Three types of calcium phosphate coating were formed on polyethersulphone (PES) rectangular plates using a biomimetic method: a 20 μm thick amorphous calcium phosphate (ACP 20) coating, a 50 μm thick amorphous calcium phosphate (ACP 50) coating, and a 50 μm thick highly crystalline hydroxyapatite (hHA 50) coating. Uncoated PES plates were used as a control group. These materials were implanted in the tibiae of rabbits and subcutaneously in rats, and the samples were harvested 8 and 16 weeks thereafter, and were examined histologically. The tensile failure loads at the bone-implant interfaces were determined using the detaching test. Each ACP coating was more degradable than the hHA 50 coating. However, newly formed bone came into direct contact with underlying materials as the coating degraded. No coating degraded in subcutaneous tissue. Soft tissue intervening was seen in uncoated samples. Failure load of ACP 20-, ACP 50- and hHA 50-coated samples were all relatively higher than that of the uncoated samples at each period. Significant increase of failure load was seen in hHA 50-coated samples by 16 weeks, however, no increase was seen in either the uncoated or ACP-coated samples. If coating longevity is desired, then the hHA coating is preferable. However, if only the osteoconducive property of calcium phosphate coating is desired for initial fixation of porous materials, the ACP coating may be advantageous.

Abstract

A novel process has been developed for the preparation of a hydroxyapatite (HA) coating with a hierarchical structure on a Ti substrate. The Ti substrate was first subjected to electrolytic deposition at −1.6 V (versus Ag/AgCl/KCl) in a solution of 0.042 M Ca(NO₃)₂·4H₂O and 0.025 M NH₄H₂PO₄ at 85 °C for 3 min, and then post-treated in a 0.25 M NaOH solution, with the addition of 0.05 M Na₃Cit at 85 °C for 5 h. The experimental results showed that the coating experienced a phase conversion from octacalcium phosphate to HA after the post-treatment step. The HA coating had well-distributed, micro-sized pores comprising three-dimensional interconnected mesoporous HA belts, which would greatly increase the porosity and surface area of the coating.

Various bioceramic materials were implanted into 6-mm-diameter holes made in the femoral condyles of mature Japanese white rabbits using different-sized granules to find an optimal material and granule diameter for use as a bone graft. Bioceramics include a bioinert ceramic (Alumina), surface-bioactive ceramics [hydroxyapatite (HAp) and Bioglass®], and resorbable bioactive ceramics [αtricalcium phosphate (α-TCP), β-TCP, tetracalcium phosphate (TeCP), Te · DCPD, Te · DCPA, and low-crystalline HAp]. Granule sizes were 100–300, 10, and 1–3 μm. Bone growth behavior varied with the kind of bioceramic and the size used. For surface-bioactive ceramics, 45S5 Bioglass® led to more rapid bone proliferation than synthetic HAp. In resorbable bioactive ceramics, the order of resorption was: low-crystalline HAp and OCP > TeCP, Te DCPD, Te DCPA > α-TCP, β-TCP. In terms of biocompatibility, α-TCP was better than β-TCP. © 1999 John Wiley & Sons, Inc. J Biomed Mater Res, 44, 31–43, 1999.

Abstract

Plasma sprayed hydroxyapatite (HA) coatings on titanium alloy substrate have been used extensively due to their excellent biocompatibility and osteoconductivity. However, the erratic bond strength between HA and Ti alloy has raised concern over the long-term reliability of the implant. In this paper, HA/yttria stabilized zirconia (YSZ)/Ti–6Al–4V composite coatings that possess superior mechanical properties to conventional plasma sprayed HA coatings were developed. Ti–6Al–4V powders coated with fine YSZ and HA particles were prepared through a unique ceramic slurry mixing method. The so-formed composite powder was employed as feedstock for plasma spraying of the HA/YSZ/Ti–6Al–4V coatings. The influence of net plasma energy, plasma spray standoff distance, and post-spray heat treatment on microstructure, phase composition and mechanical properties were investigated. Results showed that coatings prepared with the optimum plasma sprayed condition showed a well-defined splat structure. HA/YSZ/Ti–6Al–4V solid solution was formed during plasma spraying which was beneficial for the improvement of mechanical properties. There was no evidence of Ti oxidation from the successful processing of YSZ and HA coated Ti–6Al–4V composite powders. Small amount of CaO apart from HA, ZrO₂ and Ti was present in the composite coatings. The microhardness, Young's modulus, fracture toughness, and bond strength increased significantly with the addition of YSZ. Post-spray heat treatment at 600°C and 700°C for up to 12 h was found to further improve the mechanical properties of coatings. After the post-spray heat treatment, 17.6% increment in Young's modulus (E) and 16.3% increment in Vicker's hardness were achieved. The strengthening mechanisms of HA/YSZ/Ti–6Al–4V composite coatings were related to the dispersion strengthening by homogeneous distribution of YSZ particles in the matrix, the good mechanical properties of Ti–6Al–4V and the formation of solid solution among HA, Ti alloy and YSZ components.

One of the most important clinical applications of hydroxyapatite (HA) is as a coating on metal implants, especially plasma-sprayed HA coating applied on Ti alloy substrate. However, the poor bonding strength between HA and Ti alloy has been of concern to orthopedists. In this paper, an attempt has been made to enhance the bonding strength of HA coating by forming a composite coating with Ti. The bioactivity of the coating has also been studied. HA/Ti composite coatings were prepared via atmospheric plasma spraying on Ti–6Al–4V alloy substrates. The bond strength evaluation of HA/Ti composite coatings was performed according to ASTM C-633 test method. X-ray diffractometer and scanning electron microscopy were applied to identify the phases and the morphologies of the coatings. The bioactivity of HA/Ti composite coating was qualified by immersion of coating in simulated body fluid (SBF). The obtained results revealed that the addition of Ti to HA improved the bonding strength of coating significantly. In the SBF test, the coating surface was covered by carbonate-apatite, which was testified by X-ray photoelectron spectroscope, indicating good bioactivity for HA/Ti composite coating. The bioactivity of the coating has not been reduced by the addition of Ti.

The low bonding strength between hydroxyapatite (HA) and the metal substrate interface of plasma-sprayed HA coating has been a point of potential weakness in its application as a biomedical prosthesis. In the present study, yttria-stabilized (8 wt%) zirconia (YSZ) has been used to enhance the mechanical properties of HA coatings. The effects of YSZ additions (in the range 10–50 wt%) on the phase composition, microstructure, bond strength, elastic modulus, and fracture toughness of plasma-sprayed HA/YSZ composite coatings have been studied. The results indicated that decomposition of HA during plasma spraying was reduced significantly with the addition of zirconia. The higher the zirconia content, the lower the amount of calcium oxide, tricalcium phosphate, and tetracalcium phosphate formed in the coatings. In addition, there was a trace of calcium zirconate formed when less than 30 wt% zirconia was present. A solid solution of HA mixed with YSZ formed during plasma spraying; however, the amount of unmelted particles increased as the zirconia increased. The mechanical properties of the HA/YSZ composite coatings, such as bond strength, elastic modulus, and fracture toughness, increased significantly as the contents of zirconia increased.

Abstract

The increasing interest in strontium incorporation into biomaterials for hard tissue repair is justified by the growing evidence of its beneficial effect on bone. We successfully synthesized hydroxyapatite (HA) thin films with different extents of strontium substitution for calcium (0, 1, 3 or 7 at.%) by pulsed-laser deposition. The coatings displayed a granular surface and a good degree of crystallinity, which slightly diminished as strontium content increased. Osteoblast-like MG63 cells and human osteoclasts were cultured on the thin films up to 21 days. MG63 cells grown on the strontium-doped HA coatings displayed normal morphology, good proliferation and increased values of the differentiation parameters, whereas the number of osteoclasts was negatively influenced by the presence of strontium. The positive effect of the ion on bone cells was particularly evident in the case of coatings deposited from HA at relatively high strontium contents (3–7%), where significantly increased values of alkaline phosphatase activity, osteocalcin, type I collagen and osteoprotegerin/TNF-related activation-induced cytokine receptor ratio, and considerably reduced values of osteoclast proliferation, were observed.

In this study, the bone-like apatite-formation ability of akermanite ceramics (Ca₂MgSi₂O₇) in simulated body fluid (SBF) and the effects of ionic products from akermanite dissolution on osteoblasts and mouse fibroblasts (cell line L929) were investigated. In addition, osteoblast morphology and proliferation on the ceramics were evaluated. The results showed that akermanite ceramics possessed bone-like apatite-formation ability comparable with bioactive wollastonite ceramics (CaSiO₃) after 20 days of soaking in SBF and the mechanism of bone-like apatite formation on akermanite ceramics is similar to that of wollastonite ceramics. The Ca, Si, and Mg ions from akermanite dissolution at certain ranges of concentration significantly stimulated osteoblast and L929 cell proliferation. Furthermore, osteoblasts spread well on the surface of akermanite ceramics, and proliferated with increasing the culture time. The results showed that akermanite ceramics possess bone-like apatite-formation ability and can release soluble ionic products to stimulate cell proliferation, which indicated good bioactivity. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2006

Abstract

In the present study, the effects of a calcium magnesium silicate bioactive ceramic (akermanite) on proliferation and osteoblastic differentiation of human bone marrow stromal cells (hBMSC) have been investigated and compared with the classical ceramic (β-tricalcium phosphate,β-TCP). Akermanite andβ-TCP disks were seeded with hBMSC and kept in growth medium or osteogenic medium for 10 days. Proliferation and osteoblastic differentiation were evaluated on day 1, 4, 7 and 10. The data from the Alamar Blue assay and lactic acid production assay showed that hBMSC proliferated more significantly on akermanite than onβ-TCP. The analysis of osteoblast-related genes, including alkaline phosphatase (ALP), osteopontin (OPN), bone sialoprotein (BSP) and osteocalcin (OC), indicated that akermanite ceramics enhanced the expression of osteoblast-related genes, but type I collagen (COL I) showed no noticeable difference among akermanite andβ-TCP ceramics. Furthermore, this stimulatory effect was observed not only in osteogenic medium, but also in normal growth medium without osteogenic reagents such asl-ascorbic acid, glycerophosphate and dexamethasone. This result suggests that akermanite can promote osteoblastic differentiation of hBMSC in vitro even without osteogenic reagents, and may be used as a bioactive material for bone regeneration and tissue engineering applications.

Poly(lactide-co-glycolide) (PLGA) beads have been widely studied as a potential drug/protein carrier. The main shortcomings of PLGA beads are that they lack bioactivity and controllable drug-delivery ability, and their acidic degradation by-products can lead to pH decrease in the vicinity of the implants. Akermanite (AK) (Ca₂MgSi₂O₇) is a novel bioactive ceramic which has shown excellent bioactivity and degradationin vivo. This study aimed to incorporate AK to PLGA beads to improve the physiochemical, drug-delivery, and biological properties of PLGA beads. The microstructure of beads was characterized by SEM. The effect of AK incorporating into PLGA beads on the mechanical strength, apatite-formation ability, the loading and release of BSA, and the proliferation, and differentiation of bone marrow stromal cells (BMSCs) was investigated. The results showed that the incorporation of AK into PLGA beads altered the anisotropic microporous structure into homogenous one and improved their compressive strength and apatite-formation ability in simulated body fluids (SBF). AK neutralized the acidic products from PLGA beads, leading to stable pH value of 7.4 in biological environment. AK led to a sustainable and controllable release of bovine serum albumin (BSA) in PLGA beads. The incorporation of AK into PLGA beads enhanced the proliferation and alkaline phosphatase activity of BMSCs. This study implies that the incorporation of AK into PLGA beads is a promising method to enhance their physiochemical and biological property. AK/PLGA composite beads are a potential bioactive drug-delivery system for bone tissue repair. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2011.

Abstract

This study investigated thein vitro effects of akermanite, a new kind of Ca-, Mg-, Si-containing bioceramic, on the attachment, proliferation and osteogenic differentiation of human adipose-derived stem cells (hASCs). Parallel comparison of the cellular behaviors of hASCs on the akermanite was made with those on beta-tricalcium phosphate (β-TCP). Scanning electron microscope (SEM) observation and fluorescent DiO labeling were carried out to reveal the attachment and growth of hASCs on the two ceramic surfaces, while the quantitative assay of cell proliferation with time was detected by DNA assay. Osteogenic differentiation of hASCs cultured on the akermanite and β-TCP was assayed by ALP expression and osteocalcin (OCN) deposition, which was further confirmed by Real-time PCR analysis for markers of osteogenic differentiation. It was shown that hASCs attached and spread well on the akermanite as those on β-TCP, and similar proliferation behaviors of hASCs were observed on the two ceramics. Both of them exhibited good compatibility to hASCs with only minor cytotoxicity as compared with the tissue culture plates. Interestingly, the osteogenic differentiation of hASCs could be enhanced on the akermanite compared with that on the β-TCP when the culture time was extended to ∼10 days. Thus, it can be ascertained that akermanite ceramics may serve as a potential scaffold for bone tissue engineering.

Abstract

This study investigated the effects of a calcium magnesium silicate bioceramic (akermanite) for bone regeneration in vitro and in vivo, with β-tricalcium phosphate (β-TCP) as a control. In vitro, the human bone marrow-derived mesenchymal stromal cells (hBMSCs) were cultured in an osteogenic medium supplemented with a certain concentration of two bioceramics' extracts for 20 days. An MTT assay showed that akermanite extract promoted proliferation of hBMSC significantly more than did β-TCP extract. The results of alkaline phosphatase (ALP) activity test and the expression of osteogenic marker genes such as ALP, osteopontin (OPN), osteocalcin (OCN) and bone sialoprotein (BSP) demonstrated that the osteogenic differentiation of hBMSC was enhanced more by akermanite extract than by β-TCP extract. In vivo, a histomorphology analysis and histomorphometry of the two porous bioceramics implants in rabbit femur defect models indicated that both in early- and late-stage implantations, akermanite promoted more osteogenesis and biodegradation than did β-TCP; and in late-stage implantations, the rate of new bone formation was faster in akermanite than in β-TCP. These results suggest that akermanite might be a potential and attractive bioceramic for tissue engineering.

Wollastonite coatings were prepared by plasma spraying and their behaviour during heat treatment was investigated. The phase compositions and the surface morphologies of these coatings were examined by XRD and SEM. While the as-sprayed coating contained plentiful amorphous phase, the heat-treated coating showed high crystallinity. The dissolution behavior of coatings was evaluated by immersion in TRIS-buffer solution. The surface and cross-section morphologies of the coatings after immersion were observed. The results indicated that the preferential dissolution of the amorphous phase led to the disintegration of the coating. In contrast, the heat-treated coating exhibited lower solubility and remained integer. After immersion, pH changes and the concentrations of Ca and Si in the solutions were also measured. It was found that the wollastonite dissolved incongruently, whereby Ca was released at a higher rate than Si, resulting in the presence of a reactive layer enriched in silica at the coating surface. The difference in bioconductivity of wollastonite coatings with different crystallinity was investigated by immersion in simulated body fluid (SBF) solution. While apatite granules appeared on the as-sprayed coating surface after 1 day of immersion, they could not be found at the surface of the heat-treated coating.

Abstract

In this paper, hydroxyapatite (HA) coatings having the crystallinities of 56% and 98% were deposited by the plasma spraying and vapor-flame treatment process. The phase composition and crystallinity of the coatings were investigated by X-ray diffraction and infrared spectra. The dissolution behavior of the coatings in tris-buffer solutions was examined. The results obtained indicated that the coating having the high crystallinity showed the lower dissolution as compared to the low crystallinity coating. The bone bonding ability of HA coatings were observed in vivo by implanted in dog's femur. After 3 months implantation, the high crystallinity coating showed the higher shear strengths and remained integrated, whereas the separation of the coating fragments was clearly observed in the coating having low crystallinity.

For the last 15 years, orthopedic implants have been coated with hydroxyapatite (HA) to improve implant fixation. The osteoconductive effect of HA coatings has been demonstrated in experimental and clinical studies. However, there are ongoing developments to improve the quality of HA coatings. The objective of this study was to investigate whether a rough and highly crystalline HA coating applied by vacuum plasma spraying (VPS) had a positive effect on the osseointegration of special, high-grade titanium (Ti) implants with the same surface roughness. Ti alloy implants were coated (VPS) with special, high-grade Ti or HA. The osseointegration of the implants was evaluated by either light microscopy or pullout tests after 1, 2, and 4 weeks of unloaded implantation in the cancellous bone of 18 sheep. The interface shear strength increased significantly over all time intervals. By 4 weeks, values had reached ∼10N/mm². However, the difference between the coatings was not significant at any time interval. Direct bone–implant contact was significantly different between the coatings after 2 and 4 weeks, and reached 46% for Ti and 68% for HA implants by 4 weeks. This study indicates that the use of a rough and highly crystalline HA coating, applied by VPS, enhances early osseointegration. Accelerated establishment of secondary implant fixation decreases the risk of early loosening. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 66A: 356–363, 2003

Abstract

The bone-bonding ability of a material is often evaluated by examining the ability of apatite to form on its surface in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. However, the validity of this method for evaluating bone-bonding ability has not been assessed systematically. Here, the history of SBF, correlation of the ability of apatite to form on various materials in SBF with their in vivo bone bioactivities, and some examples of the development of novel bioactive materials based on apatite formation in SBF are reviewed. It was concluded that examination of apatite formation on a material in SBF is useful for predicting the in vivo bone bioactivity of a material, and the number of animals used in and the duration of animal experiments can be reduced remarkably by using this method.

Abstract

Dicalcium silicate coatings on titanium alloys substrates were prepared by plasma spraying and immersed in simulated body fluids for a period of time to investigate the nucleation and growth of apatite on the surface of the coatings. Surface structural changes of the specimens were analyzed by XRD and IR technologies. SEM and EDS were used to observe surface morphologies and determine the composition of dicalcium silicate coatings before and after immersion in simulated body fluid. The plasma sprayed dicalcium silicate coating was bonding tightly to the substrate. The coating was mainly composed ofβ-Ca₂SiO₄ and glassy phase. A dense carbonate-containing hydroxyapatite (CHA) layer was formed on the surface of the plasma sprayed dicalcium silicate coating soaked in SBF solution for 2 days. In addition, a silica-rich layer was also observed between CHA layer and coatings. With an increase in the immersion time, the CHA layer gradually became thicker. The results obtained indicated that the plasma sprayed dicalcium silicate coating possesses excellent bioactivity.

Abstract

Wollastonite coatings on titanium alloys substrates were prepared by plasma spraying and incubated in simulated body fluids for different periods to investigate the nucleation and growth of apatite on their surface. Surface structural changes of the specimens were analyzed by XRD and IR technologies. SEM and EDS were used to observe surface morphologies and determine the composition of wollastonite coatings before and after immersion in simulated body fluid. The changes in the concentrations of calcium, silicon and phosphorus in the simulated body fluids due to the immersion of the specimens were measured by inductively coupled plasma atomic emission spectroscopy. The results obtained showed that hydroxycarbonate apatite can be formed on the surface of the coating soaked in SBF for 1 day. With longer immersion periods, the coating surface was covered by hydroxycarbonate apatite, which indicated that the wollastonite coating possesses good bioactivity.

Abstract

Bioactive glass and glass-ceramics in the system CaO–MgO–SiO₂–P₂O₅ have been prepared by the sol–gel and high temperature sintering techniques. The obtained samples were characterized by thermogravimetric and differential thermal analysis (TG/DTA), N₂-adsorption measurement, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). In vitro bioactivity tests were also conducted in simulated body fluid (SBF). The studies of crystallization kinetics under non-isothermal conditions showed the activation energy for crystallization to be 381 kJ/mol and the crystallization mechanism gradually changed from three-dimension growth to two-dimension crystallization with the increase of heating rate. Sintering temperature had great influence on the samples texture and structure. In addition, the apatite-formation on glass and glass-ceramics was confirmed by in vitro tests, and crystallization decreased the samples bioactivity.

Abstract

Single-phase nanocrystalline bredigite powder was successfully synthesized by mechanical activation of talc, calcium carbonate, and amorphous silica powder mixture followed by annealing. Simultaneous thermal analysis (STA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS),and Fourier transform infrared spectroscopy (FT-IR) techniques were employed to characterize various powders. Single-phase nanostructure bredigite powder with crystallite size of about 65 nm was synthesized by 20 h of mechanical activation with subsequent annealing at 1200 °C for 1 h. The bredigite formation mechanism was studied. During the formation process of nanostructure bredigite powder some intermediate compounds such as wollastonite (CaSiO₃), larnite (Ca₂SiO₄), merwinite (Ca₃MgSi₂O₈), and calcium magnesium silicate (Ca₅MgSi₃O₁₂) were formed. It was found that bredigite was not produced directly and that the formation of merwinite, enstatite and Ca₅MgSi₃O₁₂was unavoidable during the synthesis of bredigite.

Graphical abstract

This paper reports the successful synthesis of nanostructure bredigite powder by mechanical activation with subsequent annealing. The results showed that during the formation of bredigite powder some transition compounds such as wollastonite (CaSiO₃), larnite (Ca₂SiO₄), merwinite (Ca₃MgSi₂O₈), and calcium magnesium silicate (Ca₅MgSi₃O₁₂) were formed.

We incubated wollastonite coatings prepared with plasma spraying in simulated body fluids for different periods to investigate the reactivity. The surface structures of wollastonite coatings immersed in simulated body fluids were analyzed with scanning electron microscopy, Auger electron spectroscopy, and transmission electron microscopy. The results showed a carbonate-containing hydroxyapatite layer formed on the surface of a plasma-sprayed wollastonite coating soaked in simulated body fluids, and a silica-rich layer appeared on the surface of the coating before the formation of the carbonate-containing hydroxyapatite layer. The formation mechanism of apatite on the coating surface could be explained in terms of the ionic exchange between H⁺ within simulated body fluids and Ca²⁺ in the coating, which resulted in an increase in the ionic activity product of the apatite in simulated body fluids and provided a specific surface with a lower interface energy to the formation of apatite nuclei. © 2001 Wiley Periodicals, Inc. J Biomed Mater Res 59: 259–264, 2002

Bioceramic spheres have been widely studied for bone/dental filler materials. Conventional methods, such as alginate cross-linking, microemulsion andspray drying, have distinct disadvantages for preparing pure bioceramic spheres with controllable size, bioactivity and degradation. In this study, a containerless processing method, for the first time, was applied to prepare bioceramic spheres for potential bone/dental filling applications. Akermanite (Ca₂MgSi₂O₇, AKT) glass spheres were firstly prepared by a unique containerless processing method. Then, the as-prepared AKT glass spheres were heat-treated at varied temperatures. Furthermore, the effect of heat treatment on the phase transition, surface microstructure,apatite mineralization and ionic dissolution production of AKT spheres has been systematically studied. The interaction of MC3T3 cells with AKT spheres was further studied by investigating cell attachment, proliferation and alkaline phosphate (ALP) activity. The results show that containerless processing is a quite effective method to prepare homogeneous AKT glass spheres with controllable size. Heat-treatment promotes the phase transition from amorphous, semi-crystalline to fully crystalline AKT spheres. Thus, AKT spheres with controllable crystallinity were successfully prepared by combining containerless processing and heat treatment. The as-prepared AKT glass spheres inducedapatite mineralization after soaking in simulated body fluids (SBF) for 7 days; however, AKT spheres treated at 800 °C suppressedapatite mineralization in SBF. Interestingly, AKT spheres treated at 1000 or 1350 °C had distinctapatite mineralization, indicating that the bioactivity of the AKT spheres can be regulated by modulating the heat-treatment-induced crystallinity. Further study has shown that the ionic dissolution production of the containerless-processed AKT spheres can be tailored by controlling the heat-treatment temperatures. The prepared crystalline AKT spheres supported the attachment, spreading, growth and early differentiation of MC3T3 cells, and significantly stimulated the proliferation of MC3T3. Therefore, the containerless-processed AKT spheres may be a unique bone/dental filler material due to their homogeneous structure, controllable size, bioactivity and ionic degradation, as well as their excellent cytocompatibility.

Many animals such as crustacean periodically undergo cyclic molt of the exoskeleton. During this process, amorphous calcium mineral phases are biologically stabilized by magnesium and are reserved for the subsequent rapid formation of new shell tissue. However, it is a mystery how living organisms can regulate the transition of the precursor phases precisely. We reveal that the shell mineralization from the magnesium stabilized precursors is associated with the presence of Asp-rich proteins. It is suggested that a cooperative effect of magnesium and Asp-rich compound can result into a crystallization switch in biomineralization. Our in vitro experiments confirm that magnesium increases the lifetime of amorphous calcium carbonate and calcium phosphate in solution so that the crystallization can be temporarily switched off. Although Asp monomer alone inhibits the crystallization of pure amorphous calcium minerals, it actually reduces the stability of the magnesium-stabilized precursors to switch on the transformation from the amorphous to crystallized phases. These modification effects on crystallization kinetics can be understood by an Asp-enhanced magnesium desolvation model. The interesting magnesium-Asp-based switch is a biologically inspired lesson from nature, which can be developed into an advanced strategy to control material fabrications.