Zhaoming Liu

Biomineralization: From Material Tactics to Biological Strategy

Biomineralization is an important tactic by which biological organisms produce hierarchically structured minerals with marvellous functions. Biomineralization studies typically focus on the mediation function of organic matrices on inorganic minerals, which helps scientists to design and synthesize bioinspired functional materials. However, the presence of inorganic minerals may also alter the native behaviours of organic matrices and even biological organisms. This progress report discusses the latest achievements relating to biomineralization mechanisms, the manufacturing of biomimetic materials and relevant applications in biological and biomedical fields. In particular, biomineralized vaccines and algae with improved thermostability and photosynthesis, respectively, demonstrate that biomineralization is a strategy for organism evolution via the rational design of organism-material complexes. The successful modification of biological systems using materials is based on the regulatory effect of inorganic materials on organic organisms, which is another aspect of biomineralization control. Unlike previous studies, this study integrates materials and biological science to achieve a more comprehensive view of the mechanisms and applications of biomineralization.

Calcium phosphate nanoparticles primarily induce cell necrosis through lysosomal rupture: the origination of material cytotoxicity

The application of nanotechnology for in medicine is developing rapidly, thereby increasing human exposure to nanomaterials and significantly so. A rising question is the biosecurity of nanoparticles (NPs). Although calcium phosphate (CaP) phase is biocompatible and biodegradable, many in vitro experiments have demonstrated that its NPs have significant cytotoxicity. This toxicity is due to that the released Ca2+ ions from the internalized CaP NPs within cells initiate apoptosis. Different from such an understanding, we reveal that the internalized CaP NPs actually result in lysosomal ruptures caused by the fast dissolution of CaP under acidic conditions. The suddenly released ions disturb the osmotic pressure balance across the lysosomal membranes destroying the lysosomes, and excessive lysosomal ruptures lead to cell necrosis. We find that the necrosis process can be regulated by intracellular environments. For examples, the lysosomal ruptures can be inhibited by increasing either cytoplasmic osmotic pressure or lysosomal pH (reduce the dissolution rates of CaP). These changes can significantly decrease the cytotoxicity of CaP NPs. It follows that lysosomal rupture prevention is important in the biomedical applications of CaP NPs. More generally, the study suggests that control of material degradation in lysosomes and cytoplasm osmotic pressure may improve the biosecurity of nanomaterials, which is of special importance to biomimetic nanomaterials.

Biomimetic construction of cellular shell by adjusting the interfacial energy

Many unicellular organisms take their outer proteinaceous and lipidic membranes or carbonhydrate‐rich cell walls as a template for biomineralization to synthesize a thin mineral layer as a functional covering. In nature most cells cannot be mineralized spontaneously in the normal states. Inspired by nature, we develop cytocompatible methods for cells encapsulated inside a mineral shell, called “cellular shellization.” Using Layer‐by‐Layer (LbL) assembly, the precipitation of calcium minerals can be induced on the yeast cell surfaces. The effects of different synthetic polyelectrolytes on the calcifications of yeast, such as interfacial energy, zeta‐potential, introduction time, and the affinity of mineral phase on the yeast cell surface have been studied by using constant composition method (CC) systemically and quantitatively. The results demonstrate that the effective adsorption of polyelectrolytes with carboxyl or sulfonate‐rich groups on the yeast can enhance mineralization abilities of yeast cells readily, and the factor of interfacial energy plays a key role in the superficial mineralization of the cells. Furthermore, the influences of ion concentrations, as well as titration rates on the formation of inorganic shell, have also been examined. It is found that the biomimetic shell formation on the cell can also be achieved by using an appropriate selection of titration conditions rather than the pretreatment of LbL. Thus, the control of cellular biomineralization can become more feasible. In this study, we show that adjusting the interfacial energy is the key to cellular mineralization and suggest that these biomineralization treatments of single‐cell may be applied as a potential and universal approach for cell‐based sensing and therapy. Biotechnol. Bioeng. 2014;111: 386–395.

Realignment of Nanocrystal Aggregates into Single Crystals as a Result of Inherent Surface Stress

Crystallization by particle attachment is widely observed in both natural and synthetic environments. Although this form of nonclassical crystallization is generally described by oriented attachment, random aggregation of building blocks to give single-crystal products is also observed, but the mechanism of crystallographic realignment is unknown. We herein reveal that 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 demonstrated a predictive relationship between the two. These findings advance our understandings about aggregation-based growth via nanocrystal blocks and suggest an approach to material synthesis that takes advantage of stress-induced coalignment.

Evolution from Classical to Non-classical Aggregation-Based Crystal Growth of Calcite by Organic Additive Control

Aggregation-based crystal growth is distinct from the classical understanding of solution crystallization. In this study, we reveal that N-stearoyl-l-glutamic acid (C18-Glu, an amphiphile that mimics a biomineralization-relevant biomolecule) can switch calcite crystallization from a classical ion-by-ion growth to a non-classical particle-by-particle pathway, which combines the classical and non-classical crystallization in one system. This growth mechanism change is controlled by the concentration ratio of [C18-Glu]/[Ca(2+)] in solution. The high [C18-Glu]/[Ca(2+)] can stabilize precursor nanoparticles to provide building blocks for aggregation-based crystallization, in which the interaction between C18-Glu and the nanoprecursor phase rather than that of C18-Glu on calcite steps is highlighted. Our finding emphasizes the enrollment of organic additives on metastable nano building blocks, which provides an alternative understanding about organic control in inorganic crystallization.