A nanoporous small Anodic Aluminum Oxide (AAO) tube for long-acting drug release

Abstract

The objective of this study is to develop a long-acting and implantable drug-release device that can effectively control the release rate and concentration of the loaded drug. The proposed device consists of a tubular nanoporous anodic aluminum oxide (AAO) encapsulating a microporous chitosan/collagen composite. The nanopore size of the AAO tube can be modified by adjusting the anodization parameters, which in turn adjust the release rate and concentration, while the microporous chitosan/collagen composite provides the long-acting release feature. Fabrication results indicate that the AAO tube has a uniform pore arrangement with a pore size around 50 nm. The synthesized microporous chitosan/collagen composite containing 90% chitosan yielded the highest moisture content and was therefore used as the drug carrier. Release experiments demonstrate that the proposed long-acting drug-release device had released less than 65% of the loading drug on the 17th release day. We then applied the proposed long-acting drug-release scheme as a recombinant human-bone morphogenetic-protein 2 (rh-BMP2) release device to induce differentiation of pre-osteoblast MC3T3-E1 cells into osteoblasts. Results from alkaline phosphate (ALP) and alizarin red S assays demonstrate that the total amount of rh-BMP2 consumed by the proposed AAO tube is much less than that consumed using the conventional culture approach. Furthermore, our approach has the advantage of requiring only one-time dosing, whereas the conventional approach requires the periodic renewal of rh-BMP2. AAO's one-time dosing feature combined with its biocompatablity and biodegradability can be beneficial in real implant applications.

本研究開發出一新型低成本且具長效型之奈微米藥物釋放裝置，其主要由具奈米孔洞之陽極氧化鋁圓管以及具微米孔洞之幾丁聚醣/膠原蛋白薄膜所組成。首先，以不銹鋼外環電極為陰極，並於外環電極中心處以橫置放方式將放置純度98.6%之3003鋁錳銅合金管置中，封裝後接上陽極以進行環型陽極氧化製程，以0.3 M之草酸為蝕刻液，於溫度0C之工作環境下施以30 V之定電壓，進行陽極氧化製程24小時，經移除未氧化之鋁合金後再以濃度為之30%之H3PO4去除背阻障層，產生具貫穿之奈米孔洞之陽極氧化鋁管。接著以冷凍乾燥法製作具微米孔洞之幾丁聚醣/膠原蛋白薄膜。最後，將經冷凍乾燥後之幾丁聚醣/膠原蛋白薄膜將做為藥物包埋之載體，包埋藥物後並置入具奈米孔洞陽極氧化鋁管中後，進行封裝完成本裝置。 本研究所製備出之陽極氧化鋁管其孔洞排列與大小具均勻性其平均孔徑約為50 nm，而幾丁聚醣/膠原蛋白薄膜藉由調整兩者不同混和比例可製備出最大173.12±26.89 μm以及最小34.20±8.0 7μm之微米孔洞。包埋於幾丁聚醣/膠原蛋白薄膜內之藥物將透過陽極氧化鋁管上之奈米孔洞控制其釋放之速率，進而達到緩釋的效果。本裝置以濃度0.5%之牛血清蛋白(bovine serum albumin)做為釋放藥物，實驗結果發現於37C環境下，本裝置可藉由奈/微米孔洞之相互配合，使釋放時間達兩週。 另外，本研究將藥物釋放裝置應用於骨組織再生，以可誘導前趨骨母細胞 (pre-osteoblast) MC3T3-E1分化成成骨細胞之生長因子rh-BMP2做為藥物，填充於幾丁聚醣/膠原蛋白複合束後再包覆於具奈米孔洞之陽極氧化鋁圓管中，進行細胞培養實驗。經由鹼性磷酸脢活性測試(ALP)以及茜素紅染色(ARS)實驗發現以rh-BMP2培養之前趨骨母細胞確實能分化為成骨細胞。由茜素紅染色實驗比較出本裝置在細胞培養過程中可以用較低劑量的生長因子，並且透過一次性的投藥即可促進細胞分化為成骨細胞。倘若未來可進一步將本研究之藥物釋放裝置應用於體內藥物釋放，除了具有生物可降解性外也有一次性投藥的優點，因此可以改善舊型裝置需要重複開刀進行藥物補充的缺點。