Luukudosteknologisten borosilikaattiskaffoldien valmistus

Tissue engineering utilizes artificial porous structures, scaffolds, to temporarily replace parts of tissues or organs in order to enhance the healing process. Scaffolds for bone tissue repair should fulfill several structural, mechanical and chemical criteria. Bioactive glasses and biodegradable polymers are typical materials used in scaffold fabrication for bone tissue engineering. Bioactive glasses have remarkable biological performances but suffer from poor mechanical properties and processability. Whereas biodegradable polymers have a wide variety of processing options but generally have low strength and biological activity. In his study, borosilicate glasses were utilized to produce 3D scaffolds. In a first time, the aim was to produce mechanically strong scaffolds without significant crystalline phase which could lead to loss of bioactivity. The reactivity of the scaffolds in aqueous solution was studied in the light of the scaffolds´ morphologies. In a second time, the potential for developing porous glass/polymer scaffolds was investigated. In this study, borosilicate glasses were under investigation and calcium was substituted by magnesium and/or strontium to enhance the hot working domain while providing therapeutic effect. Structures and thermal properties of the glasses were determined. Glass scaffolds were prepared via the porogen burn-off method and robocasting using sintering temperatures enabling viscous flow without significant crystallization. Composite scaffolds were produced using supercritical carbon dioxide processing by adding glass powder to poly(lactide-co-ε-caprolactone) matrix. The scaffolds´ morphologies, mechanical properties and in vitro behavior were analyzed. Based on the results, it was concluded that both magnesium and strontium substitution enhanced the sinterability of the base glass but had a decreasing effect on reactivity. Utilized production methods yielded promising scaffold morphologies that seemed to be suitable for clinical applications. Robocasted scaffolds were found to have slightly higher reactivities than the scaffolds produced via porogen burn-off method, which was suspected to be due to higher interconnectivity of the pore network. Addition of glass particles into polymeric matrix was found to promote the polymer´s biological properties

Impact of borosilicate bioactive glass scaffold processing and reactivity on in-vitro dissolution properties

In this study, bulk borosilicate glasses and 3D scaffolds (processed by the burn-off technique and by robocasting) were synthesized to investigate the impact of the manufacturing method, glass composition and preincubation time on in vitro dissolution and cell response. The studied compositions are based on commercial bioactive glass S53P4 (BonAlive) where 12.5% SiO2 has been replaced by B2O (labelled B12.5), and part of the CaO is replaced with MgO and SrO (labelled B12.5-Mg-Sr). First, the impact of the processing and glass composition, on the dissolution rate, was assessed. As expected, scaffolds were found to exhibit faster dissolution, due to the increased surface area, when compared to the bulk glass. Furthermore, the 3D printed scaffolds were found to dissolve faster than the burn-off scaffolds. Moreover, scaffolds made from B12.5-Mg-Sr glass composition exhibited slower ion release and precipitation of calcium phosphate (CaP) layer, when compared to B12.5, due to the stabilizing effect of Mg and Sr. Finally, dynamic condition produces lower ion releases that static condition and could be more optimal for in vitro cell growth. Secondly, in culture with murine MC3T3-E1 cells, it was shown that 3 days preincubation would be optimal to decrease the burst of ions that is known to lead to cell death. However, it was found that MC3T3-E1 survived and proliferated only in presence of B12.5-Mg-Sr scaffolds. Finally, it was shown that despite scaffolds having different porosities, they had no significant difference on human adipose-derived stem cells (hADSCs) survival. This manuscript brings new information on 1) the impact of material design (porosity) and composition on dissolution kinetic sand reactivity, 2) the impact of static vs dynamic testing on in-vitro dissolution and 3) the impact of materials’ pre-incubation on cell behavior.publishedVersionPeer reviewe

Luukudosteknologisten borosilikaattiskaffoldien valmistus

Tissue engineering utilizes artificial porous structures, scaffolds, to temporarily replace parts of tissues or organs in order to enhance the healing process. Scaffolds for bone tissue repair should fulfill several structural, mechanical and chemical criteria. Bioactive glasses and biodegradable polymers are typical materials used in scaffold fabrication for bone tissue engineering. Bioactive glasses have remarkable biological performances but suffer from poor mechanical properties and processability. Whereas biodegradable polymers have a wide variety of processing options but generally have low strength and biological activity. In his study, borosilicate glasses were utilized to produce 3D scaffolds. In a first time, the aim was to produce mechanically strong scaffolds without significant crystalline phase which could lead to loss of bioactivity. The reactivity of the scaffolds in aqueous solution was studied in the light of the scaffolds´ morphologies. In a second time, the potential for developing porous glass/polymer scaffolds was investigated. In this study, borosilicate glasses were under investigation and calcium was substituted by magnesium and/or strontium to enhance the hot working domain while providing therapeutic effect. Structures and thermal properties of the glasses were determined. Glass scaffolds were prepared via the porogen burn-off method and robocasting using sintering temperatures enabling viscous flow without significant crystallization. Composite scaffolds were produced using supercritical carbon dioxide processing by adding glass powder to poly(lactide-co-ε-caprolactone) matrix. The scaffolds´ morphologies, mechanical properties and in vitro behavior were analyzed. Based on the results, it was concluded that both magnesium and strontium substitution enhanced the sinterability of the base glass but had a decreasing effect on reactivity. Utilized production methods yielded promising scaffold morphologies that seemed to be suitable for clinical applications. Robocasted scaffolds were found to have slightly higher reactivities than the scaffolds produced via porogen burn-off method, which was suspected to be due to higher interconnectivity of the pore network. Addition of glass particles into polymeric matrix was found to promote the polymer´s biological properties

Subpicosecond to Second Time-Scale Charge Carrier Kinetics in Hematite-Titania Nanocomposite Photoanodes

Water splitting with hematite is negatively affected by poor intrinsic charge transport properties. However, they can be modified by forming heterojunctions to improve charge separation. For this purpose, charge dynamics of TiO2:alpha-Fe2O3 nanocomposite photoanodes are studied using transient absorption spectroscopy to monitor the evolution of photogenerated charge carriers as a function of applied bias voltage. The bias affects the charge carrier dynamics, leading to trapped electrons in the submillisecond time scale and an accumulation of holes with a lifetime of 0.4 +/- 0.1 s. By contrast, slower electron trapping and only few long-lived holes are observed in a bare hematite photoanode. The decay of the long-lived holes is 1 order of magnitude faster for the composite photoanodes than previously published for doped hematite, indicative of higher catalytic efficiency. These results illustrate the advantages of using composite materials to overcome poor charge carrier dynamics, leading to a 30-fold enhancement in photocurrent.acceptedVersionPeer reviewe

Photophysical Study of a Self-Assembled Donor–Acceptor Two-Layer Film on TiO₂

The self-assembled monolayer (SAM) technique was employed to fabricate a two-layer donor–acceptor film on the surface of TiO₂. The approach is based on using donor and acceptor compounds with anchoring groups of different lengths. The acceptor, a fullerene derivative, has a carboxyl anchor attached to the fullerene moiety via a short linker that places the fullerene close to the surface. The donor, a porphyrin derivative, is equipped with a long linker that can penetrate between the fullerenes and keep porphyrin on top of the fullerene layer. The two-layer fullerene–porphyrin structures were deposited on a mesoporous film of TiO₂ nanoparticles by immersing the TiO₂ film sequentially into fullerene and porphyrin solutions. Transient absorption spectroscopy studies of the samples revealed that after the selective photoexcitation of porphyrin a fast (<5 ps) intermolecular electron transfer (ET) takes place from porphyrin to the fullerene layer, which confirms the formation of the interlayer donor–acceptor interface. Furthermore, in the second step of ET the fullerene anions donate electrons to the TiO₂ nanoparticles. The latter reaction is relatively slow with an average time constant of 230 ps. It involves roughly half of the primary generated charges, and the second half relaxes by the interlayer charge recombination. The resulting state with a porphyrin cation and electron in TiO₂ has an extremely long lifetime and recombines with an average time constant of 23 ms