Trace elements can influence the physical properties of tooth enamel

In previous studies, we showed that the size of apatite nanocrystals in tooth enamel can influence its physical properties. This important discovery raised a new question; which factors are regulating the size of these nanocrystals? Trace elements can affect crystallographic properties of synthetic apatite, therefore this study was designed to investigate how trace elements influence enamel’s crystallographic properties and ultimately its physical properties. The concentration of trace elements in tooth enamel was determined for 38 extracted human teeth using inductively coupled plasma-optical emission spectroscopy (ICP-OES). The following trace elements were detected: Al, K, Mg, S, Na, Zn, Si, B, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se and Ti. Simple and stepwise multiple regression was used to identify the correlations between trace elements concentration in enamel and its crystallographic structure, hardness, resistance to crack propagation, shade lightness and carbonate content. The presence of some trace elements in enamel was correlated with the size (Pb, Ti, Mn) and lattice parameters (Se, Cr, Ni) of apatite nanocrystals. Some trace elements such as Ti was significantly correlated with tooth crystallographic structure and consequently with hardness and shade lightness. We conclude that the presence of trace elements in enamel could influence its physical properties. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/2193-1801-2-499) contains supplementary material, which is available to authorized users

Engineered In vitro Models for Pathological Calcification: Routes Toward Mechanistic Understanding

Physiological calcification plays an essential part in the development of the skeleton and teeth; however, the occurrence of calcification in soft tissues such as the brain, heart, and kidneys associates with health impacts, creating a massive social and economic burden. The current paradigm for pathological calcification focuses on the biological factors responsible for bone-like mineralization, including osteoblast-like cells and proteins inducing nucleation and crystal growth. However, the exact mechanism responsible for calcification remains unknown. Toward this goal, this review dissects the current understanding of structure–function relationships and physico-chemical properties of pathologic calcification from a materials science point of view. We will discuss a range of potential mechanisms of pathological calcification, with the purpose of identifying universal mechanistic pathways that occur across multiple organs/tissues at multiple length scales. The possible effect of extracellular components in signaling and templating mineralization, as well as the role of intrinsically disordered proteins in calcification, is reviewed. The state-of-the-art in vitro models and strategies that can recreate the highly dynamic environment of calcification are identified

Mineralization of Bone Extracellular Matrix-like Scaffolds Fabricated as Silk Sericin-Functionalized Dense Collagen–Fibrin Hybrid Hydrogels

The design of hydrogels that combine both the biochemical cues needed to direct seeded cellular functions and mineralization to provide the structural and mechanical properties approaching those of mineralized native bone extracellular matrix (ECM) represents a significant challenge in bone tissue engineering. While fibrous hydrogels constituting of collagen or fibrin (and their hybrids) can be considered as scaffolds that mimic to some degree native bone ECM, their insufficient mechanical properties limit their application. In the present study, an automated gel aspiration–ejection (automated GAE) method was used to generate collagen–fibrin hybrid gel scaffolds with micro-architectures and mechanical properties approaching those of native bone ECM. Moreover, the functionalization of these hybrid scaffolds with negatively charged silk sericin accelerated their mineralization under acellular conditions in simulated body fluid and modulated the proliferation and osteoblastic differentiation of seeded MC3T3-E1 pre-osteoblastic cells. In the latter case, alkaline phosphatase activity measurements indicated that the hybrid gel scaffolds with seeded cells showed accelerated osteoblastic differentiation, which in turn led to increased matrix mineralization. In summary, the design of dense collagen–fibrin hybrid gels through an automated GAE process can provide a route to tailoring specific biochemical and mechanical properties to different types of bone ECM-like scaffolds, and can provide a model to better understand cell–matrix interactions in vitro for bioengineering purposes

A Three-Dimensional Dense Collagen Hydrogel to Model Cancer Cell/Osteoblast Interactions

No curative treatment options exist once breast cancer metastasizes to bone. This is due, in part, to an incomplete understanding of how osteolytic cancers interact with bone. Presented here is a novel approach to study the interactions between triple negative breast cancer cells and osteoblasts within a 3D collagenous environment. More specifically, a dense collagen hydrogel was employed to model interactions between MDA-MB-231 breast cancer cells and MC3T3-E1 pre-osteoblasts. Co-cultures with these two cell types, or MDA-MB-231-derived conditioned medium applied to MC3T3-E1 cells, were established in the context of plastically compressed dense collagen gel matrices. Importantly, breast cancer-derived conditioned medium or the establishment of breast cancer/osteoblast co-cultures did not negatively influence MC3T3-E1 cell viability. The inclusion of either conditioned medium or the presence of MDA-MB-231 cells resulted in impaired MC3T3-E1 differentiation into osteoblasts, which coincided with reduced osteoblast-mediated mineralization. The results presented here demonstrate that dense collagen gels provide a model environment to examine the effect of osteolytic breast cancer cells on osteoblast differentiation and subsequent mineralization of the collagen scaffold

Highly Bioactive Sol-Gel-Derived Borate Glasses

Attributable to their low chemical durability, borate-based glasses have been demonstrated to convert rapidly to hydroxy-carbonated apatite (HCA), the inorganic component of bone. However, the effect of sol-gel processing on the bioactivity of borate-based glasses has not been investigated. In this study, the gel and glass forming abilities of six different borate-based glass formulations with borate content ranging from 36 to 61 mol % and based on a previously studied four component melt-derived glass system [(46.1)­B₂O₃–(26.9)­CaO–(24.4)­Na₂O–(2.6)­P₂O₅; mol %] were investigated. Compared to melt-quench, sol-gel processing fabricated nanoporous glass particles with at least 2 orders of magnitude greater values for specific surface areas and total pore volumes, which translated to dramatically higher aqueous interaction and ion release rates. Surprisingly, when immersed in simulated body fluid, HCA conversion was achieved in as little as 3 h for sol-gel derived borate based glasses, demonstrating a 25-fold increase in mineralization rate when compared to melt derived equivalents. The ability of the sol-gel derived borate-based glasses to rapidly convert to bone-like HCA holds promise in numerous potential tissue engineering applications, including the repair and augmentation of mineralized tissues

Dissolution and bioactivity of a sol-gel derived borate glass in six different solution media

Sol-gel derived bioactive borate glasses (SGBGs) rapidly convert to hydroxycarbonated apatite (HCA) in simulated body fluid (SBF), in vitro. While previous studies have examined the influence of processing and composition on bioactivity, the effect of the in vitro dissolution media has not been well examined for these glasses. In this study, the mineral conversion of a SGBG substituted 45S5 Bioglass® formulation (“B46”, (46.1)B2O3-(26.9)CaO-(24.4)Na2O-(2.6)P2O5, mol%), was examined in six different dissolution media: SBF, tris(hydroxymethyl)aminomethane (TRIS, pH 7.4) buffer, Dulbecco’s phosphate buffered saline (PBS, 1X), Dulbecco’s Modified Eagle Medium (DMEM, 1X), 0.9% Saline (SAL), and deionized water (DIW) at 1.5 mg/mL for 10 min, 2h, and 1d. All media underwent a rapid increase in pH as a result of glass dissolution and ion release. B46 in SBF, TRIS, and PBS converted to HCA while B46 in DMEM, SAL, and DIW converted to calcite according to attenuated total reflectance-Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The ratio of B46 to SBF was also examined at 3, 6, 12, and 24 mg/mL for 1d. These results help elucidate the dissolution and mineral conversion of borate glasses and help provide insights into optimizing pre-conditioning treatments for both in vitro and in vivo analyses

Poly(D,L-lactide) (PDLLA) foams with TiO2 nanoparticles and PDLLA/TiO2-Bioglass (R) foam composites for tissue engineering scaffolds

Porous poly(D,L-lactide) PDLLA foams containing 0, 5 and 20 wt% of TiO2 nanoparticles were fabricated and characterised. The addition of Bioglassg particles was also studied in a composite containing 5 wt% of Bioglass(R) particles and 20 wt% of TiO2 nanoparticles. The microstructure of the four different foam types was characterised using scanning electron microscopy (SEM) and their mechanical properties assessed by quasi-static compression testing. The in vitro behaviour of the foams was studied in simulated body fluid (SBF) at three different time points: 3, 21 and 28 days. The degradation of the samples was characterised quantitatively by measuring the water absorption and weight loss as a function of immersion time in SBE The bioactivity of the foams was characterised by observing hydroxyapatite (HA) formation after 21 days of immersion in SBF using SEM and confirmed with X-ray diffraction (XRD) analysis. It was found that the amount of HA was dependent on the distribution of TiO2 nanoparticles and on the presence of Bioglassg in the foam samples. (c) 2006 Springer Science + Business Media, Inc