Alberto Lagazzo

A novel method of forming micro- and macroporous monetite cements

Second to autologous bone grafts are the calcium phosphate cements (CPCs) used as synthetic bone substitutes due to their chemical similarity to the mineral component of bone. Their ability to conform to complex bone defects and excellent osteoconductivity also render them excellent scaffolds for bone tissue engineering, although they do have their own limitations. Calcium phosphates can be divided into two main categories, namely apatite and brushite. Apatites exhibit low solubility, whereas, calcium phosphates that set to form brushite, are metastable, which degrade rapidly, but do subsequently form hydroxyapatite that retards the rate. In contrast dicalcium phosphate anhydrous (monetite) has a higher solubility than octacalcium phosphate and does not transform to an apatite; thus, it is able to continue to degrade with time. Herein, a new method was used via the addition of sodium chloride to β-tricalcium phosphate and monocalcium phosphate monohydrate to form micro- and macroporous monetite (DCPA). The X-ray diffraction and FTIR spectra confirmed the formation of monetite in the presence of both, 6.2 M NaCl solution or 60% of solid sodium chloride. The maximum compressive strength (σc = 12.3 ± 1.8 MPa) and the Youngs modulus (E = 1.0 ± 0.1 GPa) of the monetite cements obtained were comparable to the upper limits of the values reported for cancellous bone and also higher than that reported by other routes used to form monetite. The porous cements analysed by microCT revealed an interconnected porosity with the preliminary in vitro biological evaluation indicating favourable osteoblast cell attachment and growth.

Characterization of alginate-brushite in-situ hydrogel composites.

In the present study alginate-brushite composite hydrogels were in-situ synthetized and characterized with respect to preparation parameters. Specifically, the influence of initial pH value and initial concentration of phosphate precursor on the in-situ fabrication of the composite hydrogel were taken into account. The composite hydrogels were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric (TGA, DTG) and differential thermal analysis (DTA). Finally, the cell viability tests were carried out (MTT) over the incubation time period of 3, 7, and 14days. The results revealed that the formation and the crystalline stability of brushite were highly dependent on the initial pH value. It was shown that as the pH reached to the value of 6, characteristics peaks of brushite appeared in the FTIR spectra. Besides, the XRD and thermal analysis results were in a good accordance with those of FTIR. In addition, the SEM images demonstrated that the plate like brushite was formed inside the alginate matrix. Also, a considerable impact of pH variation on the biocompatibility of samples was noticed so that the majority of samples especially those prepared in the acidic conditions were toxic.

Biological and mechanical characterization of carbon fiber frameworks for dental implant applications

OBJECTIVES The aim of the present study was to investigate the biocompatibility and mechanical characteristics of dental implant frameworks made of carbon fiber composite. METHODS The biocompatibility of intact samples and fragments was evaluated by cell count and MTT test according to EN-ISO 10993-5:2009 directions. Destructive and non-destructive mechanical tests were performed in order to evaluate: porosity, static and dynamic elastic modulus of carbon fiber samples. These tests were conducted on different batches of samples manufactured by different dental technicians. The samples were evaluated by optical microscope and by SEM. A compression test was performed to compare complete implant-supported fixed dentures, provided with a metal or carbon fiber framework. RESULTS Carbon fiber intact and fragmented samples showed optimal biocompatibility. Manufacture technique strongly influenced the mechanical characteristics of fiber-reinforced composite materials. The implant-supported full-arch fixed denture provided with a carbon fiber framework, showed a yield strength comparable to the implant-supported full-arch fixed denture, provided with a metal framework. SIGNIFICANCE Carbon fiber-reinforced composites demonstrated optimal biocompatibility and mechanical characteristics. They appear suitable for the fabrication of frameworks for implant-supported full-arch dentures. Great attention must be paid to manufacture technique as it strongly affects the material mechanical characteristics.

Orthodontic miniscrews: an experimental campaign on primary stability and bone properties

OBJECTIVE To evaluate the primary stability of different shaped miniscrews through the acquisition of data regarding maximum insertion torque, pullout force, and a radiodiagnosic evaluation of bone characteristics. MATERIALS AND METHODS Sixty fresh porcine bone samples were scanned by computed tomography (CT) and cone-beam computed tomography (CBCT). By means of a dedicated software, CT and CBCT images were analysed to measure the insertion-site cortical thickness, cortical density, and marrow bone density. Sixty miniscrews of 12 different types were implanted with no predrilling pilot hole in the bone samples. Every device was tightened by means of a digital torque screwdriver and torque data were collected. Subsequently, pullout tests were performed. Spearman and Pearson correlations were employed to compare any relationship between continuous variables. RESULTS Different types of miniscrews did not show statistically significant differences in their torque value (P = 0.595), instead a significant difference was revealed by considering their load measures (P = 0.039). Cortical bone thickness resulted strongly correlated both with value of load (P < 0.001), and modestly with torque measures (P = 0.004). A strong positive correlation was found between CT and CBCT both for cortical density (P < 0.001) and marrow bone density (P < 0.001). CONCLUSION Bone characteristics play the major role in miniscrews primary stability.

Kinetic model of Chlorella vulgaris growth with and without extremely low frequency-electromagnetic fields (EM-ELF).

Chlorella vulgaris was grown in two bench-scale photobioreactors with and without the application of a low intensity, low frequency electromagnetic field (EM-ELF) of about 3mT. Cell concentration and tendency of cells to form aggregates inside the reactor were recorded over a 30 days-time period at 0.5L-constant medium volume in the temperature range 289-304K. At 304K, after a cultivation period of 15 days, the rate of cell death became predominant over that of growth. In the temperature range 289-299K, a two step-kinetic model based on the mitotic division and the clusterization processes was developed and critically discussed. The best-fitted curves turned out to have a sigmoid shape, and the competition between mitosis and clusterization was investigated. Without EM-ELF, the temperature dependence of the specific rate constant of the mitotic step yielded an apparent total enthalpy of 15±6kJmol(-1), whose value was not influenced by the EM-ELF application. The electromagnetic field was shown to exert a significant effect on the exothermic clusterization step. The heat exchange due to binding between cells and liquid medium turned out to be -44±5kJmol(-1) in the absence of EM-ELF and -68±8kJmol(-1) when it was active. Optical microscopy observations were in agreement with the model predictions and confirmed that EM-ELF was able to enhance cell clusterization.

An experimental model of vitreous motion induced by eye rotations

BackgroundDuring eye rotations the vitreous humour moves with respect to the eye globe. This relative motion has been suggested to possibly have an important role in inducing degradation of the gel structure, which might lead to vitreous liquefaction and/or posterior vitreous detachment. Aim of the present work is to study the characteristics of vitreous motion induced by eye rotations.MethodsWe use an experimental setup, consisting of a Perspex model of the vitreous chamber that, for simplicity, is taken to have a spherical shape. The model is filled with an artificial vitreous humour, prepared as a solution of agar powder and hyaluronic acid sodium salt in deionised water, which has viscoelastic mechanical properties similar to those of the real vitreous. The model rotates about an axis passing through the centre of the sphere and velocity measurements are taken on the equatorial plane orthogonal to the axis of rotation, using an optical technique.ResultsThe results show that fluid viscoelasticity has a strong influence on flow characteristics. In particular, at certain frequencies of oscillation of the eye model, fluid motion can be resonantly excited. This means that fluid velocity within the domain can be significantly larger than that of the wall.ConclusionsThe frequencies for which resonant excitation occurs are within the range of possible eye rotations frequencies. Therefore, the present results suggest that resonant excitation of vitreous motion is likely to occur in practice. This, in turn, implies that eye rotations produce large stresses on the retina and within the vitreous that may contribute to the disruption of the vitreous gel structure. The present results also have implications for the choice of the ideal properties for vitreous substitute fluids.

New in-situ synthetized hydrogel composite based on alginate and brushite as a potential pH sensitive drug delivery system

A Series of in-situ alginate-brushite (Alg-Bru) hydrogel composites were fabricated to optimize release profile of ibuprofen (Ibu) and to avoid burst releases associated with the pure form of the hydrogels. The Bru crystals were synthetized and dispersed during the crosslinking process of Alg matrix. The beads with different formulations were subject to various characterization tests such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), and swelling. In addition, the entrapment Efficiency (%EE) and drug release profile were obtained to investigate the impacts of initial concentration of Alg and content of Bru on these parameters. FTIR and XRD outcomes confirmed the successful fabricating of Alg-Bru composite as well as the loading of Ibu. Besides, the results showed that the presence of Bru within Alg matrix restricted polymer chain movement, improved mechanical properties, and decreased swelling ratio. Although the presence of Bru crystals did not improve%EE, they optimized the release profile in a more gradual manner.

The role of new zinc incorporated monetite cements on osteogenic differentiation of human mesenchymal stem cells

β-Tricalcium phosphate particles were sintered in the presence of different amounts (0-0.72mol) of zinc oxide (ZnO) to prepare zinc doped β-TCP (Znβ-TCP) particles for further use in novel monetite (DCPA: CaHPO4) zinc incorporated bone cements with osteogenic differentiation potential towards human mesenchymal stem cells (hMSCs). XRD analysis of zinc incorporated cements prepared with β-TCP reagent particles doped with different amount of ZnO (i.e. 0.03, 0.09 and 0.18mol ZnO) revealed the presence of unreacted Znβ-TCP and monetite. Furthermore, it was shown that zinc ions preferentially occupied the β-TCP crystal lattice rather than the monetite one. Release experiments indicated a burst release of ions from the different fabricated cements during the first 24h of immersion with zinc concentrations ranging between 85 and 100% of the total concentration released over a period of 21days. Cell proliferation significantly increased (P<0.05) on zinc incorporated monetite respect to control samples (Zinc-free cement) at 7 and 14days post seeding. The expression of Runx-2 was significantly up regulated (P<0.05) in the case of cells seeded on monetite prepared with β-TCP doped with 0.03 moles of ZnO. On the other hand, the cell mineralization as well as the expression of osteogenic marker genes ALP and OSC decreased significantly (P<0.05) at 14days post cell seeding. In conclusion, these results suggest that the zinc ions released from the cements during the first 24h of culture played a critical role in regulating the osteogenic differentiation of hMSCs.

3D Porous Gelatin/PVA Hydrogel as Meniscus Substitute Using Alginate Micro-Particles as Porogens

One of the current major challenges in orthopedic surgery is the treatment of meniscal lesions. Some of the main issues include mechanical consistency of meniscal implants, besides their fixation methods and integration with the host tissues. To tackle these aspects we realized a micro-porous, gelatin/polyvinyl alcohol (PVA)-based hydrogel to approach the high percentage of water present in the native meniscal tissue, recapitulating its biomechanical features, and, at the same time, realizing a porous implant, permissive to cell infiltration and tissue integration. In particular, we adopted aerodynamically-assisted jetting technology to realize sodium alginate micro-particles with controlled dimensions to be used as porogens. The porous hydrogels were realized through freezing-thawing cycles, followed by alginate particles leaching. Composite hydrogels showed a high porosity (74%) and an open porous structure, while preserving the elasticity behavior (E = 0.25 MPa) and high water content, typical of PVA-based hydrogels. The ex vivo animal model validation proved that the addition of gelatin, combined with the micro-porosity of the hydrogel, enhanced implant integration with the host tissue, allowing penetration of host cells within the construct boundaries. Altogether, these results show that the combined use of a water-insoluble micro-porogen and gelatin, as a bioactive agent, allowed the realization of a porous composite PVA-based hydrogel to be envisaged as a potential meniscal substitute.

Molecular level interactions in brushite-aminoacids composites

The interaction of aminoacids (Glycine, Proline, Lysine) with brushite based bone cements has been investigated by several techniques (FTIR spectroscopy, Thermogravimetry-TG, Scanning Electron Microscopy-SEM, mechanical properties studies), with the aim to elucidate the properties of the resulting composite materials and the interaction occurring at molecular level between the inorganic matrix and the organic moieties. Brushite phase is predominantly obtained also in the presence of aminoacids added during preparation of the bone cement. Focusing on Glycine incorporation, the presence of a fraction of bulk Glycine, weakly interacting with the inorganic matrix, together with Glycine specifically interacting with adsorption sites can be envisaged, as pointed out by FT IR and thermogravimetric data. In detail, FT-IR data evidenced changes in shape and position of bands associated to stretching modes of the carboxylic groups in Glycine structure, which can be explained by the coordination of these functional groups with the Ca ions in the matrix. Heating this composite at controlled temperature results in the detection of a condensation products, either cyclic condensation product, either dipeptide. Diffuse and not specific H-bonding seems to be the main form of interaction of Proline and Lysine with brushite. Due to the coordination with Ca ions here described, Glycine can act as retardant during brushite preparation, allowing good workability of the resulting composite.