Bioprocess-inspired Synthesis And Processing Of Inorganic Materials In A Confined Space

Over billions of years of evolution,living organisms possess various unique hierarchical structures and superior properties to adapt surrounding environment.Inspired by the exquisite structure of living organisms,mimicking the structure with artificial building blocks in order to obtain similar structural characterizations or biological functions,which are called“bio-inspired materials”or“bio-inspired functions”.Moreover,the elaborate biological processes to form biominerals is also fascinating.Taking lessons from the structure-forming process of biominerals,one can find tremendous inspiration and ideas for developing advanced synthesis techniques,which may be called“bioprocess-inspired synthesis and processing”.One of the major features of structure-forming process is the existence of confined space.Various biomacromolecules determine the morphology,orientation,and polymorph type of a biomineral within a confined space.The growth of biomineral is the resultant of transformation of amorphous precursor.Due to the highly hydrated and liquid-like characteristics of amorphous precursor,which can be moulded into a confined space with any complex geometry shape.The involvement of cell is ubiquitous in the construction of confined space,synthesis of biomacromolecules and uptake of inorganic ions.As a representative biomineral,bone has elaborate hierarchical strurture.The building blocks of bone are the mineralized collagen fibrils.The specific chemical structures and elaborate spatial distribution of collagen fibrils is resulting from the unique composition and arrangement of tropocollagen molecules.However,the process remains elusive for the infiltration of amorphous precursors into collagen fibril under the control of confinement.Therefore,calcium carbonate was chosen to mineralize inside collagen fibrils,the functions of cofinement on intrafibrillar mineralization were investigated.The organized intrafibrillar mineralization of apatite was also explored under the synergistic effects between biomacromolecule and confinement.The artificially combined systems of biomacromolecule and confinement on the surface of cell was directed to synthesize nanostructured titania,which exhibits superior lithium storage properties.First,we explore the confined mineralization of amorphous calcium carbonate?ACC?within collagen fibrils,including the driving mechanism of ACC infiltration into collagen fibrils and phase transformation inside collagen fibrils.The negatively charged ACC droplets were attracted to positively charged gap regions of collagen fibrils through electrostatic interaction,infiltrated into collagen fibrils,and then transformed into crystalline phase.The observation of juxtaposed crystalline and amorphous phases on the surface of fibrils indicates that a secondary nucleation mechanism may be responsible for the co-orientation of calcite nanocrystals.Through modifying the wettability of amorphous calcium carbonate with magnesium ions,it is verified that the infiltration of ACC into collagen fibrils was driven by capillary forces.Second,we design and express a multi-functional protein,and investigate the synergistic effect between biomacromolecule and confined space for directing the intrafibrillar mineralization process in vitro.The recombinant protein mimicking natural bone formation was rationally designed and constructed to possess common features of NCPs,including binding calcium ions,binding collagen and binding hydroxyapatite.The present study shows that BSP-HAP can act as a templating analogue to bind collagen fibrils through hydrophobic interaction and regulate the nucleation and growth behavior of hydroxyapatite.Bone-like highly organized hydroxyapatite becomes periodically arranged inside the collagen fibrils as?MBP?-BSP-HAP functions in synergy with polyacrylic acid.Third,we design an ideal platform to combine biomacromolecule and confined space on the surface of cell,and direct the synthesis of artificial materials.The cell surface display technology combines a catalytically active protein 5R5 in a three-dimensionally confined space.The positively charged 5R5 interacted with negatively charged titanium source through electrostatic interaction.The hydrogen bonding interaction catalyzed the hydrolysis and condensation of titania precursors on the E.coli cell surface.Upon heating treatment,E.coli cells acted as framework,to allow the transformation of titania precursors into well-assembled 5 nm anatase TiO₂nanoparticles.Furthermore,the size of nanoparticles was controlled by changing the repeating units of R5 segments.Finally,the bioprocess-inspired synthesis of products can be applied to lithium ion batteries.The genetically engineered bacteria not only provide a three-dimensionally confined space as a template to controllable synthesis of rod-shaped anatase,but also serve as a carbon source through carbonization in situ.Carbon coating on the assembled anatase TiO₂ nanoparticles was achieved by annealing in inert atmosphere.This unique nanostructured anatase possesses nanosized anatase crystals,mesoporous structure,and carbon coating.Nanoparticles reduce the lithium ion transport distance.The mesoporous structure can tolerate the volume change during lithium ion insertion and extraction,provide more channels for lithium ion diffusion.Carbon coating improves the intrinsically poor conductivity of anatase,enhances the lithium ion apparent diffusion coefficient.As an anode electrode,this unique nanostructured anode shows higher specific capacity,rate capability,and cycling stability compared to conventional electrodes.