Effects of amino acids on conversion of calcium carbonate to hydroxyapatite

Enhanced anti-biofilm and anti-caries potential of arginine combined with calcium glycerophosphate and fluoride

OBJECTIVE

The aim of this work was to evaluate the antibiofilm and anticaries properties of the association of arginine (Arg) with calcium glycerophosphate (CaGP) and fluoride (F).

METHODS

An active attachment, polymicrobial biofilm model obtained from saliva and bovine teeth discs were used. After the initial biofilm growth period, the enamel discs were transferred to culture medium. The treatment solutions were added to the culture media to achieve the desired final concentration. The following groups were used: negative control (Control); F (110 ppm F); CaGP (0.05 %); Arg (0.8 %) and their associations (F + CaGP; Arg + F; Arg + CaGP; Arg +F + CaGP). The following analyses were carried out: bacterial viability (total bacteria, aciduric bacteria and mutans streptococci), pH assessment of the spent culture medium, dry weight quantification, evaluation of surface hardness loss (%SH) and subsurface mineral content. Normality and homoscedasticity were tested (Shapiro-Wilk and Levene's test) and the following tests were applied: two-way ANOVA (acidogenicity), Kruskall-Wallis (microbial viability) and one way ANOVA (dry weight, %SH, mineral content).

RESULTS

The association Arg + F + CaGP resulted in the lowest surface hardness loss in tooth enamel (-10.9 ± 2.3 %; p < 0.05). Arg +F + CaGP exhibited highest values of subsurface mineral content (10.1 ± 2.9 gHAP/cm3) in comparison to Control and F (p < 0.05). In comparison to Control and F, Arg +F + CaGP promoted the highest reduction in aciduric bacteria and mutans streptococci (5.7 ± 0.4; 4.4 ± 0.5 logCFU/mL, p < 0.05).

CONCLUSIONS

The Arg-F-Ca association demonstrated to be the most effective combination in protecting the loss of surface hardness and subsurface mineral content, in addition to controlling important virulence factors of the cariogenic biofilm.

CLINICAL SIGNIFICANCE

Our findings provide evidence that the Arg-F-Ca association showed an additive effect, particularly concerning protection against enamel demineralization. The combination of these compounds may be a strategy for patients at high risk of caries.

Rapid Deposition of the Biomimetic Hydroxyapatite-Polydopamine-Amino Acid Composite Layers onto the Natural Enamel

In this work, we developed a technology that enables rapid deposition of biomimetic composite films onto natural enamel slices (known as biotemplates). These films are composed of polydopamine (PDA) and nanocrystalline carbonate-substituted hydroxyapatite (nano-cHAp) that have been functionalized with amino acid l-Arginine. We utilized atomic force microscopy (AFM) and scattering scanning near-field optical microscopy (s-SNOM) combined with infrared (IR) synchrotron to achieve nanoscale spatial resolution for both IR absorption and topography analyses. This combined analytical modality allowed us to understand how morphology connects to local changes in the chemical environment on the biotemplate surface during the deposition of the bioinspired coating. Our findings revealed that when using the proposed technology and after the deposition of the first PDA layer, the film formed on the enamel surface nearly covers the entire surface of the specimen whose thickness is larger on the surface of the emerging enamel prisms. Calculation of the crystallinity index for the biomimetic layer showed a multiple increase compared with natural enamel. This indicates regular and dense aggregation of nano-cHAp into larger crystals, imitating the morphology of natural enamel rods. The microhardness of the formed PDA-based biomimetic layer mineralized with nano-cHAp functionalized with amino acid l-Arginine deposited on natural enamel was practically the same as that of natural enamel. The characterization of nano-cHAp-amino acid-PDA layers using IR and Raman microspectroscopy showed that l-arginine acts as a conjunction agent in the formation of mineralized biomimetic composite coatings. The uniformity of the mechanisms of PDA layer formation under different deposition conditions and substrate types allows for the formation of coatings regardless of the macro- and micromorphology of the template. Therefore, the results obtained in this work have a high potential for future clinical applications in dental practice.

3D stem cell spheroids with urchin-like hydroxyapatite microparticles enhance osteogenesis of stem cells

Cell therapy (also known as cell transplantation) has been considered promising as a next-generation living-cell therapy strategy to surpass the effects of traditional drugs. However, their practical clinical uses and product conversion are hampered by the unsatisfied viability and efficacy of the transplanted cells. Herein, we propose a synergistic enhancement strategy to address these issues by constructing 3D stem cell spheroids integrated with urchin-like hydroxyapatite microparticles (uHA). Specifically, cell-sized uHA microparticles were synthesized via a simple hydrothermal method using glutamic acid (Glu, E) as the co-template with good biocompatibility and structural antimicrobial performance (denoted as E-uHA). Combining with a hanging drop method, stem cell spheroids integrated with E-uHA were successfully obtained by culturing bone marrow mesenchymal stem cells (BMSCs) with a low concentration of the E-uHA suspensions (10 μg mL-1). The resulting composite spheroids of BMSCs/E-uHA deliver a high cellular viability, migration activity, and a superior osteogenic property compared to the 2D cultured counterpart or other BMSC spheroids. This work provides an effective strategy for integrating a secondary bio-functional component into stem cell spheroids for designing more cell therapy options with boosted cellular viability and therapeutic effect.

Ceramic Materials for Biomedical Applications: An Overview on Properties and Fabrication Processes

A growing interest in creating advanced biomaterials with specific physical and chemical properties is currently being observed. These high-standard materials must be capable to integrate into biological environments such as the oral cavity or other anatomical regions in the human body. Given these requirements, ceramic biomaterials offer a feasible solution in terms of mechanical strength, biological functionality, and biocompatibility. In this review, the fundamental physical, chemical, and mechanical properties of the main ceramic biomaterials and ceramic nanocomposites are drawn, along with some primary related applications in biomedical fields, such as orthopedics, dentistry, and regenerative medicine. Furthermore, an in-depth focus on bone-tissue engineering and biomimetic ceramic scaffold design and fabrication is presented.

Hydroxyapatite-Tethered Peptide Hydrogel Promotes Osteogenesis

Hydroxyapatite (HAp) as natural bone composition is highly osteoinductive. To harvest its osteoinductivity in bone regenerative engineering, the HAp-supporting hydrogel is urgently needed to minimize inhomogeneous aggregation of HAp. Here, we developed a HAp-stabilizing hydrogel based on peptide self-assembly. FmocFFRR was efficient for HAp-capping due to arginine-phosphate interaction. Tethering FmocFFRR on the HAp surface facilitated self-assembly to form FmocFFRR/HAp hybrid hydrogel, enabling stable dispersion of HAp in it. The molecular interactions between FmocFFRR and HAp particles were studied using microscopic and spectral characterizations. FmocFFRR/HAp hydrogel exhibited more enhanced mechanical properties than FmocFFRR. The biocompatibility of FmocFFRR/HAp hydrogel was verified using an ATP assay and live-dead staining assay. More importantly, FmocFFRR/HAp hydrogel not only enabled cell attachment on its surface, but also supported 3D cell culturing inside the hydrogel. Further, 3D culturing of MC3T3-E1 preosteoblasts inside FmocFFRR/HAp hydrogel significantly enhanced the expressions of osteogenesis markers, including alkaline phosphate (ALP), type-I collagen (COL1), and osteocalcin (OCN), demonstrating the promoting effect of osteoblast differentiation. These findings inspire its potential application in bone regenerative engineering.

Pea pod-mimicking hydroxyapatite nanowhisker-reinforced poly(lactic acid) composites with bone-like strength

The anisotropic hierarchical structures of naturally derived materials have offered useful design principles for the fabrication of high-strength and functional materials. Herein, we unraveled a structure-by-bionics approach to construction of pea pod-mimicking architecture for poly(lactic acid) (PLA) composites impregnated with hydroxyapatite nanowhiskers (HANWs). The HANWs (length of 80-120 nm, diameter of ~30 nm) were customized using microwave-assisted aqueous biomineralization at minute level, which were incorporated into PLA microfibers by electrospinning with filler loadings of 10-30 wt%. The membranes comprising HANW-modified PLA microfibers were stacked and structured into composite films, strategically involving high-pressure compression at a relatively low temperature to impart the confined structuring mechanisms. It thus allowed partial melting and thinning of PLA microfibers into nanofibers, onto which the discrete HANWs were tightly adhered and embedded, showing distinguished architectural configurations identical with pea pod. More importantly, the mechanical properties and bioactivity were remarkably promoted, as demonstrated by the increments of over 54 % and nearly 72 % for the yield strength and elastic modulus (71.6 and 2547 MPa) of the structured composite loaded 30 wt% HANWs compared to those of pure PLA (46.4 and 1484 MPa), as accompanied by significant improvements in the bioactivity to nucleate and create apatite entities in mineral solution. The unusual combination of excellent biological characteristics and bone-like mechanical elasticity and extensibility make the structured PLA composites promising for guided bone/tissue regeneration therapy.

Biomimetic Mineralization of Tooth Enamel Using Nanocrystalline Hydroxyapatite under Various Dental Surface Pretreatment Conditions

In this report, we demonstrated the formation of a biomimetic mineralizing layer obtained on the surface of dental enamel (biotemplate) using bioinspired nanocrystalline carbonate-substituted calcium hydroxyapatite (ncHAp), whose physical and chemical properties are closest to the natural apatite dental matrix, together with a complex of polyfunctional organic and polar amino acids. Using a set of structural, spectroscopy, and advanced microscopy techniques, we confirmed the formation of a nanosized ncHAp-based mineralized layer, as well as studying its chemical, substructural, and morphological features by means of various methods for the pretreatment of dental enamel. The pretreatment of a biotemplate in an alkaline solution of Ca(OH)₂ and an amino acid booster, together with the executed subsequent mineralization with ncHAp, led to the formation of a mineralized layer with homogeneous micromorphology and the preferential orientation of the ncHAp nanocrystals. It was shown that the homogeneous crystallization of hydroxyapatite on the biotemplate surface and binding of individual nanocrystals and agglomerates into a single complex by an amino acid booster resulted in an increase (~15%) in the nanohardness value in the enamel rods area, compared to that of healthy natural enamel. Obtaining a similar hierarchy and cleavage characteristics as natural enamel in the mineralized layer, taking into account the micromorphological features of dental tissue, is an urgent problem for future research.

Process optimization for the rapid conversion of calcite into hydroxyapatite microspheres for chromatographic applications

Microsphere hydroxyapatite (HAp) is widely used in various biomedical and chromatographic applications. The work described in this manuscript focuses on a dissolution precipitation method for production of HAp microspheres. This method overcomes certain drawbacks of conventional preparation methods used for HAp preparation, which produce polydisperse particles and are time-consuming and expensive. In the present work, the calcium carbonate (calcite) particles were directly and rapidly converted into HAp microspheres using an inexpensive dissolution precipitation method. The effects of the reaction temperature, time, and mechanical stirring rates were studied, and the reaction parameters were optimized. As confirmed by the XRD studies, the higher reaction temperature and time promote complete HAp conversion, while calcite residues were observed for lower temperatures and times. SEM images show the influence of reaction parameters on the surface microstructure of the microspheres produced. It was observed that the HAp microspheres undergo disintegration at a higher stirring rate. The reaction parameters optimized in this work were ideal for preparing HAp microspheres. The resultant HAp particles were utilized as matrices for chromatographic separation of protein mixtures.

The influence of single and binary mixtures of collagen amino acids on the structure of synthetic calcium hydroxyapatite as a nanobiomaterial

The influence of mixtures of collagen amino acids on hydroxyapatite has been determined. Glycine has the strongest effect on hydroxyapatite, and proline the weakest. Proline abolishes the effect of other amino acids on hydroxyapatite.

Synthesis and transformation of calcium carbonate polymorphs with chiral purine nucleotides

Crystallization of CaCO3 polymorphs is controlled using the chiral purine nucleotides adenosine triphosphate (ATP) and guanosine triphosphate (GTP). The effects of ATP and GTP on the transformation of calcite into vaterite are investigated.

Investigation of the Effect of Nanocrystalline Calcium Carbonate-Substituted Hydroxyapatite and L-Lysine and L-Arginine Surface Interactions on the Molecular Properties of Dental Biomimetic Composites

Differences in the surface interactions of non-stoichiometric nanocrystalline B-type carbonate-substituted hydroxyapatite (n-cHAp) with the amino acids L-Lysine hydrochloride (L-LysHCl) and L-Arginine hydrochloride (L-ArgHCl) in acidic and alkaline media were determined using structural and spectroscopic analysis methods. The obtained data confirm that hydroxyapatite synthesized using our technique, which was used to develop the n-cHAp/L-LysHCl and n-cHAp/L-ArgHCl composites, is nanocrystalline. Studies of molecular composition of the samples by Fourier transform infrared spectroscopy under the change in the charge state of L-Lysine in environments with different alkalinity are consistent with the results of X-ray diffraction analysis, as evidenced by the redistribution of the modes' intensities in the spectra that is correlated with the side chains, i.e., amide and carboxyl groups, of the amino acid. During the formation of a biomimetic composite containing L-Lysine hydrochloride and n-cHAp, the interaction occurred through bonding of the L-Lysine side chain and the hydroxyl groups of hydroxyapatite, which created an anionic form of L-Lysine at pH ≤ 5. In contrast, in biocomposites based on L-Arginine and n-cHAp, the interaction only slightly depends on pH value, and it proceeds by molecular orientation mechanisms. The X-ray diffraction and infrared spectroscopy results confirm that changes in the molecular composition of n-cHAp/L-ArgHCl biomimetic composites are caused by the electrostatic interaction between the L-ArgHCl molecule and the carbonate-substituted calcium hydroxyapatite. In this case, the bond formation was detected by Fourier transform infrared (FTIR) spectroscopy; the vibrational modes attributed to the main carbon chain and the guanidine group of L-Arginine are shifted during the interaction. The discovered interaction mechanisms between nanocrystalline carbonate-substituted hydroxyapatite that has physicochemical properties characteristic of the apatite in human dental enamel and specific amino acids are important for selecting the formation conditions of biomimetic composites and their integration with the natural dental tissue.

Functionalized Porous Hydroxyapatite Scaffolds for Tissue Engineering Applications: A Focused Review

Biomaterials have been widely used in tissue engineering applications at an increasing rate in recent years. The increased clinical demand for safe scaffolds, as well as the diversity and availability of biomaterials, has sparked rapid interest in fabricating diverse scaffolds to make significant progress in tissue engineering. Hydroxyapatite (HAP) has drawn substantial attention in recent years owing to its excellent physical, chemical, and biological properties and facile adaptable surface functionalization with other innumerable essential materials. This focused review spotlights a brief introduction on HAP, scope, a historical outline, basic structural features/properties, various synthetic strategies, and their scientific applications concentrating on functionalized HAP in the diverse area of tissue engineering fields such as bone, skin, periodontal, bone tissue fixation, cartilage, blood vessel, liver, tendon/ligament, and corneal are emphasized. Besides clinical translation aspects, the future challenges and prospects of HAP based biomaterials involved in tissue engineering are also discussed. Furthermore, it is expected that researchers may find this review expedient in gaining an overall understanding of the latest advancement of HAP based biomaterials.