Joni Korventausta

Calcium phosphate formation and ion dissolution rates in silica gel-PDLLA composites

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.

Porous Biodegradable Scaffold: Predetermined Porosity by Dissolution of Poly(ester-anhydride) Fibers from Polyester Matrix

A novel selective leaching method for the porogenization of the biodegradable scaffolds was developed. Continuous, predetermined pore structure was prepared by dissolving fast eroding poly(epsilon-caprolactone)-based poly(ester-anhydride) fibers from the photo-crosslinked poly(epsilon-caprolactone) matrix. The porogen fibers dissolved in the phosphate buffer (pH 7.4, 37 degrees C) within a week, resulting in the porosity that replicated exactly the single fiber dimensions and the overall arrangement of the fibers. The amount of the porosity, estimated with micro-CT, corresponded with the initial amount of the fibers. The potential to include bioactive agents in the porogen fibers was demonstrated with the bioactive glass.

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.

Elastic Ceramic-Polymer Scaffold with Interconnected Pore Structure: Preparation and In Vitro Reactivity

A series of ceramic-polymer scaffolds were studied for bone tissue engineering applications. These applications require bone reactivity as well as suitable scaffold properties and structure. Bioactive glass (BAG) and sol-gel derived silicas were chosen for ceramic components of the scaffolds, and crosslinked poly(ε-caprolactone/D,L-lactide) copolymers with monomer ratios 90/10 and 70/30 were used as polymer matrices. Scaffolds were prepared by photo-curing crosslinkable oligomers in the presence of the ceramic component and porosity producing salt. Scaffolds with 60-80 vol-% continuous phase macroporosity were obtained by using calcium chloride hexahydrate (CaCl2⋅6H2O), and were further tested in simulated body fluid (SBF). The ceramics remained highly reactive during scaffold preparation resulting in in vitro calcium phosphate formation.

Analysis of the Energy Level Scheme of Nd3+ IN NdOBr

Summary A detailed analysis of the energy level scheme of the Nd3+ ion with the 4f3 electron configuration is described in the NdOBr matrix. 93 Stark levels were deduced from the optical absorption spectra recorded at the UV, visible and NIR spectral ranges at selected temperatures from 9 to 300 K. The experimental level scheme was simulated with a phenomenological model with 19 parameters accounting simultaneously for the free ion and crystal field effects. The results of the simulation showed increasing covalence and decreasing crystal field effect from NdOF to NdOBr.

Bioactive Glass (S53P4) and Mesoporous MCM-41-Type SiO2 Adjusting In Vitro Bioactivity of Porous PDLLA

SiO2-based bioceramics, MCM-41-type SiO 2 and the bioactive glass S53P4, in composites with poly(D,L)lactide were studied in the simulated body fluid. The parameters controlling ion dissolutions and calcium phosphate formation were studied a nd the data was used to create multicomposites with locally varying properties ( .g., CaP formation on the other side, uninhibited silica dissolution and possibility to drug release from the other side of com posite)

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.

Host anion effect on the energy level scheme of Sm3+ in SmOX (X = F, Cl and Br)

The energy level schemes obtained from the optical absorption and luminescence data for the Sm3+ doped oxyhalides (SmOX, X = F, Cl and Br) were simulated with a phenomenological model accounting simultaneously for the free ion interactions and the crystal field (c.f.) effect. The values of the Slater integrals (Fk) describing the electrostatic interactions increase as a function of the ionic radius of the anion from SmOF to SmOBr. The value of the host independent c.f. strength parameter S for the hexagonal SmOF matrix (580 cm−1) is more than 50% higher than for the tetragonal SmOCl or SmOBr. This indicates the importance of the ionic contribution to the c.f. effect.