Application of a calcium and phosphorus biomineralization strategy in tooth repair: a systematic review

Biomineralization is a natural process in which organisms regulate the growth of inorganic minerals to form biominerals with unique layered structures, such as bones and teeth, primarily composed of calcium and phosphorus. Tooth decay significantly impacts our daily lives, and the key to tooth regeneration lies in restoring teeth through biomimetic approaches, utilizing mineralization strategies or materials that mimic natural processes. This review delves into the types, properties, and transformations of calcium and phosphorus minerals, followed by an exploration of the mechanisms behind physiological and pathological mineralization in living organisms. It summarizes the mechanisms and commonalities of biomineralization and discusses the advancements in dental biomineralization research, guided by insights into calcium and phosphorus mineral biomineralization. This review concludes by addressing the current challenges and future directions in the field of dental biomimetic mineralization.

Biomimetic Remineralization of Artificial Caries Lesions with a Calcium Coacervate, Its Components and Self-Assembling Peptide P11-4 In Vitro

The application of calcium coacervates (CCs) may hold promise for dental hard tissue remineralization. The aim of this study was to evaluate the effect of the infiltration of artificial enamel lesions with a CC and its single components including polyacrylic acid (PAA) compared to that of the self-assembling peptide P11-4 in a pH-cycling (pHC) model. Enamel specimens were prepared from bovine incisors, partly varnished, and stored in demineralizing solution (DS; pH 4.95; 17 d) to create two enamel lesions per sample. The specimens were randomly allocated to six groups (n = 15). While one lesion per specimen served as the no-treatment control (NTC), another lesion (treatment, T) was etched (H3PO4, 5 s), air-dried and subsequently infiltrated for 10 min with either a CC (10 mg/mL PAA, 50 mM CaCl2 (Ca) and 1 M K2HPO4 (PO4)) (groups CC and CC + DS) or its components PAA, Ca or PO4. As a commercial control, the self-assembling peptide P11-4 (CurodontTM Repair, Credentis, Switzerland) was tested. The specimens were cut perpendicularly to the lesions, with half serving as the baseline (BL) while the other half was exposed to either a demineralization solution for 20 d (pH 4.95; group CC + DS) or pHC for 28 d (pH 4.95, 3 h; pH 7, 21 h; all five of the other groups). The difference in integrated mineral loss between the lesions at BL and after the DS or pHC, respectively, was analyzed using transversal microradiography (ΔΔZ = ΔZpHC - ΔZbaseline). Compared to the NTC, the mineral gain in the T group was significantly higher in the CC + DS, CC and PAA (p < 0.05, Wilcoxon). In all of the other groups, no significant differences between treated and untreated lesions were detected (p > 0.05). Infiltration with the CC and PAA resulted in a consistent mineral gain throughout the lesion body. The CC as well as its component PAA alone promoted the remineralization of artificial caries lesions in the tested pHC model. Infiltration with PAA further resulted in mineral gain in deeper areas of the lesion body.

In Situ Construction of Morphologically Different Hydroxyapatite-Mineralized Structures on a Three-Dimensional Bionic Chitin Scaffold

Slow healing at the tendon-bone interface is a prominent factor in the failure of tendon repair surgeries. The development of functional biomaterials with 3D gradient structures is urgently needed to improve tendon-bone integration. The crystalline form of hydroxyapatite (HAP) has a crucial impact on cell behavior, which directly influences protein adsorption, such as bone morphogenetic protein 2, the adhesion, proliferation, and osteogenic differentiation with cells. This work aimed to generate gradient mineral structures in situ by stabilizing calcium and phosphate ions using a polymer-induced liquid precursor process. To regulate the crystalline growth of HAP at the interface of β-chitin, this work made use of the surface properties of the organic matrix found in cuttlefish bone. These techniques allowed us to prepare an organic-inorganic composite gradient scaffold comprising plate-like HAP mineralized in situ on the surface of the scaffold and fibrous HAP in the scaffold's interior. Organic-inorganic composite gradient materials are anticipated for use in tendon-bone healing produced via the in situ construction of gradient-distributed HAP mineralization layers having varying crystalline morphologies on chitin scaffolds that possess a three-dimensional bionic structure.

Remineralization of Dentinal Lesions Using Biomimetic Agents: A Systematic Review and Meta-Analysis

The objective of this article was to systematically provide an up-to-date review on the different methods of remineralizing human dentine using different biomimetic agents. The authors performed a systematic search within PubMed, Scopus, and Web of Science in addition to the grey literature in Google Scholar^® using MeSH terms. The PICO question was P: human teeth dentinal sections; I: application of biomimetic remineralizing agents; C: other non-biomimetic approaches; O: extent of remineralization and physical properties of remineralized dentine. The initially identified studies were screened for titles and abstracts. Non-English articles, reviews, animal studies, studies involving the resin-dentine interface, and other irrelevant articles were then excluded. The other remaining full-text articles were retrieved. Bibliographies of the remaining articles were searched for relevant studies that could be included. A total of 4741 articles were found, and finally, 39 full-text articles were incorporated in the current systematic review. From these, twenty-six research studies used non-collagenous protein (NCP) analogs to biomineralize dentine, six studies used bioactive materials derived from natural sources, six studies used zinc hydroxyapatite, and one study used amelogenin peptide to induce hydroxyapatite formation on the surface of demineralized dentine. Additive effects of triclosan and epigenin were assessed when combined with commonly available NCPs. Overall, a moderate risk of bias was observed and, hence, the findings of the included studies could be acceptable. A meta-analysis of some similar studies was performed to assess the depth of remineralization and elastic modulus. Despite having high heterogeneity (I² > 90), all the studies showed a significant improvement in biomimetic remineralization efficacy as compared to the control. All the included studies carried out a functional remineralization assessment and found a 90-98% efficacy in the extent of remineralization while the elastic modulus reached 88.78 ± 8.35 GPa, which is close to natural dentine. It is pertinent to note the limitations of these studies that have been carried out in vitro under controlled settings, which lack the effects of a natural oral environment. To conclude, the authors suggest that the biomimetic remineralization of dentine using NCP analogs, bioactive materials, and natural products carries significant potential in treating dentinal lesions; however, more long-term studies are needed to assess their clinical applications in vivo.

Evaluation of different remineralization agents in the treatment of natural caries-affected dentin in permanent teeth

BACKGROUND

In the preventive treatment protocol, providing remineralization of the tissue in demineralized dentin caries is an important step.

OBJECTIVE

In this in vitro study, the effectiveness of remineralization agents in natural caries-affected dentin (NCAD) were investigated.

METHODS

Forty caries slices were prepared from permanent molar dentin with International Caries Detection and Assessment System (ICDAS 2) (Code 3). The interventions with 8 days pH cycling were as follows: Deionized water (DW); 5% Sodium Fluoride (5% NaF) Varnish; Casein Phosphopeptide-Amorphous Calcium Fluoride Phosphate (CPP-ACFP); Calcium Glyserophosphate (CaGP) + Magnesium (Mg) + Xylitol. DIAGNOdent (Laser Fluorescence, LF), Surface Microhardness (SMH), and X-ray Fluorescence (XRF) Spectroscopy measurements were calculated before and after pH cycling.

RESULTS

LF values decreased between 5% NaF, CCP-ACFP and CaGP. NCAD treated with 5% NaF, CaGP and CCP-ACFP exhibited statistically higher hardness compared to the control group. After 5% NaF application, SMH values were significantly higher than the others. There was no statistically significant difference between baseline and after pH cycling hardness of the control group. After cycling, XRF showed that Ca and P concentrations were increased in all groups.

CONCLUSION

The application of agents used in the study could be recommended and promoted as a treatment option of caries dentin for conventional management of caries.

Dentin Biomodification with Flavonoids and Calcium Phosphate Ion Clusters to Improve Dentin Bonding Stability

The purpose of this study was to evaluate the effects of flavonoids and calcium phosphate ion clusters (CPIC) on dentin bonding stability. Seven experimental solutions were synthesized using icaritin (ICT), fisetin (FIS), silibinin (SIB), CPIC, and combinations of one of three flavonoids and CPIC (ICT + C, FIS + C, SIB + C). The experimental solutions were applied to demineralized dentin prior to the application of a universal adhesive. A group without any experimental solution served as a control. Dentin specimens pretreated with the experimental solutions were assayed using Fourier transform infrared (FTIR) spectroscopy. The microtensile bond strength (µTBS) and nanoleakage were evaluated at 24 h and after 10,000 thermocycles. FIS and ICT + C showed significantly higher µTBS than the control group at 24 h. CPIC, ICT + C, FIS + C, and SIB + C showed significantly higher µTBS than the control group after thermocycling. After thermocycling, silver infiltration into the hybrid layer and interfacial gaps was more noticeable in the control group than in the other groups. The FTIR spectra revealed the formation of apatitic minerals in the demineralized dentin in the flavonoid and CPIC combination groups. The pretreatment of demineralized dentin with flavonoids and CPIC improved dentin bonding stability. The flavonoid and CPIC combinations preserved dentin bond strength.

Advances in biomineralization-inspired materials for hard tissue repair

Biomineralization is the process by which organisms form mineralized tissues with hierarchical structures and excellent properties, including the bones and teeth in vertebrates. The underlying mechanisms and pathways of biomineralization provide inspiration for designing and constructing materials to repair hard tissues. In particular, the formation processes of minerals can be partly replicated by utilizing bioinspired artificial materials to mimic the functions of biomolecules or stabilize intermediate mineral phases involved in biomineralization. Here, we review recent advances in biomineralization-inspired materials developed for hard tissue repair. Biomineralization-inspired materials are categorized into different types based on their specific applications, which include bone repair, dentin remineralization, and enamel remineralization. Finally, the advantages and limitations of these materials are summarized, and several perspectives on future directions are discussed.

Highly aligned hierarchical intrafibrillar mineralization of collagen induced by periodic fluid shear stress

Periodic fluid shear stress (FSS) is one of the main mechanical microenvironments in mineralization of bone matrix. To elucidate the mechanism of periodic FSS in collagen mineralization, a mechanical loading induced mineralization system is developed and compared with traditional polyacrylic acid (PAA) induced mineralization. Fourier transform infrared (FTIR) spectroscopy, calcium-to-phosphorus molar ratio and transmission electron microscopy (TEM) demonstrate that both periodic FSS and PAA can control the size of amorphous calcium phosphate (ACP) to avoid aggregation and help the formation of intrafibrillar mineralization. Differently, periodic FSS under a proper cycle and range can accelerate the conversion of ACP to apatite crystals and alleviate the reduced transformation caused by PAA. Under the action of template analogues, periodic FSS can also promote the formation of highly oriented hierarchical intrafibrillar mineralized (HIM) collagen. These findings are helpful for understanding the mechanism of collagen mineralization in natural bone matrix and contribute to the design of novel bone substitute materials with hierarchical structures.

Appropriate regulation of magnesium on hydroxyapatite crystallization in simulated body fluids

The regulation effect of Mg²⁺ on HAP crystallization is closely related to the adding time of Mg²⁺. The introduction of Mg²⁺ in the ACP unstable stage is unable to inhibit HAP crystallization.

Effect of Remineralized Collagen on Dentin Bond Strength through Calcium Phosphate Ion Clusters or Metastable Calcium Phosphate Solution

This study aimed to investigate whether dentin remineralization and micro-tensile bond strength increase when using calcium phosphate ion clusters (CPICs) or metastable Ca-P. After being etched, each dentin specimen was designated into four groups and treated with the appropriate solution for 1 min: 100% ethanol, 2 and 1 mg/mL of CPICs, and metastable Ca-P. The specimens were then prepared for scanning electron microscopy (SEM), transmission electron microscropy (TEM) imaging, a matrix metalloproteinases inhibition assay, and the micro-tensile bond strength test. To compare among the groups, one-way analysis of variance was performed. In the SEM imaging, with a rising concentration of CPICs, the degree of remineralization of dentin increased significantly. The metastable Ca-P treated specimens showed a similar level of remineralization as the 1 mg/mL CPICs treated specimens. The TEM imaging also revealed that dentin remineralization occurs in a CPICs concentration-dependent manner between the demineralized dentin and the resin layer. Furthermore, the results of micro-tensile bond strength showed the same trend as the results confirmed by SEM and TEM. We demonstrated that a 1 min pretreatment of CPICs or metastable Ca-P in etched dentin collagen fibril can achieve biomimetic remineralization and increase micro-tensile bond strength.

Effect of silver diamine fluoride and proanthocyanidin on resistance of carious dentin to acid challenges

The aim of this study was to evaluate the effect of silver diamine fluoride and grape seed extract on the microstructure and mechanical properties of carious dentin following exposure to acidic challenge. Ninety-eight molars with occlusal caries were used. In the control group the specimens were kept in distilled water. In the GSE group, the specimens were immersed in 6.5% grape seed extract solution for 30 minutes. In the SDF group, the specimens were immersed in 30% SDF solution for 4 minutes. In the GSE+SDF group, the specimens were immersed in 6.5% grape seed extract solution for 30 minutes and then exposed to 30% SDF solution for 4 minutes. All the groups underwent pH cycling model for 8 days. Microhardness measurements were taken at the baseline before surface treatments and after pH cycling. Elastic modulus was measured, after pH cycling. In the control group, the final hardness was significantly lower than the initial hardness (P = 0.001). In the SDF group, the final hardness was significantly higher than the initial hardness (P < 0.001). There was no significant difference between the initial and final hardness values in the GSE and GSE + SDF groups (p = 0.92, p = 0.07). The H₁-H₀ in the SDF group was significantly higher than the other groups (P<0.05). Moreover, elastic modulus of the experimental groups except GSE+SDF group was significantly higher than control. The highest mean elastic modulus was detected in the SDF group (P<0.001). The use of SDF and GSE prior to the acid challenge improved mechanical properties. Microstructural investigation, using scanning electron microscope showed dentin structure protection against acid challenges with SDF treatment and collagen matrix stabilization with GSE treatment. However combined use of these agents was not beneficious.

The Significance and Utilisation of Biomimetic and Bioinspired Strategies in the Field of Biomedical Material Engineering: The Case of Calcium Phosphat-Protein Template Constructs

This review provides a summary of recent research on biomimetic and bioinspired strategies applied in the field of biomedical material engineering and focusing particularly on calcium phosphate-protein template constructs inspired by biomineralisation. A description of and discussion on the biomineralisation process is followed by a general summary of the application of the biomimetic and bioinspired strategies in the fields of biomedical material engineering and regenerative medicine. Particular attention is devoted to the description of individual peptides and proteins that serve as templates for the biomimetic mineralisation of calcium phosphate. Moreover, the review also presents a description of smart devices including delivery systems and constructs with specific functions. The paper concludes with a summary of and discussion on potential future developments in this field.

Influence of molecular weight and concentration of carboxymethyl chitosan on biomimetic mineralization of collagen

The objective of the present study was to systematically investigate the influence of molecular weight (MW) and concentration of carboxymethyl chitosan (CMC), which served as non-collagenous protein (NCP) surrogates, on biomimetic mineralization of type I collagen. Supersaturated CMC-stabilized amorphous calcium-phosphate (CMC-ACP) dispersions containing different MWs (20 kDa, 60 kDa, 150 kDa) and concentrations (25, 50, 100, 200, 400 μg ml⁻¹) of CMC were prepared. After mineralization in the aforementioned dispersions for 7 days, the pattern and extent of biomimetic mineralization of collagen scaffolds were investigated. Our study showed that increasing CMC concentration resulted in increasing stability and decreasing particle size of CMC-ACP dispersions. Images from scanning and transmission electron microscopy revealed that intrafibrillar mineralization of collagen was obtained with 20k-200, 60k-100, 60k-200 and 150k-200 CMC-ACP dispersions, with hydroxyapatite (HAp) formation confirmed by Fourier transform infrared spectroscopy and X-ray diffraction measurements, whereas HAp formed extrafibrillar clusters in other collagen scaffolds. Thermogravimetric analysis showed that the combined effect of MW and concentration of CMC contributed to different extents of biomimetic mineralization, and was correlated with the stability and particle size of CMC-ACP dispersions, and the size-exclusion characteristics of type I collagen. The results of this work support the effective function of CMC as NCP analogs, and provide parameters of MWs and concentrations of CMC for applications in hard tissue engineering as well as insights into intersections of mechanisms in biomimetic mineralization.

The study systematically investigated the influence of molecular weight and concentration of CMC on CMC-ACP nanoparticles and biomimetic mineralization.

[Effect of genipin pretreatment on type Ⅰ collagen mineralization]

OBJECTIVE

To investigate the effects of bio-crosslinker genipin pretreatment on type Ⅰ collagen mineralization.

METHODS

Type Ⅰ collagen gels were prepared and pretreated with 0.5wt%genipin (experimental group) and deionized water (control group) for 2 h, respectively. The pretreated products were subjected to Fourier transform infrared spectroscopy (FT-IR). Reconstituted collagen fibrils were pretreated with genipin or deionized water for 2 h and were mineralized for 4 h. The collagen density and mineralization degree were examined with transmission electron microscopy (TEM) and analyzed with ImageJ software. Then scanning electron microscopy (SEM) and TEM were used to observe the mineralization of cross-linked demineralized dentin collagen.

RESULTS

FT-IR spectrum showed that the genipin was crosslinked with collagen. TEM observation and ImageJ results showed that after 4 h mineralization, the mineralization effect of 0.5wt% genipin group was significantly better than that of the control group[(73.3±5.3)%vs.(7.4±3.5)%,P<0.01]. TEM and SEM observation showed that the mineralization rate of type Ⅰ collagen and demineralized dentin pretreated with genipin were significantly faster than that of the control group.

CONCLUSIONS

The study demonstrates that 0.5 wt% concentration of genipin can significantly promote the mineralization of type Ⅰ collagen.

Multiscale micromechanical modeling of the elastic properties of dentin

The paper focuses on multiscale modeling of the elastic properties of dentin. It is modeled as a hierarchical structure consisting of collagen fibers and hydroxyapatite particles at the lower level. Different concentrations of hydroxyapatite in this tissue correspond to peritubular and intertubular dentins. Then, the overall material is modeled as intertubular dentin matrix containing parallel cylindrical holes (the tubules) surrounded by layers of peritubular dentin. At each microstructural level, the model accounts for anisotropy of the constituents. The model predictions are compared with experimental data available in literature.

Promotion effect of immobilized chondroitin sulfate on intrafibrillar mineralization of collagen

Chondroitin sulfate (CS) is widespread in mineralized tissues and is considered to play crucial roles during the mineralization process. However, its role in biomineralization remains controversial. In the present study, CS is immobilized to collagen fibrils to mimic its state in biomineralization. The results demonstrate that immobilized CS on collagen fibrils accelerates calcium phosphate nucleation and significantly promotes collagen mineralization by accumulating calcium ions in collagen fibrils. The stochastic optical reconstruction microscopy results confirm that CS gives the specific nucleation sites for calcium phosphate to preferentially form, the improved intrafibrillar heterogeneous nucleation of calcium phosphate facilitates intrafibrillar mineralization. It is found remarkably accelerated remineralization of CS immobilized demineralized dentin is achieved. This study offers insight on the understanding of the function of the biomacromolecule CS on the biomineralization front. In addition, CS effectively promotes intrafibrillar mineralization, which highlights fine prospect for CS to reconstruct collagen-mineralized tissues as a natural material.

The importance of being amorphous: calcium and magnesium phosphates in the human body

This article focuses on the relevance of amorphous calcium (and magnesium) phosphates in living organisms. Although crystalline calcium phosphate (CaP)-based materials are known to constitute the major inorganic constituents of human hard tissues, amorphous CaP-based structures, often in combination with magnesium, are frequently employed by Nature to build up components of our body and guarantee their proper functioning. After a brief description of amorphous calcium phosphate (ACP) formation mechanism and structure, this paper is focused on the stabilization strategies that can be used to enhance the lifetime of the poorly stable amorphous phase. The various locations of our body in which ACP (pure or in combination with Mg²⁺) can be found (i.e. bone, enamel, small intestine, calciprotein particles and casein micelles) are highlighted, showing how the amorphous nature of ACP is often of paramount importance for the achievement of a specific physiological function. The last section is devoted to ACP-based biomaterials, focusing on how these materials differ from their crystalline counterparts in terms of biological response.

Apatite minerals derived from collagen phosphorylation modification induce the hierarchical intrafibrillar mineralization of collagen fibers

Collagen is the critical organic component of bone matrix, which is the template for bone biomineralization. Phosphorylation modification of collagen plays an important role in the process of biomineralization in vivo, but its mechanism on in vitro biomimetic mineralization of bone matrix remains unclear at the molecular level. Sodium tripolyphosphate is used to phosphorylate collagen in this study and new phosphate groups appear on collagen fibrils after phosphorylation modification. The chelating amount of calcium is improved linearly with increasing the phosphorylation degree of collagen fibrils, which demonstrates that the introduced phosphate groups serve as new nucleation sites and participate in the formation of apatite minerals inside the collagen fibers. Stabilized nanosized amorphous calcium phosphate by polyacrylic acid can also permeate into collagen fibers and further transform into another layer of hydroxyapatite minerals. Both layers of apatite minerals eventually induce the formation of hierarchical intrafibrillar mineralization structure within the phosphorylated collagen fibers. The present research enriches the previous biomineralization mechanism of bone matrix, provides a facile strategy for biomimetic mineralization of collagen, and offers the basis for future investigation of the advanced bone substitute materials.

A Biomimetic Model for Mineralization of Type-I Collagen Fibrils

The bone and dentin mainly consist of type-I collagen fibrils mineralized by hydroxyapatite (HAP) nanocrystals. In vitro biomimetic models based on self-assembled collagen fibrils have been widely used in studying the mineralization mechanism of type-I collagen. In this chapter, the protocol we used to build a biomimetic model for the mechanistic study of type-I collagen mineralization is described. Type-I collagen extracted from rat tail tendon or horse tendon is self-assembled into fibrils and mineralized by HAP in vitro. The mineralization process is monitored by cryoTEM in combination with two-dimensional (2D) and three-dimensional (3D) stochastic optical reconstruction microscopy (STORM), which enables in situ and high-resolution visualization of the process.

Phosphorylated chitosan to promote biomimetic mineralization of type I collagen as a strategy for dentin repair and bone tissue engineering

This novel biomimetic mineralization technique provides an efficient method to produce an advanced mineralized matrix.

Enhanced Intrafibrillar Mineralization of Collagen Fibrils Induced by Brushlike Polymers

Biomimetic mineralization of collagen fibrils is an essential process because the mineralized collagen fibers constitute the basic building block of natural bone. To overcome the limited availability and high cost of the noncollagenous proteins (NCPs) that regulate the mineralization process of collagen, commercially available analogues were developed to replicate sequestration and templating functions of NCPs. The use of branched polymers in intrafibrillar mineralization applications has never been explored. In this work, two novel carboxyl-rich brushlike polymers, a carboxylated polyethylene glycol terpolymer (PEG-COOH) and a polyethylene glycol/poly(acrylic acid) copolymer (PEG-PAA), were synthesized and modified to mimic the sequestration function of NCPs to induce intrafibrillar mineralization of collagen fibrils. It was found that these synthetic brushlike polymers are able to induce intrafibrillar mineralization by stabilizing the amorphous calcium phosphate (ACP) nanoprecursors and subsequently facilitating the infiltration of ACP into the gap zone of collagen microfibrils. Moreover, the weight ratios of mineral to collagen in the mineralized collagen fibrils in the presence of these brushlike polymers were 2.17 ± 0.07 for PEG-COOH and 2.23 ± 0.03 for PEG-PAA, while it is only 1.81 ± 0.21 for linear PAA. Plausible mineralization mechanisms using brushlike polymers are proposed that offer significant insight into the understanding of collagen mineralization induced by synthetic NCP analogues.

Effects of Molecular Weight and Concentration of Poly(Acrylic Acid) on Biomimetic Mineralization of Collagen

Inspired by nature, poly(acrylic acid) (PAA) and other polyelectrolytes have been used as noncollagenous proteins (NCPs) surrogates for biomimetic intrafibrillar mineralization of collagen fibrils and thus, to model the ultrastructure of bone, to study the mechanism of bone mineralization and, more scarcely to fabricate scaffolds for hard tissue engineering. The objective of this study was to systematically investigate the effect of the molecular weight (MW) and the concentration of PAA on the rate and pattern of biomineralization of collagen matrices. Densified type I collagen films were mineralized in supersaturated PAA-stabilized amorphous calcium-phosphate (PAA-ACP) solutions containing increasing MW (2 kDa, 50 kDA, 450 kDa) and concentrations (10, 25, 50 mg/L) of PAA up to 7 days. The stability and physical properties of collagen-free PAA-ACP solutions were also investigated. In our system, lowering PAA MW and increasing PAA concentration resulted in solutions with increasing stability. Over stable PAA-ACP solutions that fully inhibited mineralization of the collagen matrices were achieved using PAA 2k-50. Conversely, unstable solutions were obtained using high PAA MW at low concentrations. Nucleation and growth of significant amount of extrafibrillar minerals on the collagen fibrils was obtained using these solutions. In a wide range of combined MW and concentration of PAA we obtained intrafibrillar mineralization of collagen with hydroxyapatite crystals aligned parallel to the collagen fibril as in natural tissues. Intrafibrillar mineralization was correlated with PAA-ACP stability and growth of the PAA-ACP particles in solution. Our results support using PAA to surrogate NCPs function as selective inhibitors or promoters of biological mineralization and provide parameters to manufacture new biomimetic scaffolds and constructs for bone and dentin tissue engineering.

Polyphenol uses in biomaterials engineering

Polyphenols are micronutrients obtained from diet that have been suggested to play an important role in health. The health benefits of polyphenols and their protective effects in food systems as antioxidant compounds are well known and have been extensively investigated. However, their functional roles as a "processing cofactor" in tissue engineering applications are less widely known. This review focuses on the functionality of polyphenols and their application in biomaterials. Polyphenols have been used to stabilize collagen and to improve its resistance to degradation in biological systems. Therefore, they have been proposed to improve the performance of biomedical devices used in cardiovascular systems by improving the mechanical properties of grafted heart valves, enhancing microcirculation through the relaxation of the arterial walls and improving the capillary blood flow and pressure resistance. Polyphenols have been found to stimulate bone formation, mineralization, as well as the proliferation, differentiation, and the survival of osteoblasts. These effects are brought about by the stimulatory effect of polyphenols on osteoblast cells and their protective effect against oxidative stress and inflammatory cytokines. In addition, polyphenols inhibit the differentiation of the osteoclast cells. Collectively, these actions lead to promote bone formation and to reduce bone resorption, respectively. Moreover, polyphenols can increase the cross-linking of dentine and hence its mechanical stability. Overall, polyphenols provide interesting properties that will stimulate further research in the bioengineering field.

Self-Etch Adhesive as a Carrier for ACP Nanoprecursors to Deliver Biomimetic Remineralization

Lab biomineralization should be carried out in an actual clinical practice. This study evaluated self-etch adhesive as a carrier for amorphous calcium phosphate (ACP) nanoprecursors to continuously deliver biomimetic remineralization of self-assembly type I collagen and demineralized dentin. Si-containing ACP particles (Si-ACP) stabilized with polyaspartic acid (PAsp) were synthesized and characterized by transmission electron microscopy (TEM), scanning electron microscopy-energy-dispersive X-ray spectroscopy, Fourier transform infrared analysis, X-ray powder diffractometry, and X-ray phototelectron spectroscopy. The biomimetic remineralization of single-layer reconstituted type I collagen fibrils and demineralized dentin was analyzed by using two one-bottle self-etch dentin adhesives (Clearfil S3 Bond (S3), Kurraray-Noritake; Adper Easy One (AEO), 3 M ESPE) as a carrier loaded (or not, in the case of the control) with 25 wt % of Si-ACP particles. In vitro cytotoxicity assessed by the Cell Counting Kit-8 indicated that the Si-ACP particles had no adverse effect on cell viability. The capacity for Ca and P ions release from cured Si-ACP-containing adhesives (S3, AEO) was evaluated by inductively coupled plasma-atomic emission spectrometry, revealing the successively increasing release of Ca and P ions for 28 days. The intra- and extrafibrillar remineralization of type I collagen and demineralized dentin was confirmed by TEM and selected-area electron diffraction when the adhesives were used as a carrier loaded with Si-ACP particles. Therefore, we propose self-etch adhesive as a novel carrier for ACP nanoprecursors to continuously deliver biomimetic remineralization.

Chlorhexidine-Loaded Amorphous Calcium Phosphate Nanoparticles for Inhibiting Degradation and Inducing Mineralization of Type I Collagen

A major shortcoming of contemporary dentin adhesives is their limited durability. Exposed collagen fibrils within the bonding interface are degraded by matrix metalloproteinases (MMPs), resulting in aging of the resin-dentin bond. In this study, chlorhexidine-loaded amorphous calcium phosphate (ACP) nanoparticles were synthesized to induce the mineralization of collagen fibrils. The nanoparticles sustainably released chlorhexidine to inhibit MMPs during mineralization. Three types of ACP nanoparticles were prepared: N-ACP containing no chlorhexidine, C-ACP containing chlorhexidine acetate, and G-ACP containing chlorhexidine gluconate, which had a higher drug-loading than C-ACP. Scanning and transmission electron microscopy indicated that the synthesized nanoparticles had diameters of less than 100 nm. Some had diameters of less than 40 nm, which was smaller than the width of gap zones in the collagen fibrils. Energy dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and high performance liquid chromatography confirmed the presence of chlorhexidine in the nanoparticles. X-ray diffraction confirmed that the nanoparticles were amorphous. The drug loading was 0.11% for C-ACP and 0.53% for G-ACP. In vitro release profiles indicated that chlorhexidine was released sustainably via first-order kinetics. Released chlorhexidine inhibited the degradation of collagen in human dentine powder, and its effect lasted longer than that of pure chlorhexidine of the same concentration. The ACP could induce the mineralization of self-assembled type I collagen fibrils. The chlorhexidine-loaded ACP nanoparticles sustainably released chlorhexidine and ACP under appropriate conditions. This is useful for inhibiting degradation and inducing the mineralization of dentine collagen fibrils.

From molecules to macrostructures: recent development of bioinspired hard tissue repair

This review summarizes the bioinspired strategies for hard tissue repair, ranging from molecule-induced mineralization, to microscale assembly to macroscaffold fabrication.

Methods for biomimetic remineralization of human dentine: a systematic review

This study aimed to review the laboratory methods on biomimetic remineralization of demineralized human dentine. A systematic search of the publications in the PubMed, TRIP, and Web of Science databases was performed. Titles and abstracts of initially identified publications were screened. Clinical trials, reviews, non-English articles, resin-dentine interface studies, hybrid layer studies, hybrid scaffolds studies, and irrelevant studies were excluded. The remaining papers were retrieved with full texts. Manual screening was conducted on the bibliographies of remaining papers to identify relevant articles. A total of 716 studies were found, and 690 were excluded after initial screening. Two articles were identified from the bibliographies of the remaining papers. After retrieving the full text, 23 were included in this systematic review. Sixteen studies used analogues to mimic the functions of non-collagenous proteins in biomineralization of dentine, and four studies used bioactive materials to induce apatite formation on demineralized dentine surface. One study used zinc as a bioactive element, one study used polydopamine, and another study constructed an agarose hydrogel system for biomimetic mineralization of dentine. Many studies reported success in biomimetic mineralization of dentine, including the use of non-collagenous protein analogues, bioactive materials, or elements and agarose hydrogel system.

Stabilizing amorphous calcium phosphate phase by citrate adsorption

Citrate controls nucleation by association with a precursor amorphous phase, which inhibits the surface reaction for nucleation.

Biomimetic promotion of dentin remineralization usingl-glutamic acid: inspiration from biomineralization proteins

The decalcified dentin layer was remineralized in two days using the cooperative effect of PAA and Glu.