Selective localization of graphene oxide in electrospun polylactic acid/poly(ε-caprolactone) blended nanofibers

Despite their immiscibility, blending polylactic acid (PLA) with poly(ε-caprolactone) (PCL) provides an efficient strategy for obtaining a biopolymer blend with tailored properties due to their complementary physical properties. In this study, graphene oxide (GO) was employed as a 2-D nanofiller and nucleating agent to improve the properties of the immiscible PLA/PCL blends at 70/30, 50/50, and 30/70 wt ratios. Nanofibers of PLA/PCL blends and PLA/PCL/GO composites were investigated. It was interesting to find that the GO selectively localized in the minor phase resulting from the phase separation. The selective localization of the GO as the nucleating agent had an influence on the degree of crystallinity and crystalline morphology in the blended composites. This study also demonstrated that the molecular chains in the PLA phase oriented along the fiber axes, while in the PCL phase, the partial crystallites changed their orientation direction to be perpendicular to the fiber axes with the addition of GO.     

Effect of the surface topography of electrospun poly(ε-caprolactone)/poly(3-hydroxybuterate-co-3-hydroxyvalerate) fibrous substrates on cultured bone cell behavior

The use of electrospun fibrous matrices as substrates for cell/tissue culture has usually been confined to those consisting of smooth fibers. Here, we demonstrated that in vitro responses of mouse-calvaria-derived preosteoblastic cells (MC3T3-E1) that had been cultured on electrospun fibrous substrates made from blend solutions of 50/50 w/w poly(ε-caprolactone) (PCL) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) of varying concentrations, ranging from 4 to 14 wt %, depended strongly on the topography of the individual fibers. As the concentration of the blend solutions increased from 4 to 14 wt %, the topography of the individual fibers changed from discrete beads/smooth fibers to beaded fibers/smooth fibers and finally to smooth fibers, and the average diameter of the individual, smooth fibers increased from ～0.4 to ～1.8 μm. The results clearly showed that MC3T3-E1 preferred the smooth hydrophilic surface of the fibrous substrate from 10 wt % PCL/PHBV solution because the cells appeared to attach, proliferate, and differentiate on the surface of this substrate particularly well.     

Thermal,mechanical, and topographical evaluation of nonstoichiometric α-cyclodextrin/poly(ε-caprolactone) pseudorotaxane nucleated poly(ε-caprolactone) composite films

Three pseudorotaxanes (PpR) comprised of poly (ε-caprolactone) (PCL) and α-cyclodextrin (α-CD) with varying stoichiometric ratios were synthesized and characterized. Wide-angle X-ray diffraction (WAXD) and thermogravimetric (TGA) analyses provided conclusive evidence for complexation between the guest PCL and host α-CD. The as-synthesized and characterized PpRs were used at 10 and 20% concentrations as nucleants to promote the bulk PCL crystallization in composite films. Both WAXD and TGA provided evidence for intact PpR structures in the composite films. Isothermal differential scanning calorimetric (I-DSC) analyses, performed at various crystallization temperatures demonstrated significant differences in the crystallization patterns among the composite films. In addition, I-DSC analyses showed higher Avrami constant values (n) in the PpR-nucleated composite PCL films (n ~ 3), indicating 3-dimensional crystal growth. In the case of neat PCL films, however, lower n values indicated crystal growth in 1-dimensions or 2-dimensions. Moreover, atomic force microscopic analyses showed large crests and pits in PpR-nucleated PCL composites, with irregular morphologies leading to higher surface roughness. To the contrary, the crests and pits were much smaller in the neat PCL films, resulting in lower surface roughness values. Finally, mechanical testing revealed higher tensile strength for PpR-nucleated PCL composites films, demonstrating larger load bearing capabilities. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1529–1537     

A facile synthesis of hydrophilic poly(ε-caprolactone)-based poly(ether-ester-amide)s

Segmented poly(ether-ester-amide)s, (PEEA)s, of controlled hydrophilicity degree, based on poly(ε-caprolactone) (PCL), were synthesized according to a facile two-step procedure using α,ω-dihydroxy oligomeric PCL, 4,7,10-trioxa-1,13-tridecanediamine and macromers prepared from poly(ethylene glycol)s and adipoyl chloride. The PEEAs showed M _n values in the range 5–11.5 kDa. A PCL-type crystallinity was found by WAXS. DSC indicated T_m values (49–51 °C) close to that of PCL macromer. Single glass transitions were observed both by DSC and DMTA techniques and the T_g values (−58–−50 °C by DSC) were slightly higher than that of PCL. The water uptake was in the range 4.8–26.0 wt.-% depending on the length of the poly(ethylene glycol) segment.

Monomers used to prepare the PEEAs.     

Melting of poly(ε-caprolactone) studied by step-heating calorimetry

This study demonstrates that the step-heating calorimetry, which is a kind of temperature-modulated differential scanning calorimetry, can provide valuable information on the polymer melting. Time-dependent heat flow due to the melting of lamellar crystallites in a narrow range of thickness can be directly observed, from which thickness distribution of lamellar crystallites and thickness dependence of the melting kinetics are deduced. A sample of poly(ε-caprolactone) was used as a model material of semi-crystalline polymer, which has high crystallinity (0.79) so that no recrystallization and/or reorganization occur during melting in the step-heating scan. It was revealed that superheating dependence of the melting rate coefficient increases with increasing lamellar thickness, which may be attributed to variation of the fold surface roughness with respect to lamellar thickness. Analysis based on the cylindrical nucleation model revealed much lower free energy values of lateral surface than that evaluated from crystallization behavior, suggesting that the nucleus for melting is more stable than that for crystallization.     

Development of orientation during electrospinning of fibres of poly(ε-caprolactone)

We explore the influence of a rotating collector on the internal structure of poly(ε-caprolactone) fibres electrospun from a solution in dichloroethane. We find that above a threshold collector speed, the mean fibre diameter reduces as the speed increases and the fibres are further extended. Small-angle and wide-angle X-ray scattering techniques show a preferred orientation of the lamellar crystals normal to the fibre axis which increases with collector speed to a maximum and then reduces. We have separated out the processes of fibre alignment on the collector and the orientation of crystals within the fibres. There are several stages to this behaviour which correspond to the situations (a) where the collector speed is slower than the fibre spinning rate, (b) the fibre is mechanically extended by the rotating collector and (c) where the deformation leads to fibre fracture. The mechanical deformation leads to a development of preferred orientation with extension which is similar to the prediction of the pseudo-affine deformation model and suggests that the deformation takes place during the spinning process after the crystals have formed.     

Zein supports scaffolding capacity toward mammalian cells and bactericidal and antiadhesive properties on poly(ε-caprolactone)/zein electrospun fibers

Studies investigate the electrospinnability of poly(ε-caprolactone)/protein blends to produce fibers for tissue engineering applications. However, no reports show that zein can improve the scaffolding capacity toward stem cells and promote antiadhesive and bactericidal properties to the poly(ε-caprolactone)/zein fibers. We create fibers with average diameters ranging from 200 to 400 nm from the electrospinning of poly(ε-caprolactone)/protein mixtures. Poly(ε-caprolactone)/zein blends are electrospinnable at zein concentration between 20 and 40 wt% in a 70/30 formic acid/acetic acid mixture. Water contact angle measurements indicate that zein increases fiber hydrophilicity. The water contact angle decreases from 118° (pure poly(ε-caprolactone) fiber) to 73° for the scaffold containing 40 wt% zein. The zein (40 wt%) significantly increases Young's modulus from 260 MPa (pure poly(ε-caprolactone) fibers) to 980 MPa (poly(ε-caprolactone)/zein fibers) with no substantial influence on elongation at break (ε ≥ 125%) and tensile strength (≥0.040 MPa). The electrospun scaffolds containing zein also promote cell adhesion, proliferation, and spreading of adipose-derived human mesenchymal stem cells for at least 7 days of culture. The zein on poly(ε-caprolactone)/zein fibers can prevent the attachment and proliferation of Escherichia coli and Staphylococcus aureus. We propose these materials for wound healing and skin repair.     

Novel electrospun poly(ε-caprolactone)-based bicomponent nanofibers possessing surface enriched in tertiary amino groups

For the first time preparation of electrospun poly(ε-caprolactone) (PCL) based nanofibers possessing surface enriched in tertiary amino groups is shown. For that purpose the pair PCL and poly(ε-caprolactone)-b-poly[(2-dimethylamino)ethyl methacrylate] (PCL-b-PDMAEMA) diblock copolymers was used. PCL-b-PDMAEMA copolymers were synthesized using a combination of ring-opening polymerization and atom transfer radical polymerization (ATRP). Nanofibers with mean diameters ranging from 400 to 800 nm were obtained. Their morphology was evaluated by scanning electron (SEM) and atomic force microscopy (AFM). It was found that the morphology of the fibers depended on the weight ratio between the partners and the length of the PDMAEMA-block in the copolymers. The enrichment of the fiber surface in tertiary amino groups was studied by X-ray photoelectron spectroscopy (XPS). Increasing the copolymer content and the length of the PDMAEMA-block led to increase of the amount of tertiary amino groups on the fiber surface. The AFM analyses of the mechanical properties of the fiber surface showed that increasing the copolymer content led to decrease of the surface stiffness. The increase of the copolymer content led also to decrease of the melting temperature and the crystallinity degree in respect to PCL from the (co)polymer as determined by differential scanning calorimetry.     

Controlled-release and antibacterial studies of doxycycline-loaded poly(ε-caprolactone) microspheres

The objective of the present study is to achieve doxycycline’s maximum therapeutic efficacy. Doxycycline-loaded poly(ε-caprolactone) microspheres were prepared by water-in-oil-in-water (w/o/w) double emulsion solvent evaporation technique with different formulation variables such as concentrations of drug and polymer. The effects of these variables on surface morphology, particle size distribution, encapsulation efficiency, and in vitro release behavior were examined. To observe the nature of microspheres, X-ray diffraction studies were carried out. The release data obtained were determined using various kinetic models and Korsmeyer–Peppas model showed an acceptable regression value for all compositions. Antibacterial efficiency of doxycycline-loaded poly(ε-caprolactone) microspheres were assessed by determining Minimum Inhibition Concentration (MIC) by standard tube dilution method against four standard pathogenic strains. The in vitro drug release studies were carried out in phosphate buffer solution (pH 7.2). The results showed marked retardation of doxycycline release and higher percentage of polymer gave longer drug release profile. This may definitely provide a useful controlled-release drug therapy and also prove to be effective over a long period of time (76 h).     

Effect of ethanol solution of iodine on degradation of poly(ε-caprolactone)

The study of the effect of iodine on the degradation of poly(ε-caprolactone) fibers has revealed a drastic decrease in their molecular weight upon 24 h exposure to a 10% iodine solution in ethanol. It has been assumed that the main mechanism of this degradation is alcoholysis which proceeds with an efficient rate constant of nearly 7.5 × 10^–3 h^–1     

Time-dependent mussel-inspired functionalization of poly(L-lactide-co-ɛ-caprolactone) substrates for tunable cell behaviors

Surface properties of biomaterials, such as hydrophobic/hydrophilic balance, chemical group distribution, and topography play important roles in regulation of many cellular behaviors. In this study, we present a bio-inspired coating of synthetic biodegradable poly(L-lactide-co-?-caprolactone) (PLCL) films by using polydopamine for tunable cell behaviors such as adhesion and proliferation. Polydopamine coating decreased the water contact angles of the PLCL film from 75° to 40°, while the amount of coated polydopamine increased from 0.6 μg/cm(2) to 177.9 μg/cm(2). During the process, dopamine could be directly polymerized on the surface of the PLCL film to form a thin layer or nanosized particles of self-aggregates, which resulted in increase of overall roughness in a time-dependent manner. Characterization of surface atomic composition revealed an increase in signals from nitrogen and the C-N bond, both suggesting homogeneous polydopamine coating with prolonged coating time. The mechanical properties were similar following reaction with polydopamine for a time shorter than 30 min, while alterations in elongation and Young's modulus were observed when the coating time exceeded 240 min. Cell adhesion and proliferation on the polydopamine-coated films were significantly greater than those on the non-coated films. Interestingly, these cell behaviors were significantly improved even under the minimal coating time (5 min). In summary, the bio-inspired coating is of use to generate modular surface of biomaterial based on synthetic poly(α-hydroxy ester)s for tunable cell behaviors with optimization of coating time within the range in which their mechanical properties are not compromised.     

Stability improvement by incorporating poly(ε-caprolactone) in dimethylformamide-potassium iodide liquid electrolyte for dye-sensitized solar cell

Journal of Solid State Electrochemistry - Poly(ε-caprolactone) (PCL) was chosen as a gelator for dimethylformamide (DMF)-potassium iodide (KI) liquid electrolyte. The mass fraction of PCL,...     

Phase behavior and its viscoelastic response of polylactide/poly(ε-caprolactone) blend

Polylactide (PLA)/polycaprolactone (PCL) blends with various blend ratios were prepared via melt mixing. The morphology, linear and non-linear viscoelastic properties of the blend were studied using scanning electron microscope (SEM) and cone-plate rheometer. Three typical immiscible morphologies, i.e., spherical droplet, fibrous and co-continuous structure can be observed at various compositions. The elasticity ratio was proposed to play an important role together with the viscosity on the phase inversion because PLA/PCL blend presents a high viscosity ratio between two components. Two emulsion models were used to predict the linear viscoelastic properties of the blend with various morphologies. The Palierne model gives better fit compared with the G–M model, but both fail to predict the viscoelastic properties of the co-continuous blend. The viscoelastic behavior of those blends shows different temperature dependence due to their different morphologies. The principle of time–temperature superposition (TTS) is only valid for the co-continuous blend while fails with the rheological data of those blends with discrete spherical and fibrous domain structure. Moreover, although the discrete phase is difficult to be broken up due to the high viscosity ratio of the systems, the change of viscoelastic responses of those blends before and after preshear shows large difference, indicating that different morphologies have different sensitivity to the steady shear flow.     

Enhanced photodegradation of TiO2-containing poly(ε-caprolactone)/poly(lactic acid) blends

The calamitous accumulation of plastic waste in the environment, especially single-use disposables, calls for new approaches to materials design. One method to address the persistence of plastics beyond their intended use is to impart them with functionalities that will either allow for their recyclability or their degradation to basic natural components. This work focuses on the fabrication of photodegradable polyester blends and investigates the impact of compatibilization on photodegradation rates. Specifically, we blended poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) polymers by (reactive) extrusion in the presence or absence of dicumyl peroxide (DCP), a radical generator, and titanium dioxide (TiO₂), an inorganic photocatalyst. We examined the effects of DCP and TiO₂ loadings as well as copolymer composition on the thermomechanical properties, photodegradability, and morphology. We found that the inclusion of TiO₂ dramatically increased flexural moduli and photodegradation rates in both dry and wet conditions, while reactive compatibilization had little effect of the tested properties. This simple and scalable approach is promising to fabricate materials that can readily photodegrade.     

Hydrophobicities of poly(ε-caprolactone) oligomers functionalized with different succinic anhydrides

Different succinic anhydrides were used for modification of hydrophobicities of linear and star-shaped poly (ε-caprolactone) oligomers with different molecular weights. Hydroxyl-terminated poly(ε-caprolactone) oligomers were acid-functionalized either with succinic anhydride (SAH) or with alkenylsuccinic anhydrides (ASAs) containing 8 or 18 carbons in their alkenyl chains. Hydrophobicities of the linear and corresponding star-shaped oligomers were investigated by immersion studies and by water contact angle measurements. In comparison with SAH functionalized oligomers, alkenyl chain containing oligomers showed lower thermal transitions and higher hydrophobicities. In addition, oligomers with 18 carbons alkenyl chain showed considerably higher hydrophobicities than corresponding oligomers with 8 carbon alkenyl chain.     

Synthesis and properties of poly(isosorbide 2,5-furandicarboxylate-co-ε-caprolactone) copolyesters

Bio-based poly(isosorbide 2,5-furandicarboxylate-co-ε-caprolactone) (PIFCL) copolyesters were synthesized from 2,5-furandicarboxylic acid, isosorbide and ε-caprolactone. The obtained copolyesters were characterized by ¹H NMR, ¹³C NMR, intrinsic viscosity, GPC, DSC, TGA and tensile testing. The NMR characterization results confirmed the insertion of lactones units into poly(isosorbide 2,5-furandicarboxylate) (PIF) chains. All PIFCL copolyesters were amorphous with T_{D, 5%} higher than 300 °C. The glass transition temperatures of PIFCLs with FDCA molar ratio from 74% to 45% were within the range of 132.1 °C and 72.4 °C. Tensile testing revealed that introduction of ε-caprolactone into PIF chain imparted PIFCL with excellent mechanical performance, typically, PIFCL polyseter with FDCA molar ratio of 45% had a Young's modulus 858 ± 92 MPa, a tensile strength 44 ± 4 MPa and an elongation at break 480 ± 45%.     

Nanoparticle carriers based on copolymers of poly(ε-caprolactone) and hyperbranched polymers for drug delivery

Novel amphiphilic copolymers based on poly(ε-caprolactone) (PCL) and hyperbranched poly (amine-ester) (HPAE) with various compositions were synthesized. The amphiphilic copolymers can self-assemble into nanoscopic micelles and their hydrophobic cores can encapsulate doxorubicin (DOX) in aqueous solutions. The DOX-loaded HPAE-co-PCL nanoparticles diameter increased from 121 to 184 nm with the increasing PCL segment in the copolymer composition. An in vitro study at 37°C demonstrated that DOX-release from nanoparticles at pH 5.0 was much faster than that at pH 7.4. The cytotoxicity for HeLa cells study demonstrated that DOX-loaded HPAE-co-PCL nanoparticles exhibited the anti-tumor effect was enhanced significantly, suggesting that the DOX-loaded HPAE-co-PCL nanoparticles have great potential as a tumor drug carrier.     

Fabrication of highly porous poly (ɛ-caprolactone) fibers for novel tissue scaffold via water-bath electrospinning

A non-toxic route was used for the preparation of silver nanoparticles using tryptophan (Trp) as reducing/stabilizing agent in the presence of cetyltrimethyl ammonium bromide (CTAB). Role of water soluble neutral polymer poly(vinylpyrrolidone) (PVP) has been studied on the growth of yellow colour silver nanoparticle formation. The synthesized nanostructures were characterized by UV–Visible absorption spectroscopy, transmission electron microscopy (TEM) by observing the size and distribution of silver nanoparticles. As the reaction proceeded, particles grew up to about 10 and 20 nm in the presence and absence of PVP, respectively, as determined by TEM. The formed nanoparticles showed the highest absorption plasmon band at 425 nm. Rate of silver sol formation increases with the [Trp], [CTAB] and [PVP], reaching a limiting value and then decreases with the increase in concentrations of these reagents. It was observed that nanoparticles are spherical, aggregated and poly dispersed in the absence and presence of PVP, respectively. On the basis of kinetic data, a suitable mechanism is proposed and discussed for the silver sol formation.