Mervi Puska

Evaluation of bis-GMA/MMA resin adhesion to silica-coated and silanized titanium

The effects of pH value and alcohol solvent type of a silane solution on the bonding of an experimental resin to the silica-coated titanium (Ti) surface were studied. First, Ti surfaces underwent tribochemical Rocatec™ treatment followed by silanization of the surface with 3-methacryloxypropyltrimethoxysilane (MPS). Then, resin stubs based on a mixture of bisphenol-A-glycidyl dimethacrylate and methyl methacrylate were bonded and light-cured onto each silica-coated Ti surface (n = 6 per group). Two different solvents for MPS, namely iso-propanol (i-PrOH)/H2O and ethanol (EtOH)/H2O were used, at pH values of 4.5, 5.0, and 5.5, and shear bond strengths were tested both under dry storage conditions and after water sorption induced by accelerated aging (i.e. thermo-cycling). The shear bond strengths were also re-determined after the silane solutions had been stored at 4°C for 15 weeks before the silanization step. For dry samples, the shear bond strengths ranged from 7.5 to 10.6 MPa (ANOVA, p < 0.05) when the Ti surface had been silanized with MPS in i-PrOH/H2O, and from 6.5 to 12.4 MPa (ANOVA, p < 0.05) when the Ti surface had been silanized with MPS in EtOH/H2O at pH 4.5. Fifteen weeks of storage of the silane solution increased the shear bond strength of dry samples by ca. 1–4 MPa per test group. In contrast, thermo-cycling reduced the shear bond strength in both solvent systems. The weight of the test sample stubs increased by ca. 3.5 wt% after 187 days of being subjected to the water sorption test.

Silane-Treated E-Glass Fiber-Reinforced Telechelic Macromer-Based Polymer-Matrix Composites

The aim of this in vitro study was to investigate the water sorption and flexural properties of fiber reinforced composites (FRC) prepared from telechelic macromer extended urethane dimethacrylate (PEG-400-E-UEDMA)(PEG), hydroxypropyl methacrylate (HPMA) and E-glass fibers. Three experimental groups of test specimens based on poly(PEG-400-E-UEDMA-HPMA) polymer matrices and continuous unidirectional E-glass fibers were light polymerized and stored in deionized water for 0, 4, 12 or 24 weeks. The weight ratios (%) of PEG-HPMA were 27.5–70.5, 49.0–49.0 and 70.5–27.5 with an initiator-activator percentage of 1.0–1.0. After each time period of storage the water absorption and flexural properties were measured. There were six test specimens in each of the test groups (N = 6) and the specimen’s fracture surfaces were analyzed using scanning electron microscopy (SEM). All the PEG-HPMA groups exhibited the highest water absorption at the time point of two days (5.5 to 6.4 %), which thereafter decreased to the level of 3.8–4.7 % at the time point of 30 days. The flexural strength varied from dry specimens’ 128 to 283 MPa to the 30 days water-stored specimens’ of 30 to 49 MPa. The flexural modulus exhibited values from 7.9 to 14.8 GPa (dry specimens) and ca. 0.5 to 1.8 GPa after 30 days of water-storage. Both the flexural strength and modulus decrease dramatically with a longer water storage time. The SEM images showed good adhesion between the fibers and the resin matrix. In the wet conditions, the telechelic macromer based hydrophilic PEG polymer-matrix FRCs formed a plasticized composite that decreased the flexural properties.

Calcium Phosphate Formation on Ethylphosphoester of Poly(ε-Caprolactone) and Poly[Bis(Methacrylate)]Phosphazene In Vitro

Phosphorus containing biopolymers have been synthesized and studied as polymeric candidates for potential tissue engineering applications. The presence of phosphorus in the polymeric structure may improve the biocompatibility of polymers by enhancing their tissue contact. One aim of this study was to examine the chain extending reaction of poly(ε-caprolactone), PCL, using ethyldichlorophosphate as a coupling agent. A preliminary survey was done to find out whether the presence of phosphoester units in a rapidly degradable polymeric structure improves the Ca phosphate formation on PCL. Another aim of this study was to synthesize one kind of polyphosphazene, i.e. poly[bis(methacrylate)]phosphazene, PMAP. In addition, a preliminary biomineralization study for PMAP polymer was carried out. The results of the biomineralization studies indicated some bioactivity of both biopolymers.

Preliminary In Vitro Biocompatibility of Injectable Calcium Ceramic-Polymer Composite Bone Cement

In the coming decades, the need for reconstructive surgery of bones is predicted to increase with the ageing of the population as well as the increase of injuries needing traumatologic treatments. Therefore, there is still a constant search for tissue engineering and bone substitute materials. Xenografts, synthetic hydroxyapatitite, bioactive glasses and other bone substitutes have widely been studied. When bone defects are filled using bioceramics in granules, their utilization is limited to small size defects, because the injected granules do not give immediate support against the biomechanical loading of the bone. The aim of this study was to evaluate the preliminary biomineralization and the compression strength of experimental injectable bone cements modified with calcium ceramics. Our studies have focused on the development of injectable composites of bone cements, i.e. in situ curable resin systems containing impregnated Ca ceramics. The polymerized bone cement composites aspire to simulate as closely as possible the mechanical and structural properties properties of bone. The present compressive strength of our inorganic-organic bone cements are >65 up to ~180 MPa. These cements are slightly porous from their outermost surface and showed preliminarily osteoconductivity of some degree.

The Release and Bioactivity of Lysozyme from Selected Sol-Gel Derived SiO2 Matrices

Local drug release has many benefits – a steadier distribution, improved compliance, but most importantly it allows the convenient use of protein based molecules as therapeutic agents. Many different types of materials have been studied as drug carriers, including sol-gel derived SiO2 matrices. In this study lysozyme was used as a model protein and its release from prepared SiO2 monoliths and its biological activity thereafter was studied spectroscopically. Sucrose was used in some preparations to assess its ability to function as a protective agent during storing. Lysozyme release and bioactivity was similar in both preparations containing it when tested fresh. In monoliths stored for ten weeks, however, differences were observed in the biological activity of released lysozyme. In the preparations containing sucrose, lysozyme had retained its activity, while it was virtually nil in the preparations containing only lysozyme. This shows that sol-gel derived SiO2 matrices can be used as carriers for small proteins and that sucrose can function as a protective agent in them.

Biomineralization of Glass Fibre Reinforced Porous Acrylic Bone Cement

Acrylic bone cements are used to fix joint replacements to bone. The main substance in acrylic bone cement is biologically inert poly(methylmethacrylate), PMMA. The dense PMMA polymer structure of cement does not allow bone ingrowth into cement. Therefore, the main focus of our studies is to modify acrylic bone cement in order to improve its biological properties e.g., by creating porosity in the cement matrix. The porous structure is in situ created using pore-generating filler (i.e., 20 wt% of an experimental biodegradable polyamide) that is incorporated in acrylic bone cement. The aim of this in vitro study was to investigate the biomineralization of acrylic bone cement modified using an experimental biodegradable polyamide.

Modified Poly-ε-Caprolactone (PCL) with Phosphorous Containing Compounds for Biomineralization

Biodegradable polymers (e.g. poly-ε-caprolactone, PCL) have been studied largely for tissue engineering applications. The aim of this study was to evaluate the composite fabrication technique on PCL modified with the phosphate salts (i.e. NaH2PO4, Na2HPO4, KH2PO4, or K2HPO4) as well as to determine the compression strengths thereof. The chemical structure and morphology of composites were analyzed using FTIR and SEM/EDX. The influence of a plain phosphate salt in different quantities on the hydrophilic properties of PCL was evaluated by measuring the water contact angle. The results of this study indicated that the addition of phosphate salts led to an improvement in compression strength of PCL composites. According to the results of preliminary biomimetic mineralization, Na2HPO4 seems to increase the bioactivity of PCL.

Glass Fibre Reinforced Porous Bone Cement Implanted in Rat Tibia or Femur: Histological and Histomorphometric Analysis

Acrylic bone cements are used to fix joint replacements to bone. Typically, these cements are fabricated combining a polymer powder and a monomer liquid component together, of which the monomer phase autopolymerizes within 10 – 15 min after mixing the components. The main substance in powder is poly(methylmethacrylate) or related copolymers, and in liquid, methylmethacrylate monomer or related monomer. Shortcomings of the bone cements include among others the dense polymer structure of cement that does not allow bone ingrowth into cement. In this study, the biological behavior of porous bone cement was investigated in vivo. The porous structure was in situ created using pore-generating filler (20 wt%), i.e. an experimental biodegradable polyamide of naturally occuring trans-4-hydroxy-L-proline, which was incorporated in non-degradable acrylic bone cement. According to the histological evaluation of the modified bone cement, signs of bone ingrowth to the cement were noticed.

Macrophage Induced Effect of Particulate Silica on Rat Mesenchymal Stem Cells In Vitro

The role of silica and macrophages in fibrosis is well documented, but in bone formation it is relatively unknown despite decades of research with bioactive glasses. In this study macrophages were isolated from rat peritoneal and then cultured for five days in the presence of two types of silica microparticles with different solubilities. After the fifth day the culture medium was collected, purified and used as an additive in bone marrow derived rat stem cell cultures. The stem cells were cultured for five days in α-mem containing only 0,5% of FCS, enabling cell survival but disrupting their proliferation. As controls, stem cells were also cultured in α-mem containing silica microparticles. At days one and five the amount of soluble collagen was assayed from the culture medium and the cells were counted. All stem cell cultures with macrophage medium additives were found to be proliferative, with statistically significant difference to controls. However, collagen was only produced in cultures containing medium from macrophages cultured with fast-dissolving silica microparticles. This suggests that silica can induce cell proliferation and extra cellular matrix protein secretion which is mediated by macrophages, and that the solubility of silica is also a major factor in this reaction.