Institute of Fundamental Technological Research

The present study aims to theoretically model and verify the mechanical behavior of electrospun fibers of poly(vinyl alcohol) (PVA) reinforced by nanohydroxy apatite (nHAp) and cellulose nanofibers (CNF), the three composites designated as PVA/nHAp, PVA/CNF, and PVA/nHAp/CNF. Tensile tests and AFM nanoindentation studies were used to measure tensile modulus of electrospun scaffolds and single fibers respectively. Halpin–Tsai and Ouali models were applied to predict the stiffness of electrospun mats. Theoretical analysis according to the Halpin–Tsai model showed that CNF have no preferred orientation in the electrospun fibers, particularly at higher filler content. Additionally, this model provided a better prediction than Ouali model, especially at lower filler content. Theoretical models based on the geometry of an unit cell in open-cell structure such as honeycomb, tetrakaidecahedron and cube models simulate electrospun scaffolds. Among the structural models for analysis of porous scaffolds, the honeycomb model showed the best prediction, tetrakaidecahedron model—a moderate one, and cube model was the worst. In general, it was proved by both experiment and theory that the porous structure of electrospun mat caused significant modulus reduction of nanocomposites.

Nanocomposites, Cellulose nanofibers, Electrospinning, Modulus

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.

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

Bicomponent polycaprolactone/gelatin and polycaprolactone/collagen fibres were formed by electrospinning using two kinds of solvents: a representative of commonly used solvents with this polymer composition, highly toxic hexafluoroisopropanol (HFIP) and alternative, less harmful one, the mixture of acetic (AA) and formic (FA) acids. Both material types were subjected to investigations of structure and in-vitro cellular activity. Viscosity and Fourier transform infrared spectroscopy (FTIR) measurements shown that the type of solvent used influences the structure of solution and conformation of polymer molecules. In-vitro quantitative tests as well as cell culture morphology observations proved that materials electrospun with the use of ‘green’ solvents can yield similar results to those obtained by made with toxic ones. Slightly better cellular response to materials electrospun from HFIP can be explained by relatively well dispersed components within the fibre and more expanded conformation of molecules, resulting in better exposition of RGD (Arg-Gly-Asp) binding sites to cells’ integrin receptors.

Cellular tests, Electrospinning, Biopolymers, Viscosity, Solvents

The article is focused on the role of nanohydroxy apatite (nHAp) and cellulose nanofibers (CNFs) as fillers in the electrospun poly (vinyl alcohol) (ES-PVA) nanofibers for bone tissue engineering (TE). Fibrous scaffolds of PVA, PVA/nHAp (10 wt.%), and PVA/nHAp(10 wt.%)/CNF(3 wt.%) were successfully fabricated and characterized. Tensile test on electrospun PVA/nHAp10 and PVA/nHAp10/CNF3 revealed a three-fold and seven-fold increase in modulus compared with pure ES-PVA (45.45 ± 4.77). Although, nanofiller loading slightly reduced the porosity percentage, all scaffolds had porosity higher than 70%. In addition, contact angle test proved the great hydrophilicity of scaffolds. The presence of fillers reduced in vitro biodegradation rate in PBS while accelerates biomineralization in simulated body fluid (SBF). Furthermore, cell viability, cell attachment, and functional activity of osteoblast MG-63 cells were studied on scaffolds showing higher cellular activity for scaffolds with nanofillers. Generally, the obtained results confirm that the 3-componemnt fibrous scaffold of PVA/nHAp/CNF has promising potential in hard TE.

electrospinning, PVA bionanocomposites, scaffolds, bone tissue engineering, cell culture

Cartilage loss due to age‐related degeneration and mechanical trauma is a significant and challenging problem in the field of surgical medicine. Unfortunately, cartilage tissue can be characterized by the lack of regenerative ability. Limitations of conventional treatment strategies, such as auto‐, allo‐ and xenografts or implants stimulate an increasing interest in the tissue engineering approach to cartilage repair. This review discusses the application of polymer‐based scaffolds, with an emphasis on hydrogels in cartilage tissue engineering. We highlight injectable hydrogels with various micro‐ and nanoparticles, as they constitute a novel and attractive type of scaffolds. We discuss advantages, limitations and future perspectives of injectable nanocomposite hydrogels for cartilage tissue regeneration.

polymers, hydrogels, injectable hydrogels, injectable nanocomposite hydrogels, cartilage repair, cartilage tissue engineering

Approach. Injuries of the central nervous system (CNS) can cause serious and permanent disability due to limited regeneration ability of the CNS. Presently available therapies are focused on lesion spreading inhibition rather than on tissue regeneration. Recent investigations in the field of neural tissue engineering indicate extremely promising properties of novel injectable and non-injectable hydrogels which are tailored to serve as biodegradable scaffolds for CNS regeneration. Objective. This review discusses the state-of-the-art and barriers in application of novel polymer-based hydrogels without and with nanoparticles for CNS regeneration. Main results. Pure hydrogels suffer from lack of similarities to natural neural tissue. Many of the biological studies indicated nano-additives in hydrogels may improve their topography, mechanical properties, electroconductivity and biological functions. The most promising biomaterials which meet the requirements of CNS tissue engineering seem to be injectable thermosensitive hydrogels loaded with specific micro-and nanoparticles. Significance. We highlight injectable hydrogels with various micro-and nanoparticles, because of novelty and attractiveness of this type of materials for CNS regeneration and future development perspectives.

hydrogels, nanoparticles, injectable, microparticles, nanofibers, central nervous system

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.

The aim of this research was to study the effect of charge polarity applied to the spinning nozzle on the structure and properties of polycaprolactone/chitosan (PCL/CHT) blends, in particular the efficiency of further surface modification by chondroitin sulphate (CS). The observed differences in the morphology and properties of fibres formed at different polarities were interpreted in terms of molecular interactions occurring in the system. FTIR results indicate stronger PCL-chitosan interactions at negative polarity, resulting in lower PCL crystallinity and crystal size distribution determined by DSC, as well as lower wettability. The charge polarity influences PCL/CHT fibre morphology and tailors some of their properties, e.g. wettability, mechanical properties and the efficiency of surface modification. Better efficiency of CS attachment was observed at negative polarity using atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) is most probably related to higher chitosan content at the fibres' surface being attracted by the negative external potential.

Polycaprolactone/chitosan nanofibres, Charge potential effect in electrospinning, Polycaprolactone-chitosan interactions

Electrospinning of chitosan blends is a reasonable idea to prepare fibre mats for biomedical applications. Synthetic and natural components provide, for example, appropriate mechanical strength and biocompatibility, respectively. However, solvent characteristics and the polyelectrolyte nature of chitosan influence the spinnability of these blends. In order to compare the effect of solvent on polycaprolactone/chitosan fibres, two types of the most commonly used solvent systems were chosen, namely 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and acetic acid (AA)/formic acid (FA). Results obtained by various experimental methods clearly indicated the effect of the solvent system on the structure and properties of electrospun polycaprolactone/chitosan fibres. Viscosity measurements confirmed different polymer–solvent interactions. Various molecular interactions resulting in different macromolecular conformations of chitosan influenced its spinnability and properties. HFIP enabled fibres to be obtained whose average diameter was less than 250 nm while maintaining the brittle and hydrophilic character of the nonwoven, typical for the chitosan component. Spectroscopy studies revealed the formation of chitosan salts in the case of the AA/FA solvent system. Chitosan salts visibly influenced the structure and properties of the prepared fibre mats. The use of AA/FA caused a reduction of Young's modulus and wettability of the proposed blends. It was confirmed that wettability, mechanical properties and the antibacterial effect of polycaprolactone/chitosan fibres may be tailored by selecting an appropriate solvent system. The MTT cell proliferation assay revealed an increase of cytotoxicity to mouse fibroblasts in the case of 25% w/w of chitosan in electrospun nonwovens.

chitosan, electrospinning, PCL/chitosan fibres, solvent system, chitosan salts

Crystallization from melt of poly(vinylidene fluoride) was studied by thin film chip calorimetry at cooling rates from 500 to 100,000 Ks−1 and isothermally down to 76°C. At ca. 70°C, for cooling rates higher than 2000 Ks−1, there appears a change in crystallization from high temperature α phase to low temperature β phase. The amorphous state is preserved at cooling rate 100,000 Ks−1. Analysis of the crystallization kinetics with Ziabicki model reveals maximum of the steady-state crystallization rate of β phase as 2200 s−1 at 22°C, and the highest crystallization rate of α phase as 200 s−1 at 70°C. Approximation of the temperature dependent steady-state crystallization rate with the Turnbull and Fisher nucleation model results in the equilibrium melting temperatures 227 and 173°C for the α and β phase, respectively, and in the energy barrier for short-distance transport, ED, as 70–80 kJ mol−1 at high supercooling.

Poly(vinylidene fluoride), Ultra-fast calorimetry, Crystallization kinetics

Bicomponent polycaprolactone/gelatin and polycaprolactone/collagen nanofibers formed by electrospinning using various solvents were subjected to biodegradation and compared. Hexafluoroisopropanol (HFIP) was used as a reference solvent, while the second, alternative solvent system was the mixture of acetic acid (AA) with formic acid (FA). Biodegradation of investigated materials was manifested mainly by the gelatin leaching, including collagen which is indeed denaturated to gelatin during electrospinning, leading to nanofibers erosion. There was no molecular degradation of PCL during 90 days of biodegradation procedure as deduced from no change in the elongation stress at break. The rate of biopolymer leaching was very fast from all materials during the first 24 h of biodegradation, being related to surface leaching, followed by a slower rate leaching from deeper material layers. Mass measurements showed much faster biopolymer leaching from nanofibers electrospun from AA/FA than from HFIP because of strongly emulsive nature of the solution in the former case. Irrespective of the solvent used, the leaching rate increased with initial content of gelatin. The analysis of Young modulus during biodegradation indicated complex mechanism of changes, including biopolymer mass loss, increase of PCL crystallinity and partial gelatin renaturation.

Bicomponent nanofibers, Biodegradation, Biopolymer

This study aims to explore crystallinity variations of polyvinyl alcohol (PVA) as a result of electrospinning, filler addition, and heat treatment. Pure PVA and PVA nanocomposite fibers containing only nanohydroxy apatite (nHAp) and together with cellulose nanofibers (CNF) were electrospun. Electrospun nanofibers were heat treated at 180°C for 8 h. The morphology of electrospun fibers was evaluated by scanning electron microscopy (SEM) while Fourier transform infrared spectroscopy, differential scanning calorimetry, and wide angle X-ray scattering were used to analyze nanofibers crystallinity. Un-treated electrospun nanofibers were shrank and lost their porous structure in water, while heat treatment of nanofibers caused stabilization of fibrous mats in boiling water. It was concluded that the crystallinity of electrospun PVA were considerably reduced compared to PVA powder due to formation of metastable—small and/or defective crystals. Adding small content (1 wt%) of nHAp led to increase in electrospun nanofibers crystallinity. However, incorporation of higher content of nHAp and CNF caused reduction of crystallinity most probably due to possible interactions among components which interrupt the orientation of macromolecules. All analyzing methods proved the crystallinity enhancement of nanofibers upon heat treatment which can be attributed mostly to water evaporation from electrospun fibers structure.

Polyvinyl alcohol, Crystallinity, Electrospinning, Nanofiber, Nanofiller, Heat treatment

Biological interaction between cells and scaffolds is mediated through events at surfaces. Proteins present in the culture medium adsorb on substrates, generating a protein adlayer that triggers further downstream events governing cell adhesion. Polymer blends often combine the properties of the individual components, for example, can provide mechanical as well as surface properties in one fibre. Therefore, mixtures of synthetic polycaprolactone and gelatin as a denatured form of collagen were electrospun at selected conditions and polymer weight ratios. Fibre morphologies and chemical properties of the surfaces were analysed. These scaffolds were seeded with human mesenchymal stromal cells and their viability was studied. Gelatin addition to polycaprolactone leads to a reduction in fibre diameter. A linear increase in gelatin at the fibre surface was observed in function of the weighed polymers, except for polycaprolactone/gelatin fibres incorporating equal weight ratios. Thereby, a depletion of gelatin at the fibre surface is stated for equally mixed polymers. The depletion of gelatin at the fibre surface is most probably due to hydrophobic interactions between hydrophobic segments of polycaprolactone and gelatin, affecting the spinning mechanism and thus fibre structure. Furthermore, polycaprolactone/gelatin blends show enhanced wettability properties compared to pure gelatin, at least partly due to molecular segregation. Results of in vitro studies reveal an increase in cellular viability and proliferation for cells cultivated on nanofibres containing gelatin, caused by the cell-attractive surface composition as well as the hydrophilic nature of the scaffolds. Contact guidance of cells seeded on parallelised fibres is observed, and DNA tests show evidently enhanced cell numbers on nanofibres containing 20 wt% of gelatin.

Mesenchymal stromal cells, electrospinning, surface, blends, biocompatibility, polymers, bioactivity

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.

Bionanocomposite, cellulose nanofibers, electrospinning, nanohydroxy apatite

The effect of electrospinning parameters on morphology, molecular, and supermolecular structure of polycaprolactone (PCL) fibers was analyzed, with respect to tissue engineering applications. Fibers morphology and structure are mainly determined by solution concentration and collector type. Applied voltage does not significantly influence supermolecular structure (crystallinity) and mechanical stiffness. There is correlation between changes in structure and proliferation of 3T3 cells as evidenced by in vitro study. Processing window of optimal scaffolds is relatively wide, however, variation of electrospinning parameters do not significantly affect their biological functionality.

3T3 cells, crystallinity, electrospinning, molecular orientation, polycaprolactone, porosity, tissue engineering

Bicomponent polycaprolactone/gelatin (PCL/Gt) nanofibers were successfully formed for the first time by electrospinning using a novel polymer–solvent system with solvents being alternative to the commonly used toxic solvents like fluorinated alcohols. The mixture of acetic acid (AA) with formic acid (FA; 90:10) was applied. Stable electrospinning was possible despite the fact the mixture of PCL and gelatin in AA/FA solvent showed emulsive structure. From the practical perspective, there is no doubt that it is possible to obtain PCL/Gt fibers using AA/FA mixture with morphology similar to that for fibers spun from hexafluoroisopropanol (HFIP) solutions.

Alternative solvents, electrospinning, gelatin, nanofibers, polycaprolactone, structure

Gelatin is one of the most promising materials in tissue engineering as a scaffold component. This biopolymer indicates biocompatibility and bioactivity caused by the existence of specific amino acid sequences, being preferred sites for interactions with cells, with high similarity to natural extracellular matrix. The present paper does not aspire to be a full review of electrospinning of gelatin and gelatin containing nanofibers as scaffolds in tissue engineering. It is focused on the still open question of the role of the higher order structures of gelatin in scaffold’s bioactivity/functionality. Gelatin molecules can adopt various conformations depending on temperature, solvent, pH, etc. Our review indicates the potential ways for formation of α-helix conformation during electrospinning and the methods of further structure stabilization. It is intuitively expected that the native α-helix conformation appearing as a result of partial renaturation of gelatin can be beneficial from the viewpoint of bioactivity of scaffolds, providing thus a much cheaper alternative approach as opposed to expensive electrospinning of native collagen.

gelatin, molecular conformation, electrospinning, nanofibers, scaffolds

Novel polyurethanes based on synthetic, atactic poly[(R, S)-3-hydroxybutyrate] (a-PHB) and polycaprolactone (PCL) or polyoxytetramethylene (PTMG) diols were synthesized. It was shown that the presence of a-PHB within soft segments reduces crystallinity of PUR. Because of the low melting temperature for polyurethanes with PCL in soft segments, at this stage of work, electrospinning was limited to polyurethanes containing PTMG and a-PHB. Polyurethane containing 80% of PTMG and 20% of a-PHB was electrospun at various parameters from hexafluoro-2-propanole solution, resulting in formation of fibers with the average diameter ca. 2 μm. The fiber diameter decreased with decreasing polymer concentration in a solution and was practically insensitive to the needle-collector distance in the applied range of distances.

polyurethane, polyhydroxybutyrate, electrospinning, scaffolds

Wide Angle X-ray Scattering (WAXS), Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared spectroscopy (FTIR) analyses of phase composition and of thermal properties of PVDF samples, crystallized at temperatures 27 - 155°C by casting from N,N-dimethyl formamide (DMF) solution, are reported. Samples obtained at 27°C contain only β crystal phase and with increase of casting temperature content of β phase decreases in favor of α phase. Evaluation of combined: phase content (WAXS) and melting heat (DSC), leads to two fold higher than for 100 % α phase value of 100% β melting enthalpy, ΔHβ0= 219.7 J.g-1, which may be justified by strong polar interactions in β phase TTT conformation. The relation ΔHβ0 > ΔHα0 leads either to the thermodynamic stability of β phase in whole temperature range (if Tmβ0 ≥ Tmα0) or to the limited temperature range of thermodynamic stability of α phase (if Tmβ0 < Tmα0).

pvdf, WAXS, FTIR, DSC, crystallinity, polymorphism

Blends of polycaprolactone (PCL) and gelatine (Ge), being effective materials for tissue engineering strategies, were electrospun at various conditions and polymer weight ratios. The morphology, the supermolecular structure as well as the mechanical properties of resulting submicron sized fibres have been analyzed in relation to electrospinning conditions and PCL/Ge weight ratio. Compared to pure PCL, Ge addition leads to large reduction of fibre diameter and finally to changes of fibre morphology. For parallelised fibres collected on a rotating drum, preferred molecular orientation of PCL crystals is found. With increasing Ge content a general reduction of molecular orientation is observed. In addition, there is peculiar dependence of polycaprolactone crystallinity on the content of Ge, showing maximum at low Ge concentration (20%) as determined by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). Such a trend can be explained by hydrophobic interactions in the system containing PCL, gelatine and water, being additional driving forces for crystallization of nonpolar PCL molecules. The presence of water within investigated blend systems has been evidenced experimentally using thermal gravimetric analysis (TGA). Young’s modulus of nonwovens, as determined by uniaxial tensile testing, indicates the effect of additivity of the stiffness of both polymers as well as the influence of preferred molecular orientation. Additional experiments were performed using collagen (Col) as a biopolymeric alternative to Ge. WAXS results show evidently amorphous structure of Col within the blended fibres, indicating strong tendency for denaturation of collagen into gelatine under the influence of hexafluoroisopropanol as a solvent.

Electrospinning, Nanofibres, Blend, Gelatine polycaprolactone, Molecular structure

Analysis of the thermo-mechanical behavior of electrospun thermoplastic polyurethane (TPU) block co-polymer nanofibers (glass transition temperature ∼−50°C) is presented. Upon heating, nanofibers began to massively contract, at ∼70°C, whereas TPU cast films started to expand. Radial wide-angle X-ray scattering (WAXS) profiles of the nanofibers and the films showed no diffraction peaks related to crystals, whereas their amorphous halo had an asymmetric shape, which can be approximated by two components, associated with hard and soft segments. During heating, noticeable changes in the contribution of these components were only observed in nanofibers. These changes, which were accompanied with an endothermic DSC peak, coinciding with the start of the nanofibers contraction, can be attributed to relaxation of an oriented stretched amorphous phase created during electrospinning. Such structure relaxation becomes possible when a portion of the hard segment clusters, forming an effective physical network, is destroyed upon heating.

Block-copolymer, Electrospinning, Nanofibers, Thermo-mechanical properties

Synthetic and natural polymers blends represent a new brand of materials with application in wound healing, scaffolds or drug delivery systems. Polycaprolactone/gelatin (PCL/Gt) blends were analyzed in terms of their miscibility. The PCL structure was investigated as a function of Gt content. Changes in the PCL spherulitic structure with Gt content were investigated by a polarizing-interference microscope. The analysis of the glass transition temperature (Tg) of both components as a function of PCL/Gt ratio by differential scanning calorimetry indicates that the system of polycaprolactone/gelatin belongs to a type of s.c. compatible system, being intermediate between miscible and immiscible systems. There is possibility of very limited miscibility of both components. Supplementary wide angle X-ray scattering results are presented.

lends, compatibility, miscibility, polycaprolactone, gelatin

The potential of polarizing-interference Pluta microscope for determination of optical birefringence of individual nanofibers formed by electrospinning was shown. This technique can be applied for measurements of fiber birefringence, practically at diameter above 300 nm. The molecular orientation of individual polycaprolactone (PCL) nanofibers was determined from birefringence assuming the same orientation of both phases, crystal and amorphous. The molecular orientation was determined using DSC crystallinity, crystal intrinsic birefringence calculated for the first time for PCL from bond polarizabilities as well as estimated value of amorphous intrinsic birefringence. Our results indicate that the birefringence and thus molecular orientation are strongly inhomogeneous along the nanofibers, reflecting a complex nature of forces acting during electrospinning process. The average molecular orientation is weak if any, being dependent together with fiber thickness and crystallinity on electrospinning parameters, like applied voltage, concentration and type of solvent. The obtained results indicate that the average molecular orientation displays similar dependence on applied voltage as fiber diameter. Relatively low melting temperature of electrospun nanofibers suggests low crystal size and/or high concentration of defects in crystals. This observation corresponds with low crystallinity and molecular orientation, indicating together relatively low degree of crystal ordering due to high rate of cooling and solvent evaporation during electrospinning, limiting thus crystallization process.

Nanofibers, Electrospinning, Birefringence, Polarizing-interference microscopy, Polycaprolactone

The kinetics of isothermal crystallization of various polymers was investigated by light depolarization technique (LDT) using the new setup with direct registration of depolarization ratio. Experimental data were analyzed using new method proposed by Ziabicki who shown that degree of crystallinity is a non-linear function of degree of depolarization, crystal thickness, and its birefringence. Other experimental methods were involved providing supplementary information on crystal thickness (SAXS) and allowing comparison of crystallization kinetics (WAXS, DSC). The advantage of LDT relies on high sampling rate allowing on-line measurements and lack of inertia effects that exist in other methods like calorimetry. The limitations of the applicability of the method are discussed. The method needs supplementary information not only on crystal thickness but also on variable optical birefringence of real crystals. Our results show that LDT can be used in a simple way for investigation of crystallization kinetics at relatively high temperatures, providing large and perfect crystals. In such a case it is sufficient to use crystal intrinsic birefringence and final crystal thickness typical at particular temperature of crystallization. On the other hand, depolarization ratio combined with measurements by other methods (crystallinity and crystal thickness) can be used for estimation of crystal birefringence.

Polymer, Crystallization kinetics, Light depolarization, Crystal birefringence

Phase transitions in isotactic polypropylene were investigated during isothermal crystallization and heating after isothermal crystallization using various experimental techniques. The results obtained by wide angle x-ray scattering (WAXS), light depolarization technique (LDT), differential scanning calorimetry (DSC) and optical microscopy show that crystallization of isotactic polypropylene can result in simultaneous formation of two crystal modifications, alpha and beta. There is clear experimental evidence that beta phase tends to convert into alpha modification during crystallization as well as during subsequent heating. Experimental results are compared with numerical simulation performed according to the model of nucleation-controlled phase transitions in multiphase systems. The results of simulation show that beta phase is not thermodynamically stable in any temperature range. The reason for the appearance of beta phase is related to low interfacial tension of melt vs. beta. It has been also shown that maximum crystallinity reached in experiments does not exceed 40–50% in agreement with the concept of constrained amorphous phase.

polypropylene, polymorphism, metastability, crystallization

A new setup for light depolarization measurements was designed. Two innovative elements have been introduced. The first is an electronic system which enables depolarization ratio to be registered directly. The second is a system of temperature control allowing effective implementation of a temperature–time program according to the particular requirements. Direct registration of depolarization ratio instead of intensity of depolarized light for individual components (parallel and perpendicular), as is performed in the usual apparatus, allows elimination of light scattering effects because of the insensitivity of depolarization ratio to the scattering level. Application of the new setup was shown for crystallization and melting of isotactic polypropylene (i-PP). Comparison of phase transitions in i-PP, as registered by light depolarization and DSC, indicates some differences. Possible sources of the observed differences are discussed.

Light depolarization, Polymers, Crystallization, Melting, Kinetics of phase transitions

Studies of kinetics of polymer crystallization are generally performed by heating the material above the melting point, in order to erase previous thermal and mechanical history, followed by rapid cooling to the desired crystallization temperature or by cooling at a constant rate. For poly(3-hydroxybutyrate) this procedure implies some degradation of the polymer chain, which starts below the onset of melting. In this article the effects of melting conditions on the subsequent crystallization kinetics are discussed. It is shown that in order to sufficiently cancel memories of previous crystalline order of the analyzed PHB, it is necessary to bring the material at a temperature higher than 192 °C. Thermal treatments conducted at lower temperatures are not sufficient to destroy all solid aggregates, and crystallization of PHB has an anticipated onset of crystallization due to nucleation occurring via self-seeding. The chain degradation attained upon exposure at high temperatures has much lesser influence on crystallization kinetics than incomplete melting, with some effects detectable on the spherulitic morphology and on the final degree of crystallinity.

PHB, thermal history, crystallization, degradation

The time dependence of nucleation rate in isothermal crystallization of poly(3-hydroxybutyrate) was experimentally shown, both in heterogeneous and homogeneous nucleation. The time dependence of nucleation rate is one of the important limitations for the applicability of the simplified form of Kolmogoroff- Avrami-Evans model with time independent kinetic characteristics. The presented results are interpreted in terms of non-steady-state cluster size distribution underlying transient nature of nucleation. The relaxation time needed for reaching a steady-state cluster size distribution and thus steady-state nucleation rate is relatively long, exceeding the time of exhaustion of heterogeneities. The relaxation time estimated from homogeneous process was tens of seconds in the temperature range between 83 and 120 oC. Application of Arrhenius law allows estimation of relaxation time in broader temperature range, showing an increase of relaxation time with decreasing temperature.

PHB, isothermal crystallization, nucleation rate

Melt-crystallization of polyvinylidene fluoride (PVDF) was investigated in non-isothermal mode at ultra-high cooling rates ranging between 30–3000 K/s as well as at constant temperatures after quenching at 6000 K/s. An increase of the cooling rate above 150 K/s leads to the formation of betaphase manifested by a low temperature shoulder of crystallization exotherm in addition to the alphamodification. At the cooling rates above 2000 K/s there is only low temperature exothermic peak that is attributed to the crystallization of pure betamodification. Isothermal crystallization was possible to realize at 110 oC as the lowest, resulting in form. Much higher crystallization rate in submicrogram samples, as compared to standard DSC experiments, is also reported.

Polyvinylidene fluoride, Crystallization, Ultra-fast calorimetry, Polymorphism

This article details a study of irregularly shaped DSC exotherms of poly(3-hydroxybutyrate) (PHB) developed during isothermal and non-isothermal crystallization. Due to the extreme purity of the polymer, PHB crystallization is mainly initiated by homogeneous nucleation, with the formation of very large spherulites, especially under slow nucleation conditions. When the number of growing spherulites is low, the evolution of latent heat is very sensitive to every act of nucleation as well as to the space limitations in the process of growth, resulting in non-monotonous development of latent heat, with sudden increases and decreases in crystallization rates. This results in non conventional DSC exotherms, under given crystallization conditions, characterized by spikes or shoulders associated to nucleation of new spherulites.

PHB, crystallization, nucleation, DSC

The analysis of WAXS profiles for various polyethylenes indicates that the proper description of a structure needs the introduction of a kind of ‘third phase’ in addition to the classical crystalline and amorphous phases. The structure of the additional phase is intermediate between that of the amorphous and crystalline phase. With increasing branch content and molecular weight the intermediate phase becomes more similar to the structure of amorphous phase. The experimental evidence for the intermediate phase is derived not only from the crude approximation of WAXS profiles based on the two phase model but also from the unexpected behavior of the parameters of amorphous halo during crystallization. When crystallization is started, an analysis based upon two-phase model results in an apparent increase of the diffraction angle and width of amorphous halo with time above the values anticipated from the range before the start of crystallization. This is caused by the fact that the amorphous fitting function tries to cover a peak of the intermediate component that appears between morphous halo and (110) reflection of crystalline phase. The conventionally applied two-phase model leads to several serious errors in determination of structural parameters of both phases. The analysis of crystallization kinetics using three-phase model provides additional information on the nature of crystallization itself.

Polyethylene, Crystallization, Intermediate phase

Crystallization of polypropylene (PP) can result in formation of different crystal modifications depending on external conditions. The mechanisms of formation of various crystal modifications in polypropylene are still under discussion.We have investigated non-isothermal melt crystallization of isotactic polypropylene at cooling rates ranging from 1 up to 180,000 K/min using two types of differential scanning calorimeters-standard device Perkin–Elmer DSC Pyris-1 and ultra-fast calorimeter. Additional results were obtained by means of wide angle X-ray scattering and optical microscopy. At cooling rates below 6000 K/min there is only one exothermic peak corresponding to simultaneous crystallization ofalpha andbeta modifications. At cooling rates higher than 6000 K/min there is additional low temperature DSC peak corresponding to formation of mesomorphic phase. At the rates higher than 36,000 K/min there is no trace of formation of any ordered phase. In our opinion this complex behavior observed during crystallization of polypropylene can be explained using the concept of metastable phases. An increase ofbeta content in samples with quinacridone pigment has been observed only at very low cooling rates, corresponding to high temperatures of crystallization and low homogeneous nucleation rate.

Polypropylene, Crystallization, Utra-fast calorimetry, Crystallographic modifications, Metastable phases

In the present study, a full bionanocomposite scaffold from poly (vinyl alcohol) (PVA), nanohydroxy apatite (nHAp) and cellulose nanofibers (CNF) was fabricated by electospinning and its potential application for bone tissue engineering was investigated. Morphology of the electrospun scaffolds was seen by field emission scanning electron microscope (FE-SEM). Both nHAp and CNF enhanced the tensile modulus of the scaffolds; however, both tensile strength as well as slongation at break showed reduced behaviour. Porosity measurement showed that scaffolds had porosity more than 70% which is appropriate for tissue engineering scaffolds. Contact angle test proved high hydrophilicty of electrospun mats while nanofiller incorporation promoted hydrophilicity. Biodegradability was investigated in phosphate buffer saline (PBS). In vitro biomineralization in simulated body fluid (SBF) and MTT cytotoxicity analysis showed that addition of nHAp and CNF increased bioactivity and cell viability of the scaffolds. The obtained results offered a 3-component promising scaffold for bone tissue engineering.

Bionanocomposite, Scaffold, Electrospinning, Poly (vinyl alcohol) and Bone tissue engineering

Three types of membrane structures with wide pores were compared in this study. One of the membranes was obtained from polyethersulfone using cellulose fibers as the macropore precursors. Two of the fibers were obtained from poly(L-lactide). As the macropore precursors olyvinylpyrrolidone (1.2 MDa) and pork gelatin non-woven were used, the influence of non-woven fibers on the structure of membranes was shown. Necessity of specific membrane structure application was explained. The hoice of polymers and co-polymers with a range of biodegradation times can determine the scaffold type suitable for the age of a patient.

Polysulfone membrane, Polyester membranes, Membrane structures, Biodegradable membranes, 3D scaffold

methylcellulose, agarose, hydrogel, cross-linking kinetics, DMA, modulus

Electrospun nonwovens from PCL/gelatin and PCL/collagen structurally mimic native extracellular matrix and provide cells with chemical cues affecting them. Electrospinning of bicomponent nanofibres requires the use of a solvent which dissolves both of the polymers.
We have optimized the process of electrospinning of PCL/gelatin and PCL/collagen nanofibers based on the use of non-toxic, alternative solvents: acetic acid and formic acid (AA/FA) as previously described [1].
Bicomponent PCL/gelatin and PCL/collagen nanofibers were formed by electrospinning using the mixture of acetic acid and formic acid (9:1 w/w ratio), while hexafluoroisopropanol (HFIP) was used as a reference solvent. Nonwoven materials were subjected to cellular in vitro and biodegradation tests and compared.
All in vitro tests were performed using L929 mouse fibroblast cells. Cytotoxicity test was carried out on extracts and showed that all type of materials are not cytotoxic. Materials with 10% biopolymer content as well as made from PCL only underwent experiment in direct contact. Cells were cultured on materials for 3, 5 and 7 days and afterwards taken for SEM as well as fluorescent dying of nuclei and cytoskeleton. Obtained results proved that the addition of Arg-Gly-Asp (RGD) amino acid sequences from biopolymer, in comparison to pure PCL materials, facilitates cell adhesion and spreading on the surface of nonwovens regardless of solvent used in electrospinning.
PCL/gelatin and PCL/collagen nonwovens underwent biodegradation in PBS solution at 37°C. After different times, ranging from 1 to 90 days samples were subjected for comparative analysis via various methods.
Despite the fact that bicomponent nanofibers electrospun from alternative solvents have similar morphology to those electrospun from perfluorinated alcohols, they differ in the internal structure which seriously affects biodegradation process. Biodegradation of investigated materials is manifested mainly by the gelatin leaching, which leads to nanofibers erosion, particularly large for nanofibers spun from AA/FA.

electrospinning, bicomponent nanofibers, biodegradation, cellular studies

electrospinning, fibres, surface, chitosan

Bicomponent polycaprolactone/gelatin nanofibers were formed by electrospinning as previously described [1] using a novel polymer – solvent system with solvents being alternative to the commonly used toxic solvents like fluorinated alcohols. PCL/Gelatin nanofibres were electrospun from the mixture of acetic acid (AA) with formic acid (FA) (90:10) and from hexafluoroisopropanol (HFIP), that was used as reference solvent. PCL/Gelatin nanofibres with polymers w/w ratios 9:1, 8:2 and 7:3, underwent biodegradation in PBS solution at 37°C. After different times, ranging from 1 to 90 days, they were rinsed in demineralized water and dried. Weight loss and FTIR tests were performed to assess the kinetics of gelatin leaching, while SEM imaging and hydrophobicity tests to show its depletion from the surface. DSC measurements were carried out to examine changes in fibres’ internal structure and uniaxial tensile testing to compare their mechanical properties. Morphology of PCL/Gt fibers obtained from AA/FA is similar to that obtained from HFIP. Despite similar morphology, the internal structure of nanofibers formed from alternative solvents is different, reflecting the emulsive nature of PCL/gelati n mixture in AA/FA solvents contrary to clear, transparent solutions in HFIP. This apparent difference affects strongly the kinetics of leaching of gelatin from bicomponent fibres and thus how their mechanical and bioactive properties are changing in time after placing in living organism. There is substantial difference in kinetics of gelatin leaching depending on solvent used. Mass measurements show much faster gelatin degradation in nanofibres electrospun from AA/FA than from HFIP . For instance, for PCL/Gt 7:3 samples, gelatin content loss is 85% for AA/FA and 68% for HFIP after 90 days. Moreover, irrespective of the solvent used, the degradation rate increases with initial content of gelatin and is the highest in the first 24 hours: 27% for AA/FA 9:1 and 67% for 7:3 and 13% and 32% for HFIP respectively. The observed changes can be explained by nonuniform distribution of gelatin within fibres spun form AA/FA due to emulsive character of solution. Comparison of SEM images reveals linear groove-like sites remaining after gelatin leaching on a surface of fibres spun from AA/FA solvent. Contrary to this, fibres spun from HFIP remain smooth which can be attributed to molecular dispersion of both components.

nanofibers, biodegradation, polycaprolactone, gelatin

Cells sense subtract stiffness, elasticity and transduce that information into morphological changes and lineage specification. Polymer molecular order and mechanical properties, specially stiffness and elasticity indicate influence on cellular response during in- vitro study [e.g. Bershadskye et al 2013]. The aim of proposed presentation is to evaluate the effect of tailored crystallinity and mechanical properties of one- and bicomponent polymer films in terms of cells morphology and proliferation without changing other parameters. Polycaprolactone (PCL) and Gelatin (Ge) were used. As a solvents: Hexafluoroisopropanole (H), Acetic Acid (AA) were chosen. Two methods of foil preparation were analysed: forming from melt (onecomponent), forming from solution (one- and bicomponent).In both methods, the degree of crystallinity was modified mainly by the different type of PCL molecular weight, solvent type and/or annealing. Films were analysed using polarizinginterference microscopy allowing characterization of spherulities morphology. Degree of crystallinity was analysed by differential scanning calorimetry. Foils topography was analysed by atomic force microscopy, selected mechanical properties and hydrophilicity (contact angle) as the significant from the viewpoint of cellular activity were determined as well. L929 cells adhesion and morphology ware analysed by immunohistochemical staining for actin and nuclei. Cell activity and proliferation were analysed also. It is evident that conditions of PCL films preparation affect the morphology of spherulites. All samples were birefringent, indicating in general crystallinity, being different for particular samples. Maltese cross was observed in few samples. Crystallinity of PCL films determined from DSC measurements was in range 0,45-0,70 depending on solvent and polymer molecular weight used. Young Modulus strongly depends on Mw of PCL and Ge additive. L929 cells interact with subtract; morphology and proliferation degree change with crystallinity and elasticity of one- and bicomponet films.

crystallinity, PCL, mechanical properties, casted films

chitosan, PCL, cellular responce, electrospinning

chitozan, polikaprolakton, electrospinning, L929, cytotoksyczność

Few research groups have highlighted the unexpected degree of cell proliferation depending on the degree of crystallinity of the substrate. Commonly used methods of forming three-dimensional scaffolds do not take into account crystallinity optimisation.
The aim of proposed presentation is to investigate polycaprolactone (PCL) substrate supermolecular structure effect, mainly crystallinity, on cells spreading, activity and proliferation.

crystalllinity, PCL, solvent, molecular structure, L929

In this study bicomponent polycaprolactone/gelatin nanofibers were successfully formed by electrospinning using for the first time a novel polymer – solvent system consisting of acetic acid and formic acid. Such solvent system is alternative to the commonly used toxic solvents like fluorinated alcohols, mainly hexafluoroisopropanol. The effect of electrospinning conditions on morphology and structure of nanofibers were investigated.

nanofibers, electrospinning, polycaprolactone, gelatin, alternative solvents, structure

Introduction In the case of semicrystalline polymers, crystallinity is the parameter determining their physical properties. Some research groups indicate influence of crystallinity on cells response during in- vitro study. Commonly used methods of three-dimensional scaffolds formation do not take into account crystallinity optimisation. The aim of proposed presentation is to evaluate the effect of molecular weight and solvent on crystallinity and crystal size in case of polycaprolactone (PCL) films. Methodology Material: PCL with Mn:10, 45 and 80k g/mol (Sigma Aldrich) was used. As a solvents: Hexafluoroisopropanole, HFIP (Iris Biotech GmbH.), Acetic Acid, AA and Dichloromethane, DCM (Avantor and Chempol respectively) were used. Methods: Films were prepared from the PCL with different molecular weight using various solvents differing in evaporation rate. Characterization: Films were analysed using polarizing-interference microscopy (MPI) allowing characterization ofspherulities morphology. Degree of crystallinity was analysed by differential scanning calorimetry (DSC) and comparatively bywide angle X-ray scattering (WAXS). Results and Discussion It is evident from MPI observations that conditions of PCL films preparation affect the morphology of spherulites. All samples were birefringent, indicating in general crystallinity, being different for particular samples. Sphorulities size depends on Mw and solvent type; sharp Maltese cross was observed on few samples. Crystallinity of PCL films determined from DSC measurements was in the range 0,45-0,68 depending on solvent and polymer Mn used. Generally crystallinity of films formed from DCM is lower than from AA as a result of lower boiling point of DCM. Additional annealing enables increase in crystallinity to 0,8. WAXS crystallinity correlates with values determined by DSC. Changes of full width of half maximum(FWHM) of crystal peaks indicate variations of crystal size and/or defects depending on molecular weight and solvent what correlates with MPI observations also. Conclusions spherulites shape and crystallinity are strongly dependent on Mn and solvent type. Structural parameters of films decide on Young modulus and elasticity in terms of applications

crystallinity, PCL, solvents WAXS, molecular structure