Crystallization Mechanisms In Biomineralization And Their Applications

Recent studies on biomineralization reveal that crystals are not always formed via ion-by-ion attachment,which is understood as the classical crystal growth mechanism.Oppositely,the non-classical crystal growth with clusters,liquid phases,amorphous phases or nanoparticles as the precursor phases is being understood.This thesis mainly focuses on the mechanisms of crystal growth in biomineralization,and the developments of materials inspired by the mechanisms we discovered.The concerned issues include the particle aggregation based crystal growth and their orientation;the alternation of phase transition pathways;the growth and dissolution of crystals by regulating the ionization degree,and applied for carbon dioxide chemical looping;development of an universal method for poly-ionic cluster synthesizing by the strategy of termination from polymer chemistry,and using the poly-ionic cluster to produce continues materials or repairing the enamel structures;understanding of the influences of biomineral dissolution on biological system.We firstly introduce the basic knowledge of biomineralization and crystal growth,The non-classical crystal growth is mainly presented,and their debates are discussed.Then,the unsolved problems in biomineralization are summarized,and the issues we concern are demonstrated.Mechanisms of aggregation based crystal growth is one of the hot topics in the world.By using nano-vaterite particles,a random aggregation based single crystal growth can be observed.We discover that the random attachment during aggregation based growth initially produces a nonoriented growth front.Subsequent evolution of the orientation is driven by the inherent surface stress applied by the disordered surface layer and results in single-crystal formation by grain-boundary migration.This mechanism is corroborated by measurements of orientation rate versus external stress,which demonstrates a predictive relationship between the two.These findings help understanding the single crystal formation in biomineralization,advance our understandings about aggregation-based growth via nanocrystal blocks and suggest an approach to material synthesis that takes advantage of stress-induced coalignment.Phase transformation based crystal growth is also an important issue in biomineralization.We use the in-situ transmission electron microscopy to observe the phase transition from amorphous calcium carbonate(ACC)to calcite,and reveal the mechanism of phase transition pathway regulation.The additives can stabilize the ACC,but in-situ observation discovers that different additives have different mechanisms on stabilization.Besides,the magnesium ions can alter the phase transition of ACC to calcite between two different pathways,the dissolution-re-precipitation or solid-state transition.We proved that magnesium ions can increase the water content in ACC,promoting the nucleation rate inside ACC phase and subsequently leads to the solid-state transition.Notably,the calcite that is transformed from solid-state transition can remain the morphology of its amorphous precursor.According to this discovery,we can make calcite with unusual morphology.The mechanism deepen the understanding of biomineralization,and help producing materials with complex morphologies.Biomineralization is regulated by multiple factors,we focus on understanding the mechanism of pH regulation and combine it with theories of solution chemistry to prepare an ionization controllable system.Multiple biomimetic systems can be set up by adding specific molecules into the ionization controllable system.Firstly,we use the ionization controllable system to prepare a mixed solvent system for CO2 capture and release at room temperature.Typically,the calcium acetate-ethanol-water system is chosen to control the ionization degree of acetic acid.When at high ethanol content,calcium acetate reacts with CO2 to produce CaCO3 and acetic acid,which is the CO2 capture process.While increasing the water content in the system,the acetic acid starts to dissolve CaCO3,which is the CO2 release process.The looping can be resumed by adding ethanol.This research highlights the fundamental principle of solution chemistry in reaction control and provides a bioinspired strategy for CO2 capture/release with very low cost and easy availability.Besides,we combine the theory of end capping in polymer chemistry and ionization controllable system to produce the calcium carbonate and calcium phosphate poly-ionic clusters,which act as the precursor phases in biomineralization.The poly-ionic cluster can be easily and largely synthesized with a liquid like feature.We discover the poly-ionic cluster is a partially branched liner polymer with uneven distribution of positive charges.The triethylamine in our system act as the terminator molecules,which stabilize the poly-ionic clusters in low dielectric constant solvent.When removing the triethylamine,the poly-ionic clusters start to polymerization to form amorphous phases.This method realizes the fast synthesizing of continuous monolith of ionic compounds,advances the strategy for monolith and membrane producing,and develops a feasible material for 3D printing.Then,the poly-ionic cluster of calcium phosphate is used for the structural repair of enamel.A large scaled amorlphous calcium phosphate layer,which integrates perfectly with enamel,can be easily prepared with poly-ionic cluster.The solid-state phase transition subsequently occurs and the hydroxyapatites grow epitaxially alone the enamel prisms.This fast structural repair is of large scale with high thickness.Nano indentation further confirms the repaired layer has similar mechanical property with native enamel.This work provides a useful and reliable method for decayed enamel repair in clinical medicine.Calcium phosphate is a biocompatible and biodegradable material.However,many in vitro experiments have demonstrated that calcium phosphate nanoparticles still have significant cytotoxicity.According to the dissolution manner of calcium phosphate,we discover the calcium phosphate nanoparticles will dissolve quickly in lysosome after uptaken by cells.What's worse,the dissolution releases large quantities of ions inside lysosome,leading to the osmotic pressure imbalance across the lysosomal membranes and subsequently disrupting the lysosomal structure.If the osmotic pressure in cytoplasma or pH in lysosome is increased,the cytotoxicity of calcium phosphate nanoparticles can be decreased.The understanding of crystal dissolution helps understanding a possible mechanism of cytotoxicity induced by degradable nanoparticles.Controlling the dissolution of nanoparticles and cellular osmotic pressure can effectively improve the biosecurity of nanoparticles.At last,we summarise the results and meanings of our researches,as well as the unsolved problems.The futures of these works are also proposed.