Dopamine Modified Polyelectrolyte And Its Construction Of Self-assembled Multilayers Inspired By Marine Mussel

Marine mussels have excellent properties of biocompatibility, water-endurance adhesion and easy attachment on varied surfaces (eg. metal, glass, teflon, etc.). Furthermore, this super adhesion could even suffer the harsh marine environment. The universal adhesion of the marine mussel's adhesive proteins (MAPs) could be applied on modification of varied surfaces and this natural resource won't harm human cells nor cause immune response. MAPs are ideal candidates for medical adhesives. The layer-by-layer (LbL) self-assembly technique has been extensively developed as a tool for the preparation of multilayers by the alternating adsorption of cationic and anionic polyelectrolyte solutions. This technique has unique advantages such as mild and eco-friendly process, rich membrane candidates, universal shapes of substrates and tunable physical-chemical properties of films, which all make it an important method in biomedical applications. In recent years, there has been great interest in the use of multilayers containing biomimetic polyelectrolytes due to the low toxicity and good modification efficiency.In this paper, poly(acrylic acid) (PAA) was chosen as polymer backbone and dopamine as the donor of functional catechol groups for synthesizing the high performance material, PAADopa. Influences of metal-chelating, crosslinking degree, curing temperature etc. were studied on adhesives and further manipulation of pH could change the adhesive into hydrogel. Then, PAADopa and polyethylenimine (PEI) were used to assemble layer-by-layer films. Influences on the construction process and physical-chemical property were studied to reveal mechanisms of interactions. Main work and conclusions as follow:1. Poly(acrylic acid) (PAA) and dopamine were used as raw material for the reaction in 1-Methyl-2-pyrrolidinone (NMP) solution. By the complexation of borate and catechol groups, the functional Dopa groups were protected reversibly to get PAADopa product, which prevented the metamorphism of Dopa during the amidation reaction. FT-IR proved the successful synthesis of PAADopa qualitatively. 1H NMR and UV-vis were introduced to calculate the grafting ratio of Dopa groups, respectively. The grafting ratio ranges from 15% to 40%.2. PAADopa-Zn adhesives could form adhesives at pH 4 and hydrogels at pH 8.5. By manipulating the crosslinking degree, rheological properties were controlled to reach the optimized performance of adhesives at pH 4. After changing the curing condition, adhesives were found with high adhesion both under dry and wet curing method. Besides, this system responses to pH changes. By increasing pH to 8.5, adhesives could change into hydrogel with good self-healing and mechanical properties.3. PAADopa and polyethylenimine (PEI) were chosen as polyanion and polycation to form layer-by-layer films on surfaces. Quartz crystal microbalance with dissipation (QCM-D) detected the multilayer assembly in-situ and AFM observed the surface morphology both in dry and wet environment. By comparing with the control experiment of PEI/PAA multilayers, the PEI/PAADopa ones were found to grow in a faster mode and surfaces were much rougher, which proved Dopa's contribution to high mass uptake and rougher structure forming. Under high salt condition (0.6M NaCl), multilayers of PEI/PAADopa grow to ?m-scale, which showed a stable structure. Besides, by increasing pH from 4 to 8.5, Young's modulus decreased, which make it possible to manipulate the mechanical property of multilayers by changing pH.4. PEI/PAADopa-Zn multilayers were assembled and QCM-D was used to detect the in-situ construction. Firstly, different crosslinking degrees of PAADopa-Zn were studied on adsorption kinetics and structural changes. It was found that at the optimum crosslinking ratio (Zn/Dopa= 2), multilayer reached the high adsorption and more compact structure, which was used in the flowing study. Comparing with the (PEI/PAA-Zn)8 multilayers, the (PEI/PAADopa-Zn)8 ones were found to grow in an exponential way with rougher surfaces, which further confirm the Dopa contribution to film construction. Besides, PEI/PAADopa-Zn multilayers could coat on various surfaces (Ti, Al2O3, SiO2, Au) showing similar hydrophilicity, which make the method a universal coating approach. Furthermore, pH could trigger the changes of mechanical property of this multilayer.5. By increasing the salt concentration in solution (0-0.6 M NaCl), mass uptake of PEI/PAADopa-Zn multilayers increased with a relatively stable structure. Under high salt concentration (0.6 M NaCl), there is an pronounced "odd-even" effect, a regular change of surface thickness and roughness by alternating PEI and PAADopa-Zn on the outer part of films. This effect is aroused by the different structure between the compact PAADopa-Zn layer and the loose PEI layer.