膠原蛋白是人體內含量最多的蛋白質，因具有高生物相容性、低細胞毒性等特色，常應用於生物相關領域，包括細胞修復、藥物傳輸等，其基本結構為第二型聚脯胺酸構形所形成之三股螺旋。穩定三股螺旋的作用力有很多種，包括氫鍵、靜電作用力、疏水作用力等；cation-π作用力即是由正電與芳香環系統所形成之非共價作用力，根據實驗室過去之研究，此作用力對膠原蛋白穩定度也有很大的貢獻。
在第一部分中，參考過去研究之RG(POG)10F，希望能藉由增加頭尾cation-π作用力或置換賴胺酸與戊二醛進行交聯反應，幫助膠原蛋白模擬胜肽自組裝成大型結構，並進一步形成水凝膠。而實驗結果顯示，雖然cation-π作用力可以增加三股螺旋穩定度，但仍無法促使水凝膠之形成；而利用賴胺酸與戊二醛交聯雖有助於水凝膠的生成，但仍不足以形成穩定的水凝膠。
在第二部分中，參考Hartgerink教授與Fei Xu教授之研究，想探討不同胺基酸組合以及不同位向之cation-π作用力對於三股螺旋穩定度的影響。根據實驗結果顯示，以胺基酸種類而言，精胺酸與苯丙胺酸及酪胺酸的cation-π作用力強度相似，而與色胺酸的作用力則較弱，與實驗室先前研究結果符合；以cation-π作用力位向而言，將三股螺旋N端朝上擺放，帶正電胺基酸位於上方，芳香環胺基酸位於下方之正向軸向作用力最大，其次為徑向作用力，最弱為芳香環胺基酸位於上方，正電胺基酸位於下方之負向軸向作用力。從實驗結果可看出，作用力的方向對於作用力的強弱有很大的影響，同樣的胺基酸若擺放的位置不同，產生的作用力也可能會有所差別，故設計胜肽時也須考慮此因素，希望此結果能幫助未來的研究進行。

Collagen is the most abundant protein in human body. Since collagen has high biocompatibility and low cytotoxicity, it is often used in biological related fields, including cell repair, drug delivery. Collagen is a triple helix composed of three polyproline-II chains. Various forces can be used to stabilize the triple helix, including hydrogen bonds, electrostatic interactions, hydrophobic interactions. According to our pervious study, cation-π interaction, the noncovalent force between a positive charge and aromatic π-system, was also shown to play an important role in stabilizing collagen.
In the first part, based on the peptide RG(POG)10F, we attempted to promote the collagen peptide self-assembly into large-scale structures and hydrogels by implanting multiple cation-π interactions or the interchain cross-linking via lysine-glutaraldehyde reactions. The results show that cation-π interactions can stabilize the triple helix and promote the self-assembly, but are not strong enough to assist the formation of hydrogels. Although the cross-linking can increase the forming propensity of hydrogels, the strength is not sufficient to form stable hydrogels.
In the second part, according to previous studies, we explored the cation-π interactions of different cationic-aromatic pairs within the collagen triple helix, and investigated how the orientation of cation-π interactions affects collagen stability. The results show that the strength of the cation-π interaction between arginine and phenylalanine or tyrosine is similar, but the interaction between arginine and tryptophan is weaker, which is consistent with our previous results. Considering the orientation of the cation-π interaction, when the N-terminus of the triple helix is placed on top, and positively charged amino acid is located above the aromatic amino acid, this is assigned as the positive axial interaction. In contrast, the negative axial interaction is assigned when the aromatic amino acid is located above the positively charged amino acid. The strength of the positive axial interaction is greater than that of the lateral interaction, and the lateral interaction is stronger than the negative axial interaction. The results show that the orientation of the cation-π interaction has a large influence on its strength within the triple helix.

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