Fabrication Of Hierarchically Structured Zeolites Based On 3D Printing Technology For Bone Tissue Engineering And Gas Separation

Zeolites with uniform pore size distribution in molecular dimensions,large surface area,suitable acidity,unique shape selectivity,excellent thermal and chemical stability are widely used in catalysis and gas separation.In addition,the excellent biocompatibility,biostability,and bioactivity of zeolites also make them promising materials in the field of bone tissue engineering.For practical applications in gas separation and catalysis,the primary nano or micrometer-sized zeolite crystals are agglomerated into macroscopic(mm)secondary structures(e.g.,granules,pellets,and extrudates).The conventional-shaped zeolites are limited in single configuration,low attrition resistance,high pressure drop,poor mass transfer and heat transfer.In addition,as a potential bone tissue-engineered scaffold,zeolites should have inter-connected porous structures to promote the diffusion of nutrients and the transport of metabolic waste.Therefore,how to construct hierarchically structured zeolites has become an important research topic and the systematic exploration of the hierarchically structured zeolites is of great significance in the fields of adsorption,catalysis and even biomedical.At present,two categories of conventional strategies have been adopted for designing and manufacturing hierarchically structured zeolites.One is to directly coat or deposit zeolite powders onto the surface of the preprocessed porous supports by in-situ or ex-situ methods.The other strategy is fabricating self-supporting structured zeolites.3D printing,also known as additive manufacturing,is a fabrication processing technology that emerged in the late 1980 s.The ability of quickly and flexibly designing and manufacturing geometries with complex structures has played an important role in the development of construction,machinery,electronics,energy,gas separation,catalysis,and biomedical fields.As a revolutionary innovative technology,3D printing is promising for rapidly and precisely constructing structured zeolites depending on the requirements of specific process parameters in the practical applications.At the same time,3D printing can easily and efficiently customize hierarchically structured zeolites adsorbents,catalysts and zeolite-based biomedical scaffolds with complex structure and high performance.Through the 3D printing technology,we can not only construct the macroporous support carrier for supporting active zeolites,but also directly fabricate self-supporting structured zeolites with tailorable geometries.In this thesis,we aim to fabricate high-performance hierarchically structured zeolite based on 3D printing technology for bone tissue engineering and gas separation.We have fabricated Sr ion-incorporated zeolite-A coatings(SZCs)on 3D printed TC4 titanium alloy with complex porous structure via in situ hydrothermal crystallization method.The SZCs can be uniformly coated on the outer and inner surface of the 3D porous scaffolds,which show an improved osteogenesis and osteointegration capacity.In addition,we have manufactured a self-supporting zeolite scaffold via extrusion-based 3D printing method.The zincosilicate zeolite VPI-7(without Al)is selected as the precursor material,and the functional Ag ions are incorporated into zeolite VPI-7 by the ion-exchange method.The obtained zeolite scaffolds demonstrate excellent antibacterial property and bioactivity.Furthermore,we have developed a facile “3D printing & zeolite soldering” strategy to construct binder-free zeolite monolith(ZM-BF)with robust mechanical integrity,hierarchical porous structure,and outstanding CO2 adsorption capacity.The introduction of halloysite nanotubes(HNTs)with high aspect ratio,nano-tubular structure,and high strength as a printing ink additive is beneficial to keep robust mechanical integrity of the 3D printed zeolite monoliths.Moreover,the successful transformation of HNTs into zeolites can further enhance the mechanical strength and CO2 uptake of ZM-BF.Comparing with conventional-shaped zeolites,ZM-BF Na X demonstrates the superiority for selectively capturing CO2.The main research results of this thesis are as follows:1.We have demonstrated a facile strategy to design bioactive 3D printed porous titanium implants with strontium(Sr)ion incorporated zeolite coatings(SZCs).The SZCs can be uniformly fabricated on the 3D porous scaffolds using an in situ hydrothermal crystal growth method to improve their osteogenesis and osteointegration capacity.The obtained materials show excellent apatite-forming ability,biocompatibility,and corrosion resistance compared with bare titanium alloys.With the continuous release of Sr ions from SZCs@TC4 by means of ion-exchange with SBF,zeolite coatings can further enhance the osteogenic activity and mineralization ability.The Sr ion incorporated zeolite-A coatings on TC4 could significantly induce new bone formation both in and around the pores within the initial 4 weeks,which is rather beneficial for earlier fixation of the implant.This work demonstrates that Sr ion-exchange zeolite-A coatings can remarkably enhance the biocompatibility and osteoinductive ability of porous TC4 alloys,which opens up a new approach for the development of bioactive customized implants in orthopedic applications.2.We have developed a facile and feasible strategy to construct an antibacterial scaffold for bone tissue engineering.The zincosilicate zeolite VPI-7 is selected as a precursor material,and the functional Ag ions are incorporated into zeolite VPI-7 by ion-exchange method.The Ag-incorporated zincosilicate zeolite scaffold(Ag-3DPZS)for bone tissue engineering is successfully constructed via the extrusion 3D printer,avoiding the presence of harmful element of aluminum when using zeolites with ion-exchange capacity.The resulted Ag-3DPZS demonstrates excellent mechanical properties by introducing nano-fibrous attapulgite as an inorganic binder,which is similar to the mechanical properties of human cancellous bone.Moreover,the obtained Ag-3DPZS possesses excellent antibacterial properties towards S.aureus and E.coli,demonstrating that Ag-3DPZS is a potential antimicrobial material for bone substitutes.3.A facile and versatile “3D printing & zeolite soldering” strategy has been developed to manufacture self-supporting binder-free Na X zeolite monoliths(ZM-BF)with robust mechanical integrity,hierarchical porous structure,and outstanding CO2 adsorption capacity.The introduction of HNTs with high aspect ratio,nano-tubular structure,and high strength as a printing ink additive is beneficial to keep robust mechanical integrity of the 3D printed zeolite monoliths.Moreover,the successful transformation of HNTs into zeolites can further enhance the mechanical strength and CO2 uptake of ZM-BF.Compared with conventional-shaped zeolites,ZM-BF demonstrates the superiority for selectively capturing CO2 from flue gas,natural gas,and biogas.To the best of our knowledge,this 3D printed binder-free zeolite monolith is the first case of structured zeolites that fully overcomes the trade-off among mechanical strength,diffusion kinetics,and adsorption capacity.We believe that the “3D printing & zeolite soldering” strategy of the current study may afford a versatile pathway for designing and fabricating other binder-free structured zeolites,which may open more advanced applications of 3D printed zeolites not only in adsorption but also in other areas such as catalysis and sensing.