Solvent-cast Poly Research Articles

Functionalization Strategies and Fabrication of Solvent-Cast PLLA for Bioresorbable Stents

Actual polymer bioresorbable stents (BRS) generate a risk of device thrombosis as a consequence of the incomplete endothelialization after stent implantation. The material-tissue interactions are not fully controlled and stent fabrication techniques do not allow personalized medical solutions. This work investigates the effect of different functionalization strategies onto solvent-cast poly(l-lactic acid) (PLLA) surfaces with the capacity to enhance surface endothelial adhesion and the fabrication of 3D printed BRS. PLLA films were obtained by solvent casting and treated thermally to increase mechanical properties. Surface functionalization was performed by oxygen plasma (OP), sodium hydroxide (SH) etching, or cutinase enzyme (ET) hydrolysis, generating hydroxyl and carboxyl groups. A higher amount of carboxyl and hydroxyl groups was determined on OP and ET compared to the SH surfaces, as determined by contact angle and X-ray photoelectron spectroscopy (XPS). Endothelial cells (ECs) adhesion and spreading was higher on OP and ET functionalized surfaces correlated with the increase of functional groups without affecting the degradation. To verify the feasibility of the approach proposed, 3D printed PLLA BRS stents were produced by the solvent-cast direct writing technique.

Electrochemical and dielectric behavior in poly(vinyl alcohol)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) blend for energy storage applications

Herein, dielectric studies of solvent-cast poly(vinyl alcohol) (PVA) with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) freestanding films are conducted in the frequency range of 100 Hz–1 MHz and temperature ranging from 303 to 453 K. An insulator to semiconducting transition is observed for PVA/PEDOT:PSS blend above 413 K. Existence of two types of conduction mechanism, hopping between nearest neighbor at low-temperature region (303–383 K) and free-band conduction at high temperatures (above 413 K) within PVA/PEDOT:PSS films under the influence of applied field, is observed and supported by electric moduli formalisms. An increase in dielectric constant and a significant reduction in $$\tan \delta$$ values are observed under high temperature and low frequency with the addition of PEDOT:PSS. Greater than 100% Coulombic efficiency and 82% specific capacitance retention at 5000 cycles are observed for 7.5 vol% PEDOT:PSS in PVA working electrode for supercapacitor. Thus, the fabricated films find potential applications in the field of flexible conventional capacitors and as working electrodes for supercapacitor.

Comparing Soft Semicrystalline Polymer Nanocomposites Reinforced with Cellulose Nanocrystals and Fumed Silica

This work compares solvent-cast poly(ethylene oxide) (PEO) nanocomposites reinforced with cellulose nanocrystals (CNCs) and fumed silica. Mechanical properties and crystallization behavior were investigated over a range of polymer molecular weights (10 000–100 000 g/mol) and particle loadings (1–10 wt %). Polymer adsorption to CNCs and fumed silica was found to alter PEO undercooling and inhibit crystal nucleation. Atomic force microscopy revealed PEO adsorbs to CNCs in a shish-kebab morphology that is readily incorporated into the crystalline domains of the polymer. Tensile testing and nanoindentation showed that Young’s modulus increased by more than 60% for CNC reinforced nanocomposites, and that the Halpin–Kardos model could effectively describe the mechanical properties. Fumed silica reinforced nanocomposites were fit to the Guth–Gold micromechanical model using effective particle volume fractions. Although only solvent-cast nanocomposites were investigated, this work provides new insight into the in...

Thermal and mechanical characterization of solvent-cast poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

The copolymer poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(HB-co-HHx)], is produced by engineered Ralstonia eutropha strains using lipids and fatty acids as carbon feedstocks. The presence of the 3-hydroxyhexanoate (HHx) monomer disrupts the packing of polymer chains, resulting in less numerous polymer crystals and producing a polymer with favorable thermal and mechanical properties. In this study, copolymers varying in HHx content were recovered from different R. eutropha strains. Tensile constitutive response of solvent-cast samples of PHB and P(HB-co-17 mol%HHx), P(HB-co-23 mol%HHx), and P(HB-co-30 mol%HHx) was investigated using a custom-built micro-tensile tester. Our results show that presence and quantity of HHx monomer has a noticeable impact on P(HB-co-HHx) mechanical properties, such as tensile strength, elongation at break, toughness and thermal properties. It was found that with higher content of HHx in the material, the more flexible and tougher the polymer is, and the greater the reduction of Tm and crystallinity.

Functionalised nanoscale coatings using layer-by-layer assembly for imparting antibacterial properties to polylactide-co-glycolide surfaces

In order to achieve high local biological activity and reduce the risk of side effects of antibiotics in the treatment of periodontal and bone infections, a localised and temporally controlled delivery system is desirable. The aim of this research was to develop a functionalised and resorbable surface to contact soft tissues to improve the antibacterial behaviour during the first week after its implantation in the treatment of periodontal and bone infections. Solvent-cast poly(d,l-lactide-co-glycolide acid) (PLGA) films were aminolysed and then modified by Layer-by-Layer technique to obtain a nano-layered coating using poly(sodium4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) as polyelectrolytes. The water-soluble antibiotic, metronidazole (MET), was incorporated from the ninth layer. Infrared spectroscopy showed that the PSS and PAH absorption bands increased with the layer number. The contact angle values had a regular alternate behaviour from the ninth layer. X-ray Photoelectron Spectroscopy evidenced two distinct peaks, N1s and S2p, indicating PAH and PSS had been introduced. Atomic Force Microscopy showed the presence of polyelectrolytes on the surface with a measured roughness about 10nm after 20 layers’ deposition. The drug release was monitored by Ultraviolet–visible spectroscopy showing 80% loaded-drug delivery in 14days. Finally, the biocompatibility was evaluated in vitro with L929 mouse fibroblasts and the antibacterial properties were demonstrated successfully against the keystone periodontal bacteria Porphyromonas gingivalis, which has an influence on implant failure, without compromising in vitro biocompatibility. In this study, PLGA was successfully modified to obtain a localised and temporally controlled drug delivery system, demonstrating the potential value of LbL as a coating technology for the manufacture of medical devices with advanced functional properties.

Modulation of anabolic and catabolic responses via a porous polymer scaffold manufactured using thermally induced phase separation

We describe two studies encompassing the iterative refinement of a polymer-based rhBMP-2 delivery system for bone tissue engineering. Firstly, we compared the bone-forming capacity of porous poly(D,L-lactic-co-glycolic acid) (PLGA) scaffolds produced by thermally induced phase separation (TIPS) with non-porous solvent cast poly(D,L-lactic acid) (PDLLA) used previously. Secondly, we examined the potential synergy between rhBMP-2 and local bisphosphonate in the PLGA scaffold system. In vivo ectopic bone formation studies were performed in C57BL6/J mice. Polymer scaffolds containing 0, 5, 10 or 20 µg rhBMP-2 were inserted into the dorsal musculature. At all rhBMP-2 doses, porous PLGA produced significantly higher bone volume (BV, mm3) than the solid PDLLA scaffolds. Next, porous PLGA scaffolds containing 10 µg rhBMP-2 ± 0.2, or 2 µg zoledronic acid (ZA) were inserted into the hind-limb musculature. Co-delivery of local 10 µg rhBMP-2/2 µg ZA significantly augmented bone formation compared with rhBMP-2 alone (400 % BV increase, p < 0.01). Hydroxyapatite microparticle (HAp) addition (2 % w/w) to the 10 µg rhBMP-2/0.2 µg ZA group increased BV (200 %, p < 0.01). We propose that this was due to controlled ZA release of HAp-bound ZA. Consistent with this, elution analyses showed that HAp addition did not alter the rhBMP-2 elution, but delayed ZA release. Moreover, 2 % w/w HAp addition reduced the scaffold's compressive properties, but did not alter ease of surgical handling. In summary, our data show that refinement of the polymer selection and scaffold fabrication can enhance rhBMP-2 induced bone formation in our bone tissue engineering implant, and this can be further optimised by the local co-delivery of ZA/HAp.

Compatibility in Immiscible Poly(Vinyl Chloride)/Poly(Styrene) Blends

The morphology, orientation and mechanical studies of solvent cast poly (vinyl chloride) (PVC) /poly (styrene) (PS) blend films were carried out for various concentrations and draw ratios. Samples of pure PVC, PS and its blends were prepared using standard solution casting method. The thermal studies revealed that PVC/PS blends remain ‘incompatible’ for the compositions PVC/PS-80/20, 60/40, and 30/70; compatibility is suggested for the compositions PVC/PS-20/80, 10/90 and 05/95. Microscopy results indicate that PVC/PS 20/80, 10/90 and 05/95 blends show uniform distribution of PVC dispersed phase in PS matrix phase. Orientation studies showed that PVC/PS-20/80, 10/90 and 05/95 blend compositions gave a systematic change in orientation function with draw ratio; matching with their respective pure forms; while all other blend compositions indicate independent random orientation behaviour. The mechanical properties like storage modulus and tensile strength of the blends PVC/PS-20/80, 10/90and 05/95 are very close to pure PVC. The blends 80/20, 60/40, and 30/70 showed inferior properties to pure PVC for all draw ratios. The results were explained in terms of morphology of the blends.

Medical grade sterilization affects synthetic polymer film properties intended for peripheral nerve repair: an in vitro study

In vitro characterization of synthetic scaffolds in the laboratory commonly employs sterilization techniques, such as, ultraviolet light or ethanol (EtOH) soaking. These sterilization methods are not sufficient, however, to gain Regulatory approval for therapeutic use. Neglecting the effects medical grade sterilization may have on material properties could lead to years of research never translating to the clinic. The objective of this study was to ascertain whether medical grade gamma irradiation affected the properties of solvent-cast poly(ε-caprolactone)/poly(D, L-lactic acid) blend films for peripheral nerve repair. Scaffolds were sterilized at eight incremental doses of Gamma radiation (0-45 kGy). With increasing radiation dose, tensile testing identified significant reductions in both maximum tensile strength (>40 %) and strain (>90 %); gel permeation chromatography showed a dose-dependent reduction in polymer molecular weight (>46 %) and differential scanning calorimetry highlighted an increase in crystallinity. NG108-15 nerve cells were cultured up to 7 days on gamma irradiated and EtOH soaked films (control). Scanning electron microscopy showed cells proliferated on all films during this time and confirmed cell morphology was unaffected by sterilization method. However, cellular proliferation and number were greater for gamma irradiated films compared to EtOH soaked. Despite material properties being significantly altered, the in vitro response was encouraging and gamma irradiation may prove effective for medical grade sterilization of films intended for peripheral nerve repair.

Surface changes in polyhydroxyalkanoate films during biodegradation and biofouling

AbstractBACKGROUND: Despite the recognition that microbial biofilms play a role in environmental degradation of bioplastics, few studies investigate the relationship between bioplastic biodegradation and microbial colonisation. We have developed protocols based on a combination of confocal laser scanning microscopy and contact angle goniometry to qualitatively and quantitatively map surface changes due to biofilm formation and biopolymer degradation of solvent cast poly(3‐hydroxyalkanoate) films in an accelerated in vitro biodegradation system.RESULTS: A significant regression relationship between biofilm formation and polymer biodegradation (R2 = 0.96) was primarily conducted by cells loosely attached to the film surfaces (R2 = 0.95), rather than the strongly attached biofilm (R2 = 0.78). During biodegradation the surface rugosity of poly(3‐hydroxybutyrate) and poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyvalerate)] increased by factors of 1.5 and 1.76, respectively. In contrast, poly(3‐hydroxyoctanoate) films showed little microbial attachment, negligible weight loss and insignificant changes in surface rugosity.CONCLUSION: A statistically significant link is established between polymer weight loss and biofilm formation. Our results suggest that this degradation is primarily conducted by cells loosely attached to the polymer rather than those strongly attached. Biofilm formation and its type are dependent upon numerous factors; the flat undifferentiated biofilms observed in this study produce a gradual increase in surface rugosity, observed as an increase in waviness. Copyright © 2008 Society of Chemical Industry

Physical characterization of thin semi-porous poly(L-lactic acid)/poly(ethylene glycol) membranes for tissue engineering

This study examines physical properties of solvent-cast poly(L-lactic acid) (PLLA): poly(ethylene glycol) PEG membranes as a function of PEG molecular weight (MW) and incubation in vitro for 6 weeks. PEGs of MW 400, 1450 and 8000 were used. The morphological, thermal, mechanical and permeability properties of the membranes were studied prior to and after 3 and 6 weeks of incubation in phosphate-buffered saline (PBS) at 37°C. The membranes showed a thickness of about 35±5 μm and were found to be semi-porous, with a non-porous surface as well as a porous surface with pore-diameters of 0.5–5 μm. The surface pore size was found to be a function of PEG MW used. All membranes were mechanically strong, with elastic moduli and tensile strength of 150–440 MPa and 7–36 MPa, respectively, all through the 6-week incubation period. The lower-MW PEGs plasticized PLLA based on high initial percent elongation; however, the effect was lost after 3 weeks of incubation in PBS. All membranes except those fabricated with PEG 8000 were impermeable for up to 6 weeks of incubation in PBS. Permeability studies showed that only PLLA:PEG 8000 membranes were permeable to methylene blue after 3 weeks of degradation.

Effects of Methanol on Stereocomplexation of Solvent-Cast Poly (lactic acid)

Effects of Methanol on Stereocomplexation of Solvent-Cast Poly (lactic acid)

Thermal analysis, X-ray and electron diffraction studies on crystalline phase transitions in solvent-treated poly(hexamethylene terephthalate)

The crystal polymorphism, transformation, and morphologies in chloroform solvent-cast poly(hexamethylene terephthalate) (PHT) were examined by using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and temperature in situ transmission electron microscopy (TEM). Solvent-induced crystallization of PHT at room temperature yielded an initial crystal of γ-form, as confirmed by WAXD. Upon DSC scanning, the original γ-form in PHT exhibited three endothermic peaks, whose origins and association were carefully analyzed. The first peak, much smaller than the other two, is in the temperature range of ca. 100–120°C. It was found that the solvent-induced γ-form was transformed to β-form at 125°C via a solid-to-solid transformation mechanism. In addition, WAXD showed that γ- and β-forms co-existed in the temperature range of 100–125°C. These mixed crystal forms were further identified using TEM, and the selected-area electron diffraction (ED) patterns revealed that both γ- and β-form crystals co-existed and were packed within the same spherulite. Solid–solid transformation from the solvent-induced γ-form to β-form in PHT upon heat scanning was presented with evidence and discussed.

Effect of the casting solvent on the crystal characteristics and pervaporative separation performances of P(VDF- co-HFP) membranes

In this paper, two different crystalline phase compositions appear in the isothermally dried solvent-cast poly(vinylidene fluoride- co-hexafluoropropylene) (P(VDF- co-HFP)) membranes, which was explained based on the different solvent–polymer interactions. The dipolar intermolecular interaction between P(VDF- co-HFP) and dimethylacetamide (DMAc) induces polar γ phase with trans conformation, which is absent in the P(VDF- co-HFP)–acetone system. The different pervaporation behavior of the two solvent-cast membranes in separating ethyl acetate (EtAc) from water was explained based on the different permeant–polymer interactions which were further deduced from the affinity differences. The difference of polarity between EtAc molecules and the acetone-cast P(VDF- co-HFP) membrane is smaller than that between EtAc molecules and the DMAc-cast P(VDF- co-HFP) membrane, which makes for the different solubilities and diffusivities of EtAc in the two different solvent-cast membranes. And the separation properties of them in pervaporation of EtAc/water mixture are inevitably varied.

In vitro study of human vascular endothelial cell function on materials with various surface roughness.

In recent years, creating a biodegradable polymer scaffold with an endothelialized surface has become an attractive concept for replacement of small-diameter blood vessels. Toward this end, a better understanding of the interaction between endothelial cells and biodegradable polymer substrates is particularly important. Surface roughness of biomaterials is one of the important parameters that affect cell behavior. In this study, human vascular endothelial cells were cultured on electrospun and solvent-cast poly(L-lactic acid) substrates with different surface roughness. Cell responses were evaluated via both qualitative examinations of cell morphology changes as well as quantitative assessment of cell adhesion and proliferation rate on the different substrates. The results proved that endothelial cell function was enhanced on the smooth solvent-cast surface rather than on the rough electrospun surface of poly(L-lactic acid). Together with our previous findings that electrospun substrates favor vascular smooth muscle cell behavior, it is possible to design a unique three-dimensional scaffold for application of tissue-engineered small-diameter vessel replacement by combining the fabrication technique of solvent casting and electrospinning.

Surface properties and biocompatibility of solvent-cast poly[ ε-caprolactone] films

Poly( ε-caprolactone) (PCL) was dissolved in four solvent systems, chloroform, tetrahydrofuran, acetone and ethyl acetate, and cast onto glass Petri dishes. The surface properties of the resulting films were investigated. The extent to which their properties were determined by the solvent used in each case was quantified in terms of contact angle, surface morphology, attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), and the adhesion and proliferation of fibroblasts by direct contact. The surface of the PCL film in contact with glass was denoted the SG surface, and the other, which was exposed to the gas phase, a mixture of air and residual solvent vapour, was denoted the SA surface. In the case of hydrophobic solvent systems, the advancing contact angle of the SG surface was always lower than that of the SA surface. With hydrophilic solvent systems, on the other hand, the advancing contact angle of the SG film surface was higher when the contact angle of the Petri dish was higher than that of the gaseous mixture of the air and solvent vapour, otherwise it was lower or equal to that of the surface on which it was cast. The surface morphology was dictated by the solubility of PCL in the respective solvent systems: high dissolution solvents such as chloroform and tetrahydrofuran produced films that comprised PCL aggregates, the particles being larger in the case of chloroform, whereas the less efficient solvents (acetone and ethyl acetate) resulted in a filamentous structure. The ATR-FTIR results confirmed that the chemistry of the SA surfaces differed according to the solvent system used. Preliminary cell culture experiments carried out with the PCL films established that murine (L929) fibroblasts grew well on all surfaces regardless of the solvent used, although the rates of adhesion and proliferation were not as great as on tissue culture plastic controls. Of all the surfaces examined in this study, the cells favoured the SG aspect of ethyl acetate cast PCL films, the surface of which had the finest pore size and relatively low contact angle.

Ferroelectric behavior in solvent cast poly(vinylidene fluoride/hexafluoropropylene) copolymer films

The ferroelectric behavior of thin films of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) random copolymers with two different HFP molar contents was investigated. Films were prepared by solvent casting using dimethyl formamide (DMF) as the solvent. The HFP molar content of the solvent cast films were 5 and 15%. The observed remanent polarization (Pr) obtained from dielectric displacement versus electric field (D–E) data for the 5 and 15% HFP copolymer samples were 80 and 50mC/m2, respectively. The Pr of these films is discussed in terms of the HFP molar content.

Thermal Conversion of Hydroxy-Containing Imides to Benzoxazoles: Polymer and Model Compound Study

A series of hydroxy-containing polyimides, containing pendent hydroxyl groups ortho to the heterocyclic imide nitrogen, were prepared via the solution condensation of aromatic dianhydrides with bisaminophenols. The polyimides were found to undergo thermal conversion to polybenzoxazoles upon heating between 350 and 500 °C under nitrogen or vacuum. The thermal conversion was accompanied by loss of carbon dioxide. No other volatile byproducts were detected by IR or NMR. Structures were confirmed by IR, solid-state NMR, and elemental analysis. Polybenzoxazole films, obtained by the thermolysis of solvent-cast poly(amic acid) or polyimide solutions, displayed excellent solvent resistance and good thermal stability. Insolubility of the polybenzoxazoles in all solvents tested indicates possible cross-linking. No crystallinity was observed by X-ray diffraction. Due to the insolubility of the resulting polybenzoxazoles, model compound reactions were also investigated. In the vapor phase at 400 °C, N-(2-hydroxyphenyl)phthalimide underwent intramolecular thermal conversion to 2-phenylbenzoxazole in 83% yield, emulating the polyimide reactions. Thermal conversion of N-(2-hydroxyphenyl)phthalimide in the melt at 400 °C resulted in the formation of intermolecular reaction products. The intermolecular reactions may be a source of possible cross-links, which would explain the insolubility of the polybenzoxazoles.

Direct Imaging of Surface and Bulk Structures in Solvent Cast Polymer Blend Films

We have used laser confocal fluorescent microscopy and atomic force microscopy to study surface and bulk morphologies in solvent cast poly(methyl methacrylate) (PMMA)/polystyrene (PS) films. The solvent evaporation rate strongly affects the surface morphology. Sufficient suppression of solvent evaporation results in a periodic distribution of highly monodisperse PMMA-rich domains. Formation of the surface pattern is interpreted in terms of diffusion-driven coarsening of the minor phase and flow induced by the diffusive transport of PMMA molecules from the bulk of the liquid film to the air−film interface.

Surface studies of solvent-cast poly(vinyl alcohol-co-vinyl acetate) copolymer films

A series of solvent cast poly(vinyl alcohol-co-vinyl acetate) (PVA/PVAc) copolymer films with PVAc concentrations ranging from 0% to 12% have been characterized with bulk nuclear magnetic resonance and surface [variable angle x-ray photoelectron spectroscopy (XPS) and time-of-flight (TOF) secondary ion mass spectroscopy (SIMS)] analytical techniques. PVAc was observed to preferentially segregate to the top most surface region, and despite variations in the bulk levels of PVAc the surface is composed of approximately 40% PVAc. The data suggests segregation is driven by the methyl groups of the acetate functionality and can be predicted based on the minimization of surface energy. TOF–SIMS data aided XPS peak assignments and observed minute manufacturing impurities (Na, K, Ca, and Si) undetected by XPS.

Water permeability in poly(ortho ester)s

The permeation of water through thin, solvent-cast poly(ortho ester) films was determined as a function of the polymer weight-average molecular weight (7,800 to 104,200). A 2-chambered diffusion cell was employed using tritiated water (HTO) and H 2O 18 as tracers. The permeability coefficients (2.5 to 5.0×10 −10 cm 2/sec; not statistically significantly different; 37°C) were independent of the polymer molecular weight over the range 29,400 to 104,200. A poly(ortho ester) film with a weight-average molecular weight of 7,800 exhibited a significantly larger water permeability coefficient (24.6×10 −10 cm 2/sec; 37°C). These results were consistent with an increased hydrophilicity of the low molecular weight poly(ortho ester) film and predict an accelerated rate of hydrolytic degradation as the polymer molecular weight falls below a limiting value.