PCL Foams Research Articles

Preparation and characterization of shape memory composite foams based on solid foaming method

ABSTRACTAs we know, shape‐memory foams with porous feature are better suited for a certain application compared with their solid counterparts, especially in tissue engineering, drug delivery, filtration, etc. In this study, a type of biocompatible composite foam with shape‐memory property has been developed on the basis of biocompatible materials cross‐linked poly(ε‐caprolactone) (PCL) and silk fibrin (SF). Solid‐state foaming method was used to fabricate the composite shape‐memory foam. Hierarchical cellular foam with micropore on the cellular wall was observed. To optimize pore morphology, the relationship between cross‐linking agent content/reinforcement filler content and PCL matrix was investigated. Excellent shape‐recovery property (>97.6%) and shape‐fixing property (>98%) have been achieved for PCL foam. For composite foams, SF addition is not too much effective on their shape‐memory property by varying SF content. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46767.

Morphological study on the pore growth profile of poly(ε-caprolactone) bi-modal porous foams using a modified supercritical CO2 foaming process

Bi-modal porous material is considered to have superior physical and tissue-inducing properties. This study reports on the fabrication of bi-modal porous poly(ε-caprolactone) (PCL) scaffolds using two-step depressurization supercritical CO2 foaming process. In a single process, large pores over 100 μm nucleated in the slow depressurization step, and coalesced during holding stage; small pores below 40 μm were formed in the rapid depressurization step. Investigation on foaming parameters demonstrated that soaking time longer than 0.5 h was necessary to produce bi-modal pores. It was noted that the holding stage had a significant impact on the final pores. In particular, intermediate pressure would affect the plasticizing capabilities of CO2 to increase (5–7 MPa) or decrease (7–12 MPa) pore size. In all, bi-modal porous PCL foams with around 80% porosity were produced, and this work provided a potential reference to efficient design of bone tissue engineering scaffolds.

Removal of textile dyes from water by TiO2 nanoparticles immobilized on poly(ε-caprolactone) beads and foams

This study discusses the possibility of immobilization of colloidal TiO2 nanoparticles (NPs) onto poly(?-caprolactone) (PCL) beads and foams that could be utilized for the removal of textile dyes from water by photodegradation. PCL foams were fabricated by environmentally friendly treatment of PCL beads in supercritical carbon dioxide. PCL beads and foams loaded with colloidal TiO2 NPs were used as photocatalysts for the removal of the textile dyes C.I. Acid Orange 7 and C.I. Basic Yellow 28 from aqueous solutions (10 mg L-1) under illumination that simulated sunlight. Unlike the PCL beads, the PCL foams provided complete discoloration of the dye solution within 24 h of illumination. The PCL foams also exhibited excellent floatability that was maintained for more than four weeks. Additionally, their photocatalytic activity was preserved within three repeated photodegradation cycles, indicating that the floating photocatalyst provided superior photocatalytic activity compared to the non-floating PCL beads.

Influence of expansion cooling regime on morphology of poly(ε‐caprolactone) foams prepared by pressure quenching using supercritical CO2

Creation of foam structures from hydrolytically degradable poly(ε‐caprolactone) (PCL) is a current task in biomaterial research. One example are degradable scaffolds. The thermodynamic and kinetic conditions in a supercritical CO2 (scCO2) supported foaming process of PCL can influence the resulting morphology of the foam. PCL foaming with scCO2 was systematically investigated in the pressure range from 78 to 200 bar at temperatures between 25°C and 50°C with the help of a view cell. PCL foams could be obtained at both conditions above the pressure dependent melting temperature as well as below this temperature, i.e. from supercooled melt states. Differential scanning calorimetry investigations of the PCL foam samples were used for the analysis of the relationship between pore morphology and foaming conditions. Three characteristic regions could be distinguished in the PCL/CO2 phase diagram. Only when the foaming was conducted above the critical temperature of CO2, a significant influence of the depressurization rate could be observed. Here, an increase in the quenching rate resulted in a decreasing pore size while the pore density was found to increase. Copyright © 2014 John Wiley & Sons, Ltd.

A clean and sustainable route towards the design and fabrication of biodegradable foams by means of supercritical CO2/ethyl lactate solid-state foaming

Polymeric foams are essential elements of our life as they are widely used for applications requiring light-weight materials coupled with good mechanical properties and controlled energy and mass transfer. However, foams are often made of petroleum-derivate non degradable materials and manufactured by means of toxic and often hazardous blowing agents. In this work, a clean and sustainable approach to design and fabricate porous biodegradable poly(e-caprolactone) (PCL) materials via solid-state foaming is investigated. The foaming process was performed by using supercritical mixtures of carbon dioxide (CO2) and ethyl lactate (EL) as non-toxic and environmentally friendly blowing agents. Operating temperatures, in the range of 35–40 °C, a small amount of EL (up to 0.2%) and either one or two step depressurization profiles were used to control PCL foaming. The results of this study demonstrate that supercritical CO2/EL binary mixtures are promising safer and sustainable blowing agents to design and fabricate renewable PCL foams at relatively low temperatures and with density as low as 0.2 g cm−3, mean pore size in the 14–530 μm range and pore density from 3.9 × 104 to 1.4 x 108 pore cm−3.

Graded biomimetic osteochondral scaffold prepared via CO2 foaming and micronized NaCl leaching

This study reports for the first time the design and fabrication of an osteochondral biomimetic poly(ε-caprolactone) (PCL) and nano-metric hydroxyapatite (HA) scaffold for tissue engineering via CO2 foaming and micronized NaCl particles leaching.The control of the NaCl concentration, in the range from 30 to 80wt.%, and the foaming temperature, in the range from 25 to 40°C, allowed for the design and fabrication of PCL foams with different combinations of morphology, porosity and mean pore size. Furthermore, by creating concentration gradients of NaCl micro-particles and HA nano-crystals, we fabricated a novel graded biomimetic PCL-HA scaffold with biochemical and biophysical properties suitable for osteochondral tissue engineering.

Development of a biodegradable foam for use in negative pressure wound therapy

Treatment of wounds using negative pressure wound therapy (NPWT) uses a nondegradable polyvinyl alcohol (PVA) foam in the application of negative pressures typically for 1-3 days. The purpose of this study was to construct and test biodegradable poly(ε-caprolactone) (PCL) foam as a substitute for the PVA foam. Such a foam would be left within the wound until healing was achieved and form a biodegradable matrix into which tissue would grow. The use of such foam would obviate the need for any serial foam changes and a final foam removal, thus making patient care much easier and more economical. PCL foams were prepared by salt leaching and phase separation. Morphological and mechanical properties of the foams were characterized and compared to PVA foam. PCL and PVA foams were tested on the uncut surface of a pig liver maintained in a hydration chamber continuously replenished with saline under the conditions of negative pressure of 50 mm Hg for 72 h. The results demonstrated that PCL foam made from phase separation had the similar properties and function as the PVA foam. The results demonstrate that PCL foam is an appropriate substitute for currently used nondegradable PVA foam in NPWT applications.

Solid-state supercritical CO 2 foaming of PCL and PCL-HA nano-composite: Effect of composition, thermal history and foaming process on foam pore structure

In this work we investigated the solid-state supercritical CO 2 (scCO 2) foaming of poly(ɛ-caprolactone) (PCL), a semi-crystalline, biodegradable polyester, and PCL loaded with 5 wt% of hydroxyapatite (HA) nano-particles. In order to investigate the effect of the thermal history and eventual residue of the crystalline phase on the pore structure of the foams, samples were subjected to three different cooling protocols from the melt, and subsequently foamed by using scCO 2 as blowing agent. The foaming process was performed in the 37–40 °C temperature range, melting point of PCL being 60 °C. The saturation pressure, in the range from 10 to 20 MPa, and the foaming time, from 2 to 900 s, were modulated in order to control the final morphology, porosity and pore structure of the foams and, possibly, to amplify the original differences among the different samples. The results of this study demonstrated that by the scCO 2 foaming it was possible to produce PCL and PCL-HA foams with homogeneous morphologies at relatively low temperatures. Furthermore, by the appropriate combination of materials properties and foaming parameters, we prepared foams with porosities in the 55–85% range, mean pore size from 40 to 250 μm and pore density from 10 5 to 10 8 pore/cm 3. Finally, we also proposed a two-step depressurization foaming process for the design of bi-modal and highly interconnected foams suitable as scaffolds for tissue engineering.

Study of the biodegradable poly(ε‐caprolactone)/clay nanocomposite foams

AbstractIn this article, biodegradable poly(ε‐caprolactone)/layered silicate nanocomposites were prepared and characterized. The dispersion state of modified clay in PCL matrix and its effect on thermal, rheological and mechanical properties of PCL were studied. The PCL/clay nanocomposites were then foamed using chemical foaming method. Cellular parameters such as mean cell size, cell wall thickness and cell densities of nanocomposite foams with different clay loading were collected. Effect of layered silicate on the structure and mechanical properties of PCL foams were evaluated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The relationship between the mechanical properties and cell behaviour on PLGA and PCL scaffolds for bladder tissue engineering

Previous work on 2D synthetic films showed growth of human bladder stromal cells was enhanced on materials with lower moduli that mimic the elastic properties of native tissue. This study developed 3D synthetic foam scaffolds for soft tissue engineering by emulsion freeze-drying. Foams of poly(lactide-co-glycolide) (PLGA) and poly(ɛ-caprolactone) (PCL) were extensively characterised using scanning electron microscopy, mercury porosimetry, dynamic mechanical analysis, degradation analysis, size exclusion chromatography and differential scanning calorimetry. Foams of 85–88% porosity and 35 μm pore diameter were selected for further study; the storage modulus of PCL foams was around half that of PLGA (2 MPa vs 4 MPa) and closer to the reported value for native bladder tissue. Urinary tract stromal cells showed a 4.4 and 2.4-fold higher attachment and rate of growth, respectively, on PCL scaffolds, as assessed by a modified 3-[4,5-dimethyl(thiazol-2yl)-3,5-diphery] tetrazolium bromide assay. A greater contractile force was exerted by cells seeded in PLGA than on PCL scaffolds, raising the possibility that the reduced rate of proliferation of cells on PLGA scaffolds may reflect differentiation into a contractile phenotype. This study has generated PCL foam scaffolds with properties that may be pertinent to the tissue engineering of the bladder and other soft tissues.

Open‐Pore Biodegradable Foams Prepared via Gas Foaming and Microparticulate Templating

Open-pore biodegradable foams with controlled porous architectures were prepared by combining gas foaming and microparticulate templating. Microparticulate composites of poly(epsilon-caprolactone) (PCL) and micrometric sodium chloride particles (NaCl), in concentrations ranging from 70/30 to 20/80 wt.-% of PCL/NaCl were melt-mixed and gas-foamed using carbon dioxide as physical blowing agent. The effects of microparticle concentration, foaming temperature, and pressure drop rate on foam microstructure were surveyed and related to the viscoelastic properties of the polymer/microparticle composite melt. Results showed that foams with open-pore networks can be obtained and that porosity, pore size, and interconnectivity may be finely modulated by optimizing the processing parameters. Furthermore, the ability to obtain a spatial gradient of porosity embossed within the three-dimensional polymer structure was exploited by using a heterogeneous microparticle filling. Results indicated that by foaming composites with microparticle concentration gradients, it was also possible to control the porosity and pore-size spatial distribution of the open-pore PCL foams.

Process-structure Relationships in PCL Foaming

The foaming behavior of poly(ε-caprolactone) (PCL) with nitrogen as the foaming agent has been investigated. By using a uniquely designed and instrumented batch foaming apparatus it is possible to study the correlation between the foam structure (i.e., foam density and mean cell diameter) and the main processing variables (i.e., foaming temperature, foaming agent concentration, and pressure drop rate). A narrow experimental range has been used to describe the complex dependencies by a simple model. In particular, linear algebraic functions have been used to describe the effect of the processing variables on both the foam density and the mean cell diameter. With the aim to better depict these relationships, 3D graphs are also reported. This visualization/ parametrization allows the rapid selection of the proper process parameters to obtain PCL foams with the desired density and morphology.

Autoclave Foaming of Poly(ε-Caprolactone) Using Carbon Dioxide: Impact of Crystallization on Cell Structure

The purpose of this study is to develop a better understanding of the main mechanisms controlling the foaming of poly(ε-caprolactone) (PCL), a semi-crystalline biodegradable polymer, using batch processing and CO 2 as the physical blowing agent. A detailed study of the dissolution of CO2 is conducted in order to establish its impact on the transition temperatures of PCL. In a following step, particular attention is paid to the effects of crystallization on cell structure. This foam structure is subsequently linked to the processing window, expressed in terms of the processing temperature with respect to the shifted crystallization temperature and modified crystallization kinetics of PCL. The effects of talc addition on PCL crystallization and foam structure are also investigated, as talc is expected to modify the nucleation rate of crystallites and cells.

Changes of porous poly( ε-caprolactone) bone grafts resulted from e-beam sterilization process

The most important mechanical feature of poly( ε-caprolactone) (PCL) foams applied in bone tissue engineering as a scaffold, has been investigated as a function of irradiation dose. Radiation is proposed for the sterilization of the polymer before the implantation. Polycaprolactone scaffold foams were obtained by combination of compression molding and particulate leaching techniques. The porogen was changed in the range 74–96 w% and the irradiation dose was varied from 25 to 150 kGy. Our results show that yield strength is not a function of radiation dose, but is rather influenced by the porosity, while the critical strain is mainly dependent on the dose. All these together mean that the modulus of the elasticity of PCL foams is dependent on both the porosity and the dose.

Effect of Molecular Modification on PCL Foam Formation and Morphology of PCL

AbstractPoly(ϵ‐caprolactone) was chemically modified by using dicumyl peroxide from 0.25 to 2 % (w/w) and the effects of molecular architecture on the density and morphology of PCL foams were examined. The polymer was first blended with dicumyl peroxide at a low temperature (80°C), to prevent premature peroxide decomposition. The peroxide modification was then performed at different temperatures, from 110°C to 150°C. The reaction kinetic was followed by measuring the dynamical rheological properties of the melt in isothermal experiments by using a parallel plate rheometer. The evolution of the macromolecular structure during the chemical reaction was followed by analyzing the time evolution of the complex viscosity. Foams were prepared from the peroxide modified PCL with a batch foaming process using nitrogen as the foaming agent under different process conditions. As expected, the increase of the molecular modification led to a shift towards higher temperatures of the foaming window and, moreover, influenced the viscoelastic behavior of the expanding polymeric matrix so that the final foam properties are affected.

Characterization of Microcellular Biodegradable Polymeric Foams Produced from Supercritical Carbon Dioxide Solutions

The formation of foams of biodegradable poly(ε-caprolactone) (PCL) from CO2 solutions in molten PCL was investigated. This study included characterization of the CO2 diffusion and equilibrium solubility in molten PCL in contact with supercritical CO2 (scCO2). Experiments were performed at 70, 80, and 90 °C at CO2 pressures up to 25 MPa. The effective mutual diffusivity of CO2 in molten PCL was measured as a function of the CO2 pressure. The data revealed a dramatic increase in apparent effective diffusivity at elevated pressure, likely related to the formation of fluid bubbles, phase-separated from the previously homogeneous, molten PCL solution of CO2. Microcellular PCL foams were produced by starting from an equilibrium CO2−PCL solution at 70 °C over a wide range of initial pressures (from 6.9 to 32 MPa) by quenching down to foaming temperatures (from 24 to 30 °C) followed by rapid depressurization to atmospheric pressure. Foam structures were characterized by scanning electron microscopy, and cell sizes and density were determined quantitatively. The various foam structures were analyzed and interpreted in connection with the independently measured kinetics and equilibrium of CO2 sorption in PCL by considering the effects of starting pressure and foaming temperature on bubble nucleation and growth.

Improvement of processability of poly(?-caprolactone) by radiation techniques

Improvement of processability of Poly(ε-caprolactone) (PCL) was achieved by introduction of a branch structure using gamma-irradiation from a 60Co source. Irradiated PCL has higher molecular weight by producting a branch structure. Hence, the irradiation at a lower dose, such as 3 Mrad, leads to a higher melt viscosity. The branched structure gave improved properties for dynamic viscoelasticity and elongational viscosity. High elongational viscosity was observed by entanglement due to branch chain formed during irradiation, and the elongational viscosity for 3 Mrad is higher than 1.5 Mrad. Due to a higher elongational viscosity, PCL foam can be produced by a molding process. Foam produced from irradiated PCL pellets at 3 Mrad has honeycomb-like structure, and the foam showed higher enzymatic degradation compared to film samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1815–1820, 1999

Evaluation of wound‐covering materials

Physical and in vivo (burned rat model) evaluations as wound coverings were performed for 1) a freeze-dried collagen/poly (epsilon-caprolactone) (PCL) film laminate, 2) a freeze-dried PCL "foam"/PCL film laminate, and 3) a heat-dried collagen/PCL film laminate. Porcine skin and cadaver skin were also evaluated in vivo for the purpose of comparison. Water-vapor transmission rates and Young's moduli were measured. The degree of adherence of the coverings to the wound were measured. Grafts which became significantly adherent (greater than 150 dyne/cm2) to the wound within 1 day were most successful in promoting the formation of a viable tissue bed which appeared ready to accept further grafting. The force required to remove the PCL foam laminate from a full-thickness excision wound was found to increase from 170 dyne/cm2 on the first day postgraft to 1500 dyne/cm2 by the tenth day. The force required to remove freeze-dried collagen laminate remained constant at 200 dyne/cm2 over the 10 day test period. For the heat-dried collagen laminate, a force of only 50 dyne/cm2 was required on day 1, increasing to 200 dyne/cm2 on day 6. Insensible water-loss rates of animals grafted with the laminates were found to be similar to those from animals with human cadaver skin grafts and less than that from animals with porcine skin grafts. When moistened, the laminates prepared using the freeze-dried materials were flexible and somewhat transparent permitting observation of the wound.