Instytut Podstawowych Problemów Techniki

Streszczenie:

Injection of cell‐laden scaffolds in the form of mesoscopic particles directly to the site of treatment is one of the most promising approaches to tissue regeneration. Here, a novel and highly efficient method is presented for preparation of porous microbeads of tailorable dimensions (in the range ≈300–1500 mm) and with a uniform and fully interconnected internal porous texture. The method starts with generation of a monodisperse oil‐in‐water emulsion inside a flow‐focusing microfluidic device. This emulsion is later broken‐up, with the use of electric field, into mesoscopic double droplets, that in turn serve as a template for the porous microbeads. By tuning the amplitude and frequency of the electric pulses, the template droplets and the resulting porous bead scaffolds are precisely produced. Furthermore, a model of pulsed electrodripping is proposed that predicts the size of the template droplets as a function of the applied voltage. To prove the potential of the porous microbeads as cell carries, they are tested with human mesenchymal stem cells and hepatic cells, with their viability and degree of microbead colonization being monitored. Finally, the presented porous microbeads are benchmarked against conventional microparticles with nonhomogenous internal texture, revealing their superior performance.

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The degradation in vivo and its effect on the supermolecular structure of poly(caprolactone) was examined. Poly(caprolactone) (PCL) samples were prepared in the form of porous scaffolds implanted into rat calvarial defects. The degradation was investigated by means of gel permeation chromatography, wide angle X-ray scattering (WAXS), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The study showed that the observed decrease of PCL crystallinity during degradation is accompanied by reduction of crystal size and/or perfection. The observed phenomenon could be explained by the presence of the high content of the low mobile fraction of investigated polymer, consisting not only almost 50% of crystal fraction but also most probably relatively high fraction of s.c. rigid amorphous fraction (RAF). Considering the type of structure characterized by the dominance of low mobile fraction, it is expected that the degradation will mainly concern these fractions, which in turn will lead to a decrease in the degree of crystallinity as well as crystal size and/or perfection.

Słowa kluczowe:

PCL degradation, In-vivo conditions, Crystallinity, Rigid amorphous fraction

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Physical and chemical factors resulting from the sterilization methods may affect the structure and properties of the materials which undergo this procedure. Poly(l-lactide-co-glicolide) (PLGA) is commonly used for medical applications, but, due to its inadequate mechanical properties, it is not recommended for load-bearing applications. One of the methods for improving PLGA mechanical properties is addition of hydroxyapatite nanoparticles (nHAp). The aim of this study was to evaluate the effect of nanoparticles addition on PLGA structure and properties after gamma radiation. According to our results, reduction of the molecular mass caused by gamma radiation was lower for PLGA with nHAp addition. Differential scanning calorimetry (DSC) analysis indicates an increase of crystallinity caused both by nHAp and gamma radiation. The first phenomenon can be explained by heteronucleation, while the second one is most probably related to higher molecular mobility of degrading polymer. Moreover, addition of nanoparticles increases thermal stability and affects the Young's modulus changes after gamma radiation.

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In this research, the effect of the presence of living cells (SaOS-2) on in vitro degradation of Mg-2.0Zn-0.98Mn (ZM21) magnesium alloy was examined by two methods simple immersion/cell culture tests and electrochemical measurements (electrochemical impedance spectroscopy and potentiodynamic polarization) under cell culture conditions. In immersion/cell culture tests, when SaOS-2 cells were cultured on ZM21 samples, pH of cell culture medium decreased, therefore weight loss and Mg2+ ion release from the samples increased. Electrochemical measurements revealed the presence of living cells increased corrosion rate (Icorr) and decreased polarization resistance (Rp) after 48 h of incubation. This acceleration of ZM21 corrosion can mainly be attributed to the decrease of medium pH due to cellular metabolic activities.

Słowa kluczowe:

Biodegradable metals, Biomaterials, Electrochemical impedance spectroscopy, Immersion, Cell culture condition

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Four kinds of biodegradable polymers were employed to prepare bioresorbable coatings on Mg-2.0Zn-0.98Mn (ZM21) alloy to understand the relationship between polymer characteristics, protective effects on substrate corrosion, cytocompatibility and cell functionality. Poly-l-lactide (PLLA), poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) or poly(lactic-co-glycolic) acid (PLGA) was spin-coated on ZM21, obtaining a smooth, non-porous coating less than 0.5 μm in thickness. Polymer coating characterization, a degradation study, and biocompatibility evaluations were performed. After 4 w of immersion into cell culture medium, degradation of PLGA and PLLA coatings were confirmed by ATR-FTIR observation. The coatings of PLLA, PHB and PHBV, which have lower water permeability and slower degradation than PLGA, provide better suppression of initial ZM21 degradation and faster promotion of human osteosarcoma cell growth and differentiation.

Słowa kluczowe:

Biodegradable metal, Magnesium alloy, Biodegradable polymer, SaOS-2 differentiation, Calcification

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In vitro degradation behavior of squeeze cast (CAST) and equal channel angular pressed (ECAP) ZM21 magnesium alloy (2.0 wt% Zn-0.98 wt% Mn) was studied using immersion tests up to 4 w in three different biological environments. Hanks' Balanced Salt Solution (Hanks), Earle's Balanced Salt Solution (Earle) and Eagle minimum essential medium supplemented with 10% (v/v) fetal bovine serum (E-MEM + 10% FBS) were used to investigate the effect of carbonate buffer system, organic compounds and material processing on the degradation behavior of the ZM21 alloy samples. Corrosion rate of the samples was evaluated by their Mg2 + ion release, weight loss and volume loss. In the first 24 h, the corrosion rate sequence of the CAST samples was as following: Hanks > E-MEM + 10% FBS > Earle. However, in longer immersion periods, the corrosion rate sequence was Earle > E-MEM + 10% FBS ≥ Hanks. Strong buffering effect provided by carbonate buffer system helped to maintain the pH avoiding drastic increase of the corrosion rate of ZM21 in the initial stage of immersion. Organic compounds also contributed to maintain the pH of the fluid. Moreover, they adsorbed on the sample surface and formed an additional barrier on the insoluble salt layer, which was effective to retard the corrosion of CAST samples. In case of ECAP, however, this effect was overcome by the occurrence of strong localized corrosion due to the lower pH of the medium. Corrosion of ECAP samples was much greater than that of CAST, especially in Hanks, due to higher sensitivity of ECAP to localized corrosion and the presence of Cl−.

The present work demonstrates the importance of using an appropriate solution for a reliable estimation of the degradation rate of Mg-base degradable implants in biological environments, and concludes that the most appropriate solution for this purpose is E-MEM + 10% FBS, which has the closest chemical composition to human blood plasma.

Słowa kluczowe:

ZM21 magnesium alloy, ECAP, Simulated body fluids, In vitro degradationBicomponent nanofibers, Biodegradation, Biopolymer

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The aim of the present study was preparation, optimization, and systematic characterization of electrospun bionanocomposite fibers based on polyvinyl alcohol (PVA) as matrix and nanohydroxy apatite (nHAp) and cellulose nanofibers (CNF) as nanoreinforcements. The presence of nHAp and nHAp-CNF affected the morphology of electrospun mats and reduced fiber diameter, particularly at a higher content of nanofillers. The obtained results of FTIR, DSC, and WAXS proved the crystallinity reduction of electrospun nancomposites. Both nHAp and nHAp-CNF addition led to a significant increase of Young modulus with the highest stiffness for nanocomposite fibers at 10 wt% of nHAp and 3 wt% of CNF.

Słowa kluczowe:

Bionanocomposite, cellulose nanofibers, electrospinning, nanohydroxy apatite

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The aim of this paper is to describe the effects of wear particles, generated during articulation of the bearing surfaces of the total joint prosthesis on bone-implant interface. Submicron particles migrate into effective joint space and stimulate cells present in the fibrous tissue to release molecular signal. Cytokines activate the osteoclasts and in consequence bone loss may result. It weakens the bone-implant fixation and may cause aseptic loosening of the prosthesis.

Słowa kluczowe:

wear debris, bone–implant interface, total joint replacemtnt

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Streszczenie:

Application of a biodegradable polymer coating is one of the methods to improve the initial corrosion resistance and cytocompatibility of magnesium (Mg) alloys. However, bulging of the coating film during long term immersion has been reported. Therefore, improvement of interface strength between the coating and the substrate surface is a key for the success of this method. Combination of surface modification [silanization with 3- (glycidyloxypropyl) triethoxysilane (GPTES)] and biodegradable polymer coating [poly-L-lactide (PLLA)] were applied to a Mg- 2.0Zn-0.98Mn (ZM21) cast alloy. Results of a cell proliferation assay show that PLLA and GPTES+PLLA coating successfully improved cell growth during 7 days of incubation and suppressed Mg2+ release after 4 days of incubation. The silanization process had no impact on suppression of corrosion. Calcification was observed on all samples after 1 week of incubation with calcification medium, but the calcified area was much larger on the GPTES+PLLA coated sample than on the uncoated sample.

Słowa kluczowe:

biodegradable metal, ZM21, cytocompatibility, silane-coupling, PLLA

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The use of the ultrasonically destructible microcapsules as local drug delivery systems continues to grow. Microbubble destruction requires correct ultrasonic frequency equal to its resonance. This frequency depends on the bubble size and polymer shell stiffness. Measurements of the ultrasonic signal, backscattered from microspheres gives practical information of the bubble resonance and nonlinearity.
In experiment, the backscattered power spectrum of measured sample was recorded by an ultrasonic scanner. Radio frequency (RF) data was recorded at 2.0 – 6.6 MHz. The mean particle diameter in the measured sample was 21 μm. The resonance frequency, measured under the microscope, was 0.60 MHz for 43 μm diameter microsphere. The sample volume was 10cm³ and the mean quantity of scatterers was 6•103/cm³.
The simulated power spectrum of the ultrasonic backscattered signal was calculated from the resonance scattering theory for the gas bubbles surrounded by elastic shell.
In conclusion, the measured spectra matched those calculated from the theory. The use of the ultrasonic scanner with RF data output and the high sensitivity, wide bandwidth ultrasonic transducer allows to measure the backscattered signal from the very small quantity of resonance scatterers with satisfactory results at 40 dB signal to noise ratio.

Słowa kluczowe:

ultrasound, microcapsules, controlled drug delivery, backscattering

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The paper presents the results of experimental investigation on polymer foam with shape memory properties. The research is focused on characterization of the microstructure of the foam and understanding the mechanisms of deformation under static and dynamic loading. Up till now, selected experimental techniques have been applied. Dynamic Mechanical Analysis (DMA) allows determining the extent of the value of the glass transition temperature under different load conditions, which also reveals the transformation temperature range for the SMP foam. Scanning electron microscopy (SEM) shows the foam microstructure in various scales, while X-ray tomography gave 3D microstructure results presenting in addition mechanism of the cells deformation and changes in their geometry under 30 % and 50% strain. BOSE system enables obtaining the results on dynamic loading.

Słowa kluczowe:

Shape memory polymer foam, Dynamic mechanical analysis, Glass transition temperature, X-ray tomography

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