Institute of Fundamental Technological Research
Polish Academy of Sciences

Staff

Arkadiusz Gradys, PhD

Laboratory of Polymers and Biomaterials (SPPiB)
position: Assistant Professor
telephone: (+48) 22 826 12 81 ext.: 171
room: 334
e-mail:
ORCID: 0000-0002-9489-6236

Doctoral thesis
2010-11-25 Przemiany polimorficzne substancji małocząsteczkowych i polimerów 
supervisor -- Paweł Sajkiewicz, PhD, DSc, IPPT PAN
 

Recent publications
1.  Zaszczyńska A., Kołbuk-Konieczny D., Gradys A. D., Sajkiewicz P. Ł., Development of Poly(methyl methacrylate)/nano-hydroxyapatite (PMMA/nHA) Nanofibers for Tissue Engineering Regeneration Using an Electrospinning Technique, Polymers, ISSN: 2073-4360, DOI: 10.3390/polym16040531, Vol.16, No.4, pp.531-1-19, 2024

Abstract:
The study explores the in vitro biocompatibility and osteoconductivity of poly(methyl methacrylate)/nano-hydroxyapatite (PMMA/nHA) composite nanofibrous scaffolds for bone tissue engineering (BTE). Electrospun scaffolds, exhibiting both low and high fiber orientation, were investigated. The inclusion of hydroxyapatite nanoparticles enhances the osteoconductivity of the scaffolds while maintaining the ease of fabrication through electrospinning. SEM analysis confirms the high-quality morphology of the scaffolds, with successful incorporation of nHA evidenced by SEM-EDS and FTIR methods. DSC analysis indicates that nHA addition increases the PMMA glass transition temperature (Tg) and reduces stress relaxation during electrospinning. Furthermore, higher fiber orientation affects PMMA Tg and stress relaxation differently. Biological studies demonstrate the composite material’s non-toxicity, excellent osteoblast viability, attachment, spreading, and proliferation. Overall, PMMA/nHA composite scaffolds show promise for BTE applications.

Keywords:
biomaterials, nanofibrous scaffolds, bone tissue engineering

Affiliations:
Zaszczyńska A. - IPPT PAN
Kołbuk-Konieczny D. - IPPT PAN
Gradys A. D. - IPPT PAN
Sajkiewicz P. Ł. - IPPT PAN
2.  Altangerel A., Moazzami Goudarzi Z., Cegielska O., Gradys A.D., Kołbuk-Konieczny D., Kalaska B., Ruszczyńska A., Sajkiewicz P.Ł., A facile one-stone-two-birds strategy for fabricating multifunctional 3D nanofibrous scaffolds, Biomaterials Science, ISSN: 2047-4849, DOI: 10.1039/D3BM00837A, Vol.11, No.16, pp.5502-5516, 2023

Abstract:
Local bacterial infections lead to delayed wound healing and in extreme cases, such as diabetic foot ulcers, to non-healing due to the impaired cellular function in such wounds. Thus, many scientists have focused on developing advanced therapeutic platforms to treat infections and promote cellular proliferation and angiogenesis. This study presents a facile approach for designing nanofibrous scaffolds in three dimensions (3D) with enhanced antibacterial activity to meet the need of treating chronic diabetic wounds. Being a cationic surfactant as well as an antimicrobial agent, octenidine (OCT) makes a 2D membrane hydrophilic, enabling it to be modified into a 3D scaffold in a “one stone, two birds” manner. Aqueous sodium borohydride (NaBH4) solution plays a dual role in the fabrication process, functioning as both a reducing agent for the in situ synthesis of silver nanoparticles (Ag NPs) anchored on the nanofiber surface and a hydrogen gas producer for expanding the 2D membranes into fully formed 3D nanofiber scaffolds, as demonstrated by morphological analyses. Various techniques were used to characterize the developed scaffold (e.g., SEM, XRD, DSC, FTIR, and surface wettability), demonstrating a multilayered porous structure and superhydrophilic properties besides showing sustained and prolonged release of OCT (61% ± 1.97 in 144 h). Thanks to the synergistic effect of OCT and Ag NPs, the antibacterial performance of the 3D scaffold was significantly higher than that of the 2D membrane. Moreover, cell viability was studied in vitro on mouse fibroblasts L929, and the noncytotoxic character of the 3D scaffold was confirmed. Overall, it is shown that the obtained multifunctional 3D scaffold is an excellent candidate for diabetic wound healing and skin repair.

Affiliations:
Altangerel A. - IPPT PAN
Moazzami Goudarzi Z. - IPPT PAN
Cegielska O. - IPPT PAN
Gradys A.D. - IPPT PAN
Kołbuk-Konieczny D. - IPPT PAN
Kalaska B. - other affiliation
Ruszczyńska A. - other affiliation
Sajkiewicz P.Ł. - IPPT PAN
3.  Golasiński K., Maj M., Urbański L., Staszczak M., Gradys A.D., Pieczyska E.A., Experimental study of thermomechanical behaviour of Gum Metal during cyclic tensile loadings: the quantitative contribution of IRT and DIC, Quantitative InfraRed Thermography Journal, ISSN: 1768-6733, DOI: 10.1080/17686733.2023.2205762, pp.1-18, 2023

Abstract:
Thermomechanical behaviour of Gum Metal (Ti–23Nb–0.7Ta–2.0Zr–1.2O, at.%) under cyclic tension was experimentally investigated using infrared thermography and digital image correlation. The thermomechanical characteristics of particular stages of the subsequent loading-unloading cycles of Gum Metal were identified, i.e. (I) the linear, elastic loading accompanied by the temperature drop, (II) the nonlinear super-elastic loading related to the temperature growth, (III) the transient stage (at which both the superelastic-like behaviour and the plastic one are present simultaneously) and the temperature starts growing fast, (IV) the plastic deformation with a significant growth of temperature, (V) the superelastic-like unloading accompanied by a fast drop in temperature, (VI) the transient unloading with a slower decrease in temperature and (VII) the elastic unloading, with a slight increase in temperature. Thermoelastic effect in Gum Metal during both loading and unloading was analysed in each tensile cycle. Finally, the evolution of strain and temperature fields just before unloading in each cycle was discussed and a comparison of the fields at selected stages of cycles 12 and 24 was presented. The results of this work enabled us to identify the non-dissipative processes of elastic and superelastic-like deformations as well as the dissipative process of plastic deformation.

Keywords:
Gum Metal,β-Ti alloy,cyclic tension,superelasticity,thermoelastic effect,infrared thermography,digital image correlation

Affiliations:
Golasiński K. - IPPT PAN
Maj M. - IPPT PAN
Urbański L. - IPPT PAN
Staszczak M. - IPPT PAN
Gradys A.D. - IPPT PAN
Pieczyska E.A. - IPPT PAN
4.  Staszczak M., Gradys A.D., Golasiński K., Pieczyska E.A., Polyurethane Shape Memory Polymer: structure characterization and estimation of energy storage and dissipation during tension process, BULLETIN OF THE POLISH ACADEMY OF SCIENCES: TECHNICAL SCIENCES, ISSN: 0239-7528, DOI: 10.24425/bpasts.2023.147343, Vol.71(6), No.e147343, pp.1-12, 2023

Abstract:
Shape memory polymers (SMP) are new multifunctional materials that are of increasing interest in various functional applications. Among them, polyurethane shape memory polymers (PU-SMP) are particularly attractive due to their combination of shape memory, high strength and biocompatible properties. Developing new applications for PU-SMP requires comprehensive research on their characteristics. This work involved investigating the structure and mechanical behaviour and characterizing the energy storage and dissipation of a thermoplastic PU-SMP with a glass transition temperature (Tg) of 25 °C during tensile loading-unloading. The process of energy storage and dissipation in the PU-SMP was investigated based on the stress-strain curves recorded by a quasi-static testing machine and the temperature changes, accompanying the deformation process, obtained by using a fast and sensitive infrared camera. The results showed that the thermomechanical behaviour of the examined PU-SMP depends significantly on the strain rate. At a higher strain rate, there are higher stress and related temperature changes, which lead to greater energy dissipation. However, the energy storage values estimated during the deformation process turned out to be not significant, indicating that the work supplied to the PU-SMP structure during loading is mainly converted into heat. It should also be noted that the structural investigation revealed no crystalline phase in the investigated PU-SMP

Keywords:
shape memory polymer,infrared camera,thermomechanical couplings,energy storage and dissipation,tension test

Affiliations:
Staszczak M. - IPPT PAN
Gradys A.D. - IPPT PAN
Golasiński K. - other affiliation
Pieczyska E.A. - IPPT PAN
5.  Zakrzewska A., Zargarian S.S., Rinoldi C., Gradys A.D., Jarząbek D.M., Zanoni M., Gualandi C., Lanzi M., Pierini F., Electrospun Poly(vinyl alcohol)-Based Conductive Semi-interpenetrating Polymer Network Fibrous Hydrogel: A Toolbox for Optimal Cross-Linking, ACS Materials Au, ISSN: 2694-2461, DOI: 10.1021/acsmaterialsau.3c00025, Vol.3, No.5, pp.464-482, 2023

Abstract:
Cross-linking of poly(vinyl alcohol) (PVA) creates a three-dimensional network by bonding adjacent polymer chains. The cross-linked structure, upon immersion in water, turns into a hydrogel, which exhibits unique absorption properties due to the presence of hydrophilic groups within the PVA polymer chains and, simultaneously, ceases to be soluble in water. The properties of PVA can be adjusted by chemical modification or blending with other substances, such as polymers, e.g., conductive poly[3-(potassium-5-butanoate)thiophene-2,5-diyl] (P3KBT). In this work, PVA-based conductive semi-interpenetrating polymer networks (semi-IPNs) are successfully fabricated. The systems are obtained as a result of electrospinning of PVA/P3KBT precursor solutions with different polymer concentrations and then cross-linking using “green”, environmentally safe methods. One approach consists of thermal treatment (H), while the second approach combines stabilization with ethanol and heating (E). The comprehensive characterization allows to evaluate the correlation between the cross-linking methods and properties of nanofibrous hydrogels. While both methods are successful, the cross-linking density is higher in the thermally cross-linked samples, resulting in lower conductivity and swelling ratio compared to the E-treated samples. Moreover, the H-cross-linked systems have better mechanical properties─lower stiffness and greater tensile strength. All the tested systems are biocompatible, and interestingly, due to the presence of P3KBT, they show photoresponsivity to solar radiation generated by the simulator. The results indicate that both methods of PVA cross-linking are highly effective and can be applied to a specific system depending on the target, e.g., biomedical or electronic applications.

Keywords:
poly(vinyl alcohol),poly[3-(potassium-5-butanoate)thiophene-2.5-diyl],electrospun nanofibers,cross-linking,fibrous hydrogel,semi-IPN

Affiliations:
Zakrzewska A. - IPPT PAN
Zargarian S.S. - IPPT PAN
Rinoldi C. - IPPT PAN
Gradys A.D. - IPPT PAN
Jarząbek D.M. - IPPT PAN
Zanoni M. - other affiliation
Gualandi C. - University of Bologna (IT)
Lanzi M. - University of Bologna (IT)
Pierini F. - IPPT PAN
6.  Niemczyk-Soczyńska B., Gradys A., Kołbuk D., Krzton-Maziopa A., Rogujski P., Stanaszek L., Lukomska B., Sajkiewicz P., A methylcellulose/agarose hydrogel as an innovative scaffold for tissue engineering, RSC Advances, ISSN: 2046-2069, DOI: 10.1039/D2RA04841H, Vol.12, No.41, pp.26882-26894, 2022

Abstract:
In situ crosslinked materials are the main interests of both scientific and industrial research. Methylcellulose (MC) aqueous solution is one of the representatives that belongs to this family of thermosensitive materials. At room temperature, MC is a liquid whereupon during temperature increase up to 37 °C, it crosslinks physically and turns into a hydrogel. This feature makes it unique, especially for tissue engineering applications. However, the crosslinking rate of MC alone is relatively slow considering tissue engineering expectations. According to these expectations, the crosslinking should take place slowly enough to allow for complete injection and fill the injury avoiding clogging in the needle, and simultanously, it should be sufficiently fast to prevent it from relocation from the lesion. One of the methods to overcome this problem is MC blending with another substance that increases the crosslinking rate of MC. In these studies, we used agarose (AGR). These studies aim to investigate the effect of different AGR amounts on MC crosslinking kinetics, and thermal, viscoelastic, and biological properties. Differential Scanning Calorimetry (DSC) and dynamic mechanical analysis (DMA) measurements proved that AGR addition accelerates the beginning of MC crosslinking. This phenomenon resulted from AGR's greater affinity to water, which is crucial in this particular crosslinking part. In vitro tests, carried out using the L929 fibroblast line and mesenchymal stem cells (MSCs), confirmed that most of the hydrogel samples were non-cytotoxic in contact with extracts and directly with cells. Not only does this type of thermosensitive hydrogel system provide excellent mechanical and biological cues but also its stimuli-responsive character provides more novel functionalities for designing innovative scaffold/cell delivery systems for tissue engineering applications.

Affiliations:
Niemczyk-Soczyńska B. - IPPT PAN
Gradys A. - IPPT PAN
Kołbuk D. - IPPT PAN
Krzton-Maziopa A. - Warsaw University of Technology (PL)
Rogujski P. - other affiliation
Stanaszek L. - other affiliation
Lukomska B. - other affiliation
Sajkiewicz P. - IPPT PAN
7.  Niemczyk-Soczyńska B., Sajkiewicz P., Gradys A., Toward a Better Understanding of the Gelation Mechanism of Methylcellulose via Systematic DSC Studies, Polymers, ISSN: 2073-4360, DOI: 10.3390/polym14091810, Vol.14, No.9, pp.1810-1-13, 2022

Abstract:
A methylcellulose (MC) is one of the materials representatives performing unique thermal-responsive properties. While reaching a critical temperature upon heating MC undergoes a physical sol-gel transition and consequently becomes a gel. The MC has been studied for many years and researchers agree that the MC gelation is related to the lower critical solution temperature (LCST). Nevertheless, a precise description of the MC gelation mechanism remains under discussion. In this study, we explained the MC gelation mechanism through examination of a wide range of MC concentrations via differential scanning calorimetry (DSC). The results evidenced that MC gelation is a multistep thermoreversible process, manifested by three and two endotherms depending on MC concentration. The occurrence of the three endotherms for low MC concentrations during heating has not been reported in the literature before. We justify this phenomenon by manifestation of three various transitions. The first one manifests water–water interactions, i.e., spanning water network breakdown into small water clusters. It is clearly evidenced by additional normalization to the water content. The second effect corresponds to polymer–water interactions, i.e., breakdown of water cages surrounded methoxy groups of MC. The last one is related to the polymer–polymer interactions, i.e., fibril hydrophobic domain formation. Not only did these results clarify the MC crosslinking mechanism, but also in the future will help to assess MC relevance for various potential application fields.

Keywords:
methylcellulose, thermosensitive hydrogel, crosslinking, DSC

Affiliations:
Niemczyk-Soczyńska B. - IPPT PAN
Sajkiewicz P. - IPPT PAN
Gradys A. - IPPT PAN
8.  Zaszczyńska A., Moczulska-Heljak M., Gradys A., Sajkiewicz P., Advances in 3D printing for tissue engineering, Materials, ISSN: 1996-1944, DOI: 10.3390/ma14123149, Vol.14, No.12, pp.3149-1-28, 2021

Abstract:
Tissue engineering (TE) scaffolds have enormous significance for the possibility of regeneration of complex tissue structures or even whole organs. Three-dimensional (3D) printing techniques allow fabricating TE scaffolds, having an extremely complex structure, in a repeatable and precise manner. Moreover, they enable the easy application of computer-assisted methods to TE scaffold design. The latest additive manufacturing techniques open up opportunities not otherwise available. This study aimed to summarize the state-of-art field of 3D printing techniques in applications for tissue engineering with a focus on the latest advancements. The following topics are discussed: systematics of the available 3D printing techniques applied for TE scaffold fabrication; overview of 3D printable biomaterials and advancements in 3D-printing-assisted tissue engineering.

Keywords:
tissue engineering, 3D printing, biomaterials

Affiliations:
Zaszczyńska A. - IPPT PAN
Moczulska-Heljak M. - IPPT PAN
Gradys A. - IPPT PAN
Sajkiewicz P. - IPPT PAN
9.  Szewczyk P.K., Gradys A., Kyun Kim S., Persano L., Marzec M., Kryshtal A., Busolo T., Toncelli A., Pisignano D., Bernasik A., Kar-Narayan S., Sajkiewicz P., Stachewicz U., Enhanced piezoelectricity of electrospun polyvinylidene fluoride fibers for energy harvesting, ACS Applied Materials and Interfaces, ISSN: 1944-8244, DOI: 10.1021/acsami.0c02578, Vol.12, No.11, pp.13575-13583, 2020

Abstract:
Piezoelectric polymers are promising energy materials for wearable and implantable applications for replacing bulky batteries in small and flexible electronics. Therefore, many research studies are focused on understanding the behavior of polymers at a molecular level and designing new polymer-based generators using polyvinylidene fluoride (PVDF). In this work, we investigated the influence of voltage polarity and ambient relative humidity in electrospinning of PVDF for energy-harvesting applications. A multitechnique approach combining microscopy and spectroscopy was used to study the content of the β-phase and piezoelectric properties of PVDF fibers. We shed new light on β-phase crystallization in electrospun PVDF and showed the enhanced piezoelectric response of the PVDF fiber-based generator produced with the negative voltage polarity at a relative humidity of 60%. Above all, we proved that not only crystallinity but also surface chemistry is crucial for improving piezoelectric performance in PVDF fibers. Controlling relative humidity and voltage polarity increased the d33 piezoelectric coefficient for PVDF fibers by more than three times and allowed us to generate a power density of 0.6 μW·cm^–2 from PVDF membranes. This study showed that the electrospinning technique can be used as a single-step process for obtaining a vast spectrum of PVDF fibers exhibiting different physicochemical properties with β-phase crystallinity reaching up to 74%. The humidity and voltage polarity are critical factors in respect of chemistry of the material on piezoelectricity of PVDF fibers, which establishes a novel route to engineer materials for energy-harvesting and sensing applications.

Keywords:
PVDF, polymer crystallinity, electrospinning, piezoelectricity, voltage polarity

Affiliations:
Szewczyk P.K. - other affiliation
Gradys A. - IPPT PAN
Kyun Kim S. - other affiliation
Persano L. - other affiliation
Marzec M. - other affiliation
Kryshtal A. - other affiliation
Busolo T. - other affiliation
Toncelli A. - other affiliation
Pisignano D. - other affiliation
Bernasik A. - other affiliation
Kar-Narayan S. - other affiliation
Sajkiewicz P. - IPPT PAN
Stachewicz U. - AGH University of Science and Technology (PL)
10.  Ura D.P., Rosell-Llompart J., Zaszczyńska A., Vasilyev G., Gradys A., Szewczyk P.K., Knapczyk-Korczak J., Avrahami R., Šišková A.O., Arinstein A., Sajkiewicz P., Zussman E., Stachewicz U., The role of electrical polarity in electrospinning and on the mechanical and structural properties of as-spun fibers, Materials, ISSN: 1996-1944, DOI: 10.3390/ma13184169, Vol.13, No.18, pp.4169-1-18, 2020

Abstract:
Electric field strength and polarity in electrospinning processes and their effect on process dynamics and the physical properties of as-spun fibers is studied. Using a solution of the neutral polymer such as poly(methyl methacrylate) (PMMA) we explored the electrospun jet motion issued from a Taylor cone. We focused on the straight jet section up to the incipient stage of the bending instability and on the radius of the disk of the fibers deposited on the collecting electrode. A new correlation formula using dimensionless parameters was found, characterizing the effect of the electric field on the length of the straight jet, L˜E~E˜0.55. This correlation was found to be valid when the spinneret was either negatively or positively charged and the electrode grounded. The fiber deposition radius was found to be independent of the electric field strength and polarity. When the spinneret was negatively charged, L˜E was longer, the as-spun fibers were wider. The positively charged setup resulted in fibers with enhanced mechanical properties and higher crystallinity. This work demonstrates that often-overlooked electrical polarity and field strength parameters influence the dynamics of fiber electrospinning, which is crucial for designing polymer fiber properties and optimizing their collection.

Keywords:
fibers, electrical polarity, charges, electrospinning, PMMA, mechanical properties

Affiliations:
Ura D.P. - AGH University of Science and Technology (PL)
Rosell-Llompart J. - other affiliation
Zaszczyńska A. - IPPT PAN
Vasilyev G. - Technion-Israel Institute of Technology (IL)
Gradys A. - IPPT PAN
Szewczyk P.K. - other affiliation
Knapczyk-Korczak J. - other affiliation
Avrahami R. - other affiliation
Šišková A.O. - other affiliation
Arinstein A. - Technion-Israel Institute of Technology (IL)
Sajkiewicz P. - IPPT PAN
Zussman E. - Technion-Israel Institute of Technology (IL)
Stachewicz U. - AGH University of Science and Technology (PL)
11.  Zaszczyńska A., Gradys A., Sajkiewicz P., Progress in the applications of smart piezoelectric materials for medical devices, Polymers, ISSN: 2073-4360, DOI: 10.3390/polym12112754, Vol.12, No.11, pp.2754-1-19, 2020

Abstract:
Smart piezoelectric materials are of great interest due to their unique properties. Piezoelectric materials can transform mechanical energy into electricity and vice versa. There are mono and polycrystals (piezoceramics), polymers, and composites in the group of piezoelectric materials. Recent years show progress in the applications of piezoelectric materials in biomedical devices due to their biocompatibility and biodegradability. Medical devices such as actuators and sensors, energy harvesting devices, and active scaffolds for neural tissue engineering are continually explored. Sensors and actuators from piezoelectric materials can convert flow rate, pressure, etc., to generate energy or consume it. This paper consists of using smart materials to design medical devices and provide a greater understanding of the piezoelectric effect in the medical industry presently. A greater understanding of piezoelectricity is necessary regarding the future development and industry challenges.

Keywords:
polymers, smart materials, piezoelectric materials, inorganic materials, organic materials, biomedical devices

Affiliations:
Zaszczyńska A. - IPPT PAN
Gradys A. - IPPT PAN
Sajkiewicz P. - IPPT PAN
12.  Niemczyk-Soczyńska B., Gradys A., Sajkiewicz P., Hydrophilic surface functionalization of electrospun nanofibrous scaffolds in tissue engineering, Polymers, ISSN: 2073-4360, DOI: 10.3390/polym12112636, Vol.12, No.11, pp.2636-1-20, 2020

Abstract:
Electrospun polymer nanofibers have received much attention in tissue engineering due to their valuable properties such as biocompatibility, biodegradation ability, appropriate mechanical properties, and, most importantly, fibrous structure, which resembles the morphology of extracellular matrix (ECM) proteins. However, they are usually hydrophobic and suffer from a lack of bioactive molecules, which provide good cell adhesion to the scaffold surface. Post-electrospinning surface functionalization allows overcoming these limitations through polar groups covalent incorporation to the fibers surface, with subsequent functionalization with biologically active molecules or direct deposition of the biomolecule solution. Hydrophilic surface functionalization methods are classified into chemical approaches, including wet chemical functionalization and covalent grafting, a physiochemical approach with the use of a plasma treatment, and a physical approach that might be divided into physical adsorption and layer-by-layer assembly. This review discusses the state-of-the-art of hydrophilic surface functionalization strategies of electrospun nanofibers for tissue engineering applications. We highlighted the major advantages and drawbacks of each method, at the same time, pointing out future perspectives and solutions in the hydrophilic functionalization strategies.

Keywords:
surface functionalization, electrospinning, polymers, nanofiber, immobilization, tissue engineering

Affiliations:
Niemczyk-Soczyńska B. - IPPT PAN
Gradys A. - IPPT PAN
Sajkiewicz P. - IPPT PAN
13.  Zaszczyńska A., Sajkiewicz P.Ł., Gradys A., Tymkiewicz R., Urbanek O., Kołbuk D., Influence of process-material conditions on the structure and biological properties of electrospun polyvinylidene fluoride fibers, BULLETIN OF THE POLISH ACADEMY OF SCIENCES: TECHNICAL SCIENCES, ISSN: 0239-7528, DOI: 10.24425/bpasts.2020.133368, Vol.68, No.3, pp.627-633, 2020

Abstract:
Polyvinylidene fluoride (PVDF) is one of the most important piezoelectric polymers. Piezoelectricity in PVDF appears in polar β and ɣ phases. Piezoelectric fibers obtained by means of electrospinning may be used in tissue engineering (TE) as a smart analogue of the natural extracellular matrix (ECM). We present results showing the effect of rotational speed of the collecting drum on morphology, phase content and in vitro biological properties of PVDF nonwovens. Morphology and phase composition were analyzed using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR), respectively. It was shown that increasing rotational speed of the collector leads to an increase in fiber orientation, reduction in fiber diameter and considerable increase of polar phase content, both b and g. In vitro cell culture experiments, carried out with the use of ultrasounds in order to generate electrical potential via piezoelectricity, indicate a positive effect of polar phases on fibroblasts. Our preliminary results demonstrate that piezoelectric PVDF scaffolds are promising materials for tissue engineering applications, particularly for neural tissue regeneration, where the electric potential is crucial.

Keywords:
scaffolds, electrospinning, polyvinylidene fluoride, tissue engineering

Affiliations:
Zaszczyńska A. - IPPT PAN
Sajkiewicz P.Ł. - IPPT PAN
Gradys A. - IPPT PAN
Tymkiewicz R. - IPPT PAN
Urbanek O. - IPPT PAN
Kołbuk D. - IPPT PAN
14.  Zaszczyńska A., Sajkiewicz P., Gradys A., Piezoelectric scaffolds as smart materials for neural tissue engineering, Polymers, ISSN: 2073-4360, DOI: 10.3390/polym12010161, Vol.12, No.1, pp.161-1-25, 2020

Abstract:
Injury to the central or peripheral nervous systems leads to the loss of cognitive and/or sensorimotor capabilities, which still lacks an effective treatment. Tissue engineering in the post-injury brain represents a promising option for cellular replacement and rescue, providing a cell scaffold for either transplanted or resident cells. Tissue engineering relies on scaffolds for supporting cell differentiation and growth with recent emphasis on stimuli responsive scaffolds, sometimes called smart scaffolds. One of the representatives of this material group is piezoelectric scaffolds, being able to generate electrical charges under mechanical stimulation, which creates a real prospect for using such scaffolds in non-invasive therapy of neural tissue. This paper summarizes the recent knowledge on piezoelectric materials used for tissue engineering, especially neural tissue engineering. The most used materials for tissue engineering strategies are reported together with the main achievements, challenges, and future needs for research and actual therapies. This review provides thus a compilation of the most relevant results and strategies and serves as a starting point for novel research pathways in the most relevant and challenging open questions.

Keywords:
neural tissue engineering, piezoelectric scaffolds, smart materials, polymers

Affiliations:
Zaszczyńska A. - IPPT PAN
Sajkiewicz P. - IPPT PAN
Gradys A. - IPPT PAN
15.  Niemczyk-Soczyńska B., Gradys A., Kołbuk D., Krzton-Maziopa A., Sajkiewicz P., Crosslinking kinetics of methylcellulose qqueous solution and its potential as a scaffold for tissue engineering, Polymers, ISSN: 2073-4360, DOI: 10.3390/polym11111772, Vol.11, No.11, pp.1772-1-17, 2019

Abstract:
Thermosensitive, physically crosslinked injectable hydrogels are in the area of interests of various scientific fields. One of the representatives of this materials group is an aqueous solution of methylcellulose. At ambient conditions, methylcellulose (MC) is a sol while on heating up to 37 °C, MC undergoes physical crosslinking and transforms into a gel. Injectability at room temperature, and crosslinkability during subsequent heating to physiological temperature raises hopes, especially for tissue engineering applications. This research work aimed at studying crosslinking kinetics, thermal, viscoelastic, and biological properties of MC aqueous solution in a broad range of MC concentrations. It was evidenced by Differential Scanning Calorimetry (DSC) that crosslinking of MC is a reversible two-stage process, manifested by the appearance of two endothermic effects, related to the destruction of water cages around methoxy groups, followed by crosslinking via the formation of hydrophobic interactions between methoxy groups in the polymeric chains. The DSC results also allowed the determination of MC crosslinking kinetics. Complementary measurements of MC crosslinking kinetics performed by dynamic mechanical analysis (DMA) provided information on the final storage modulus, which was important from the perspective of tissue engineering applications. Cytotoxicity tests were performed using mouse fibroblasts and showed that MC at low concentration did not cause cytotoxicity. All these efforts allowed to assess MC hydrogel relevance for tissue engineering applications.

Keywords:
methylcellulose, thermosensitive hydrogel, crosslinking kinetics, DSC, DMA, cellular tests

Affiliations:
Niemczyk-Soczyńska B. - IPPT PAN
Gradys A. - IPPT PAN
Kołbuk D. - IPPT PAN
Krzton-Maziopa A. - Warsaw University of Technology (PL)
Sajkiewicz P. - IPPT PAN
16.  Zaszczyńska A., Sajkiewicz P., Gradys A., Kołbuk D., Urbanek O., Cellular studies on piezoelectric polyvinylidene fluoride nanofibers subjected to ultrasounds stimulations, ENGINEERING OF BIOMATERIALS / INŻYNIERIA BIOMATERIAŁÓW, ISSN: 1429-7248, Vol.22, No.153, pp.25-25, 2019
17.  Sajkiewicz P., Heljak M.K., Gradys A., Choińska E., Rumiński S., Jaroszewicz T., Bissenik I., Święszkowski W., Degradation and related changes in supermolecular structure of poly(caprolactone) in vivo conditions, Polymer Degradation and Stability, ISSN: 0141-3910, DOI: 10.1016/j.polymdegradstab.2018.09.023, Vol.157, pp.70-79, 2018

Abstract:
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.

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

Affiliations:
Sajkiewicz P. - IPPT PAN
Heljak M.K. - Warsaw University of Technology (PL)
Gradys A. - IPPT PAN
Choińska E. - Warsaw University of Technology (PL)
Rumiński S. - Medical University of Warsaw (PL)
Jaroszewicz T. - Warsaw University of Technology (PL)
Bissenik I. - Warsaw University of Life Sciences (PL)
Święszkowski W. - other affiliation
18.  Gradys A., Geometrical effects during crystallization under confinement in electrospun core-shell fibers. DSC study of crystallization kinetics, POLYMER, ISSN: 0032-3861, DOI: 10.1016/j.polymer.2016.12.009, Vol.108, pp.383-394, 2017

Abstract:
Calorimetric studies on poly(ethylene glycol) Mn = 400 g/mol, encapsulated in polystyrene fibers show non-trivial crystallization behavior. Analysis, assuming constant Avrami exponent n, is unsuitable. Approach allowing for changes in the exponent n, requires assumption of the crystallization rate function, derived from the nucleation theory. Changes in Avrami exponent n, follow the changes in geometry of crystal growth and in nucleation mechanisms. Crystallization in micrometer fibers starts from heterogeneous nucleation with three-dimensional crystal growth e as in bulk e but changes to two and one-dimensional, terminated by homogeneous nucleation. For bulk and in 1 and 0.6 micron thick fibers, the approach evidences similar thermodynamic parameters. In 0.6 micron thick fibers, crystallization rate is lower due to higher energy barrier for diffusion, ED = 10 kJ/mol versus 8.7 kJ/mol for bulk and 1 micron thick fibers. Additionally, fiber thickness depends not only on parameters of the electrospinning process but also on the thermal history.

Keywords:
core-shell fibers, confinement effects, crystallization kinetics, DSC, polyethylene glycol

Affiliations:
Gradys A. - IPPT PAN
19.  Gradys A., Sajkiewicz P., Zhuravlev E., Schick C., Kinetics of isothermal and non-isothermal crystallization of poly(vinylidene fluoride) by fast scanning calorimetry, POLYMER, ISSN: 0032-3861, DOI: 10.1016/j.polymer.2015.11.020, Vol.82, pp.40-48, 2016

Abstract:
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.

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

Affiliations:
Gradys A. - IPPT PAN
Sajkiewicz P. - IPPT PAN
Zhuravlev E. - University of Rostock (DE)
Schick C. - University of Rostock (DE)
20.  Świątek Z., Gradys A., Maj Ł., Morgiel J., Marszałek K.W., Mania R., Szlezynger M., XRD and TEM in situ Heating of Large Period Ni/Al Multilayer Coatings, ACTA PHYSICA POLONICA A, ISSN: 0587-4246, DOI: 10.12693/APhysPolA.130.880, Vol.130, No.4, pp.880-883, 2016

Abstract:
The Ni/Al multilayer coating of λ ≈100 nm was deposited onto (001)-oriented monocrystalline silicon substrate using double target magnetron sputtering system equipped with rotating sample holder. The thicknesses of alternating layers were adjusted in the way to preserve the chemical composition ratio close to 50%Al:50%Ni (at.%). The in situ X-ray diffraction and in situ transmission electron microscopy heating experiments were carried out at relatively low heating rates (20°C/min) in order to study the phase transformation sequence. The investigations revealed that the reaction between Ni and Al multilayers starts at ≈200°C with precipitation of Al₃Ni phase, while above 300°C dominates precipitation of Ni₃Al and NiAl intermetallic phases. Both the X-ray and electron diffractions acquired at 450°C confirmed presence of the Ni₃Al and NiAl intermetallics, but the former pointed at still lasting traces of Ni(Al) solid solution.

Keywords:
transmission electron microscopy, multilayers

Affiliations:
Świątek Z. - Institute of Metallurgy and Materials Science, Polish Academy of Sciences (PL)
Gradys A. - IPPT PAN
Maj Ł. - Institute of Metallurgy and Materials Science, Polish Academy of Sciences (PL)
Morgiel J. - Institute of Metallurgy and Materials Science, Polish Academy of Sciences (PL)
Marszałek K.W. - AGH University of Science and Technology (PL)
Mania R. - AGH University of Science and Technology (PL)
Szlezynger M. - Institute of Metallurgy and Materials Science, Polish Academy of Sciences (PL)
21.  Boas M., Gradys A., Vasilyev G., Burman M., Zussman E., Electrospinning polyelectrolyte complexes: pHresponsive fibers, SOFT MATTER, ISSN: 1744-683X, DOI: 10.1039/c4sm02618g, Vol.11, pp.1739-1747, 2015

Abstract:
Fibers were electrospun from a solution comprised of oppositely charged polyelectrolytes, in efforts to achieve highly confined macromolecular packaging. A stoichiometric ratio of poly(allylamine hydrochloride) and poly(acrylic acid) solution was mixed in an ethanol–water co-solvent. Differential scanning calorimetry (DSC) analysis of electrospun fibers demonstrated no indication of glass transition, Tg. Infrared spectroscopy (FTIR) analysis of the fibers as a function of temperature, demonstrated an amidation process at lower temperature compared to cast film. Polarized FTIR indicated a preference of the functional groups to be perpendicular to the fiber axis. These results imply formation of mixed phase fibers with enhanced conditions for intermolecular interactions, due to the highly aligned and confined assembly of the macromolecules. The tunable intermolecular interactions between the functional groups of the polyelectrolytes, impact pH-driven, reversible swelling–deswelling of the fibers. The degree of ionization of PAA at pH 5.5 and pH 1.8 varied from 85% to 18%, correspondingly, causing transformation of ionic interactions to hydrogen bonding between the functional groups. The chemical change led to a massive water diffusion of 500% by weight and to a marked increase of 400% in fiber diameter, at a rate of 0.50 μm s−1. These results allow for manipulation and tailoring of key fiber properties for tissue engineering, membranes, and artificial muscle applications.

Keywords:
polyelectrolytes, electrospinning, pH responsive fibers

Affiliations:
Boas M. - Technion-Israel Institute of Technology (IL)
Gradys A. - IPPT PAN
Vasilyev G. - Technion-Israel Institute of Technology (IL)
Burman M. - Technion-Israel Institute of Technology (IL)
Zussman E. - Technion-Israel Institute of Technology (IL)
22.  Pieczyska E.A., Maj M., Kowalczyk-Gajewska K., Staszczak M., Gradys A., Majewski M., Cristea M., Tobushi H., Hayashi S., Thermomechanical properties of polyurethane shape memory polymer–experiment and modelling, SMART MATERIALS AND STRUCTURES, ISSN: 0964-1726, DOI: 10.1088/0964-1726/24/4/045043, Vol.24, pp.045043-1-16, 2015

Abstract:
In this paper extensive research on the polyurethane shape memory polymer (PU-SMP) is reported, including its structure analysis, our experimental investigation of its thermomechanical properties and its modelling. The influence of the effects of thermomechanical couplings on the SMP behaviour during tension at room temperature is studied using a fast and sensitive infrared camera. It is shown that the thermomechanical behaviour of the SMP significantly depends on the strain rate: at a higher strain rate higher stress and temperature values are obtained. This indicates that an increase of the strain rate leads to activation of different deformation mechanisms at the micro-scale, along with reorientation and alignment of the molecular chains. Furthermore, influence of temperature on the SMP's mechanical behaviour is studied. It is observed during the loading in a thermal chamber that at the temperature 20°C below the glass transition temperature (Tg) the PU-SMP strengthens about six times compared to the material above Tg but does not exhibit the shape recovery. A finite-strain constitutive model is formulated, where the SMP is described as a two-phase material composed of a hyperelastic rubbery phase and elastic-viscoplastic glassy phase. The volume content of phases is governed by the current temperature. Finally, model predictions are compared with the experimental results.

Keywords:
shape memory polyurethane, thermomechanical couplings, infrared camera, temperature change, dynamic mechanical analysis, strain rate, constitutive model

Affiliations:
Pieczyska E.A. - IPPT PAN
Maj M. - IPPT PAN
Kowalczyk-Gajewska K. - IPPT PAN
Staszczak M. - IPPT PAN
Gradys A. - IPPT PAN
Majewski M. - IPPT PAN
Cristea M. - Petru Poni Institute of Macromolecular Chemistry (RO)
Tobushi H. - Aichi Institute of Technology (JP)
Hayashi S. - SMP Technologies Inc. (JP)
23.  Gradys A., Sajkiewicz P., Determination of the melting enthalpy of beta phase of poly(vinylidene fluoride), E-POLYMERS, ISSN: 1618-7229, DOI: 10.1515/epoly-2013-0119, Vol.13, No.1, pp.203-216, 2014

Abstract:
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).

Keywords:
pvdf, WAXS, FTIR, DSC, crystallinity, polymorphism

Affiliations:
Gradys A. - IPPT PAN
Sajkiewicz P. - IPPT PAN
24.  Alhazov D., Gradys A., Sajkiewicz P., Arinstein A., Zussman E., Thermo-mechanical behavior of electrospun thermoplastic polyurethane nanofibers, EUROPEAN POLYMER JOURNAL, ISSN: 0014-3057, DOI: 10.1016/j.eurpolymj.2013.09.028, Vol.49, pp.3851-3856, 2013

Abstract:
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.

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

Affiliations:
Alhazov D. - Technion-Israel Institute of Technology (IL)
Gradys A. - IPPT PAN
Sajkiewicz P. - IPPT PAN
Arinstein A. - Technion-Israel Institute of Technology (IL)
Zussman E. - Technion-Israel Institute of Technology (IL)
25.  Krasowska K., Janik H., Gradys A., Rutkowska M., Degradation of polyurethanes in compost under natural conditions, JOURNAL OF APPLIED POLYMER SCIENCE, ISSN: 0021-8995, DOI: 10.1002/app.36597, Vol.125, No.6, pp.4252-4260, 2012

Abstract:
The estimation of compostability of different polyurethanes under natural weather depending conditions in compost with active sludge at waste treatment plant was the subject of this study. The incubation of polymer samples took place for a period up to 24 months. The characteristic parameters of compost: temperature, pH, moisture content and activity of dehydrogenases were monitored and their influence on degradation of polyurethanes was discussed. The proper compoststability of polyurethanes was investigated by changes of weight, tensile strength and morphology of polyurethane samples after incubation in environment. The degradation study revealed that the degree of degradation of polyurethanes in the natural environment, like compost, is dependent on their chemical and structural composition.

Keywords:
polyurethanes, degradation, compost

Affiliations:
Krasowska K. - other affiliation
Janik H. - other affiliation
Gradys A. - IPPT PAN
Rutkowska M. - other affiliation
26.  Sajkiewicz P., Gradys A., Misztal-Faraj B., Quantitative analysis of crystallization kinetics by light depolarization technique. Possibilities and limitations, EUROPEAN POLYMER JOURNAL, ISSN: 0014-3057, DOI: 10.1016/j.eurpolymj.2010.07.011, Vol.46, pp.2051-2062, 2010

Abstract:
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.

Keywords:
Polymer, Crystallization kinetics, Light depolarization, Crystal birefringence

Affiliations:
Sajkiewicz P. - IPPT PAN
Gradys A. - IPPT PAN
Misztal-Faraj B. - IPPT PAN
27.  Sajkiewicz P., Gradys A., Ziabicki A., Misztal-Faraj B., On the metastability of beta phase in isotactic polypropylene: Experiments and numerical simulation, E-POLYMERS, ISSN: 1618-7229, No.124, pp.1-20, 2010

Abstract:
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.

Keywords:
polypropylene, polymorphism, metastability, crystallization

Affiliations:
Sajkiewicz P. - IPPT PAN
Gradys A. - IPPT PAN
Ziabicki A. - IPPT PAN
Misztal-Faraj B. - IPPT PAN
28.  Misztal-Faraj B., Sajkiewicz P., Savytskyy H., Bonchyk O., Gradys A., Ziabicki A., Following phase transitions by depolarizing light intensity. The experimental setup, POLYMER TESTING, ISSN: 0142-9418, DOI: 10.1016/j.polymertesting.2008.09.012, Vol.28, pp.36-41, 2009

Abstract:
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.

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

Affiliations:
Misztal-Faraj B. - IPPT PAN
Sajkiewicz P. - IPPT PAN
Savytskyy H. - Ya.S. Pidstryhach Institute for Applied Problems of Mechanics and Mathematics NASU (UA)
Bonchyk O. - Ya.S. Pidstryhach Institute for Applied Problems of Mechanics and Mathematics NASU (UA)
Gradys A. - IPPT PAN
Ziabicki A. - IPPT PAN
29.  Sajkiewicz P., Di Lorenzo M.L., Gradys A., Transient nucleation in isothermal crystallization of poly(3-hydroksybuty-rate), E-POLYMERS, ISSN: 1618-7229, Vol.85, pp.1-16, 2009

Abstract:
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.

Keywords:
PHB, isothermal crystallization, nucleation rate

Affiliations:
Sajkiewicz P. - IPPT PAN
Di Lorenzo M.L. - other affiliation
Gradys A. - IPPT PAN
30.  Di Lorenzo M.R., Sajkiewicz P., Gradys A., La Pietra P., Optimization of melting conditions for the analysis of crystallization kinetics of poly(3-hydroksybutyrate), E-POLYMERS, ISSN: 1618-7229, Vol.27, pp.1-12, 2009

Abstract:
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.

Keywords:
PHB, thermal history, crystallization, degradation

Affiliations:
Di Lorenzo M.R. - other affiliation
Sajkiewicz P. - IPPT PAN
Gradys A. - IPPT PAN
La Pietra P. - other affiliation
31.  Gradys A., Sajkiewicz P., Adamovsky S., Minakov A.A., Schick C., Crystallization of poly(vinylidene fluoride) during ultra-fast cooling, THERMOCHIMICA ACTA, ISSN: 0040-6031, DOI: 10.1016/j.tca.2007.05.023, Vol.461, pp.153-157, 2007

Abstract:
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.

Keywords:
Polyvinylidene fluoride, Crystallization, Ultra-fast calorimetry, Polymorphism

Affiliations:
Gradys A. - IPPT PAN
Sajkiewicz P. - IPPT PAN
Adamovsky S. - Universität Rostock (DE)
Minakov A.A. - other affiliation
Schick C. - University of Rostock (DE)
32.  Di Lorenzo M.L., Sajkiewicz P., La Pietra P., Gradys A., Irregularly shaped DSC exotherms in the analysis of polimer crystallization, POLYMER BULLETIN, ISSN: 0170-0839, DOI: 10.1007/s00289-006-0621-4, Vol.57, pp.713-721, 2006

Abstract:
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.

Keywords:
PHB, crystallization, nucleation, DSC

Affiliations:
Di Lorenzo M.L. - other affiliation
Sajkiewicz P. - IPPT PAN
La Pietra P. - other affiliation
Gradys A. - IPPT PAN
33.  Sajkiewicz P., Hashimoto T., Saijo K., Gradys A., Intermediate phase in poly(ethylene) as elucidated by the WAXS. Analysis of crystallization kinetics, POLYMER, ISSN: 0032-3861, DOI: 10.1016/j.polymer.2004.11.018, Vol.46, pp.513-521, 2005

Abstract:
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.

Keywords:
Polyethylene, Crystallization, Intermediate phase

Affiliations:
Sajkiewicz P. - IPPT PAN
Hashimoto T. - other affiliation
Saijo K. - other affiliation
Gradys A. - IPPT PAN
34.  Gradys A., Sajkiewicz P., Minakov A.A., Adamovsky S., Schick C., Hashimoto T., Saijo K., Crystallization of polypropylene at various cooling rates, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ISSN: 0921-5093, DOI: 10.1016/j.msea.2005.08.167, Vol.413-414, pp.442-446, 2005

Abstract:
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.

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

Affiliations:
Gradys A. - IPPT PAN
Sajkiewicz P. - IPPT PAN
Minakov A.A. - other affiliation
Adamovsky S. - Universität Rostock (DE)
Schick C. - University of Rostock (DE)
Hashimoto T. - other affiliation
Saijo K. - other affiliation

Conference abstracts
1.  Zaszczyńska A., Gradys A., Tymkiewicz R., Lewandowska-Szumieł M., Sajkiewicz P.Ł., ENHANCED ELECTROACTIVE PHASES OF POLYVINYLIDENE FLUORIDE NANOFIBERS FOR BONE TISSUE ENGINEERING APPLICATIONS, ICSAAM 2023, The 10th International Conference on Structural Analysis of Advanced Materials, 2023-09-10/09-14, Zakyntos (GR), pp.1-3, 2023
2.  Staszczak M., Urbański L., Gradys A., Pieczyska E., Structural characterization and investigation of shape memory performance of thermoset polyurethane shape memory polymer, ECNP 2023 , 11th ECNP International Conference on Nanostructured Polymers and Nanocomposites, 2023-08-28/08-31, Łódź (PL), No.P32, pp.93-93, 2023
3.  Nabavian Kalat M., Staszczak M., Ziai Y., Gradys A., Urbański L., Pieczyska E.A., THE EFFECT OF SHAPE MEMORY BEHAVIOR ON THE MICROSTRUCTURE OF THE PU-SMP (Tg = 45°C), ICEM, 19th International Conference on Experimental Mechanics, 2022-07-17/07-21, Kraków (PL), pp.278-279, 2022
4.  Zaszczyńska A., Sajkiewicz P., Gradys A., Smart piezoelectric scaffold for nerve regeneration, AMC, European Advanced Materials Congress, 2021-08-23/08-25, Stockholm (SE), pp.162-163, 2021

Keywords:
Piezo-nerve, scaffold, nanofibers, tissue engineering, stem cells

Affiliations:
Zaszczyńska A. - IPPT PAN
Sajkiewicz P. - IPPT PAN
Gradys A. - IPPT PAN
5.  Zaszczyńska A., Cieciuch A., Gradys A., Lewandowska-Szumieł M., Sajkiewicz P., Cellular studies on stromal cells and piezoelectric nanofibers subjected to ultrasounds stimulations for medical devices, UK-Poland Bioinspired Materials Conference, 2020-11-23/11-24, Lancaster (GB), pp.127-127, 2020
6.  Zaszczyńska A., Sajkiewicz P., Gradys A., Kołbuk D., Urbanek O., Cellular studies of piezoelectric nanofibers with ultrasound stimulations, Aerogels Processing, Modelling and Environmental-Driven Applications, 2019-10-21/10-23, Coimbra (PT), No.P04, pp.36, 2019
7.  Ura D.P., Gradys A., Zaszczyńska A., Sajkiewicz P., Stachewicz U., Controlling of mechanical properties of electrospun PMMA fibers via voltage polarity, 7th Dresden Nanoanalysis Symposium: Nano-scale characterization for cutting-edge materials research and sustainable materials development, 2019-08-30/08-30, Dresden (DE), pp.1-2, 2019
8.  Ura D.P., Gradys A., Zaszczyńska A., Sajkiewicz P., Stachewicz U., Controlling of mechanical properties of electrospun PMMA fibers via voltage polarity, 8th International PhD Meeting, 2019-08-28/08-29, Dresden (DE), pp.1, 2019
9.  Zaszczyńska A., Sajkiewicz P., Gradys A., Urbanek O., Kołbuk D., Influence of process-material conditions on the phase composition, architecture and biological properties of electrospun polyvinylidene fluoride fibers, CNM 2019, 6th CONFERENCE ON NANO- AND MICROMECHANICS, 2019-07-03/07-05, Rzeszów (PL), pp.145-147, 2019

Keywords:
scaffolds, electrospinning, polyvinylidene fluoride, tissue engineering

Affiliations:
Zaszczyńska A. - IPPT PAN
Sajkiewicz P. - IPPT PAN
Gradys A. - IPPT PAN
Urbanek O. - IPPT PAN
Kołbuk D. - IPPT PAN
10.  Ura P.D., Zaszczyńska A., Gradys A., Sajkiewicz P., Stachewicz U., Mechanical properties of electrospun non-woven PMMA mats produced with positive and negative voltage polarities, AMT 2019, XXII Physical Metallurgy and Materials Science Conference: Advanced Materials and Technologies, 2019-06-09/06-12, Bukowina Tatrzańska (PL), pp.1, 2019
11.  Ura D.P., Gradys A., Zaszczyńska A., Sajkiewicz P., Stachewicz U., Effect of voltage polarity on mechanical properties of electrospun PMMA fibers, Frontiers in Polymer Science, 2019-05-05/05-08, Budapest (HU), pp.1-2, 2019
12.  Niemczyk B., Sajkiewicz P., Gradys A., Methylcellulose as a smart thermosensitive scaffold material for tissue engineering, TERMIS EU 2019, TERMIS European Chapter Meeting 2019, Tissue Engineering Therapies: From Concept to Clinical Translation & Commercialisation, 2019-05-27/05-31, Rodos (GR), pp.1435, 2019
13.  Zaszczyńska A., Sajkiewicz P., Gradys A., Piezoelectric polymeric nanofibers as smart scaffolds for tissue engineering, TERMIS EU 2019, TERMIS European Chapter Meeting 2019, Tissue Engineering Therapies: From Concept to Clinical Translation & Commercialisation, 2019-05-27/05-31, Rodos (GR), pp.1421, 2019
14.  Niemczyk B., Gradys A., Sajkiewicz P., The effect of chemical composition on crosslinking kinetics of methylcellulose/agarose hydrogel, PICETE, Polish-Israeli Conference on Electrospinning and Tissue Engineering, 2018-10-04/10-05, Warszawa (PL), pp.25, 2018
15.  Gradys A., Core-shell fibers, geometrical stability, PICETE, Polish-Israeli Conference on Electrospinning and Tissue Engineering, 2018-10-04/10-05, Warszawa (PL), pp.12, 2018
16.  Niemczyk B., Sajkiewicz P., Gradys A., The Effect of Chemical Composition on Crosslinking Kinetics of Methylcellulose/Agarose Hydrogel, ISBPPB 2018, 4th International Conference on Biomedical Polymers and Polymeric Biomaterials, 2018-07-15/07-18, Kraków (PL), pp.174, 2018
17.  Świątek Z., Gradys A., Morgiel J., Marszałek K.W., Mania R., Szlezynger M., Maj Ł., XRD in-situ heating of large period Ni/Al reactive multilayer, XXIII Conference on Applied Crystallography, 2015-09-20/09-24, Krynica Zdrój (PL), pp.23-26, 2015
18.  Alhazov D., Gradys A., Denis P., Sajkiewicz P., Arinstein A., Zussman E., Thermo-mechanical behavior of electrospun thermoplastic polyurethane nanofibers, EPF2013, European Polymer Congress, 2013-06-16/06-21, Pisa (IT), pp.O2-23, 2013

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