Properties of Dopamine in Chemistry

Properties of Dopamine in ChemistryChapter 2. Literature Review2.1 IntroductionIn recent years, natural adhesion has attracted increase attention in the material engineering field. This can be mainly attri besidesed to the marine mussel as it has a strong ability to attach to non-homogeneous surfaces in an aqueous milieu w present they reside. These surfaces vary from natural to synthetic, and inorganic to organic.49-51 Previous studies on the mussel sticky protein have disc everywhereed that 3,4-dihydroxy-L-phenylalanine-lysine sequences, may be the main contributor for the versatile nature of the marine mussel.52, 53 Dopamine, having a similar structure with this sequence, may provide a brisk plat take a crap for bioengineers to physiologicly or chemically enhance the per configurationance of other biomaterials. some(prenominal) papers have already been published regarding the use of dopamine to augment other biomaterials, such as poly (ethylene glycol), carbon nanotubes and nanofibers. The world-class part of this review will briefly introduce the basic properties of dopamine which will be followed by its applications2.2 Properties of DopamineDopamines properties can be change integrity into chemical and adhesive properties. The chemical properties mainly focus on the autopolymerization in aerated basic solutions and polymerization of dopamine unintellectuald on vinyl groups. The adhesive property is dopamines most significant feature which gives dopamine its advantage as a biomaterial.2.2.1 Chemical Properties2.2.1.1 Autopolymerization in Aerated Basic SolutionsMessersmith and coworkers first describe that dopamine is able to auto-polymerize in aired Tris buffer of pH 8.5.8. The process of dopamine autopolymerization with a pre-existing substrate go aways in polydopamine (PDA) films being deposited on the substrate surface. semipermanent substrate exposure times and higher(prenominal) reaction temperatures result in thicker PDA films being form ed.54 Regardless of the surface type, the inserted PDA films can be cover on the desired surface, even poly(tetrafluoroethylene) (PTFE), known for its anti-adhesive property.82.2.1.2 Polymerization of Dopamine Based on Vinyl GroupsPolymers carrying pendant dopamine are normally obtained by stem turn polymerization of vinyl monomers with protected or unprotected dopamine. When meditating protected dopamine carried by polymers with double b unitary, borax (Na2B4O710H2O) is widely utilize as the protecting reactant in hunting lodge to keep dopamine from forming an annular bidentate catechol subunit.55 Normally, the polymerized reaction of protected dopamine happens in a liquid solution and forms linear chains. Deprotection reaction usually occurs in an acidulousic environment and results in the polymer carrying dopamine. Dimolybdenum trioxide56, 1-dromotoluene57 and denzophenone chloride58 can also be used as protecting agents. Zhang et al.59 material bodyed a novel polymer poly (n-acryloyl dopamine) that possesses high adhesion to wood, especially when mixed with polyethylenimine (PEI) at about 150C. They used a protected double bond dopamine as a monomer and 2,2-azobis(2-methylpropionitrile) as an instigator via root polymerization, following the deprotection of dopamine in an acid solution. When meditating unprotected dopamine, Lee BP et al.60 was the first to report a creative hydrogel that copolymerizes modified dopamine with double bond and polythene glycol diacrylate via photo initiation by using a 2,20-dimethoxy-2-phenyl-acetonephenone (DMPA) initiator. As a result of this invention, greater attention has been given to hydrogels as a new maudlin extracellular matrix (ECM) in the biomedical field. Dopamine belongs to the catechol family which leads to vinyled dopamine to act as an tameor.61, 62, as a result they can react with radicals to inhibit polyreaction. The unprotected dopamine, modified with a vinyl group, is able to undergo free-radical po lymerization. Several researches have done this experiment on radical polymerization to prove the dependableness of this method.63-75 The research group led by Metin Sitti, copolymerized a dopamine derivate (dopamine meth-acrylamide) with methoxyethylaceylate to obtain a reversible adhesion on the surface of nonflat glass under ironic or wet condition.65 In another publication, 2-(meth-acryloyloxy) ethyl phosphate was used to copolymerize with dopamine methacrylamide, followed by a complicated cohesion in which the copolymer bonded with positively supercharged polymer, divalent calcium and magnesium.71 The chemical properties of dopamine provide the platform of its strong adhesive properties.2.2.2 Adhesive PropertyThe adhesive property of dopamine is one of the most significant properties of dopamine as it has proved to be very versatile in adhering to various surfaces despite the surface chemistry. The bonding between dopamine and surfaces can be generally distributed to two pa rts covalent and non-covalent.10Surfaces which possess amine groups or thiol groups can covalently hold in to dopamine via Michael addition or Schiff base reactions. However since most surfaces dont have those groups, non-covalent bonding, like H-bond, - interaction and benzenediolcharge-transfer compounds are preferred to generate a valid layer and metallic chelating.7, 53, 76-87 In a high pH environment, metal ions and medal oxides have a high chance of being hydroxylated or hydrated, which make chelate with catechol groups of dopamine overmuch easier. This can be seen from many experiments done on polydopamine linking with metal oxides (such as Fe2O3, Fe4O3, ZrO2) through chelating bonding interaction.82, 84, 85 This can be seen when polydopamine nanoparticle suspensions are added to a solution of KMnO4 with H2SO4. A core-cuticle nanoparticle structure is created in which the polydopamine act as the core and MnO2 act as shell, followed by blending the KOH solution to obtain MnO 2 nanospheres. This adhesive property of dopamine provides brilliant opportunities for new bioengineered materials.2.2.3 CNTFor decades, carbon nanotubes (CNT) have been attracting increasing attention because of their superior features, such as thermal conductivity, excellent tensile strength and remarkable conductivity. They have been use in various different areas, from sensors to catalysis, and from semiconductors to inductors for osteocytes. In order for CNTs to have a wide range of applications, surface modification is necessary. However, during this modification various intermediate reactions locomote are required which increase the complexity of the CNTs fabrication. Dopamine modification has been viewed as an promising alternative, leading to a cover multifunctional CNT with a polymeric shell that has tunable thickness by time, pH value and temperature.88 The dopamine covering facilitates the addition of alternate modifications to the surface of CNTs, such as gold nanopa rticles.88 Whats more, CNTPDAs, first, were modified with ATRP initiator and then polymerized with diethylamine methacrylateto to form brushes polymer poly (dimethylamine-thyl methacrylate) (PDMAEMA) on the surface.89 Following that the functionalized CNT were quaternized in order to combine palladium nanoparticles on the CNTs surface. These two examples indicate the capability of dopamine coated CNTs to view as to metal complexes.2.3 ApplicationsThere are many different applications in which dopamine could be applied in three of them will be the focus here including applications in hydrogels, nanofibers, and biosening. These fields are of great interest currently as they show great promise for dopamine in bioengineering.2.3.1 HydrogelThe need of a pasty hydrogel, as a unique material, is dramatically increasing in various biomedical fields. The high performance requirements of adhesive hydrogels are strict and various. This includes being sufficiently adhesive in a wet environme nt, satisfactory elasticity of artificial tissue scaffold and biocompatible.60, 90 Moreover, biomedical hydrogels also need a quick sol-gel changeover for avoiding surgical obstruction. Recently, adhesive hydrogel, inspired by strong wet adhesion of mussel and cross-bonding capabilities of dopamine, has been attracted increasing attention and considered as a hopeful candidate to fulfill this technologic niche.91Messersmith et al.92 reported the creation of four different adhesive hydrogels using dopamine differential coefficient (L-3,4-dihydroxyphenylalanine (DOPA)) as end-groups and poly(ethylene glycol) (PEG) as a backbone. The difference of these four hydrogels can be divided into 2 subcategories, linear network and branched network. They applied multiple-angle laser light scattering to study the influences of different oxidative reagents on DOPA oxidation and hydrogel formation. The result showed that gelation time of PEG-DOPA gels relied on oxidative reagents, such as concent ration and type. In Lee H.s report, they also used DOPA and PEG to form hydrogels, but this time they used DOPA modified with methacryloyl chloride and PEG diacrylate instead of pure DOPA and PEG. In order to avoid introducing toxicity of oxidative reagent to the hydrogels and any sack of adhesion, the hydrogels underwent UV initiation.60 These photo-imitated gels demonstrate appreciable elastic properties for use as a promising biomedical material. Using a similar method Phillip B. Messersmiths research group also synthesized an adhesive hydrogel, prepared by copolymerizing DOPA with hydrophobic segments of an amphiphilic block copolymer under photo-imitation. The adhesive property of the hydrogel was surprisingly improved in the bearing of DOPA in wet condition. The elasticity of the hydrogel was found to be similar to that of soft tissues leading to consider it as a encouraging candidate for biomaterial.93 push research conducted by Messersmith and coworkers focused on the biolo gical capabilities of dopamine-PEG adhesive gels. In 2010 they reported that DOPA as end-caps covalently bonded with an amine-terminated 4-arm PEG. The PEG was the core in which oxidative reagents (NaIO4) were added to form an adhesive hydrogel in less than 1 minute.94 The results of the in vivo test, performed in a murine model, showed the adhesive gels caused minimal inflammation and were stably interfaced with the surrounding tissues for more than 24 months. To form a catena degradable adhering polymer, three materials were reacted to form a semblable branched polymer, including dopamine derivative as end-group, PEG and polycaprolactone (PCL) as a backbone.95 These polymers are able to form films whose properties, such as swelling capacity and biodegradation, were flexible by changing the ratio, or concentration of these reactants or by adding other additive agents. After coating these adhesive polymers on a biologic meshes, stronger water-resistant was exhibited when compared wi th fibrin sealant or cyanoacrylated polymers.95 Applications for this biomaterial can be extended in the surgical field for hernia repair.Stewarts group published several papers about adhesive hydrogels based on complex cohesion. In 2010 they created a bio-mimic hydrogel blending with revised gelatin and a copolymer which is obtained by a dopamine derivative reacting with monoacryloxyethyl phosphate in an alkaline condition.71 The addition of Ca2+ and Mg2+ to the bio-mimic hydrogel could significantly improve the coacervation of the hydrogel, which was applied to tune agglomeration temperature to dead body temperature. The result demonstrate that the cohesion interaction was biodegradable, perfectly suited for medical applications. In another similar research, an adhesive hydrogel was synthesized by complicated cohesion of a positively charged copolymer and a terpolymer involving a dopamine derivative when its pH was higher than 4.70 The bonding property of the hydrogel to hydroxyl apatite was around 40% of common cyanoacrylate glue. T.G. Parks group demonstrable a temperature sensitive and injectable tissue-attachable hydrogel.96 The hydrogel was synthesized by conjugating hyaluronic acid and dopamine, following by cross-linking with thiol tail-ended Pluronic F127 via Michael addition. The hydrogel precursor exists at room temperature, and a cured hydrogel is formed when brought to a temperature of 37C. In a later paper, they used a similar strategy forming hydrogel by blending a dopamine derivative modified chitosan with thiol-capped Pluronic F127 at body temperature.97 The adjustable gelation time of this block copolymer made it suitable for tissue-repair at 37C. The resulting hydrogel dedicated excellent in vivo results, where chitosan served as hemostatic agent and dopamine derivative group acted as adhesive agent to soft tissues.2.3.2 NanofiberTissue engineering tends to use nanofiberous biomaterials instead of a micropores matrix since the filiform and polyporous nanolevel structure allow for artificial extracellular matrix to enhance the fundamental cellular procedures.98 Nanotechnology reformation have aided in the development of techniques for the production of such a nano-composite materials.Electro-spinning has recently obtained increasing attention, attributing to its briefness and facility for nanofiber fabrication. Through this technique, fibrous structures are comfortably tuned in order to coordinate it with the extracellular matrix (ECM).99, 100 So far, this technique has been studied in a range of biological fields, such as bone and skin regeneration.The artificial polymer ECMs usually have difficulties with interfaced reactions between tissues and materials.101 For electro-spinning nanofibers in applications of biomedicine, it is necessary to physically and chemically combine them with biomolecules or cell-recognizing ligands.102 This subsequently provides bio-modulating or biomimetic micro- environments to contactin g cells and tissues. Dopamine coating can be considered as a simple and versatile approach to modify various synthetic polymers so that they are able to serve in biomedical applications.49-51 Ku and coworkers103 firstly reported culturing clement endothelial cells on a polydopamine treated electro-spun polycaprolactone (PCL) nanofiber membrane. They used two control groups, pure PCL nanofibers and PCL nanofibers coated with gelatin, to investigate the ability of cell attachment of dopamine. The result of the water contact angle demonstrate that polydopamine uniformly was coated on the PCL nanofibers. Polydopamine also significantly improve endothelial cells attachment on the nanofiber, compared with other non-adhesive substrates. Moreover, endothelial cells culture on PCL nanofibers coated by dopamine had develop cytoskeleton, positive PECAM-1 and vWF expressions and high cell extend.Rim and coworkers104 intentional dopamine functionalized electro-spinning poly(L-lactide) (PLLA) nanofibers with minimal influence on its mechanical performances, like wetting capability and roughness. The polydopamine coated PLLA nanofibers significantly raise cell attachment and the degree of spread, contradistinguishing with pure PLLA nanofibers. Meanwhile, its fibrous morphology had changed to more of a polygon shape instead of sphere after the polydopamine coating, which lead to higher DNA content of polydopamine treated PLLA nanofibers. The higher gene expressions of cells cultivated on polydopamine treated fibers indicated better osteogenic differentiation and vasculogenesis.Extensive research regarding the chemical or physical coating of metal on the surface of scaffolds to increase tensile strength has been done.105 Jungki Ryu et al.106 used dopamine to process hydroxyapatite deposits on PCL nanofiber by coating it. The result demonstrated a combination of surface activation through dopamine coating and hydroxyapatite mineralization allowing the hybridization of vari ous shapes and surfaces. In other reported, Xie and coworkers107 considered dopamine as a superglue, allowing minerals to easily attach to fibrous surfaces. The mechanical properties of mineral functionalized electro-pinning PCL nanofibers, such as stiffness, durability and tensile strength, were near to that of natural bone. Dopamine coated nanofibers show an improvement on existed biomaterials such as their mechanical performances, and cell adhesion. This makes them quite suitable for tissue regeneration and other related bioengineering applications.2.3.3 BiosensingThere is an enormous demand to design highly sensitive and selective biosensors for multiple applications, such as diagnostics, drug screening, and drug discovery.108 Biosensors usually are in the microscale or nanoscale109 and there are legion(predicate) methods to develop them, such as DNA110 and antibody-based sensor111, 112. Scientists employ dopamine in order to optimize biosensors capabilities which have been rep orted by several research groups.Lui and coworkers first reported that dopamine could be used in a biosensor.113 They used galvanizingity to oxidize dopamine to form polydopamine on a gold galvanizing pole with existing nicotine. The dopamine-imprinted sensor showed outstanding selectiveness of nicotine and excellent repeatability. Furthermore, Ouyang and coworkers developed a one-step well-defined structure of a dopamine-imprinted sensor.114 They applied electro-polymerization of o-phenylenediamine (o-PD) and dopamine with existing glutamic acid (Glu). By using a potentiostatic time scan, the sensor exhibited satisfactory stereo selectiveness of bonding L- or D-Glu because their relative synthetic receptor. In a different publication, they designed protein imprinted nanowires which dopamine was also involved.115 First, the protein-coupled alumina membrane was immersed in dopamine solution followed by an ammonium persulfate solution in order to self-polymerize polydopamine in whic h afterward the remotion of the attached protein is necessary. The nanowires demonstrated constant bonding capability and selectiveness of template proteins due to their cavity structure with bonding spots (like amino group, hydroxyl, - stacking and van der Waals force) that can bind with protein. In another research, Zhou et al. display the creation of magnetic nanoparticles coated by imprinted polymer with a pre-existing template protein.116 The nanoparticles are able to separate butt joint protein from the mixture. In order to investigate the versatility of the imprinted nanoparticles, they operated on a binding test by using five different proteins excluding the template protein. The result indicated that more than 80% of target proteins were rebinding with imprinted nanoparticles, suggesting imprinted nanoparticles have a bright future to be employed for separating and detecting specific protein.One of the greatest difficulties for biosensors is how to immobilize enzymes on th e surface of an electric pole and preserve the enzymes functionalities. Wei et al. designed a novel glucose electrochemical sensor, prepared by using a polydopamine film to entrap glucose oxidase and gold nanoparticles.117 Their research displayed a polydopamine matrix embedded with gold nanoparticles that had high efficiency of immobilizing glucose oxidase. The dopamine film embedded gold nanoparticle biosensor showed a superior sensitivity, good repeatability, linear over broad dynamic range and a low detective threshold. Furthermore, in order to assess adaptability of this sensor, they use it to test glucose concentration in attenuated human serum. The result suggested this biosensor is an attractive material for clinical applications