and complicated traumatic disease in clinical neurosurgery. With the rapid advancement and development of medical technologies, novel tissue engineering provides alternative therapies such as nerve conduit transplantation. It has achieved significant outcomes. The scaffold surface modification is vital to the reconstruction of a pro-healing interface. Polydopamine has high chemical activity, adhesion, hydrophilicity, hygroscopicity, stability, biocompatibility, and other properties. It is often used in the surface modification of biomaterials, especially in the peripheral nerve regeneration. The present review discusses that polydopamine can promote the adhesion, proliferation, and differentiation of neural stem cells and the growth of neuronal processes. Polydopamine is widely used in the surface modification of nerve conduits and has a potential application prospect of repairing peripheral nerve injury. Polydopamine-modified scaffolds are promising in the peripheral nerve tissue engineering.

Development of tannic acid-enriched materials modified by poly(ethylene glycol) for potential applications as wound dressing

The interests in the biomedical impact of tannic acid (TA) targeting production of various types of biomaterials, such as digital microfluids, chemical sensors, wound dressings, or bioimplants constantly increase. Despite the significant disadvantage of materials obtained from natural-based compounds and their low stability and fragility, therefore, there is an imperative need to improve materials properties by addition of stabilizing formulas. In this study, we performed assessments of thin films over TA proposed as a cross-linker to be used in combination with polymeric matrix based on chitosan (CTS), i.e. CTS/TA at 80:20 or CTS/TA at 50:50 and poly(ethylene glycol) (PEG) at the concentration of 10% or 20%. We evaluated their mechanical parameters as well as the cytotoxicity assay for human bone marrow mesenchymal stem cells, human melanotic melanoma (MNT-1), and human osteosarcoma (Saos-2). The results revealed significant differences in dose-dependent of PEG regarding the maximum tensile strength (σ_max) or impact on the metabolic activity of tissue culture plastic. We observed that PEG improved mechanical parameters prominently, decreased the hemolysis rate, and did not affect cell viability negatively. Enclosed data, confirmed also by our previous reports, will undoubtedly pave the path for the future application of tannic acid-based biomaterials to treat wound healing.

Multicompartment Microreactors Prevent Excitotoxic Dysfunctions In Rat Primary Cortical Neurons

Excitotoxicity is a cellular phenomenon that comprises the consequences of toxic actions of excitatory neurotransmitters, such as glutamate. This process is usually related to overproduction of reactive oxygen species (ROS) and ammonia (NH₄ ⁺ ) toxicity. Platinum nanoparticle (Pt-NP)-based microreactors able to degrade hydrogen peroxide (H₂ O₂ ) and NH₄ ⁺ , are previously described as a novel therapeutical approach against excitotoxicity, conferring protection to neuroblasts. Now, it is demonstrated that these microreactors are compatible with rat primary cortical neurons, show high levels of neuronal membrane interaction, and are able to improve cell survival and neuronal activity when neurons are exposed to H₂ O₂ or NH₄ ⁺ . Additionally, more complex microreactors are assembled, including enzyme-loaded liposomes containing glutamate dehydrogenase and glutathione reductase, in addition to Pt-NP. The in vitro activity of these microreactors is characterized and they are compared to the Pt-NP-based microreactors in terms of biological activity, concluding that they enhance cell viability similarly or more extensively than the latter. Extracellular electrophysiological recordings demonstrate that these microreactors rescue neuronal functionality lost upon incubation with H₂ O₂ or NH₄ ⁺ . This study provides more evidence for the potential application of these microreactors in a biomedical context with more complex cellular environments.

Polydopamine and Its Derivative Surface Chemistry in Material Science: A Focused Review for Studies at KAIST

Polydopamine coating, the first material-independent surface chemistry, and its related methods significantly influence virtually all areas of material science and engineering. Functionalized surfaces of metal oxides, synthetic polymers, noble metals, and carbon materials by polydopamine and its related derivatives exhibit a variety of properties for cell culture, microfluidics, energy storage devices, superwettability, artificial photosynthesis, encapsulation, drug delivery, and numerous others. Unlike other articles, this review particularly focuses on the development of material science utilizing polydopamine and its derivatives coatings at the Korea Advanced Institute of Science and Technology for a decade. Herein, it is demonstrated how material-independent coating methods provide solutions for challenging problems existed in many interdisciplinary areas in bio-, energy-, and nanomaterial science by collaborations and independent research.

Development of Stimulus-Responsive Degradable Film via Codeposition of Dopamine and Cystamine

Herein, we report a degradable film that can be coated on various substrates by the codeposition of dopamine and cystamine. The thickness of the resulting film (pDC) varies depending on the initial ratio of dopamine/cystamine dissolved in a solution; the thickest film (ca. 60 nm) is obtained under optimized codeposition conditions. Selective degradation of pDC occurs in the presence of tris(2-carboxyethyl)phosphine (TCEP), the reaction kinetics of which are highly dependent on the TCEP concentration. For further application as a drug-delivery platform, doxorubicin can be loaded within the pDC film, which is released actively under film degradation in response to TCEP. We expect that the developed pDC film will be a useful tool for developing drug delivery cargo, antibacterial surface, and cell surface coating for various biomedical applications.

Polydopamine Nanoparticles as an Organic and Biodegradable Multitasking Tool for Neuroprotection and Remote Neuronal Stimulation

Oxidative stress represents a common issue in most neurological diseases, causing severe impairments of neuronal cell physiological activity that ultimately lead to neuron loss of function and cellular death. In this work, lipid-coated polydopamine nanoparticles (L-PDNPs) are proposed both as antioxidant and neuroprotective agents, and as a photothermal conversion platform able to stimulate neuronal activity. L-PDNPs showed the ability to counteract reactive oxygen species (ROS) accumulation in differentiated SH-SY5Y, prevented mitochondrial ROS-induced dysfunctions and stimulated neurite outgrowth. Moreover, for the first time in the literature, the photothermal conversion capacity of L-PDNPs was used to increase the intracellular temperature of neuron-like cells through near-infrared (NIR) laser stimulation, and this phenomenon was thoroughly investigated using a fluorescent temperature-sensitive dye and modeled from a mathematical point of view. It was also demonstrated that the increment in temperature caused by the NIR stimulation of L-PDNPs was able to produce a Ca²⁺ influx in differentiated SH-SY5Y, being, to the best of our knowledge, the first example of organic nanostructures used in such an approach. This work could pave the way to new and exciting applications of polydopamine-based and of other NIR-responsive antioxidant nanomaterials in neuronal research.

Melanin and Melanin-Like Hybrid Materials in Regenerative Medicine

Melanins are a group of dark insoluble pigments found widespread in nature. In mammals, the brown-black eumelanins and the reddish-yellow pheomelanins are the main determinants of skin, hair, and eye pigmentation and play a significant role in photoprotection as well as in many biological functions ensuring homeostasis. Due to their broad-spectrum light absorption, radical scavenging, electric conductivity, and paramagnetic behavior, eumelanins are widely studied in the biomedical field. The continuing advancements in the development of biomimetic design strategies offer novel opportunities toward specifically engineered multifunctional biomaterials for regenerative medicine. Melanin and melanin-like coatings have been shown to increase cell attachment and proliferation on different substrates and to promote and ameliorate skin, bone, and nerve defect healing in several in vivo models. Herein, the state of the art and future perspectives of melanins as promising bioinspired platforms for natural regeneration processes are highlighted and discussed.

A Magnetic Iron Oxide/Polydopamine Coating Can Improve Osteogenesis of 3D-Printed Porous Titanium Scaffolds with a Static Magnetic Field by Upregulating the TGFβ-Smads Pathway

3D-printed porous titanium-aluminum-vanadium (Ti6Al4V, pTi) scaffolds offer surgeons a good option for the reconstruction of large bone defects, especially at the load-bearing sites. However, poor osteogenesis limits its application in clinic. In this study, a new magnetic coating is successfully fabricated by codepositing of Fe₃ O₄ nanoparticles and polydopamine (PDA) on the surface of 3D-printed pTi scaffolds, which enhances cell attachment, proliferation, and osteogenic differentiation of hBMSCs in vitro and new bone formation of rabbit femoral bone defects in vivo with/without a static magnetic field (SMF). Furthermore, through proteomic analysis, the enhanced osteogenic effect of the magnetic Fe₃ O₄ /PDA coating with the SMF is found to be related to upregulate the TGFβ-Smads signaling pathway. Therefore, this work provides a simple protocol to improve the osteogenesis of 3D-printed porous pTi scaffolds, which will help their application in clinic.

Synthesis, Follow-Up, and Characterization of Polydopamine-like Coatings Departing from Micromolar Dopamine-o-Quinone Precursor Concentrations

The understanding of oxidized species derived from the neurotransmitter dopamine (DA) is a relevant topic for both the medical field (Parkinson's disease) as well as for the field of materials science where the formation process of polydopamine (PDA) films is an active area of research. Polymers that interact strongly with almost all surfaces but have a low electrical conductivity have been obtained by the chemical oxidation of DA. Since electrical conductivity is a desired property for several applications, deposition alternatives such as electrochemical PDA synthesis have been proposed, but the results are still insufficient. In this context, we propose a new PDA chemical-electrochemical deposition process on glassy carbon electrodes. The chemical oxidation step that converts dopamine into dopamine-o-quinone previous to the electrochemical deposition was crucial to decrease the precursor concentration to the micromolar range. The PDA-like films synthesized by this method had high adhesion and low charge-transfer resistance, which was evidenced by impedance measurements and the successful electrodeposition of a polypyrrole coating on top of a PDA-like film. In addition, we observed that anodization of GC surfaces increases sensitivity toward six electroactive couples derived from DA oxidation in the pH regimes studied. These results show the complexity of the intermediates formed during the electrochemical polymerization of PDA.

Using In Situ Polymerization to Increase Puncture Resistance and Induce Reversible Formability in Silk Membranes

Silk fibroin is an excellent biopolymer for application in a variety of areas, such as textiles, medicine, composites and as a novel material for additive manufacturing. In this work, silk membranes were surface modified by in situ polymerization of aqueous acrylic acid, initiated by the reduction of various aryldiazonium salts with vitamin C. Treatment times of 20 min gave membranes which possessed increased tensile strength, tensile modulus, and showed significant increased resistance to needle puncture (+131%), relative to 'untreated' standards. Most interestingly, the treated silk membranes were able to be reversibly formed into various shapes via the hydration and plasticizing of the surface bound poly(acrylic acid), by simply steaming the modified membranes. These membranes and their unique properties have potential applications in advanced textiles, and as medical materials.

Suppression of hypersynchronous network activity in cultured cortical neurons using an ultrasoft silicone scaffold

The spontaneous activity pattern of cortical neurons in dissociated culture is characterized by burst firing that is highly synchronized among a wide population of cells. The degree of synchrony, however, is excessively higher than that in cortical tissues. Here, we employed polydimethylsiloxane (PDMS) elastomers to establish a novel system for culturing neurons on a scaffold with an elastic modulus resembling brain tissue, and investigated the effect of the scaffold's elasticity on network activity patterns in cultured rat cortical neurons. Using whole-cell patch clamp to assess the scaffold effect on the development of synaptic connections, we found that the amplitude of excitatory postsynaptic current, as well as the frequency of spontaneous transmissions, was reduced in neuronal networks grown on an ultrasoft PDMS with an elastic modulus of 0.5 kPa. Furthermore, the ultrasoft scaffold was found to suppress neural correlations in the spontaneous activity of the cultured neuronal network. The dose of GsMTx-4, an antagonist of stretch-activated cation channels (SACs), required to reduce the generation of the events below 1.0 event per min on PDMS substrates was lower than that for neurons on a glass substrate. This suggests that the difference in the baseline level of SAC activation is a molecular mechanism underlying the alteration in neuronal network activity depending on scaffold stiffness. Our results demonstrate the potential application of PDMS with biomimetic elasticity as cell-culture scaffold for bridging the in vivo-in vitro gap in neuronal systems.

Immobilization of BMP-2-derived peptides on 3D-printed porous scaffolds for enhanced osteogenesis

Three-dimensional (3D) printing technologies open up new perspectives for customizing the external shape and internal architecture of bone scaffolds. In this study, an oligopeptide (SSVPT, Ser-Ser-Val-Pro-Thr) derived from bone morphogenetic protein 2 was conjugated with a dopamine coating on a 3D-printed poly(lactic acid) (PLA) scaffold to enhance osteogenesis. Cell experiments in vitro showed that the scaffold was highly osteoconductive to the adhesion and proliferation of rat marrow mesenchymal stem cells (MSCs). In addition, RT-PCR analysis showed that the scaffold was able to promote the expression of osteogenesis-related genes, such as alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2), osteocalcin (OCN) and osteopontin (OPN). Images of the micro-CT 3D reconstruction from the rat cranial bone defect model showed that bone regeneration patterns occurred from one side edge towards the center of the area implanted with the prepared biomimetic peptide hydrogels, demonstrating significantly accelerated bone regeneration. This work will provide a basis to explore the application potential of bioactive scaffolds further.

Thickness-Tunable Eggshell Membrane Hydrolysate Nanocoating with Enhanced Cytocompatibility and Neurite Outgrowth

The eggshell membrane is one of the easily obtainable natural biomaterials, but has been neglected in the biomaterial community, compared with marine biomaterials and discarded as a food waste. In this work, we utilized the ESM hydrolysate (ESMH), which was obtained by the enzymochemical method, as a bioactive functional material for interfacial bioengineering, exemplified by thickness-tunable, layer-by-layer (LbL) nanocoating with the Fe(III)-tannic acid (TA) complex. [Fe(III)-TA/ESMH] LbL films, ending with the ESMH layer, showed great cytocompatiblility with HeLa cells and even primary hippocampal neuron cells. More importantly, the films were found to be neurochemically active, inducing the acceleration of neurite outgrowth for the long-term neuron culture. We believe that the ability for building cytocompatible ESMH films in a thickness-tunable manner would be applicable to a broad range of different nanomaterials in shape and size and would be utilized with multimodal functionalities for biomedical applications, such as bioencapsulation, theranostics, and regenerative medicine.

Enhanced Adhesion of Fish Ovarian Germline Stem Cells on Solid Surfaces by Mussel-Inspired Polymer Coating

Development of advanced cell culture methods has gained increasing attention because it allows for efficient genetic engineering and precise regulation of animal reproduction on a cellular basis. Numerous studies have attempted to develop an advanced cell culture method. Previous studies have altered cell culture media and pretreated culture plates with functional molecules. Among them, a mussel-inspired polymer coating has been extensively utilized owing to its wide applicability. For instance, adhesion of human embryonic stem cells and neuronal cells on solid surfaces has been improved. Despite the excellent capability of the mussel-inspired polymer coating, most studies have primarily focused on mammalian cells. However, the efficacy of these coatings on the adhesion of other cell lines is yet unclear. This study aimed to assess the potential of the mussel-inspired polymer coating in the regulation of the adhesion of fish ovarian germline stem cells on solid surfaces. Solid surfaces were coated by polydopamine and poly-L-lysine, and the effect of the coatings on cellular behaviors was investigated.

Morphological Diversity, Protein Adsorption, and Cellular Uptake of Polydopamine-Coated Gold Nanoparticles

Polydopamine (PDA)-coated nanoparticles are adhesive bionanomaterials widely utilized in intracellular applications, yet how their adhesiveness affects their colloidal stability and their interactions with serum proteins and mammalian cells remain unclear. In this work, we systematically investigate the combined effects of dopamine (DA) concentration and polymerization time (both reaction parameters spanning 2 orders of magnitude) on the morphological diversity of PDA-coated nanoparticles by coating PDA onto gold nanoparticle cores. Independent of the DA concentration, Au@PDA NPs remain largely aggregated upon several hours of limited polymerization; interestingly, extended polymerization for 2 days or longer yield randomly aggregated NPs, nearly monodisperse NPs, or worm-like NP chains in the ascending order of DA concentration. Upon exposure to serum proteins, the specific type of proteins adsorbed to the Au@PDA NPs strongly depends upon the DA concentration. As DA concentration increases, less albumin and more hemoglobin subunits adhere. Moreover, cellular uptake is a strong function of polymerization time. Serum-stabilized Au@PDA NPs prepared by limited polymerization enter Neuro-2a and HeLa cancer cells more abundantly than those prepared by extended polymerization. Our data underscore the importance of DA concentration and polymerization time for tuning the morphology and degree of intracellular delivery of PDA-coated nanostructures.

Water-Dispersible Polydopamine-Coated Nanofibers for Stimulation of Neuronal Growth and Adhesion

Hybrid nanomaterials have shown great potential in regenerative medicine due to the unique opportunities to customize materials properties for effectively controlling cellular growth. The peptide nanofiber-mediated auto-oxidative polymerization of dopamine, resulting in stable aqueous dispersions of polydopamine-coated peptide hybrid nanofibers, is demonstrated. The catechol residues of the polydopamine coating on the hybrid nanofibers are accessible and provide a platform for introducing functionalities in a pH-responsive polymer analogous reaction, which is demonstrated using a boronic acid modified fluorophore. The resulting hybrid nanofibers exhibit attractive properties in their cellular interactions: they enhance neuronal cell adhesion, nerve fiber growth, and growth cone area, thus providing great potential in regenerative medicine. Furthermore, the facile modification by pH-responsive supramolecular polymer analog reactions allows tailoring the functional properties of the hybrid nanofibers in a reversible fashion.

Three-Dimensional-Bioprinted Dopamine-Based Matrix for Promoting Neural Regeneration

Central nerve repair and regeneration remain challenging problems worldwide, largely because of the extremely weak inherent regenerative capacity and accompanying fibrosis of native nerves. Inadequate solutions to the unmet needs for clinical therapeutics encourage the development of novel strategies to promote nerve regeneration. Recently, 3D bioprinting techniques, as one of a set of valuable tissue engineering technologies, have shown great promise toward fabricating complex and customizable artificial tissue scaffolds. Gelatin methacrylate (GelMA) possesses excellent biocompatible and biodegradable properties because it contains many arginine-glycine-aspartic acids (RGD) and matrix metalloproteinase sequences. Dopamine (DA), as an essential neurotransmitter, has proven effective in regulating neuronal development and enhancing neurite outgrowth. In this study, GelMA-DA neural scaffolds with hierarchical structures were 3D-fabricated using our custom-designed stereolithography-based printer. DA was functionalized on GelMA to synthesize a biocompatible printable ink (GelMA-DA) for improving neural differentiation. Additionally, neural stem cells (NSCs) were employed as the primary cell source for these scaffolds because of their ability to terminally differentiate into a variety of cell types including neurons, astrocytes, and oligodendrocytes. The resultant GelMA-DA scaffolds exhibited a highly porous and interconnected 3D environment, which is favorable for supporting NSC growth. Confocal microscopy analysis of neural differentiation demonstrated that a distinct neural network was formed on the GelMA-DA scaffolds. In particular, the most significant improvements were the enhanced neuron gene expression of TUJ1 and MAP2. Overall, our results demonstrated that 3D-printed customizable GelMA-DA scaffolds have a positive role in promoting neural differentiation, which is promising for advancing nerve repair and regeneration in the future.

Platinum Nanoparticle-Based Microreactors as Support for Neuroblastoma Cells

Excitotoxicity is a common phenomenon in several neurological diseases, associated with an impaired clearance of synaptically released glutamate, which leads to an overactivation of postsynaptic glutamate receptors. This will, in turn, start an intracellular cascade of neurotoxic events, which include exacerbated production of reactive oxygen species and ammonia toxicity. We report the assembly of microreactors equipped with platinum nanoparticles as artificial enzymes and polymer terminating layers including poly(dopamine). The biological response to these microreactors is assessed in human neuroblastoma cell culture. The microreactors' function to deplete hydrogen peroxide (H₂O₂) and ammonia is confirmed. While the proliferation of the cells depends on the number of microreactors present, no inherent toxicity is found. Furthermore, the microreactors are able to ameliorate the effects of excitotoxicity in cell culture by scavenging H₂O₂ and ammonia, thus having the potential to provide a therapeutic approach for several neurological diseases in which excitotoxicity is observed.

Polydopamine Surface Chemistry: A Decade of Discovery

Polydopamine is one of the simplest and most versatile approaches to functionalizing material surfaces, having been inspired by the adhesive nature of catechols and amines in mussel adhesive proteins. Since its first report in 2007, a decade of studies on polydopamine molecular structure, deposition conditions, and physicochemical properties have ensued. During this time, potential uses of polydopamine coatings have expanded in many unforeseen directions, seemingly only limited by the creativity of researchers seeking simple solutions to manipulating surface chemistry. In this review, we describe the current state of the art in polydopamine coating methods, describe efforts underway to uncover and tailor the complex structure and chemical properties of polydopamine, and identify emerging trends and needs in polydopamine research, including the use of dopamine analogs, nitrogen-free polyphenolic precursors, and improvement of coating mechanical properties.

Fabrication of Fe3O4@polydopamine@polyamidoamine core–shell nanocomposites and their application for Cu(ii) adsorption

Fe₃O₄@PDA@PAMAM nanocomposites were fabricated with a polydopamine assisted method, possessing excellent magnetic properties and high adsorption capacity for Cu(ii).

Enhanced Cell Adhesion on a Nano-Embossed, Sticky Surface Prepared by the Printing of a DOPA-Bolaamphiphile Assembly Ink

Inspired by adhesive mussel proteins, nanospherical self-assemblies were prepared from bolaamphiphiles containing 3,4-dihydroxyphenylalanine (DOPA) moieties, and a suspension of the bolaamphiphile assemblies was used for the preparation of a patterned surface that enhanced cell adhesion and viability. The abundant surface-exposed catechol groups on the robust bolaamphiphile self-assemblies were responsible for their outstanding adhesivity to various surfaces and showed purely elastic mechanical behaviour in response to tensile stress. Compared to other polydopamine coatings, the spherical DOPA-bolaamphiphile assemblies were coated uniformly and densely on the surface, yielding a nano-embossed surface. Cell culture tests on the surface modified by DOPA-bolaamphiphiles also showed enhanced cellular adhesivity and increased viability compared to surfaces decorated with other catecholic compounds. Furthermore, the guided growth of a cell line was demonstrated on the patterned surface, which was prepared by inkjet printing using a suspension of the self-assembled particles as an ink. The self-assembly of DOPA-bolaamphiphiles shows that they are a promising adhesive, biocompatible material with the potential to modify various substances.

Construction of Functional Coatings with Durable and Broad-Spectrum Antibacterial Potential Based on Mussel-Inspired Dendritic Polyglycerol and in Situ-Formed Copper Nanoparticles

A novel surface coating with durable broad-spectrum antibacterial ability was prepared based on mussel-inspired dendritic polyglycerol (MI-dPG) embedded with copper nanoparticles (Cu NPs). The functional surface coating is fabricated via a facile dip-coating process followed by in situ reduction of copper ions with a MI-dPG coating to introduce Cu NPs into the coating matrix. This coating has been demonstrated to possess efficient long-term antibacterial properties against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and kanamycin-resistant E. coli through an "attract-kill-release" strategy. The synergistic antibacterial activity of the coating was shown by the combination of two functions of the contact killing, reactive oxygen species production and Cu ions released from the coating. Furthermore, this coating inhibited biofilm formation and showed good compatibility to eukaryotic cells. Thus, this newly developed Cu NP-incorporated MI-dPG surface coating may find potential application in the design of antimicrobial coating, such as implantable devices.

Development of Flexible Cell-Loaded Ultrathin Ribbons for Minimally Invasive Delivery of Skeletal Muscle Cells

Cell transplantation therapy provides a potential solution for treating skeletal muscle disorders, but cell survival after transplantation is poor. This limitation could be addressed by grafting donor cells onto biomaterials to protect them against harsh environments and processing, consequently improving cell viability in situ. Thus, we present here the fabrication of poly(lactic-co-glycolic acid) (PLGA) ultrathin ribbons with "canal-like" structures using a microfabrication technique to generate ribbons of aligned murine skeletal myoblasts (C2C12). We found that the ribbons functionalized with a solution of 3,4-dihydroxy-l-phenylalanine (DOPA) and then coated with poly-l-lysine (PLL) and fibronectin (FN) improve cell attachment and support the growth of C2C12. The viability of cells on the ribbons is evaluated following the syringe-handling steps of injection with different needle sizes. C2C12 cells readily adhere to the ribbon surface, proliferate over time, align (over 74%), maintain high viability (over 80%), and differentiate to myotubes longer than 400 μm. DNA content quantification carried out before and after injection and myogenesis evaluation confirm that cell-loaded ribbons can safely retain cells with high functionality after injection and are suitable for minimally invasive cell transplantation.

Nano-silver-decorated microfibrous eggshell membrane: processing, cytotoxicity assessment and optimization, antibacterial activity and wound healing

An ideal wound dressing can both promote wound healing and prevent bacterial infection. Here, we report a potential dressing prepared by incorporating an optimized concentration of silver nanoparticles (AgNPs) into the microfibers of a natural eggshell membrane (EM) using environmentally friendly and mussel-inspired dopamine. Briefly, acid-treated EM was used as a porous membrane for polydopamine-reduced AgNPs synthesis. To obtain the optimal cytocompatible silver concentration, cellular attachment and MTT assay were performed with different concentrations of AgNPs. The morphology of the EM and AgNPs was confirmed by scanning electronic microscopy, scanning transmission electronic microscopy and Fourier transform infrared spectroscopy. The synthesized EM/AgNPs exhibited steady and safe AgNPs release, which was further tested for antibacterial activity against Escherichia coli and Staphylococcus aureus by disc diffusion method and bacterial suspension assay. Finally, in a murine full-thickness skin wound model, we found that EM/AgNPs could promote re-epithelialization, granulation tissue formation and wound healing via enhancing cell proliferation, as demonstrated by the expression of proliferating cell nuclear antigen (PCNA), and controlling inflammation response, as demonstrated by the expression of interleukin-1β (IL-1β). These findings suggest that EM/AgNPs may have a promising application in wound management.

Calcium-Mediated Control of Polydopamine Film Oxidation and Iron Chelation

The facile preparation of conformal polydopamine (PDA) films on broad classes of materials has prompted extensive research into a wide variety of potential applications for PDA. The constituent molecular species in PDA exhibit diverse chemical moieties, and therefore highly variable properties of PDA-based devices may evolve with post-processing conditions. Here we report the use of redox-inactive cations for oxidative post-processing of deposited PDA films. PDA films incubated in alkaline CaCl₂ solutions exhibit accelerated oxidative evolution in a dose-dependent manner. PDA films incubated in CaCl₂ solutions exhibit 53% of the oxidative charge transfer compared to pristine PDA films. Carboxylic acid groups generated from the oxidation process lower the isoelectric point of PDA films from pH = 4.0 ± 0.2 to pH = 3.1 ± 0.3. PDA films exposed to CaCl₂ solutions during post-processing also enhance Fe2+/Fe3+ chelation compared to pristine PDA films. These data illustrate that the molecular heterogeneity and non-equilibrium character of as-deposited PDA films afford control over the final composition by choosing post-processing conditions, but also demands forethought into how the performance of PDA-incorporated devices may change over time in salt solutions.

On-chip, multisite extracellular and intracellular recordings from primary cultured skeletal myotubes

In contrast to the extensive use of microelectrode array (MEA) technology in electrophysiological studies of cultured neurons and cardiac muscles, the vast field of skeletal muscle research has yet to adopt the technology. Here we demonstrate an empowering MEA technology for high quality, multisite, long-term electrophysiological recordings from cultured skeletal myotubes. Individual rat skeletal myotubes cultured on micrometer sized gold mushroom-shaped microelectrode (gMμE) based MEA tightly engulf the gMμEs, forming a high seal resistance between the myotubes and the gMμEs. As a consequence, spontaneous action potentials generated by the contracting myotubes are recorded as extracellular field potentials with amplitudes of up to 10 mV for over 14 days. Application of a 10 ms, 0.5-0.9 V voltage pulse through the gMμEs electroporated the myotube membrane, and transiently converted the extracellular to intracellular recording mode for 10-30 min. In a fraction of the cultures stable attenuated intracellular recordings were spontaneously produced. In these cases or after electroporation, subthreshold spontaneous potentials were also recorded. The introduction of the gMμE-MEA as a simple-to-use, high-quality electrophysiological tool together with the progress made in the use of cultured human myotubes opens up new venues for basic and clinical skeletal muscle research, preclinical drug screening, and personalized medicine.

Recent developments in polydopamine: an emerging soft matter for surface modification and biomedical applications

After more than four billion years of evolution, nature has created a large number of fascinating living organisms, which show numerous peculiar structures and wonderful properties. Nature can provide sources of plentiful inspiration for scientists to create various materials and devices with special functions and uses. Since Messersmith proposed the fabrication of multifunctional coatings through mussel-inspired chemistry, this field has attracted considerable attention for its promising and exiciting applications. Polydopamine (PDA), an emerging soft matter, has been demonstrated to be a crucial component in mussel-inspired chemistry. In this review, the recent developments of PDA for mussel-inspired surface modification are summarized and discussed. The biomedical applications of PDA-based materials are also highlighted. We believe that this review can provide important and timely information regarding mussel-inspired chemistry and will be of great interest for scientists in the chemistry, materials, biology, medicine and interdisciplinary fields.