Nonlinear Oscillatory Dynamics of the Hardening of Calcium Phosphate Bone Cements

Here we report on the nonlinear, oscillatory dynamics detected in the evolution of phase composition during the setting of different calcium phosphate cements, two of which evolved toward brushite and one toward hydroxyapatite as the final product. Whereas both brushite-forming cements contained iondoped b-tricalcium phosphate as the initial phase, the zinc-containing one yielded scholzite as an additional phase during setting and the oscillations between these two products were pronounced throughout the entire 80 h setting period, long after the hardening processes was over from the mechanical standpoint. Oscillations in the copper-containing system involved the amount of brushite as the main product of the hardening reaction and they progressed faster toward an equilibrium point than in the zinc-containing system. Initially detected with the use of in situ energy-dispersive X-ray diffractometry, the oscillations were confirmed with a sufficient level of temporal matching in an in situ Fourier transform infrared spectroscopic analysis. The kinetic reaction analysis based on the Johnson– Mehl–Avrami–Kolmogorov model indicated an edge-controlled nucleation mechanism for brushite. The hydroxyapatite-forming cement comprised gelatin as an additional phase with a role of slowing down diffusion and allowing the detection of otherwise rapid oscillations in crystallinity and in the amount of the apatitic phase on the timescale of minutes. A number of possible causes for these dynamic instabilities were discussed. The classical chemical oscillatory model should not apply to these systems unless in combination with less exotic mechanisms of physicochemical nature. One possibility is that the variations in viscosity, directly affecting diffusion and nucleation rates and accompanying growth and transformation from the lower to the higher interfacial energy per the Ostwald–Lussac rule, are responsible for the oscillatory dynamics. The conception of bone replacement materials and tissue engineering constructs capable of engaging in the dynamics of integration with the natural tissues in compliance with this oscillatory nature may open a new avenue for the future of this type of medical devices. To succeed in this goal, the mechanism of these and similar instabilities must be better understood

Electronic Supplementary Information associated with the article: Degli Esposti Lorenzo, Marković Smilja, Ignjatović Nenad, Panseri Silvia, Montesi Monica, Adamiano Alessio, Fosca Marco, Rau Julietta V., Uskoković Vuk, Iafisco Michele, "Thermal crystallization of amorphous calcium phosphate combined with citrate and fluoride doping: a novel route to produce hydroxyapatite bioceramics." Journal of Materials Chemistry B, 9, no. 24 (2021):4832-4845, https://doi.org/10.1039/D1TB00601K

Figure S1. The shift in the crystallization peak for (A) Cit-ACP-1 and (B) Cit-FACP-1 to higher temperatures in direct proportion with the heating rate; Figure S2. TGA curves of calcined Cit-ACP-4, Cit-ACP-2, and Cit-ACP-1; Figure S3. Pictures of calcined (A) Cit-ACP-4 and (B) Cit-ACP-1Related to the peer-reviewed manuscript: [https://hdl.handle.net/21.15107/rcub_dais_11640]Related to the article: [http://dx.doi.org/10.1039/D1TB00601K]Related to the article: [https://hdl.handle.net/21.15107/rcub_dais_11639

Characterization of Scardovia wiggsiae biofilm by original scanning electron microscopy protocol

Early childhood caries (ECC) is a severe manifestation of carious pathology with rapid and disruptive progression. The ECC microbiota includes a wide variety of bacterial species, among which is an anaerobic newly named species, Scardovia wiggsiae, a previously unidentified Bifidobacterium. Our aim was to provide the first ultrastructural characterization of S. wiggsiae and its biofilm by scanning electron microscopy (SEM) using a protocol that faithfully preserved the biofilm architecture and allowed an investigation at very high magnifications (order of nanometers) and with the appropriate resolution. To accomplish this task, we analyzed Streptococcus mutans’ biofilm by conventional SEM and VP-SEM protocols, in addition, we developed an original procedure, named OsO4-RR-TA-IL, which avoids dehydration, drying and sputter coating. This innovative protocol allowed high-resolution and high-magnification imaging (from 10000× to 35000×) in high-vacuum and high-voltage conditions. After comparing three methods, we chose OsO4-RR-TA-IL to investigate S. wiggsiae. It appeared as a fusiform elongated bacterium, without surface specialization, arranged in clusters and submerged in a rich biofilm matrix, which showed a well-developed micro-canalicular system. Our results provide the basis for the development of innovative strategies to quantify the effects of different treatments, in order to establish the best option to counteract ECC in pediatric patients

Strontium Substituted Tricalcium Phosphate Bone Cement: Short and Long‐Term Time‐Resolved Studies and In Vitro Properties

Due to a significant influence of strontium (Sr) on bone regeneration, Sr substituted beta-tricalcium phosphate (Sr-TCP) cement is prepared and investigated by short- and long-term time-resolved techniques. For short-term investigations, energy-dispersive X-ray diffraction, infrared spectroscopy, and, for the first time, terahertz time-domain spectroscopy techniques are applied. For long-term time-resolved studies, angular dispersive X-ray diffraction, scanning electron microscopy, mechanical tests, and behavior in Ringer solution are carried out. After 45 min of the cement setting, the Sr-TCP phase is no longer detectable. During this time period, an appearance and constant increase of the final brushite phase are registered. The compressive strength of the Sr-TCP cement increases from 4.5 MPa after 2 h of setting and reaches maximum at 13.3 MPa after 21 d. After cement soaking for 21 d in Ringer solution, apatite final product, with an admixture of brushite and TCP phases is detected. The cytotoxicity aspects of the prepared cement are investigated using NCTC 3T3 fibroblast cell line, and the cytocompatibility-by human dental pulp mesenchymal stem cells. The obtained results allow to conclude that the developed Sr-TCP cement is promising for biomedical applications for bone tissue

Phase changes in crystallization of some glasses synthesized in the RO-CaF2-P2O5-Al2O3-SiO2 system

The aim of the relearn was to study the phase changes during crystallization of some compositions of biocompatible glasses obtained in the RO-CaF2-P2O5-Al2O3-SiO2 (R=Zn, Mg) system. For this purpose, crystallization of glasses in the range of 700-1000 °C was carried out and X-ray analysis was carried out. A change in the phase composition of crystallized glass with a change in crystallization temperature and composition has been established. During crystallization, the phases of whitlockite, zinc-substituted fluorapatite, fluorapatite, anorthite, and gahnite were identified

Electrospun poly(D, L-lactide)/gelatin/glass-ceramics tricomponent nanofibrous scaffold for bone tissue engineering

Electrospun scaffolds are emerging as extracellular (ECM) mimicking structures for tissue engineering thanks to their nanofibrous architecture. For the development of suitable electrospun scaffolds for bone tissue engineering the addition of inorganic components has been implemented with the aim to confer important bioactivity like osteoinduction, osteointegration and cell adhesion to the scaffolds. In this context we propose a tricomponent electrospun scaffold composed of poly(D,L-lactide), gelatin and RKKP glass-ceramics. The bioactive RKKP glass-ceramic system has attracted interest, due to the presence of ions such as La3+ and Ta5+, which turned out to be valuable as growth supporting agents for bones. In this work, RKKP glass-ceramics were embedded inside the microfibers of electrospun scaffolds and the structural and biological properties were investigated. Our results showed that the glass-ceramic microparticles were uniformly distributed in the fibrous structure of the scaffold. Furthermore, the glass-ceramics promoted biomineralization of the scaffolds and improved cell viability and osteogenic differentiation. The mineralized layer formed on RKKP -containing scaffolds after incubation in simulated body fluid medium has been shown to be hydroxyapatite by Raman spectroscopy and X-ray diffraction. The results on differentiation studies of canine adipose-derived mesenchymal stem cells (cAMSC) grown on the electrospun scaffolds suggest that on varying the content of RKKP in the scaffold, it is possible to drive the differentiation toward chondrogenic or osteogenic commitment. The presence of ions, like La3+ and Ta5+, in the RKKP embedded polymeric composite scaffolds could play a role in supporting cell growth and promoting differentiation

Powders Based on Ca₂P₂O₇-CaCO₃-H₂O System as Model Objects for the Development of Bioceramics

Nanoscale powders of hydrated Ca2P2O7, CaCO3, and a product of mixed-anionic composition containing P2O74− and CO32− anions were synthesized from aqueous solutions of Ca(CH3COO)2, pyrophosphoric acid (H4P2O7), and/or (NH4)2CO3. Pyrophosphoric acid was previously obtained on the basis of the ion exchange process from Na4P2O7 solution and H+-cationite resin for further introduction into the reactions as an anionic precursor. The phase composition of powders after the syntheses was represented by bioresorbable phases of X-ray amorphous hydrated Ca2P2O7 phase, calcite and vaterite polymorphs of CaCO3. Based on synthesized powders, simple cylindrical constructions were prepared via mechanical pressing and fired in the temperature range of 600–800 °C. Surface morphology observation showed the presence of bimodal porosity with pore sizes up to 200 nm and 2 μm, which is likely to ensure tight particle packing and roughness of the sample surface required for the differentiation of osteogenic cells. Thus, the prepared ceramic samples can be further examined as model objects for bone tissue repair