| 摘要: | 兩性雙離子材料指的是同一個分子鏈上同時帶有正電荷及負電荷的官能基，此材料受重視，因為其材料具有超親水與良好抗生物吸附的特性。在雙離子材料內，最特別的是羧基甜菜鹼(carboxybetaine)材料，其本身具有良好抗生物吸附的特性外，其分子上的羧酸官能基(carboxylic acid)可用於化學接枝(chemical conjugation)，未來可做為功能性生物界面之應用。但是作為廣泛運用為目標的兩性雙離子材料，在分子結構上的設計是相當重要的。曾有學者發現，若羧基甜菜鹼單體內四級胺及羧酸官能基間含有兩個碳間距，在鹼性的情況下，其分子會有霍夫曼消去反應(Hofmann elimination)的現象產生，一旦此現象發生，羧基甜菜鹼就會失去其兩性雙離子材料該有的特性，其抗生物吸附的特性就會消逝，若羧基甜菜鹼作為長期應用，材料本身特性的維持是相當重要的。在本研究裡，我們設計了新型結構的羧基甜菜鹼，期望它在鹼的環境內不會有消去反應的發生，而消去反應通常發生在鏈上β的位置。而本實驗結果，我們在四級胺及羧酸官能基間碳鏈β上的位置增加一個側鏈的甲基，新型高分子單體我們稱之為β-substituted methyl carboxybetaine acrylamide (β-CB-2)，在以surface-initiated atom transfer radical polymerization (SI-ATRP)方法，合成高分子刷(polyβ-CB-2)於substrates表面，以水接觸角、X射線光電子能譜(X-ray photoelectron spectroscopy, XPS)、原子力顯微鏡(atomic force microscopy)觀察其修飾後的表面之親水性質、表面元素分析以及表面粗糙度變化。並藉由革蘭氏陽性菌表皮葡萄球菌(Staphylococcus epidermidis)、陰性菌綠膿桿菌(Pseudomonas aeruginosa)和大腸桿菌(Escherichia coli)做細菌貼附測試，牛血清白蛋白(bovine serum albumin, BSA)、黏蛋白(mucin)、溶菌酶(lysozyme)和牛血纖維蛋白原(fibrinogen)做蛋白質貼附測試，3T3纖維母細胞做細胞貼附測試。結果發現剛合成的 polyβ-CB-2皆有良好抗生物吸附的能力。接著再對polyβ-CB-2做穩定性的測試，發現其在鹼的環境下會有柴瑟夫消去反應(Zaitsev elimination)的產生，形成但有三級胺之高分子結構，在這個消去反應發生後，對其做細菌、蛋白質和細胞貼附測試，發現會失去兩性離子特性，在水接觸角及X射線光電子能譜測試上，表面也有相對疏水及元素的變化。總結上述，本研究驗證分子結構設計對其化學結構的穩定性有很大的影響，可做為未來相關學者設計分子結構的參考依據。;Zwitterions contain both positively and negatively charged moieties in a molecule, which have received much attention because of their unique properties of superhydrophilicity, excellent anti-biofouling properties and diverse structural combinations. In particular, zwitterionic carboxybetaine materials (CBs) attract particular interests from worldwide due to their dual functionalities for antifouling and functionalizable properties with biomolecules to become a functional biointerface. However, a careful molecular design for the zwitterionic structure is needed to ensure the full exploitation in many applications under various distinct conditions. Previous findings showed that carboxybetaine monomers with two-carbon spacer between carboxylate and quaternary ammonium underwent elimination in a basic solution. Once eliminations occur, materials will lose their zwitterionic characteristics, leading to loss of desired antifouling properties. Therefore, the stability of CB materials is very important for long-term applications. In this work, we present a new molecular design to investigate stability of zwitterionic carboxybetaine-based polymers with attempt to avoid the elimination. The elimination reaction originates from the fact that protons adjacent to carbonyl groups are more acidic than other protons due to the hydrogen’s acidity of the β carbon. As a result, in this work, a hydrogen group is substituted by a methyl group in the intercharge arm, which is the carbon space between two charged groups, to afford β-substituted methyl carboxybetaine acrylamide (β-CB-2). In this study, we synthesized polyβ-substituted methyl carboxybetaine acrylamide (polyβ-CB-2) brushes on substrates via surface-initiated atom transfer radical polymerization (SI-ATRP). We applied contact angle goniometer, X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM) to examine the hydrophilicity, the elemental compositions and roughness for the surfaces. The bacterial adhesion tests, protein adsorption tests and 3T3 fibroblast cell adsorption tests were conducted, showing the antifouling ability of the materials. Subsequently, we challenged the stability of the material under the basic surroundings. The results showed that Zaitsev elimination occurred to polyβ-CB-2 films, leading to loss of the fouling resistance against the adsorption of bacteria, proteins and fibroblast. In the contact angle and XPS measurements, changes in the elemental compositions on the surfaces and hydrophobic characteristic happened. Consequently, the goal of this study is to understand a structure-property relationships of CBs on the molecular level, which is valuable for the molecular design for demanded requirements. |
