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Biomineralization is the concept of biologically controlled or induced aggregations of salt ions, which is one of the most widely spread phenomena in nature. The formation of bones is one of the prototypical biomineralization processes which involves the association of calcium and phosphate ions to generate the apatite crystals on collagen fibers. In this work, the nucleation mechanism was investigated from a microscopic point of view using molecular dynamics (MD) and metadynamics simulations. Compared to other charged residues, the arginine residue was confirmed to stay at the dominant position when promoting the nucleation of calcium phosphate clusters. Based on the free energy profiles for the association of ion pairs, we combine thermodynamics and kinetics work together to affect the efficiency of nucleation of calcium phosphate in the aqueous phase. In addition, the unusual like-charge cation pair formed between two adjacent arginines could lead to losing the function of inducing calcium phosphate clusters generated on the collagen protein surface. Our study might provide a way to regulate the growth or nucleation of hydroxyapatite via a protein engineering technique, which is also helpful to further design new biomaterials.

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Stem cells sense and respond to their local dynamic mechanical niches, which further regulate the cellular behaviors. While in naturally, instead of instantly responding to real-time mechanical changes of their surrounding niches, stem cells often present a delayed cellular response over a time scale, namely cellular mechanical memory, which may finally influence their lineage choice. Here, we aim to build a dynamic mechanical niche model with alginate-based hydrogel, therein the dynamic mechanical switching can be easily realized via the introduce or removal of Ca2+. The results show that stiffening hydrogel (from soft to stiff) suppresses osteogenic differentiation of human mesenchymal stem cells (hMSCs) early on, though it finally promoted osteogenic differentiation over a long time period. Instead, softening hydrogel (from stiff to soft) still retains the strong osteogenic differentiation in the early days, though it finally showed a lower level of osteogenic differentiation compared with stiff hydrogel. Further, microRNA miR-21 has been found as a long-term mechanical memory sensor of the osteogenic program in hMSCs, as its level remains to match early mechanics of substrate over a period of time. Regulation of miR-21 level is efficient to erase the past mechanical memory and resensitize hMSCs to subsequent substrate mechanics. Our findings highlight cellular mechanical memory effect as a key factor of cell and cellular microenvironment interactions, which has been largely neglected before, and as a crucial design element of biomaterials for cell culture.

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An ab initio potential energy surface for the Ar--OCS dimer was calculated using the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)] with a large basis set containing bond functions. The interaction energies were obtained by the supermolecular approach with the full counterpoise correction for the basis set superposition error. The CCSD(T) potential was found to have two minima corresponding to the T-shaped and the collinear Ar--SCO structures. The two-dimensional discrete variable representation method was employed to calculate the rovibrational energy levels for five isotopomers Ar--OCS, Ar--OC34S, Ar--O13CS, Ar--18OCS, and Ar--17OCS. The calculated pure rotational transition frequencies for the vibrational ground state of the five isotopomers are in good agreement with the observed values. The corresponding microwave spectra show that the b-type transitions (Delta Ka = +/-1) are significantly stronger than the a-type transitions (Delta Ka = 0). Minimum-energy structures of the Ar2--OCS trimer were been determined with MP2 optimization, whereas the minimum-energy structures of the Arn--OCS clusters with n = 3-14 were obtained with the pairwise additive potentials. It was found that there are two minima corresponding to one distorted tetrahedral structure and one planar structure for the ternary complex. The 14 nearest neighbor Ar atoms form the first solvation shell around the OCS molecule.