Fluorescent (rhodamine), folate decorated and doxorubicin charged, PEGylated nanoparticles synthesis.

PEGylated silica nanoparticles, giving very stable aqueous sols, were successfully functionalised with rhodamine, one of the more stable fluorophore; they were also decorated with the targeting agent folic acid (FA) and charged with the well known drug doxorubicin. Rhodamine functionalization required a modification of the synthesis route of the nanoparticles (NP). Functionalization with FA required activation with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride. Folate decorated NP were easily charged with doxorubicin. The experimental results proved the successfulness of the functionalization. The bond to the NP does not reduce the therapeutic efficacy of the drug. The calculated encapsulation efficiency (32 %) was only a little lower than the value (47 %) reported for the very popular PEGylated PLGA NP.

In-situ sol-gel synthesis and characterization of bioactive pHEMA/SiO2 blend hybrids.

A novel procedure to synthesize poly(2-hydroxyethylmethacrylate)-silica blend hybrids is presented. Methacrylate monomers bearing an alkoxysilyl unit, prepared by Michael addition of 2-hydroxyethylmethacrylate (HEMA) to 3-Aminopropyltriethoxysilane (APTS) were employed. By (13)C NMR and mass analysis it was possible to establish the formation of coupling hybrid species. Hybrid materials, with final concentration ranging from 10% to 30% w/w of silica gel to the mass of polymer, were obtained through basic catalyzed sol-gel process of tetraethoxysilane (TEOS) and the alkoxysilyl unit of the hybrid monomer, followed by in-situ free-radical polymerization. The hybrids were characterized as far as concerns their thermal properties (glass transition temperature, decomposition temperature), their sorption behavior in water, and in-vitro bioactivity. Optical transparency, higher glass transition temperature, and higher decomposition temperature than pHEMA suggest an increase in either density or intensity of cross-links between the organic and the inorganic phases. The swelling ratio of the 30% hybrids is comparable to pHEMA, whereas it is lower for the other compositions. In-vitro bioactivity of the hybrids, due to the inorganic phase, was ascertained. Soaking time required for apatite deposition on the samples surface decreases as the content of silica gel increases. Therefore, the obtained bioactive hybrids can be used to make bioactive scaffolds for bone engineering.

Bioactive poly(2-hydroxyethylmethacrylate)/silica gel hybrid nanocomposites prepared by sol-gel process.

A hybrid of poly(2-hydroxyethylmethacrylate) (pHEMA), a polymer widely employed for biomedical applications, and silica gel, exhibiting a well-known bioactivity, was produced by sol-gel. The amount of the inorganic precursor, tetraethoxysilane (TEOS), was mixed to the organic monomer, so as to have a final concentration of 30% (w/w) of silica gel to the mass of polymer. The nanocomposite was characterized for its composition by thermogravimetric (TG) analysis, swelling behavior, glass transition temperature using differential thermal analysis (DTA), morphology through scanning electron microscopy (SEM), and bioactivity using FT-IR spectroscopy, SEM, and energy dispersive system (EDS). The nanocomposite showed phase separation between the polymer and the silica gel, improved thermal stability and swelling properties and higher glass transition temperature than pHEMA. Moreover, bioactive SiO(2) gel nanoparticles promoted apatite formation on the surface of the modified hydrogel, when it was soaked in SBF. Therefore, the obtained bioactive nanocomposite can be used to make bioactive scaffold for bone engineering.

Effect of the solution flow rate on the in vitro bioactivity of 2.5CaO x 2SiO(2) glass.

A comparative study of in vitro bioactivity of 2.5CaO x 2SiO(2) glass has been carried out by soaking it in a simulated body fluid, with continuously and periodic exchange of this solution (dynamic and differential protocols). Dynamic assays were carried out at different solution flow rates, 3 mL/h, 6 mL/h, 12 mL/h, to study the influence of flow rate on glass reactivity. Glass surface was studied by Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy so as to compare the behavior in the two procedures, revealing that in both cases an apatite layer is formed on the glass surface, although there are differences on deposition rate and morphology, which are also influenced by the solution flow rate.

Swelling properties and bioactivity of silica gel/pHEMA nanocomposites.

A novel hydrogel based on 2-hydroxyethyl- methacrilate and SiO(2) nanoparticles was prepared. The filler was added at a concentration of 30% w/w of silica nanoparticles to the mass of polymer. The composite material was characterised as far as concerns swelling behaviour in comparison to pHEMA. Swelling ratio of modified pHEMA was higher. Bioactivity of both SiO(2) nanoparticles and the modified hydrogel was evaluated by soaking samples into a simulated body fluid (SBF). FT-IR spectroscopy, scanning electron microscopy (SEM) and energy dispersive system (EDS) results suggest silica nanoparticles keep bioactive in the polymer. SiO(2) filler in a p(HEMA) matrix makes the composite bioactive. Therefore, these composites can be used to make bioactive scaffold for bone engineering.

Poly(2-hydroxyethyl methacrylate) biomimetic coating to improve osseointegration of a PMMA/HA/glass composite implant: in vivo mechanical and histomorphometric assessments.

Bone implants must simultaneously satisfy many requirements, even though the surface properties remain a crucial aspect in osseointegration success. Since a single material with a uniform structure cannot satisfy all of these requirements, composite materials specifically designed for orthopedic or dental implant application should be envisaged. Two poly(methylmethacrylate)/hydroxyapatite composites reinforced by E-glass fibres, uncoated (PMMA/HA/Glass) and poly(2-hydroxyethyl methacrylate) (PMMA/HA/Glass+pHEMA) coated by the biomimetic method, were mechanically (push-out test) and histomorphometrically (Affinity Index, AI) investigated in an in vivo rabbit model. Cylindrical implants (diameter 2 mm x 5 mm length) were inserted into rabbit femoral cortical (mid-diaphysis) and cancellous (distal epiphysis) bone, under general anesthesia. The highest values of push-out force and ultimate shear strength were observed for the PMMA/HA/Glass at 12 weeks, which significantly (p < 0.001) differed from those of PMMA/HA/Glass+pHEMA at the same experimental time and from those of PMMA/HA/Glass at 4 weeks. At both experimental times, significantly (p < 0.0005) lower values of AI were observed in the PMMA/HA/Glass+pHEMA versus PMMA/HA/Glass (distal femoral epiphysis: 4 weeks = 33%; 12 weeks = 19%; femoral diaphysis: 4 weeks = 15%; 12 weeks = 11%). The good mechanical and histomorphometric results obtained with PMMA/HA/Glass should be followed by further evaluation of bone remodeling processes and mechanical strength around loaded PMMA/HA/Glass implants at longer experimental times. Finally, the biomimetic method applied to pHEMA needs to be further investigated in order to improve the positive effect of SBF on pHEMA and to enhance the coating adhesion.

Effect of the substitution of M2O3 (M = La, Y, In, Ga, Al) for CaO on the bioactivity of 2.5CaO x 2SiO2 glass.

Glasses were prepared whose compositions are defined by the following general formula: (2.5 - x)CaO x x/3M2O3 x 2SiO2 (0 < or = x < or = 0.6) (M = Ga, Al, In). Their bioactivity was studied "in vitro" by soaking the glasses in a simulated body fluid (SBF). The consequent formation of calcium phosphate layer was studied by means of electron microscopy (EM) equipped with an energy-dispersive system (EDS) for elemental analysis and Infrared (IR) spectroscopy. The results are compared to the literature relative to the substitution of La2O3 and Y2O3 for CaO. It is observed that, in general, the substitution of M2O3 for CaO in the binary CaO-SiO2 glass composition progressively reduces the ability to form a calcium phosphate layer on the surfaces exposed to simulated body fluid (SBF). The composition limit can be related to the ionic field strength of the substituting cation and to the CaO content of the base glass. According to the mechanism reported in the literature a silica gel-like surface layer initially forms on the surfaces exposed to SBF. The observed results can be attributed to the effect of the substitution of M2O3 for CaO on the acidic properties of the silanolic groups.

Hydroxyapatite coating of titanium by biomimetic method.

The biomimetic method was used in order to deposit, on titanium substrates, an hydroxyapatite (HA) coating. The bioactive HA layer was obtained by using, in the first stage of the process, a glass having the composition 2.5CaO.2SiO(2) different from the one proposed for the application of the biomimetic method. This glass can be obtained via sol-gel, a method that allows one to obtain, easily, very pure products. The growth of HA crystals was confirmed by Fourier transform infrared, SEM, EDS and X-ray photoelectron spectroscopy (XPS) results. The experimental results suggest that, as reported in the literature for other supports, the silicate ions released from the glass in the first stage bind themselves to the titanium support. In particular, from XPS analysis it is evident that the titanium substrate is well covered by a calcium phosphate layer of the type of HA.

Improvement of swelling properties of poly(2-hydroxyethyl methacrylate) hydrogel by means of biomimetic method.

Poly(2-hydroxyethyl methacrylates) (PHEMAs) structurally modified by means of polymer blends and random copolymers are intensively studied in order to improve mechanical properties. It was recently shown that a hydroxyapatite coating, which should improve the bonding of this biomaterial to the bone, can be obtained by means of the biomimetic method. When PHEMA is submitted to the biomimetic method, its swelling ratio is improved. This can be ascribed to the deposition of a silicatic layer, which improves the hydrophilicity, on the surface of the internal pores during the first stage of the method. This appears to be a valuable result for producing modified PHEMAs with improved mechanical properties and good swelling. The experimental results indicate the following: stronger interactions with the water molecules are set up, an induction period is observed that is linked to the rate of the reactions occurring at the surface of the glass and the establishment of a convenient concentration of the silicate ions at the external surface of the polymer, and the diffusion of simulated body fluid into the pores is the limiting stage of the process.

Effect of the substitution of Y2O3 for CaO on the bioactivity of 2.5CaO.2SiO2 glass.

Glasses were prepared whose composition is defined by the following general formula: (2.5-x)CaO.x/3Y2O3.2SiO2 (0 < or = x < or = 1). Their behaviour when they were soaked in a simulated body fluid (SBF) and their thermal properties (glass transformation and softening temperatures, Tg and Ts respectively) were studied Tg and Ts increase with the Y2O3 content. The trend can be explained on the basis of the increased structural rigidity when Ca2+ ions are substituted by Y2+ ions, because of the formation of stronger bonds to the oxygen. The bioactivity was studied by means of electron microscopy equipped with an energy dispersive system for elemental analysis and IR spectroscopy. All the glasses studied except the one with the greatest amount of Y2O3. x = 1.0, reacted with SBF by forming a calcium phosphate layer. The experimental results suggest that the bioactivity is negatively influenced by the Y2O3 content: the tendency to form a calcium phosphate layer is reduced the greater the amount of CaO substituted. A comparison with literature data indicates that the amount of Y2O3 that can be substituted depends on the CaO content of the base CaO-SiO2 glass. The experimental results are in good agreement with the mechanism reported in the literature. After 7 days soaking, crystalline hydroxyapatite is formed in the Y2O3-free glass and in the glasses of low Y2O3 content (x-0.2).

Bioactivity of 1.25CaO.SiO2 glass: an FTIR and X-ray study on powdered samples.

Powdered samples (170-230 mesh) of a glass of composition 1.25CaO.SiO2 were soaked in a simulated body fluid (SBF). The powders were submitted to Fourier transform infrared transmission spectroscopy as coarse powders (such as drawn out from the SBF) and as fine powders (soaked and subsequently ground). Soaked samples were submitted to differential thermal analysis (DTA) and the crystalline phases formed during heating in the DTA apparatus were identified by means of X-ray diffraction analysis. The method appears to be useful in studying the mechanism of deposition of the hydroxyapatite layer. It is documented, by using the same method, that the mechanism involves the reactions of hydrolysis and successive condensation and repolymerization of the silicate substrate. These reactions are very fast. Extensive Ca2+ cation depletion occurs, but appears to be slower.

Effect of the substitution of La2O3 for CaO on the bioactivity of 2.5CaO.2SiO2 glass.

Glasses of the following composition were prepared: (2.5-x)CaO.x/3La2O3.2SiO2 (0 < or = x < or = 1). Their behavior when soaked in a simulated body fluid (SBF) was studied by means of electron microscopy (EM) equipped with an energy-dispersive system (EDS) for elemental analysis, IR spectroscopy, and x-ray diffraction. All the studied glasses react with SBF by forming a calcium phosphate layer. This layer appears to be increasingly thinner with increasing amounts of La2O3 substituted. The experimental results are in good agreement with mechanisms reported in the literature. Moreover they suggest that lanthanum oxide is retained in the layer below the phosphate. After 6 days of soaking, crystalline hydroxyapatite is formed in the case of La2O3 free glass.

Apatite formation on (2-x)CaO.x/3 M2O3 x 2SiO2 glasses (M = La, Y; 0 < or = x < or = 0.6) in a simulated body fluid.

Glasses were prepared by substituting La2O3 or Y2O3 for CaO in glassy wollastonite composition (CaO.SiO2). Their behaviour when they are soaked in a simulated body fluid (SBF) was studied by means of an electron microscope equipped with an energy dispersive system for elemental analysis, and by means of IR spectroscopy. Electron microscopy and energy dispersive microanalysis were performed on samples soaked as polished bulk samples, and IR analysis was on samples soaked as fine powders. A carbonate-containing hydroxyapatite layer is formed when glasses of low La2O3 content are soaked in SBF. When Y2O3-containing glasses are considered, even in the case of small substitution for CaO, the same layer forms only on fracture surfaces. The experimental results agree with the mechanism reported in the literature.