生物可降解3D列印墨水的開發與其相關生物應用

Abstract

三維列印(three-dimensional printing，3DP)技術是近幾年逐漸興起且熱門的精密製造技術，具有可客製化製作的優勢，適合運用在組織工程領域製作各種不同的組織或器官，然而，適合做為3DP生物墨水的選擇仍然很有限。因此本論文著重在3DP墨水的開發與其在生物相關的應用，論文將分為四個部分。第一部分是發展新的水性生物可降解聚胺酯(polyurethane，PU)，主要是利用聚己內酯[poly(ε-caprolactone)，PCL]與聚3-羥基丁酸酯(poly(3-hydroxybutyrate)，PHB)作為PU的軟鏈段合成一系列PCL-PHB-based PU。研究中發現PCL-PHB-based PU具有好的生物相容性與形狀記憶的特性，而PHB鏈段的長短可以調控PU的結晶度與形狀記憶的表現。在體內外降解實驗也發現，PCL-PHB-based PU比起PCL-based PU有更快的降解速率，且會促進血管新生。第二部分是發展低溫列印墨水(ink)並透過3DP製作成複雜結構雙成份的彈性氣管支架，研究中使用了不同種的水性生物可降解PU分別與聚乙二醇(polyethylene oxide，PEO)和透明質酸(hyaluronic acid，HA)組成墨水用於氣管中不同的結構部位。研究顯示，3DP PU氣管具有好的彈性且力學性質與兔子氣管相似，且間葉幹細胞(mesenchymal stem cell，MSC)在3DP氣管支架上具有正常功能性，能分化成軟骨細胞與分泌醣胺素(glycosaminoglycan，GAGs)，且在兔子氣管移植手術實驗也證實3DP氣管可維持兔子生命且不會有氣管塌陷的問題。第三部分為開發能夾帶細胞共同列印的常溫3DP生物墨水(bioink)，研究中使用了不同的水性生物可降解PU與明膠(gelatin)組成一系列不同力學性質與降解速率的3DP bioink，PU-gelatin bioink具有好的生物相容性、列印性、堆疊性(可堆疊80層以上)、機械性質和降解速率可調，可夾帶細胞常溫列印和具有高的列印解析度，以及MSC在水膠中能長時間的存活、增生和分化。PU-gelatin bioink在常溫列印成型後，會再透過二價金屬離子(Ca2+)螯合處理，穩定PU-gelatin建構物的結構避免在37oC時結構崩解，且若選用溫度敏感性PU，則可在37oC形成雙網絡結構進一步提升結構強度。研究中也證實以等滲透壓Ca2+離子處理含MSCs的PU-gelatin建構物，MSCs的健康狀態與在細胞培養液中的對照組相似，且能長時間的存活、增生和分化。第四部份為無機材料的開發和無機材料與生物墨水的結合，此部分又會在拆分兩個章節，其中一個章節開發了一種具有面選擇性蝕刻自組裝富勒烯的技術，研究中會先以液-液介面合成一維、二維和三維的富勒烯晶體，接著透過乙二胺(ethylenediamine，EDA)面選擇蝕刻技術，製作出中空或多孔親水性富勒烯晶體。此經EDA處理過的富勒烯晶體具有好的水分散性與高的酸性氣體選擇性，可作為藥物載體、感測器或氣體分離材料。另一章節是將有機金屬框架與生物墨水結合，在以維持生物墨水原先良好的性質(高含水量、列印性、堆疊性和生物活性)的基礎，進一步調控生物墨水的機械性質。研究顯示以相對微量的zeolitic imidazolate framework-8 (ZIF-8)加入PU-gelatin生物墨水後，可顯著增強生物墨水的結構穩定性和機械性質。此外，ZIF-8單獨與MSCs進行培養時，當濃度超過50 m/mL會有明顯細胞毒性，而當ZIF-8與生物墨水一起使用時，使用濃度為1250 m/mL時MSCs仍可長時間存活與增生，ZIF-8與生物墨水的結合形成了相輔相成的奈米複合材料。透過本論文四個部分的研究顯示，以水性生物可降解PU做為基礎開發的3DP ink和bioink發展性廣泛，可結合其他有機/無機材料，使製作的支架具有良好的生物相容性、力學強度、降解性、彈性與其他智慧性的功能等，且證實了在軟骨組織工程相關的應用與發展潛力。

Three-dimensional printing (3DP) has become a popular technology in manufacturing and engineering fields. 3DP is suitable for fabricating various tissues or organs for tissue engineering. However, the development of 3D bioprinting is still challenging for the limited selections of 3D bioprinting materials (or called bioink) because 3DP bioink needs to simultaneously meet all the requirements of printability, stackability, structure stabilization, and biological properties (bioactivity and cytocompatibility). Therefore, this thesis focuses on the development of 3D ink and bioink for biomedical applications, and the thesis is divided into four parts. The first part of the thesis is the development of new waterborne biodegradable polyurethane (PU), mainly using poly (ε-caprolactone) (PCL) and poly 3-hydroxybutyrate (PHB) as the soft segments of PU to synthesize a series of PCL-PHB based PU. This study found that PCL-PHB based PUs had good biocompatibility and shape memory behavior. The molecular weight of the PHB segment can regulate the crystallinity of PU and shape memory performance. In vitro and in vivo degradation experiments showed that PCL-PHB based PUs had a faster degradation rate than PCL-based PU and can promote angiogenesis. The second part is the development of low-temperature printing inks which were used to fabricate a 3DP trachea with complex structure. Different types of waterborne biodegradable PU, polyethylene oxide (PEO), and hyaluronic acid (HA) were used in the study. The 3DP trachea showed good elasticity and mechanical properties which were similar to that of rabbit trachea. Mesenchymal stem cells (MSCs) can differentiate into chondrocytes and secrete glycosaminoglycan (GAGs) on the 3DP tracheal scaffolds. Moreover, the experiments of implanting the 3DP trachea into rabbit trachea demonstrated that 3DP trachea could maintain rabbit life without tracheal collapse. The third part is the development of 3DP bioink. The composition of bioink was based on waterborne biodegradable PU and gelatin. PU-gelatin bioink has excellent rheological properties for printing, stacking ability (for over eighty layers), a wide working window, as well as high resolution (through the 80 m nozzle) printing possibility. The PU-gelatin double network hydrogel have good elasticity and mechanical strength (hand holdable) to support MSC proliferation. The mechanical strength of the printed PU-gelatin constructs could further be enhanced by immersing into a CaCl2 solution for the structure stabilization by Ca2+ chelation. After chelation, the PU-gelatin constructs can storage at 37 C without structural disintegration. In addition, formation of double network is later achieved by thermal curing of PU. This study also proved that MSCs-laden PU-gelatin constructs after treatment with Ca2+ solution could provide a niche for MSCs to survive proliferate and differentiate in long term. The fourth part is the development of inorganic materials and the combination of inorganic materials and bioinks. In this section, there are two chapters. The first chapter focuses on the development of a face-selective etching technology, which is used for post-assembled fullerenes. One-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) fullerene crystals were prepared using ultrasound assisted liquid-liquid interfacial precipitation (ULLIP). After treatment with ethylenediamine (EDA) solution, these post-assembled fullerenes would be transformed into hollow or porous hydrophilic fullerenes. The post-assembled fullerenes treated with EDA solution showed good water dispersibility and high acidic gas selectivity, which can be used as a drug carrier, sensor or gas separation materials. The other chapter is to combine the metal organic framework with PU-gelatin bioink to reinforce the structural stabilization and increase the modulus of bioink without sacrificing the origin properties of PU-gelatin bioink (high water content, printability, stackability and biological activity). The combination of ZIF-8 and PU-gelatin bioink demonstrated the benefits of complementary nanocomposite materials. A relatively small amount (< 3750 g/mL) of zeolitic imidazolate framework-8 (ZIF-8) had a significant enhancement effect on the structural stability and modulus of the PU-gelatin bioink. In addition, the shear thinning behavior of the bioink was improved after ZIF-8 were added. Before ZIF-8 were added into the PUG bioink, the concentration of ZIF-8 beyond 50 g/mL caused cytotoxicity. When ZIF-8 was added in PUG bioink, MSCs could survive and proliferate for a long term (7 days) at a ZIF-8 concentration of 1250 g/mL. To summarize, PU-based ink and bioink can be combined with other organic/inorganic materials to make the 3DP constructs with good biocompatibility, elasticity, tunable mechanical properties and degradation rate, and other smart functionality, etc. The four parts research in this thesis showed that PU-based 3DP ink and bioinks had a huge potential for biomedical fields.