Kinga Pielichowska

Bioactive Polymer/Hydroxyapatite (Nano)composites for Bone Tissue Regeneration

Bioactive polymer/hydroxyapatite (nano)composites are currently being intensively investigated as materials for promotion of bone tissue regeneration and reconstruction. The advantages of polymeric biomaterials, compared to metallic or ceramic materials, are the ease of manufacturing components having various and complex shapes, reasonable cost, and their ability to possess a wide range of physical and mechanical properties. Additionally, hydroxyapatite (HAp) is one of the most attractive materials for bone implants because of its composition and biological similarity to natural tissues. It can be obtained in a nanostructured form, which facilitates its fine dispersion in the polymer matrix as well as producing advantageous interactions with bioactive polymer and tissue. This paper reviews recent advances in polymer/(nano)HAp composites and nanocomposites for bone tissue regeneration, with particular emphasis on the material characteristics. Specific topics associated with polymer/HAp composition, molecular orientation and morphology, surface modifications, the interactions between the components, and their biological behaviours are described. Finally, the challenges facing this emerging field of research are outlined.

The influence of molecular weight on the properties of polyacetal/hydroxyapatite nanocomposites. Part 1. Microstructural analysis and phase transition studies

In this work the influence of molecular weight of three polyoxymethylene (POM) copolymers on the properties of (POM)/hydroxyapatite (HAp) nanocomposites for long-term bone implants have been investigated by various physicochemical methods. Electron microscopy observations confirmed uniform dispersion of HAp in the polymer matrix, whereby DSC results show that HAp influences the degree of crystallinity of POM matrix. Temperature modulated differential scanning calorimetry (TMDSC) was applied to study the melting and recrystallization processes of POM matrix—it was found that with decreasing of POM molecular weight the amout of reversible melting increases. WAXD results show no shift in 2θ for pure POM copolymers and all POM/hydroxyapatite nanocomposites, indicating that the addition of HAp does not change the hexagonal system of POM. For all three copolymers, Young’s modulus increases with increasing hydroxyapatite concentration, whereby elongation at break decreases. On the contrast, HAp concentration does not have a significant influence on the tensile strength.

Kinetics of Isothermal and Nonisothermal Crystallization of Poly(ethylene oxide) (PEO) in PEO/Fatty Acid Blends

In this work, isothermal and nonisothermal crystallization kinetics of poly(ethylene oxide) (PEO) and PEO in PEO/fatty acid (lauric and stearic acid) blends, that are used as thermal energy storage materials, was studied using differential scanning calorimetry (DSC) data. The Avrami equation was adopted to describe isothermal crystallization of PEO and nonisothermal crystallization was analyzed using both the modified Avrami approach and Ozawa method. Avrami exponent (n) for PEO crystallization was in the range 1.08–1.32 (10–90% relative crystallinity), despite of spherulites formation, while for PEO in PEO/fatty acid blends n was between 1.61 and 2.13. Hoffman and Lauritzen theory was applied to calculate the activation energy of nucleation (Kg) – the lowest value of Kg was observed for pure PEO, despite of heterogeneous nucleation of fatty acid crystals in PEO/fatty acid blends. For nonisothermal crystallization of PEO in PEO/lauric acid (1:1 w/w) and PEO/stearic acid (1:3 w/w) blends, secondary crystallization occurred and values of the Avrami exponent were 2.8 and 2.0, respectively. The crystallization activation energies of PEO were determined to be −260 kJ/mol for pure PEO, −538 kJ/mol for PEO/lauric acid blend, and −387 kJ/mol for PEO/stearic acid blend for isothermal crystallization and −135,6 kJ/mol, −114,5 kJ/mol, and −92,8 kJ/mol, respectively, for nonisothermal crystallization.

Mechanical and thermal properties of carbon-nanotube-reinforced self-healing polyurethanes

AbstractThe study was conducted to synthesize self-healing polyurethanes (PUs) in the presence of multiwalled carbon nanotubes (CNTs). Measurements of the self-healing ability of PUs synthesized from N3300 isocyanate and polytetrahydrofuran with various contents of CNTs were taken. The mechanical and thermal properties were studied to analyse healing efficiency in experimentally damaged composite samples. The addition of CNTs results in a slight decrease in the self-healing efficiency of nanocomposites as compared to pure PUs. PU samples containing 40% content of soft segments self-healed much better than the samples with 50% content of soft segments. Functionalized carbon nanotubes CNT-OH due to presence of surface functional groups interact with PU chains, which results in an increase in the healing efficiency of mechanical strength and thermal conductivity of nanocomposites.

Polyurethane composite foams with β-tricalcium phosphate for biomedical applications

Biocompatibility, bioactivity, bioconductivity and injectability are the most valuable features of biodegradable polyurethanes for orthopaedic applications. Injectable biomaterials may be used in bone tissue engineering for minimally invasive therapies and other medical applications. Polyurethane composites have been synthesized with concentration of β-tricalcium phosphate in the range of 0–30 wt%. Incorporation of β-tricalcium phosphate leads to an increased glass temperature of soft segments while a decrease of glass temperature was observed for hard segments. Moreover, addition of β-tricalcium phosphate caused an increase in the thermal stability of polyurethane matrix. Porosity has ranged between 27 and 53%. The mechanical and thermal properties of the polyurethane/β-tricalcium phosphate composite samples have been investigated. In vitro degradation tests have been carried out in water, Ringer’s solution and phosphate buffered saline. After 2 weeks incubation in simulated body fluid, scanning electron microscopy observations showed the presence of an inorganic phase deposition which might indicate good bioactivity of the composites. The relationships between their properties and bone regeneration quality were discussed as the composites demonstrate vast potential to be used as injectable scaffolds for bone repair.

Comparison of Hydrolytic Resistance of Polyurethanes and Poly(Urethanemethacrylate) Copolymers in Terms of their Use as Polymer Coatings in Contact with the Physiological Liquid

Abstract PU elastomers were synthesized using MDI, PTMO, butane-1,4-diol or 2,2,3,3-tetrafiuorobutane-1,4-diol. Using the same diisocyanate and polyether reagents urethane segments were prepared, to be inserted in the poly(urethane-methacrylate) copolymers. Bromourethane or tetraphenylethane-urethane macroinitiators were used as transitional products reacting with MMA according to the ARGET ATRP. 1H and 13C NMR spectral methods, as well as DSC and TGA thermal methods, were employed to confirm chemical structures of synthesised elastomers and copolymers. To investigate the possibility of using synthesized polymers as biomaterials a research on keeping them in physiological liquid at 37°C was performed. A loss in weight and ability to sorption of water was determined and by using GPC the molecular weight changes were compared. Additionally, changes in the thermal properties of the samples after exposure in physiological liquid were documented using both the TGA and DSC methods. The studies of surface properties (confocal microscopy and SFE) of the obtained polymers were performed. The structure of the polymer chains was defined by NMR. Possible reasons of hydrolysis were discussed, stating that new copolymers are more resistant and polar biomaterials can be less interesting than elastomers.

Chitosan-Based Hydrogels: Preparation, Properties, and Applications

Chitosan is a hydrophilic polysaccharide obtained by partial deacetylation of chitin, which is one of the most popular biopolymers. Chitosan is well known for its favorable properties including biocompatibility, biodegradability, antibacterial, and biological activity, as well as its renewable character. Thanks to those features chitosan’s popularity in various applications ranging from food industry to tissue engineering is constantly growing. The following chapter will more closely consider fabrication, properties, and specific applications of chitosan-based hydrogel networks. Methods for chitosan preparation will be summarized, followed by detailed characterization of chitosan properties. Strategies for their improvement and fabrication of chitosan derivatives will be discussed as well. Next, attention will be drawn to preparation of chitosanbased hydrogels via chitosan crosslinking. Both chemical and physical crosslinking methods will be considered with special emphasis on comparison between the two crosslinking methods and recent advancements in application of novel biocompatible crosslinkers. This chapter will also take a closer look at formation of stimuli-responsive (especially pHand temperature-sensitive systems) and injectable hydrogels. Utilization of chitosan hydrogels in tissue engineering will be highlighted together with different techniques for fabrication and construction of three-dimensional scaffolds. Finally, other applications of chitosan-based hydrogels and their composites will be summarized.

Polyurethane/graphene nanocomposites as phase change materials for thermal energy storage

In this work polyurethane/graphene nanocomposites containing segments of poly(ethylene glycol) with defined molecular weight were obtained as new phase change materials for thermal energy storage. The prepared materials were investigated by means of DSC, TG, SEM and ultrasonic non-destructive methods. Enhancements in the thermal stability and thermal conductivity in polyurethane systems modified with graphene were found which is important for thermal energy storage applications. Additionally materials modified with graphene showed lower supercooling in comparison to samples without graphene.

Multifunctional polymer coatings for titanium implants

The aim of this work was to modify the surface of the titanium implants by application of multifunctional polymer coatings based on polyurethane and its composites with graphene and β-TCP. Graphene was used as an antibacterial agent, TCP as a bioactive component, and polymer coating as a corrosion protection of metal. As a result, materials with different surface characteristic, from hydrophilic to hydrophobic, varying in bioactivity and biocompatibility, were obtained. Wettability of the materials was tested by the sessile drop method; surface roughness was assessed on the basis of Ra parameter, measured by contact profilometry. The surface characteristic was complemented by microhardness testing. Also, in vitro immersion tests in fluids and cell tests were performed. Obtained results suggest that it is possible to fabricate, on the surface of titanium implants, multifunctional composite coatings based on polyurethane, with optimal composition for bone surgery and dentistry applications. The study further showed that the chemical structure (composition) of the polymer and the graphene content are crucial in terms of biocompatibility of the final material, while addition of tricalcium phosphate affects its bioactivity.

The Influence of Nanohydroxyapatite on the Thermal, Mechanical, and Tribological Properties of Polyoxymethylene Nanocomposites

The influence of nanohydroxyapatite on the glass transition region and its activation energy, as well as on the tribological and mechanical properties of polyoxymethylene nanocomposites, was investigated using DMA, TOPEM DSC, nanoindentation, and nondestructive ultrasonic methods. It was found that the glass transition for unmodified POM was in the lower temperature range than in POM/HAp nanocomposites. Moreover, and activation energy were larger for POM/HAp nanocomposites. Friction coefficient was higher for POM/HAp nanocomposites in comparison to both POM homopolymer and POM copolymer. Simultaneously, the indentation test results show that microhardness is also higher for POM/HAp nanocomposites than for POM. From ultrasonic investigations it was found that the highest values of both longitudinal and transverse propagation waves and Young’s and shear modulus for POM homopolymer (DH) and POM copolymer T2H and their nanocomposites can be attributed to their higher degree of crystallinity in comparison to UH copolymer. Moreover, for POM/HAp nanocomposites with 5% of HAp, ultrasonic longitudinal wave velocity was almost constant even after 1000000 mechanical loading cycles, evidencing an enhancement of mechanical properties by HAp nanoparticles.