Water-soluble antioxidant derivative poly(triethylene glycol methyl acrylate-co-α-tocopheryl acrylate) as a potential prodrug to enable localized neuroprotection

Multilayer Assembly of Tannic Acid and an Amphiphilic Copolymer Poloxamer 188 on Planar Substrates toward Multifunctional Surfaces with Discrete Microdome-Shaped Features

Tannic acid (TA) is a natural polyphenol compound with a broad spectrum of biological activities, the most notable of which being antioxidation. Poloxamer 188 (P188), a synthetic triblock copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), is amphiphilic in nature and best known for its ability to seal structurally damaged cellular membranes. The integration of both substances onto planar substrates could bring a new option for multifunctional coatings that are advantageous for implantable biomedical devices. Here, we demonstrate the feasibility of multilayer assembly of TA/P188 toward such a coating based on hydrogen bonding between phenolic hydroxyls of TA and ether groups of P188, and the unique surface feature it generates. The interactions between these two compounds were studied both in solution and in substrate-supported layer-by-layer assembly. The multilayer assembly process exhibits an exponential growth pattern as characterized by UV-vis spectrophotometry and quartz crystal microbalance with dissipation. Morphologically unique, microdome-shaped surface features emerge and evolve with the number of layers assembled. Such features bring a reservoir function to this coating, as demonstrated by the loading of hydrophobic nile red dye. Furthermore, the presence of TA in the multilayers was revealed by silver nitrate staining, and its antioxidation activity was demonstrated through a 2,2-diphenyl-1-picryl-hydrazyl free-radical scavenging assay.

Hybrid Thin Film Organosilica Sol-Gel Coatings To Support Neuronal Growth and Limit Astrocyte Growth

Thin films of silica prepared by a sol-gel process are becoming a feasible coating option for surface modification of implantable neural sensors without imposing adverse effects on the devices' electrical properties. In order to advance the application of such silica-based coatings in the context of neural interfacing, the characteristics of silica sol-gel are further tailored to gain active control of interactions between cells and the coating materials. By incorporating various readily available organotrialkoxysilanes carrying distinct organic functional groups during the sol-gel process, a library of hybrid organosilica coatings is developed and investigated. In vitro neural cultures using PC12 cells and primary cortical neurons both reveal that, among these different types of hybrid organosilica, the introduction of aminopropyl groups drastically transforms the silica into robust neural permissive substrate, supporting neuron adhesion and neurite outgrowth. Moreover, when this organosilica is cultured with astrocytes, a key type of glial cells responsible for glial scar response toward neural implants, such cell growth promoting effect is not observed. These findings highlight the potential of organo-group-bearing silica sol-gel to function as advanced coating materials to selectively modulate cell response and promote neural integration with implantable sensing devices.

Facile Use of Cationic Hydrogel Particles for Surface Modification of Planar Substrates Toward Multifunctional Neural Permissive Surfaces: An in Vitro Investigation

Synthetic materials such as silicon have been commonly used for neural interfacing applications but are intrinsically noninteractive with neurons. Here, a facile approach has been developed to integrate both chemical and topographical cues to impart neural permissiveness for such materials. The approach simply exploits the basic phenomenon of electrostatically driven adsorption of colloidal particles onto a solid material and applies it to a cationic hydrogel particle system that we have developed recently based on "click" reaction of epoxide and amine. The particle adsorption process can be tuned by varying the adsorption time and the concentration of the original colloidal suspension, both of which directly control the surface densities of the adsorbed hydrogel particles. Using the PC12 cell line and primary cortical neurons derived from chick embryo, we demonstrate that the particle-adsorbed surface readily supports robust cell adhesion and differentiation. Although the extent of neural permissiveness exhibited by such particle-adsorbed surface was comparable to the cationic polyethylenimine-coated control surface, the adsorbed hydrogel particles offer a unique reservoir function to the modified surface that is unparalleled by the control. The successful loading of hydrophobic dye of nile red to the surface adsorbed hydrogel particles indicates that the modified surface not only provides physical support of neurons, but also can be explored in the future to exert localized therapeutic actions favorable for neural interfacing.

RAFT polymerization of ciprofloxacin prodrug monomers for the controlled intracellular delivery of antibiotics

Prodrug monomers derived from the antibiotic ciprofloxacin were synthesized with phenolic or aliphatic esters linking the drug to a polymerizable methacrylate group.

Highly Stable, Protein-Resistant Surfaces via the Layer-by-Layer Assembly of Poly(sulfobetaine methacrylate) and Tannic Acid

Zwitterionic materials have received great attention because of the non-fouling property. As a result of the electric neutrality of zwitterionic polymers, their layer-by-layer (LBL) assembly is generally conducted under specific conditions, such as very low pH values or ionic strength. The formed multilayers are unstable at high pH or in a high ionic strength environment. Therefore, the formation of highly stable multilayers of zwitterionic polymers via the LBL assembly process is still challenging. Here, we report the LBL assembly of poly(sulfobetaine methacrylate) (PSBMA) with a polyphenol, tannic acid (TA), for protein-resistant surfaces. The assembly process was monitored by a quartz crystal microbalance (QCM) and variable-angle spectroscopic ellipsometry (VASE), which confirms the formation of thin multilayer films. We found that the (TA/PSBMA)n multilayers are stable over a wide pH range of 4-10 and in saline, such as 1 M NaCl or urea solution. The surface morphology and chemical composition were characterized by specular reflectance Fourier transform infrared spectroscopy (FTIR/SR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Furthermore, (TA/PSBMA)n multilayers show high hydrophilicity, with a water contact angle lower than 15°. A QCM was used to record the dynamic protein adsorption process. Adsorption amounts of bovine serum albumin (BSA), lysozyme (Lys), and hemoglobin (Hgb) on (TA/PSBMA)20 multilayers decreased to 0.42, 52.9, and 37.9 ng/cm(2) from 328, 357, and 509 ng/cm(2) on a bare gold chip surface, respectively. In addition, the protein-resistance property depends upon the outmost layer. This work provides new insights into the LBL assembly of zwitterionic polymers.

Hydrogen-bonded multilayers of tannic acid as mediators of T-cell immunity

Type 1 diabetes is an autoimmune-mediated disease resulting in the destruction of insulin-secreting pancreatic β-cells. Transplantation of insulin-producing islets is a viable treatment to restore euglycemia in Type 1 diabetics; however, the clinical application remains limited due to the use of toxic immunosuppressive therapies to prevent immune-mediated rejection. A nanothin polymer material with dual antioxidant and immunosuppressive properties capable of modulating both innate and adaptive immune responses crucial for transplantation outcome is presented. Through the use of hollow microparticles (capsules) composed of hydrogen-bonded multilayers of natural polyphenol (tannic acid) with poly(N-vinylpyrrolidone) (TA/PVPON) and with poly(N-vinylcaprolactam) (TA/PVCL), proinflammatory reactive oxygen and nitrogen species are efficiently dissipated and the production of interferon (IFN)-γ and tumor necrosis factor (TNF)-α proinflammatory cytokines is attenuated by cognate antigen-stimulated autoreactive CD4+ T cells. These results provide evidence that TA-containing capsules are efficacious in immunomodulation and may provide physical transplant protection and prevent diabetogenic autoreactive T-cell responses. Future studies will determine if xeno- and allotransplantation with (TA/PVPON)- or (TA/PVCL)-coated pancreatic islets will decrease the risk of graft rejection due to attenuation of oxidative stress and IFN-γ, and restore euglycemia in Type 1 diabetics.

Encapsulation of anticancer drug by hydrogen-bonded multilayers of tannic acid

Tannic acid (TA)-based multilayer assemblies have attracted increasing interest for biomedical applications. Here we explore properties of TA-poly(N-vinylpyrrolidone) (TA-PVPON) hydrogen-bonded multilayers for drug encapsulation and long-term storage. We demonstrate that the small molecular weight anticancer drug, doxorubicin (DOX), can be successfully loaded into (TA-PVPON) capsules with high encapsulation efficiency. We have also found that the encapsulated DOX can be efficiently stored inside the capsules for the pH range from pH = 7.4 to pH = 5. We show that the chemical and functional stability of TA at neutral and basic pH values is achieved through complexation with PVPON. The UV-vis spectrophotometry and in situ ellipsometry analyses of the hydrogen bonding interactions between TA and PVPON at different pH values reveal pH-dependent behavior of TA-PVPON capsules for the pH range from pH = 7.4 to pH = 5. Increasing deposition pH value from pH = 5 to pH = 7.4 leads to a 2-fold decrease in capsule thickness. However, this trend is reversed when salt concentration of the deposition solutions is increased from 0.01 M to 0.1 M NaCl. We have also demonstrated that the permeability of (TA-PVPON) capsules prepared using low salt deposition conditions and pH = 7.4 can be increased 2-fold by exposure of the capsules to 0.1 M NaCl salt solutions at the same pH. Our work opens new perspectives for design of novel polymer carriers for controlled drug delivery in cancer therapy.