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ABSTRACT: A series of sol-gel derived TiO2–SiO2 mixed oxide coatings were prepared by carefully controlling the process parameters to obtain silica-releasing coatings consisting
of nanoparticles. These features are of paramount importance for enhanced cell adhesion and activation. To achieve both these
goals the Ti-alkoxide and Si-alkoxide were first separately hydrolysed and the titania–silica mixed sol was further reacted
before the dipping process to obtain the desired particle sizes resulting to the biologically favourable topographical features.
Silica release was observed from all the prepared coatings and it was dependent on SiO2 amount added to the sols, i.e., the higher the added amount the higher the release. In addition, calcium phosphate was able
to nucleate on the coatings. From the obtained SiO2 dissolution data, together with the detailed XPS peak analysis, the mixed oxide coatings are concluded to be chemically heterogeneous,
consisting of TiO2 and SiO2 species most likely linked together by Ti–O–Si bonds. TiO2 is chemically stable making long-term implant coating possible and the desired nanoscale dimensions were well preserved although
the composition was changed as a consequence of SiO2 dissolution under in vitro conditions.
Journal of Materials Science Materials in Medicine 04/2012; 18(9):1863-1873. · 2.32 Impact Factor
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ABSTRACT: Sol-gel derived silica and titania have a specific interaction with many biological molecules, microbes, algae, cells and
living tissue. The specific interactions mean that they differ from common reactions between non-viable materials and biomolecules
or living tissues and the interactions are mostly beneficial from the viewpoint of biotechnical applications. Pepetides and
proteins may preserve their activity and bacteria, algae and cells may preserve their viability and viruses their infectivity
as encapsulated in sol-gel derived silica. Silica and titania are known to form a direct bond with living tissue which can
be utilized in the biomaterial applications. Other application areas of silica and titania are in biosensing, tissue engineering,
gene therapy, controlled delivery of therapeutic agents and environmental protection.
06/2008: pages 251-268;
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ABSTRACT: A series of sol-gel derived TiO(2)-SiO(2) mixed oxide coatings were prepared by carefully controlling the process parameters to obtain silica-releasing coatings consisting of nanoparticles. These features are of paramount importance for enhanced cell adhesion and activation. To achieve both these goals the Ti-alkoxide and Si-alkoxide were first separately hydrolysed and the titania-silica mixed sol was further reacted before the dipping process to obtain the desired particle sizes resulting to the biologically favourable topographical features. Silica release was observed from all the prepared coatings and it was dependent on SiO(2) amount added to the sols, i.e., the higher the added amount the higher the release. In addition, calcium phosphate was able to nucleate on the coatings. From the obtained SiO(2) dissolution data, together with the detailed XPS peak analysis, the mixed oxide coatings are concluded to be chemically heterogeneous, consisting of TiO(2) and SiO(2) species most likely linked together by Ti-O-Si bonds. TiO(2) is chemically stable making long-term implant coating possible and the desired nanoscale dimensions were well preserved although the composition was changed as a consequence of SiO(2) dissolution under in vitro conditions.
Journal of Materials Science Materials in Medicine 10/2007; 18(9):1863-73. · 2.32 Impact Factor
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ABSTRACT: Silica-releasing sol-gel derived TiO2-SiO2 coatings with tailored nanostructure were evaluated in fibroblast and osteoblast cell cultures. The adhesion of both fibroblasts and osteoblasts proceeded within two hours. The highest fibroblast proliferation activities were observed on the TiO2-SiO2 (70:30) and (30:70) coatings. However, the cell layer on TiO2-SiO2 (30:70) coating was disordered. Prolonged osteoblast activity was observed on the coatings as a function of increased amount of released silica. At day 21 the surfaces were fully covered by the calcified nodules and extracellular matrix except for the coatings TiO2-SiO2 (10:90) i.e. having the highest SiO2 amount. The results suggested that TiO2-SiO2 (70:30) was the best for fibroblasts and TiO2-SiO2 (30:70) for osteoblasts. The applicability of the sol-gel derived TiO2 and TiO2-SiO2 coatings as an alternative for the calcium phosphate based implant coatings are discussed.
Journal of Materials Science Materials in Medicine 09/2007; 18(8):1633-42. · 2.32 Impact Factor
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ABSTRACT: Silica-releasing sol-gel derived TiO2–SiO2 coatings with tailored nanostructure were evaluated in fibroblast and osteoblast cell cultures. The adhesion of both fibroblasts
and osteoblasts proceeded within two hours. The highest fibroblast proliferation activities were observed on the TiO2–SiO2 (70:30) and (30:70) coatings. However, the cell layer on TiO2–SiO2 (30:70) coating was disordered. Prolonged osteoblast activity was observed on the coatings as a function of increased amount
of released silica. At day 21 the surfaces were fully covered by the calcified nodules and extracellular matrix except for
the coatings TiO2–SiO2 (10:90) i.e. having the highest SiO2 amount. The results suggested that TiO2–SiO2 (70:30) was the best for fibroblasts and TiO2–SiO2 (30:70) for osteoblasts. The applicability of the sol-gel derived TiO2 and TiO2–SiO2 coatings as an alternative for the calcium phosphate based implant coatings are discussed.
Journal of Materials Science Materials in Medicine 07/2007; 18(8):1633-1642. · 2.32 Impact Factor
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ABSTRACT: Both small and large biologically active agents were encapsulated into biodegradable sol-gel derived SiO2. Both fast and slowly-eroding SiO2 matrices were prepared. Propranolol represented a small molecule and a model protein, BSA (bovine serum albumin) the larger one. The release mechanisms were studied using two different dissolution media representing extreme cases with respect to the matrix erosion, free dissolution of the SiO2 matrix in sink conditions and a dissolution medium saturated with respect to the matrix. The utilisation of the two different dissolution media as such provided information on the general release mechanisms and power law-based mathematical models supported the propranolol release results. A modified power law is suggested, where both the initially released amount and time are included. BSA was not released without matrix erosion and propranolol release was mainly diffusion-controlled, although the matrix dissolution was needed for R=3 monoliths due to closed pores. It is also shown that for R=30 microparticles propranolol release was partly matrix erosion controlled.
International Journal of Pharmaceutics 06/2007; 336(2):382-90. · 3.35 Impact Factor
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ABSTRACT: Amorphous, sol-gel derived SiO2 are known to biocompatible and bioresorbable materials. Bioresorbable materials have potential applications as implants or
injectable matrices in the controlled delivery of biologically active agents in the living tissue. Bioresorbable matrices
provide desirable properties, e.g., extra removal operations that have to be done with biostable matrices are avoided and
the release of large therapeutic molecules can be controlled by matrix degradation rather than by diffusion. New important
groups of drugs, such as biotechnically-produced peptides and proteins, are potential to be encapsulated in bioresorbable
SiO2, because they are typically larger in size and their direct oral administration without protecting matrix is difficult due
to digestion. The methods to achieve a wide range of SiO2 bioresorption rates (from days to months) are introduced in this study. This is done by a “conventional” alkoxy-based sol-gel
method at protein-friendly conditions by adjusting the precursor ratios, aging of the sol and by using different preparation
methods (casting, spray-drying and freeze-drying). The prepared morphologies include implantable monolithic sticks and injectable
microspheres. The importance of chemical structure is shown in comparison with the specific surface area and pore volume.
Journal of Sol-Gel Science and Technology 10/2005; 36(2):147-156. · 1.63 Impact Factor
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ABSTRACT: A firm bond between an implant and the surrounding soft tissue is important for the performance of many medical devices (e.g., stents, canyls, and dental implants). In this study, the performance of nonresorbable and reactive sol-gel-derived nano-porous titania (TiO(2)) coatings in a soft tissue environment was investigated. A direct attachment between the soft tissue and the sol-gel-derived titania coatings was found in vivo after 2 days of implantation, whereas the titanium control implants showed no evidence of soft tissue attachment. The coated implants were in immediate contact with the connective tissue, whereas the titanium controls formed a gap and a fibrous capsule on the implant-tissue interface. The good soft tissue attachment of titania coatings may result from their ability to initiate calcium phosphate nucleation and growth on their surfaces (although the formation of poorly crystalline bonelike apatite does not occur). Thus, the formation of a bonelike CaP layer is not crucial for their integration in soft tissue. The formation of bonelike apatite was hindered by the adsorption of proteins onto the initially formed amorphous calcium phosphate growth centers, thus preventing the dissolution/reprecipitation processes required for the formation of poorly crystalline bonelike apatite. These findings might open novel application areas for sol-gel-derived titania-based coatings.
Journal of Biomedical Materials Research Part A 09/2004; 70(2):169-78. · 2.63 Impact Factor
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ABSTRACT: Sol-gel derived silicas are potential biomaterials both for tissue regeneration and drug delivery applications. In this study, both SiO(2) and calcium and phosphate-containing SiO(2) (CaPSiO(2)) are combined with poly-(DL-lactide) to form a composite. The main properties studied are the ion release rates of biologically important ions (soluble SiO(2) and Ca(2+)) and the formation of bone mineral-like calcium phosphate (CaP) on the composite surface. These properties are studied by varying the quality, content and granule size of silica gel in the composite, and porosity of the polymer. The results indicate that release rates of SiO(2) and Ca(2+) depend mostly on the formed CaP layer, but in some extent also on the granule size of silicas and polymer porosity. The formation of the bone mineral-like CaP is suggested to be induced by a thin SiO(-) layer on the composite surface. However, due to absence of active SiO(2) or CaPSiO(2) granules on the outermost surface, the suitable nanoscale dimensions do not contribute the nucleation and growth and an extra source for calcium is needed instead. The result show also that all composites with varying amount of CaPSiO(2) (10-60 wt%) formed bone mineral-like CaP on their surfaces, which provides possibilities to optimise the mechanical properties of composites.
Biomaterials 12/2003; 24(28):5173-82. · 7.40 Impact Factor
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Key Engineering Materials - KEY ENG MAT. 01/2003;
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Key Engineering Materials - KEY ENG MAT. 01/2003;
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ABSTRACT: The objective of this study was to evaluate the possibilities to control the release rate of dexmedetomidine (DMED) from different spray-dried silica gel microparticle formulations. Microparticles were prepared by spray drying a silica sol polymer solution containing the drug. Drug release was investigated both in vitro and in vivo. The influence of sol-gel synthesis parameters, like pH and the water/alkoxide ratio (r) of the sol, on the release behaviour of the drug was studied. Silica gel microparticles had a smooth surface. Microparticles prepared from diluted sol, however, were more aggregated and clustered. The drug release conformed to zero order release from microparticles prepared near the isoelectric point of silica (pH 2.3 and pH 3) and to the square root of time kinetics from microparticles prepared at pH 1 and pH 5. The release also showed a dual-phasic profile with an initial burst and after that a slower release period. The dexmedetomidine release conformed to zero order kinetics from microparticles prepared at water/ alkoxide ratios between r = 6 and r = 35 (at pH 2.3). The release rate was the slowest from microparticles prepared with water/ alkoxide ratio 35. The bioavailability of dexmedetomidine in dogs showed that the release was sustained from silica gel microparticles as compared with a subcutaneously administered reference dose of 0.1 mg.
Biomaterials 08/2002; 23(13):2795-801. · 7.40 Impact Factor
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ABSTRACT: Three different sol–gel derived silica gels having different gelation mechanism derived both from the acidic and basic sols were investigated. The aggregation processes are monitored by rheological measurements and the viscoelastic behaviour near the gel point is used to determine the critical scaling exponents for each case using frequency dependence of the loss and storage moduli (G″ and G′). The scaling exponents are further analysed in order to obtain information about particle–particle/aggregate interactions in the system. The three aggregation processes forming gels are suggested to fit to the known aggregation theories for the sol–gel transition. The analysed data including estimated fractal dimensions provide information about the gelation process with respect to aggregation. The mechanisms of aggregation have an influence on the gel structure and the data obtained give an insight about the structure formation from a sol to a gel. The dried gels are additionally characterized by atomic force microscopy (AFM).
Colloids and Surfaces A: Physicochemical and Engineering Aspects.
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ABSTRACT: The rheological behaviour of anatase dispersions was compared with the ζ potential, when the pH (from 3 to 10) and sodium chloride concentration (from 0 to 1 mol dm−3) was varied over a wide range. The isoelectric point, pHiep, is shifted to higher values with increasing salt concentration until a charge reversal was no longer observed at a concentration of 1 mol dm−3 NaCl. The rheological properties were analyzed in the form of the critical yield stress and the shear stress and viscosity at arbitrarily selected high and low shear rates, respectively. The maximum of the rheological properties was found to correlate with to the pHiep. The electrokinetic and rheological features of the system were related to a recent theory of Hunter et al. [J. Colloid Int. Sci. 28 (1968) 250] by plotting the yield stress against the square of the ζ potential for each salt concentration. The acidic branch, i.e. when pH<pHiep, of these curves followed the expectations of the theory quite well. For the alkaline branch (pH>pHiep), however, the curves did not show the expected linear behaviour. Also when comparing the influence of pH and sodium chloride concentration on the rheology, it was found that on the acidic yield stress branch the dependency of pH and salt concentration was very different from the one on the alkaline branch. On the acidic branch, low ionic strengths shared a common straight line. On the contrary, the alkaline branch had separate linear dependencies for each salt concentration. Moreover, the lines on the alkaline side seemed to be quite parallel for medium salt concentrations.
Colloids and Surfaces A: Physicochemical and Engineering Aspects.
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ABSTRACT: Sol–gel derived SiO2 have been shown to be biocompatible and bioresorbable and they have potential use in living tissue, e.g., in bone regeneration and controlled drug delivery. Bioresorbable SiO2 is a potential alternative for the controlled delivery of large biologically active agents, such as proteins and peptides. The aim was to prepare SiO2 matrices with varying bioresorption rate at protein-compatible conditions and to characterize the chemical features of the matrices. SiO2 was prepared in two morphologies, monoliths by casting and microparticles by spray drying. A model protein was encapsulated into the SiO2 matrices. Materials were carefully characterized with FTIR- and Raman spectroscopy, TGA-FTIR, solid state 29Si MAS NMR, SEM and matrix dissolution was measured in simulated physiological conditions. It is shown that both fast and slowly dissolving SiO2 matrices could be prepared at protein-compatible conditions. Fast-dissolving SiO2 microparticles contained a high proportion of Q3 and a low portion of Q4 indicating poor cross-linking of SiO2 species and an increased amount of hydrolysable terminal groups. Spectroscopic techniques and TGA-FTIR show that organic residues and moisture are left in the matrices. The amount of organic residues is larger in the fast-dissolving SiO2 matrices, but it does not significantly affect the bioresorption rate.
Journal of Non-Crystalline Solids 351:3225-3234. · 1.54 Impact Factor
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ABSTRACT: Biodegradable silica fibres were prepared from TEOS-derived silica sols by dry spinning. The spinnability of the sols and its influence on the green state fibre structure were investigated. The same sols can be used to prepare different fibre structures depending on the process stage, temperature and viscosity. The spinning moment was found to be important in order to control the biodegradation. Influence of catalysts (HNO3 and/or NH3) as well as evaporation of the liquid on the process were investigated. They did not have an influence on the spinnability, but they reduced the overall reaction time. The prepared green state fibres were aged for 1 and 3 months indicating stable structure as a function of ageing time according to the biodegradation experiments, except in the case of high catalyst concentration. A porous structure was revealed using transmission electron microscopy. Heat-treatment of the fibres induced remarkable differences in the fibre bulk structure according to FT–IR measurements.
Journal of the European Ceramic Society.
