Bio-inspired synthesis: understanding and exploitation of the crystallization process from amorphous precursors

Comprehensive characterization of the structure of Zr-based metallic glasses

Structure of metallic glasses fascinates as the generic amorphous structural template for ubiquitous systems. Its specification necessitates determination of the complete hierarchical structure, starting from short-range-order (SRO) → medium-range-order (MRO) → bulk structure and free volume (FV) distribution. This link has largely remained elusive since previous investigations adopted one-technique-at-a-time approach, focusing on limited aspects of any one domain. Reconstruction of structure from experimental data inversion is non-unique for many of these techniques. As a result, complete and precise structural understanding of glass has not emerged yet. In this work, we demonstrate the first experimental pathway for reconstruction of the integrated structure, forZr 67 Ni 33 andZr 52 Ti 6 Al 10 Cu 18 Ni 14 glasses. Our strategy engages diverse (× 7) multi-scale techniques [XAFS, 3D-APT, ABED/NBED, FEM, XRD, PAS, FHREM] on the same glass. This strategy complemented mutual limitations of techniques and corroborated common parameters to generate complete, self-consistent and precise parameters. Further, MRO domain size and inter-void separation were correlated to identify the presence of FV at MRO boundaries. This enabled the first experimental reconstruction of hierarchical subset: SRO → MRO → FV → bulk structure. The first ever image of intermediate region between MRO domains emerged from this link. We clarify that determination of all subsets is not our objective; the essence and novelty of this work lies in directing the pathway towards finite solution, in the most logical and unambiguous way.

Reinforcing hydrogels with in situ formed amorphous CaCO3

Hydrogels are often employed for tissue engineering and moistening applications. However, they are rarely used for load-bearing purposes because of their limited stiffness and the stiffness-toughness compromise inherent to them. By contrast, nature uses hydrogel-based materials as scaffolds for load-bearing and protecting materials by mineralizing them. Inspired by nature, the stiffness or toughness of synthetic hydrogels has been increased by forming minerals, such as CaCO₃, within them. However, the degree of hydrogel reinforcement achieved with CaCO₃ remains limited. To address this limitation, we form CaCO₃ biominerals in situ within a model hydrogel, poly(acrylamide) (PAM), and systematically investigate the influence of the size, structure, and morphology of the reinforcing CaCO₃ on the mechanical properties of the resulting hydrogels. We demonstrate that especially the structure of CaCO₃ and its affinity to the hydrogel matrix strongly influence the mechanical properties of mineralized hydrogels. For example, while the fracture energy of PAM hydrogels is increased 3-fold if reinforced with individual micro-sized CaCO₃ crystals, it increases by a factor of 13 if reinforced with a percolating amorphous calcium carbonate (ACC) nano-structure that forms in the presence of a sufficient quantity of Mg²⁺. If PAM is further functionalized with acrylic acid (AA) that possesses a high affinity towards ACC, the stiffness of the hydrogel increases by a factor 50. These fundamental insights on the structure-mechanical property relationship of hydrogels that have been functionalized with in situ formed minerals has the potential to enable tuning the mechanical properties of mineralized hydrogels over a much wider range than what is currently possible.

2-Dodecylmalonic acid-mediated synthesis of mineralized hydroxyapatite amicable for bone cell growth on orthopaedic implant

The present study illustrates the use of 2-dodecylmalonic acid (MA) as a template in biomineralization-inspired synthesis of hydroxyapatite nanoparticles (HANPs). HANPs synthesized in presence of various concentrations of MA displayed varying particle size and shape. The smallest particle size (22-27 nm) was obtained for MA₂-HANP synthesized in presence of 37 µM MA. The critical micelle concentration (CMC) for MA at pH 9.0 relevant for mineralization was ∼35 µM. AFM analysis revealed that at a low concentration of 10 µM and pH 9.0, MA could generate oblong-shaped aggregates. At 40 µM, comparable to the concentration used to generate MA₂-HANP, the amphiphile self-assembled to form a spherical soft scaffold, which likely regulated spatial confinement of ions during mineralization and generated small size HANPs. Osteoblast-like MG-63 cells seeded on titanium wire (TW) coated with MA₂-HANP-incorporated collagen type I (H-TW) displayed enhanced cell proliferation, high expression of osteogenic differentiation marker genes (Col I, ALP, OCN and Runx2) and copious calcium mineral deposition after 14 days of growth. The nuanced role of the self-assembly process of an amphiphilic template in HANP mineralization unravelled in the present study can guide future scaffold design for biomineralization-inspired synthesis of HANPs tailored for bone tissue engineering applications.

Controllable Synthesis of Biomimetic Hydroxyapatite Nanorods with High Osteogenic Bioactivity

The development of biodegradable materials with high osteogenic bioactivity is important for achieving rapid bone regeneration. Although hydroxyapatite (HAp) has been applied as a biomaterial for bone engineering due to its good osteoconductivity, conventional synthetic HAp nanomaterials still lack sufficient osteogenesis, likely due to their high crystallinity and uncontrollable architecture. A design of HAp nanoparticles mimicking bone features may create good microenvironments that promote osteogenesis for rapid bone regeneration. In this study, HAp nanoparticles with a comparatively less crystalline structure and nanorod shapes mimicking biological HAp nanocrystals of natural bone were fabricated using a simple chemical precipitation approach with mild temperature control in the absence of any organic solvents. Transmission electron microscopy (TEM) indicated that HAp nanorods with aspect ratios from 2.0 to 4.4 were synthesized by adjusting the reaction time as well as the reaction temperature. Fourier transform infrared spectroscopy and X-ray diffraction experiments displayed that HAp nanorods prepared at 30 °C (HAp-30 with an aspect ratio of 2.9) had a low crystalline structure and B-type CO₃^2- substitution similar to those of natural HAp originating from bone tissue. The energy-dispersive spectroscopy (EDS) results showed that the Ca/P ratio of HAp-30 was 1.66 ± 0.13. An in vitro biological evaluation against rat bone marrow-derived mesenchymal stem cells indicated that the resulting HAp nanorods had excellent biocompatibility (with an ∼80-fold increase in IC50 compared to that of conventional HAp nanoparticles). Interestingly, the alkaline phosphatase (ALP), alizarin red S, and immunofluorescence staining results all showed that stem cells display an obvious osteogenesis dependence on the HAp nanostructure. Specifically, HAp nanorods with a moderate aspect ratio had the optimal osteogenic capacity (e.g., HAp-30 offered a 2.8-fold increase in ALP expression and a 4-fold increase in OCN expression relative to that provided by irregular HAp at day 14). It is expected that HAp nanorods with controllable architectures and size have potential as a kind of new bioactive bone filler for bone defect repair.

Water: How Does It Influence the CaCO3 Formation?

Nature produces biomineral-based materials with a fascinating set of properties using only a limited number of elements. This set of properties is obtained by closely controlling the structure and local composition of the biominerals. We are far from achieving the same degree of control over the properties of synthetic biomineral-based composites. One reason for this inferior control is our incomplete understanding of the influence of the synthesis conditions and additives on the structure and composition of the forming biominerals. In this Review, we provide an overview of the current understanding of the influence of synthesis conditions and additives during different formation stages of CaCO₃ , one of the most abundant biominerals, on the structure, composition, and properties of the resulting CaCO₃ crystals. In addition, we summarize currently known means to tune these parameters. Throughout the Review, we put special emphasis on the role of water in mediating the formation of CaCO₃ and thereby influencing its structure and properties, an often overlooked aspect that is of high relevance.

Three-dimensional Printed Mg-Doped β-TCP Bone Tissue Engineering Scaffolds: Effects of Magnesium Ion Concentration on Osteogenesis and Angiogenesis In Vitro

Background

Three-dimensional (3D) printed bone tissue engineering scaffolds have been widely used in research and clinical applications. β-TCP is a biomaterial commonly used in bone tissue engineering to treat bone defects, and its multifunctionality can be achieved by co-doping different metal ions. Magnesium doping in biomaterials has been shown to alter physicochemical properties of cells and enhance osteogenesis.

Methods

A series of Mg-doped TCP scaffolds were manufactured by using cryogenic 3D printing technology and sintering. The characteristics of the porous scaffolds, such as microstructure, chemical composition, mechanical properties, apparent porosity, etc., were examined. To further study the role of magnesium ions in simultaneously inducing osteogenesis and angiogenesis, human bone marrow mesenchymal stem cells (hBMSCs) and human umblical vein endothelial cells (HUVECs) were cultured in scaffold extracts to investigate cell proliferation, viability, and expression of osteogenic and angiogenic genes.

Results

The results showed that Mg-doped TCP scaffolds have the advantages of precise design, interconnected porous structure, and similar compressive strength to natural cancellous bone. hBMSCs and HUVECs exhibit high proliferation rate, cell morphology and viability in a certain amount of Mg²⁺. In addition, this concentration of magnesium can also increase the expression levels of osteogenic and angiogenic biomarkers.

Conclusion

A certain concentration of magnesium ions plays an important role in new bone regeneration and reconstruction. It can be used as a simple and effective method to enhance the osteogenesis and angiogenesis of bioceramic scaffolds, and support the development of biomaterials and bone tissue engineering scaffolds.

Controlled crystallization of anhydrous guanine β nano-platelets via an amorphous precursor

We realized a pure phase of anhydrous guanine (AG) β form for the first time via a transformation from hydrated amorphous guanine phase (HAmG). The specified transformation was probably due to the similar short-range order between AG β and HAmG.

Charged Nanowire-Directed Growth of Amorphous Calcium Carbonate Nanosheets in a Mixed Solvent for Biomimetic Composite Films

Bio-inspired mineralization is an effective way for fabricating complex inorganic materials, which inspires us to develop new methods to synthesize materials with fascinating properties. In this article, we report that the charged tellurium nanowires (TeNWs) can be used as biomacromolecule analogues to direct the formation of amorphous calcium carbonate (ACC) nanosheets (ACCNs) in a mixed solvent. The effects of surface charges and the concentration of the TeNWs on the formation of ACCNs have been investigated. Particularly, the produced ACCNs can be functionalized by Fe₃O₄ nanoparticles to produce magnetic ACC/Fe₃O₄ hybrid nanosheets that can be used to construct ACC/Fe₃O₄ composite films through a self-evaporation process. Moreover, sodium alginate-ACC nanocomposite films with remarkable toughness and good transmittance can also be fabricated by using such ACCNs as nanoscale building blocks. This mineralization approach in a mixed solvent using charged TeNWs as biomacromolecule analogues provides a new way for the synthesis of ACCNs, which can be used as nanoscale building blocks for the fabrication of biomimetic composite films.

Nanomaterial-based bone regeneration

Bone diseases/injuries have been driving an urgent quest for bone substitutes for bone regeneration. Nanoscaled materials with bone-mimicking characteristics may create suitable microenvironments to guide effective bone regeneration. In this review, the natural hierarchical architecture of bone and its regeneration mechanisms are elucidated. Recent progress in the development of nanomaterials which can promote bone regeneration through bone-healing mimicry (e.g., compositional, nanocrystal formation, structural, and growth factor-related mimicking) is summarized. The nanoeffects of nanomaterials on the regulation of bone-related biological functions are highlighted. How to prepare nanomaterials with combinative bone-biomimicry features according to the bone healing process is prospected in order to achieve rapid bone regeneration in situ.

Morphological, chemical and kinetic characterisation of zein protein-induced biomimetic calcium phosphate films

A zein protein layer was used to mineralize thin films of calcium phosphate at the air–solution interface producing an iridescent mineral film with novel nano-morphology.

Surface structure dependent electrocatalytic activity of Co₃O₄ anchored on graphene sheets toward oxygen reduction reaction

Catalytic activity is primarily a surface phenomenon, however, little is known about Co₃O₄ nanocrystals in terms of the relationship between the oxygen reduction reaction (ORR) catalytic activity and surface structure, especially when dispersed on a highly conducting support to improve the electrical conductivity and so to enhance the catalytic activity. Herein, we report a controllable synthesis of Co₃O₄ nanorods (NR), nanocubes (NC) and nano-octahedrons (OC) with the different exposed nanocrystalline surfaces ({110}, {100}, and {111}), uniformly anchored on graphene sheets, which has allowed us to investigate the effects of the surface structure on the ORR activity. Results show that the catalytically active sites for ORR should be the surface Co²⁺ ions, whereas the surface Co³⁺ ions catalyze CO oxidation, and the catalytic ability is closely related to the density of the catalytically active sites. These results underscore the importance of morphological control in the design of highly efficient ORR catalysts.

25th anniversary article: Artificial carbonate nanocrystals and layered structural nanocomposites inspired by nacre: synthesis, fabrication and applications

Rigid biological systems are increasingly becoming a source of inspiration for the fabrication of next generation advanced functional materials due to their diverse hierarchical structures and remarkable engineering properties. Among these rigid biomaterials, nacre, as the main constituent of the armor system of seashells, exhibiting a well-defined 'brick-and-mortar' architecture, excellent mechanical properties, and interesting iridescence, has become one of the most attractive models for novel artificial materials design. In this review, recent advances in nacre-inspired artificial carbonate nanocrystals and layered structural nanocomposites are presented. To clearly illustrate the inspiration of nacre, the basic principles relating to plate-like aragonite single-crystal growth and the contribution of hierarchical structure to outstanding properties in nacre are discussed. The inspiration of nacre for the synthesis of carbonate nanocrystals and the fabrication of layered structural nanocomposites is also discussed. Furthermore, the broad applications of these nacre inspired materials are emphasized. Finally, a brief summary of present nacre-inspired materials and challenges for the next generation of nacre-inspired materials is given.

Bio-inspired motifs via tandem assembly of polypeptides for mineralization of stable CaCO3 structures

A macromolecular-assembly of polypeptides constructs a network of anionic and cationic charges vital for recognizing and coassembling Ca(2+) and CO(3)(2-) ions to mineralize and stabilize different mineral forms of CaCO(3) with core-shell or solid morphologies in an aqueous solution.