Assembly Of Poly(Dopamine)/Poly(N-isopropylacrylamide)Mixed Films And Microcapsules

Due to its easy preparation and excellent properties, poly(dopamine)(PDA) coatings are used for surface modification in biomaterials or for other subsequently functional surface modification on it, which has attracted considerable interest for a variety of applications in different biomedicine fields, including drug delivery, tissue engineering or biosensor. In this study, we try to prepare temperature-responsive poly(dopamine)/poly(N-isopropylacrylamide)(PDA/pNiPAAm) mixture films only by mixing dopamine (DA) and pNiPAAm solution. However, there is a fundamental lack of understanding about how PDA is formed and the details of its structure, so the mechanism of PDA formation was disscussed before the assembly of mixture films.In this study, nonionic polymers with different hydrogen acceptor/donor properties were respectively incorporated within a PDA coating. The effects of nonionic polymers on the forming and properties of PDA film were assessed, which gave clues to the understanding of how PDA is formed and the details of its structure. Line or highly-branched pNiPAAm were respectively mixed with PDA coating. In addition, the preparation, compositions and properties of different mixture coatings were demonstrated. Microcapsules in different sizes were assemblied from PDA/pNiPAAm mixtures, and the morphology and permeability were measured. The major contents are as follow:1. Dopamine (DA) was mixed with different nonionic polymers, and PDA/poly(ethylene glycol) and PDA/poly(vinyl alcohol) films were formed, in which poly(ethylene glycol)(PEG) and poly(vinyl alcohol)(PVA) were incorporated within PDA coatings without covalent binding only via noncovalent interactions or physical entrapment. However, poly(N-vinyl pyrrolidone)(PVP) which is with the strong hydrogen acceptor characteristics can suppressed PDA formation. Mixtures of DA with small amounts of PEG or PVA allowed for the coating of the liposomes without affecting the polydispersity of the liposomes. And increasing amounts of PEG and PVA in the mixture with DA led to the aggregation of the samples. However, the presence of PVP in the DA solution hindered the film deposition on the liposomes. Very small amounts of PVP affected the coatings of the liposomes. These findings support the the hypothesis that PDA is formed via noncovalent interactions. PDA/PVA and PDA/PEG films exhibited more transparent than PDA film, and PDA/PVA film was more transparent than PDA/PEG film. The protein absorption on PDA/PVA film was significantly reduced compared to that on the PDA film, and there were no significantly difference about the protein absorption on PDA/PEG and PDA film. The liposomes absorption on PDA/PVP, PDA/PEG or PDA/PVA coatings were significantly lower than that on PDA film. Intact (slightly aggregated) PDA/PEG capsules were obtained, however, the PDA/PVA coating of the silica colloids disintegrated upon core removal, therefore, no capsules were obtained.2. Mixture films of PDA/pNiPAAm-X obtained were independent on the end group of pNiPAAm-X, which demonstrates that the covalent binding is not necessary for the incorporation of polymer within PDA film. The optical densities of PDA/pNiPAAm-X films are lower than that of PDA film. And the ELM results showed that the thickness of PDA/24and PDA/pNiPAAm-NH2/39films were larger than that of PDA/pNiPAAm-NH2/24film; the PDA/pNiPAAm-X films were smoother than PDA film, and the roughness of the formers were lower than that of the latter. With increasing pNiPAAm-NH2amount in mixture films, the roughness decreased and the morphology became less smooth; the protein absorption on PDA/pNiPAAm-NH2/39film decreased with the pNiPAAm-NH2amount increasing in mixture films, independent on the absorption temperature. Liposome absorption on PDA films increased with the increasing PDA assembly temperature. And the amount of myoblast cells adhering to different coatings were similar, and coatings assembled at39℃yielded small and less spread cells compared to the same coating deposited at24℃.3. Highly branched poly(N-isopropylacrylamide)(pNiPAAm-HB) was incorporated within PDA coatings only via physical entrapment. Compared to PDA/24and PDA/pNiPAAm-HB/24coatings, there were more PDA/39and PDA/pNiPAAm-HB/39deposited on silica wafer; the optical densities of PDA/39and PDA/pNiPAAm-HB/39coating was larger than that of PDA/24and PDA/pNiPAAm-HB/24coatings; further, PDA/pNiPAAm-HB/24(39) and PDA/24(39) coatings were with smooth uniform morphology; protein absorption at24℃on PDA/pNiPAAm-HB/39increased with the decreasing content of pNiPAAm-HB in mixture coatings, but the amount of adsorbed proteins was unaffected by the amount of pNiPAAm in the film at39℃; PDA/39, PDA/pNiPAAm/39, and pNiPAAm/39were found to be successful capping layers for Lzw-and L+-containing films. Similar numbers of hepatocytes, macrophages, and myoblasts were adhering to these liposome-containing films. The internalization of fluorescent lipids from the surface by adhering cells was found to be dependent on the capping layer, the type of cells, and the type of carrier liposome, with PLL/PMA/L+/pNiPAAm-HB and myoblast showing the overall highest CMF after4h of adhesion time in all samples.4. Stable non-aggregated PDA, PDA/pNiPAAm-X and PDA/pNiPAAm-HB microcapsules in different sizes were obtained by using5μm,2.5μm and800nm template particles. For microcapsules from5μm template particles:when DA in1mg ml-1,microcapsules assembly from DA/pNiPAAm-X or DA/pNiPAAm-HB mixed was much stable compared to PDA capsules. With DA in2mg ml-1, microapsules assembled from DA only had scaly appearance, while when mixed with pNiPAAm-NH2, the polymer membrane looked smoother; when DA in3mg ml-1, microapsules assembled from DA and DA/pNiPAAm-X had similar smooth appearance. The membrane thickness of capsules assembled from2mg mL-1DA showed significant differences. The addition of pNiPAAm-NH2to the coating yielded a～10nm thicker membrane as compared to DA only and a～5nm thicker membrane as compared to DA with pNiPAAm-COOH. For microcapsules assembled from3mg mL-1DA, the membrane thickness was similar with that of microcapsules added pNiPAAm-X. Further, keeping the wt%between DA/pNiPAAm-HB constant but increasing the amount of DA led to thicker capsules. On the other hand, when keeping the DA concentration constant (2mg mL-1) but varying the wt%between DA/pNiPAAm-HB yielded the thickest microcapsules for the lowest amount of pNiPAAm-HB (DA/pNiPAAm-HB2/1wt%). Because of the shorter assembly time, the microcapsules from2.5μm and800nm templets were thinner than that from the5μm templet. Both DexFITC and FC can permeat into microcapsules, and the size and thickness of microcapsules had effects on the permeability of microcapsules. Liposome Lzw were coated with PDA, PDA/pNiPAAm-X orPDA/pNiPAAm-HB,but no stable non-aggregated nanocapsules were obtained by removing the liposome templet.