Preparation of Highly Porous Scaffolds with Controllable Pore Size from Microbial Polyesters

Microbial polyesters saw limited use in the field of tissue engineering, even though the biocompatibility of these polymers makes them ideal candidates for this role. The primary factor that hinders the proliferation of microbial polyesters in this market is that their processing with conventional techniques, such as electrospinning or 3D printing, is challenging. However, the full potential of these biopolymers could still be utilized by applying unconventional manufacturing methods, such as those based on the concept of salt leaching. An implementation of this concept facilitates the production of scaffolds that simultaneously have high porosity and excellent permeability. Moreover, the average pore size can also be varied in the range from 50 to 400 µm, which was reported to be optimal for the cultivation of eucaryotic cell cultures. By adjusting the pore size, the scaffold can be tailored to the eucaryotic cells the tissue consists of. Furthermore, we have developed an entirely new computational method for the approximation of the pore size distribution of the scaffolds. The method relies on 3D data reconstructed by the software of a digital optical microscope and also facilitates the modeling of the average pore size of scaffolds. Thus, besides the control of the pore size, our method enables its prediction as well

A novel method for the determination of diffusion coefficients in amorphous poly(3-hydroxybutyrate)

A novel approach is proposed for the determination of the diffusion coefficient of certain drugs in amorphous poly(hydroxybutyrate) (PHB), which can be a reliable alternative to the conventional permeation based measurements. The method requires the preparation of PHB films with various concentrations of the drug and if the latter absorbs in the visible wavelength range, its concentration gradient in the polymer film as well as the time dependence of the latter can be analyzed quantitatively by following changes in color. Color can be converted into concentration with the help of adequate calibration and thus the dependence of additive concentration on space (x) and time (t), i.e. the c(x,t) function, can be determined relatively easily. The fitting of the numerical solution of Fick's second law onto the measured values provides directly the targeted diffusion coefficient. The comparison of diffusion coefficients obtained by the proposed approach to values published in the literature proved that the new method provides reliable results and requires reasonable time and effort at the same time

The novel technique of vapor pressure analysis to monitor the enzymatic degradation of PHB by HPLC chromatography

A novel method was introduced for the quantitative determination of substances in aqueous solutions by using the evaporative light scattering (ELS) detector of a high performance liquid chromatograph (HPLC). The principle of the measurement is the different equilibrium vapor pressure of the solvent and the analyte resulting in decreasing evaporation rate, larger droplets and stronger signal with increasing concentration. The new technique based on vapor pressure analysis was validated with traditional UV-Vis detection carried out with a diode array detector (DAD). The new technique was used for monitoring the concentration of solutions obtained during the enzymatic degradation of poly(3-hydroxybutyrate) yielding the 3-hydroxybutyrate monomer as the product. The accuracy of the measurement allowed the determination of degradation kinetics as well. The results obtained with the two techniques showed excellent agreement at small concentrations. Deviations at larger concentrations were explained with the non-linear correlation between analyte concentration and detector signal and the linear regression used for calibration. Mathematical analysis of the method made possible the determination of the evaporation enthalpy of the analyte as well. The new approach is especially suitable for the quantitative analysis of compounds, which do not absorb in the detection range of the DAD detector or if their characteristic absorbance is close to the lower end of its wavelength range

A halloysit mint ásványi töltőanyag és polipropilén kompozitjainak tulajdonságai

Kereskedelmi forgalomban kapható halloysit ásvány széleskörű jellemzése, és polipropilénnel alkotott kompozitjainak előállítása és vizsgálata során felderítettük a töltőanyag összetételét és tisztaságát, jellemeztük szemcseméretét és a szemcsék morfológiáját. Számszerűsítettük a töltőanyag erősítő hatását és igazoltuk, hogy a halloysit ígéretes társító anyag. A kompozit készítés körülményeit körültekintően kell megválasztani, enélkül ugyanis a mechanikai tulajdonságok csak kismértékben javíthatók

Mechanism and kinetics of the hydrolytic degradation of amorphous poly(3-hydroxybutyrate)

Amorphous poly(3-hydroxybutyrate) films prepared by compression molding and solvent casting were degraded in aqueous media at different pH values. The time dependence of degradation was monitored by the measurement of weight loss, the extraction of the degradation products from the degrading sample, as well as by UV-Vis spectrophotometry and HPLC analysis of the aqueous solution. The results proved that degradation takes place mainly in the bulk of the samples and not on their surface. The overall rate of degradation depends strongly on pH; it increases with increasing pH values. Metabolite extraction and chromatography proved that degradation does not occur randomly, but with larger frequency at the end of the chains. By assuming that the hydrolysis of PHB is a SN2 type nucleofil substitution reaction, a kinetic model was proposed which describes the formation of various degradation products. The diffusion of metabolites was also accommodated into the model thus the concentration in the aqueous solution could also be predicted well. The correlation between prediction and experimental results is excellent. The model can be extended also for the description of the hydrolytic degradation of other aliphatic polyesters

Tear Mediators NGF along with IL-13 Predict Keratoconus Progression

L