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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.

The regeneration of tooth enamel, the hardest biological tissue, remains a considerable challenge because its complicated and well-aligned apatite structure has not been duplicated artificially. We herein reveal that a rationally designed material composed of calcium phosphate ion clusters can be used to produce a precursor layer to induce the epitaxial crystal growth of enamel apatite, which mimics the biomineralization crystalline-amorphous frontier of hard tissue development in nature. After repair, the damaged enamel can be recovered completely because its hierarchical structure and mechanical properties are identical to those of natural enamel. The suggested phase transformation–based epitaxial growth follows a promising strategy for enamel regeneration and, more generally, for biomimetic reproduction of materials with complicated structure.

Biological hard tissues such as bones always contain extremely high levels of citrate, which is believed to play an important role in bone formation as well as in osteoporosis treatments. However, its mechanism on biomineralization is not elucidated. Here, it is found that the adsorbed citrate molecules on collagen fibrils can significantly reduce the interfacial energy between the biological matrix and the amorphous calcium phosphate precursor to enhance their wetting effect at the early biomineralization stage, sequentially facilitating the intrafibrillar formation of hydroxyapatite to produce an inorganic-organic composite. It is demonstrated experimentally that only collagen fibrils containing ≈8.2 wt% of bound citrate (close to the level in biological bone) can reach the full mineralization as those in natural bones. The effect of citrate on the promotion of the collagen mineralization degree is also confirmed by in vitro dentin repair. This finding demonstrates the importance of interfacial controls in biomineralization and more generally, provides a physicochemical view about the regulation effect of small biomolecules on the biomineralization front.

Organisms use inorganic ions and macromolecules to regulate crystallization from amorphous precursors, endowing natural biominerals with complex morphologies and enhanced properties. The mechanisms by which modifiers enable these shape-preserving transformations are poorly understood. We used in situ liquid-phase transmission electron microscopy to follow the evolution from amorphous calcium carbonate to calcite in the presence of additives. A combination of contrast analysis and infrared spectroscopy shows that Mg ions, which are widely present in seawater and biological fluids, alter the transformation pathway in a concentration-dependent manner. The ions bring excess (structural) water into the amorphous bulk so that a direct transformation is triggered by dehydration in the absence of morphological changes. Molecular dynamics simulations suggest Mg-incorporated water induces structural fluctuations, allowing transformation without the need to nucleate a separate crystal. Thus, the obtained calcite retains the original morphology of the amorphous state, biomimetically achieving the morphological control of crystals seen in biominerals.

Osteoporosis is an incurable chronic disease characterized by a lack of mineral mass in the bones. Here, the full recovery of osteoporotic bone is achieved by using a calcium phosphate polymer‐induced liquid‐precursor (CaP‐PILP). This free‐flowing CaP‐PILP material displays excellent bone inductivity and is able to readily penetrate into collagen fibrils and form intrafibrillar hydroxyapatite crystals oriented along the c‐axis. This ability is attributed to the microstructure of the material, which consists of homogeneously distributed ultrasmall (≈1 nm) amorphous calcium phosphate clusters. In vitro study shows the strong affinity of CaP‐PILP to osteoporotic bone, which can be uniformly distributed throughout the bone tissue to significantly increase the bone density. In vivo experiments show that the repaired bones exhibit satisfactory mechanical performance comparable with normal ones, following a promising treatment of osteoporosis by using CaP‐PILP. The discovery provides insight into the structure and property of biological nanocluster materials and their potential for hard tissue repair.

which emphasize the presences of several intermediate states prior to nucleation, such as amorphous precursors, [5c,6] magicsize clusters, [7] condensed liquid phase, [8] prenucleation clusters, [9] etc. Although it is suggested that the energetic barrier for multistep nucleation via intermediate states is lower than that expected in a classical nucleation picture, [10] debates remain due to the lack of direct experimental evidence for early crystallization. [4b,5a,c,7,11] The diversity and details of nonclassical nucleation and crystallization pathways (e.g., multistep nucleation process and amorphous precursor phase) of nanocrystals have been revealed at the nanoscale using liquid-cell transmission electron microscopy (LC-TEM). [5a,6b] The technical advancement of LC-TEM consists in its capability of tracking ultrasmall and metastable objects in solution, [5a,6b] making it a powerful tool to analyze liquid specimens and achieving in situ visualization with high spatial resolution. [12] Motivated by these recent advancements, we presently explore details in nanocrystallization [3] to achieve a full mechanistic understanding. In this communication, we analyze Pd and Au crystallizations using LC-TEM, and unravel an alternative nanocrystallization process involving an intermediate state which we dub clustercloud. This new phase plays a vital role in nucleation and particle structural evolution: the initial nucleation results from a sudden collapse of the cluster-cloud; and the subsequent particle maturation undergoes via the cluster-cloud mediated out-and-in relaxations. This discovery underscores the diversity and complexity of crystallization pathways and improves our current knowledge by providing a more comprehensive picture of nanocrystal formation.For the in situ LC-TEM observations of Pd and Au crystallization, solutions containing 400 nL 10.0 mm Na 2 PdCl 4 and HAuCl 4 , respectively, were prepared in the liquid-cells. Highenergy electrons from TEM generated solvated electrons to reduce solution Pd 2+[13] and Au 3+[14] to Pd and Au atoms, respectively (see Method in the Supporting Information for details). The time sequenced TEM images (Figure 1a) show the prenucleation and nucleation of Pd. Similar to Mirsaidov's observation of metal-rich liquid phase, [5a] a dark region formed (0 s), corresponding to the concentration of the reduced Pd atoms from solution. This irregular region was flexible with a cloud-like behavior (18 s). It is noteworthy that instead of a random assembly of atoms, this cloud consisted of several Elucidating the early stages of crystallization from supersaturated solutions is of critical importance, but remains a great challenge. An in situ liquid cell transmission electron microscopy study reveals an intermediate state of condensed atomic clusters during Pd and Au crystallizations, which is named a "cluster-cloud." It is found that nucleation is initiated by the collapse of a cluster-cloud, first forming a nanoparticle. The subsequent particle maturation proceeds via multi...

Ionic oligomers and their crosslinking implies a possibility to produce novel organic–inorganic composites by copolymerization. Using organic acrylamide monomers and inorganic calcium phosphate oligomers as precursors, uniformly structured polyacrylamide (PAM)‐calcium phosphate copolymer is prepared by an organic–inorganic copolymerization. In contrast to the previous PAM‐based composites by mixing inorganic components into polymers, the copolymerized material has no interphase boundary owing to the homogenous incorporation of the organic and inorganic units at molecular level, resulting in a complete and continuous hybrid network. The participation of the ionic binding effect in the crosslinking process can substantially improve the mechanical strength; the copolymer can reach a modulus and hardness of 35.14±1.91 GPa and 1.34±0.09 GPa, respectively, which are far superior to any other PAM‐based composites.