包覆離子之奈米生醫材料於牙本質小管滲透及結晶機制之探討

Abstract

牙本質小管的暴露是導致牙本質敏感症與牙髓細菌感染的關鍵因素。目前的臨床治療與居家保健的策略多依賴使用生物活性的材料，如生醫玻璃或鈣鹽等，透過離子釋放與沉積，達成牙本質小管封閉，然而，此類材料多需在極端酸性環境下作用才有較好的治療成效，這容易導致牙齒硬組織結構的去礦化，且或因離子擴散受限而僅能形成較為淺層且容易脫落的封填，難以達到持久的治療效果。本研究旨在釐清無機離子於牙本質小管內的滲透模式與其機制，並依據此，開發新型奈米載體系統，以實現在中性生理條件下較短反應時間的深層封填，並期望能同時具備抗菌或是誘導牙本質再生等多重功效。 首先，本研究透過人口外牙製備的離子滲透模型，經統計分析系統性探討了pH值、離子電荷與分子量等對牙本質小管滲透效率的影響(第一部分)。研究發現，環境pH值是調控離子傳輸的主導因子。在鹼性環境下，小管壁上的醣胺聚醣去質子化後帶有高密度負電荷，形成雙電層並強烈吸附鈣、鍶等二價陽離子，顯著阻礙其深層擴散；反之，酸性環境雖能促進滲透，卻伴隨脫礦風險。此外，各元素的族、分子量、電性與電量也對牙本質小管內的離子滲透具有顯著的選擇性，如分子量較小、帶電量接近電中性的鈉元素，存在各酸鹼條件下，最佳的滲透成效。這些發現確立了電荷屏蔽與中性操作環境作為開發下一代牙本質封填製劑的關鍵設計原則。 基於對於離子滲透的分析，已成功開發一系列攜帶離子的微脂體(Liposome)專利製劑，並證實奈米劑型遞送系統有利於牙本質內藥物遞送，但是這些天然磷脂基底的製劑仍需要較長的滲透與結晶時間，且微脂體並不具備抗菌成效，故本研究進一步開發攜帶離子的奈米載體系統，希望透過不同分子結構的引入，強化牙本質小管內的封填與殺菌應用成效。 因此，本研究的第二部分利用三種不同分子結構大小的環狀糊精(Cyclodextrins)作為奈米載體，透過其特殊的空腔結構與鈣、鍶離子形成近電中性的奈米複合物。此部分的實驗證實，α-環狀糊精複合物能有效規避小管壁的靜電阻力，在中性環境下深入小管達 40 微米並形成緻密的礦化封填，同時展現優異的細胞相容性、針對三種口腔病原菌的抑制能力與牙髓幹細胞的誘導分化能力。 為突破滲透深度的限制，本研究進一步探討了線性的聚乙二醇(Polyethylene glycol，PEG)與其衍生物作為離子載體的潛力，本研究選用五種分子量的PEG，搭配兩種官能基的修飾作為材料。研究顯示，低分子量 PEG 具備優異的滲透壓效應與低黏度特性，能攜帶鍶離子深入小管達 140 微米，遠高於現行研究所報導的封填深度。而雖引入丙烯酸(AAC)官能基可增強晶體調控與抗菌性，但也伴隨滲透深度降低與細胞毒性增加的權衡，證實低分子量且電中性的 PEG 為較佳的載體選擇。 總結而言，本論文透過基礎機制的釐清，闡明牙本質小管內的離子滲透模式，並成功開發了環狀糊精與PEG兩類奈米載體系統，克服了傳統材料依賴極端pH值的局限，並實現兼具快速滲透、深層礦化礦化、抗菌成效、並誘導活髓分化的複合治療模式，未來可提供暴露牙本質小管衍生疾病之科學依據，作為治療策略的重要參考。

The exposure of dentinal tubules is a critical factor leading to dentin hypersensitivity and pulpal bacterial infection. Current clinical treatments and home-care strategies primarily rely on bioactive materials, such as bioactive glass or calcium salts, to achieve tubule occlusion through ion release and deposition. However, these materials often require highly acidic environments to achieve optimal therapeutic efficacy, which poses a risk of demineralizing the tooth. Furthermore, limited ion diffusion often results in the formation of shallow and easily dislodged seals, making it hard to develop durable therapeutic effects. This study aims to elucidate the penetration modes and mechanisms of inorganic ions within dentinal tubules. Based on these findings, the study develops novel nanocarrier systems capable of achieving deep occlusion within relatively short reaction time under neutral pH conditions, while simultaneously providing multifunctional benefits such as antibacterial properties or the induction of dentin regeneration. First, this study systematically investigated the effects of pH, ion charge, and molecular weight on dentinal tubule penetration using an ex vivo human dentin disc ion penetration model and statistical analysis (Part 1). The results indicated that environmental pH is the dominant factor that regulating ion transport. In alkaline environments, glycosaminoglycans on the tubule walls deprotonate and carry a high density of negative charges, forming an electric double layer that strongly adsorbs divalent cations, thereby significantly hindering their deep diffusion. Conversely, while acidic environments promote penetration, they are accompanied by the risk of demineralization. Additionally, the group, molecular weight and charge of elements showed significant selectivity regarding ion penetration within dentinal tubules. Therefore, sodium with smaller molecular weight and a charge closer to neutral demonstrated the best penetration efficacy across various pH conditions. These findings established charge shielding and neutral operating environments as key design principles for the development of next-generation dentin sealing agents. Although a series of patented ion-carrying liposome formulations were successfully developed based on this ion penetration analysis, confirming that nano-delivery systems facilitate intra-dentinal drug delivery, these natural phospholipid-based preparations require longer penetration and crystallization times, and liposomes lack intrinsic antibacterial properties. Consequently, this study further developed two types of polymer-based ion carrier systems, aiming to enhance tubule sealing and disinfection efficacy through molecular structure design. Therefore, the second part of this study utilized cyclodextrins (CDs) of three different molecular sizes as nanocarriers. Through their unique cavity structures, they formed near-neutral nanocomplexes with calcium and strontium ions. Results confirmed that α-cyclodextrin complexes effectively evaded the electrostatic resistance of the tubule walls, penetrating up to 40 μm into the tubules under neutral conditions to form occlusion. Simultaneously, they exhibited excellent cytocompatibility, inhibitory capabilities against three kinds of oral pathogens, and the ability to induce dental pulp stem cell differentiation. To further overcome the limitations of penetration depth, this study investigated the potential of linear polyethylene glycol (PEG) and its derivatives as ion carriers. Five molecular weights of PEG were selected, combined with two types of functional group modifications. The research showed that low-molecular-weight PEG possesses excellent osmotic effects and low viscosity characteristics, capable of carrying strontium ions deep into the tubules up to 140 μm that far exceeding the sealing depths reported in current research. Although the introduction of acrylic acid (AAC) functional groups enhanced crystal modulation and antibacterial properties, it involved a trade-off with reduced penetration depth and increased cytotoxicity, confirming that low-molecular-weight, electrically neutral PEG is the superior carrier choice. In conclusion, by clarifying fundamental mechanisms, this thesis elucidates the modes of ion penetration within dentinal tubules and successfully develops two nanocarrier systems: cyclodextrins and PEG. These systems overcome the limitations of traditional materials that rely on extreme pH levels, realizing a composite treatment mode that combines rapid penetration, deep mineralization, antibacterial efficacy, and the induction of vital pulp differentiation. These findings provide a scientific basis for addressing diseases derived from exposed dentinal tubules and serve as a significant reference for future therapeutic strategies.