Mechanical characterization of self-curing acrylic cements formulated with poly(methylmethacrylate)/poly(epsilon-caprolactone) beads

New acrylic-based cements were formulated by replacing a mass fraction of 20% of poly(methyl methacrylate) (PMMA) powder by PMMA/poly(epsilon-caprolactone) (PCL) beads (throughout this article all compositions are given as mass fractions, unless specified otherwise). PMMA/PCL beads containing 10 and 30% PCL were synthesized by suspension polymerization. Cements were prepared by replacing part of the PMMA powder of the formulation by an equivalent mass of PMMA/PCL particles. The influence of the PCL content in the beads on the mechanical behavior was assessed by testing the cements in flexure and compression. The addition of PMMA/PCL particles with 10% PCL content resulted in a marked increase in both flexural modulus and flexural strength related to the plain PMMA beads formulation. This improvement was attributed to a decrease in the cured material porosity. Conversely, by the incorporation of beads with 30% PCL content the flexural properties decreased. This behavior was attributed to the debonding of the particles from the matrix, which was revealed by SEM images. The observed compressive yield strength decrease with the increase of PCL content in the beads was attributed to a low degree of adhesion between the heterogeneous particles and the matrix as well as to the plasticizing effect of the PCL.     

Evaluations of bioactivity and mechanical properties of poly (epsilon-caprolactone)/silica nanocomposite following heat treatment

A composite material consisting of poly(epsilon-caprolactone) (PCL) and silica was prepared and evaluated as a bioactive bone substitute. The composite was synthesized by the co-condensation of tetraethyl orthosilicate and PCL and end-capped with triethoxysilane (Si-PCL). The as-prepared specimens were subjected to an initial heat treatment of 2 days at 60 degrees C, followed by further heat-treatments at 100 degrees C, 150 degrees C, and 200 degrees C for 24 h. The tensile mechanical properties of the heat-treated specimens were determined, and additional specimens were exposed to a simulated body fluid (SBF) for different periods of time. The SBF exposure led to the deposition of a layer of apatite crystals on the surface of the composites. It was found that increasing the second heat-treatment temperature produced an increase in tensile strength and Young's modulus of the composite but a decrease in the initial rate of apatite formation. These phenomena are explained in terms of the condensation reaction that takes place between the silanol groups in the silica and Si-PCL as the heat-treatment temperature is increased.     

Effect of molecular weight of poly(epsilon-caprolactone) on interpenetrating network structure,apatite-forming ability,and degradability of poly(epsilon-caprolactone)/silica nano-hybrid materials

The effect of molecular weight of poly(epsilon-caprolactone) (PCL) on the bioactivity of a PCL/silica nano-hybrid containing calcium salt was investigated. Two hybrids were prepared with low and high molecular weight PCLs, respectively, through a sol-gel method. Their bioactivities were evaluated using a simulated body fluid (SBF), which had almost the same ion concentrations with human blood plasma. Fast and uniform nucleation and growth of the apatite crystals were observed to occur all through the hybrid surface when low molecular weight PCL was used, while slow and random nucleation and growth of the apatite crystals were observed to occur when high molecular weight PCL was used, after soaking for 3 days in the SBF. This phenomenon was explained in terms of the distribution and dispersion of silica phase in the hybrid and the ionic activity product of the apatite in the SBF, which were dependent on the free volume and degradation rate of non-bioactive PCL phase, respectively.     

Development of hydroxyapatite bone scaffold for controlled drug release via poly(epsilon-caprolactone) and hydroxyapatite hybrid coatings

A scaffold-coating design, the hydroxyapatite (HA) porous bone scaffold coated with poly(epsilon-)caprolactone (PCL) and HA powder hybrids, was developed for use as tissue-regeneration and controlled-release system. An antibiotic drug, tetracycline hydrochloride (TCH), was encapsulated within the hybrid coating layer through a dip-coating and solvent-casting method. Coating cycle and drug loading amount differed to control the level of drug-release rate. The HA scaffold framework, obtained by a polymeric foam reticulate method, exhibited a highly porous structure, with porosity and pore size of approximately 87% and 180 microm, respectively. The hybrid layer, consisting of PCL sheet and HA fine powders, was uniformly coated on the scaffold surface. The coating layer exhibited only PCL and HA phases and structures, revealing no chemical interaction among the coating components, as observed by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analyses. The coated-HA scaffolds showed an effective stress distribution behavior in response to an applied load, as confirmed by the compressive stress-strain curve. The mechanical properties of the coated scaffolds were improved highly with coatings; the compressive strength and elastic modulus of the cyclic coated scaffolds were approximately 3-4 times, and the energy absorption were approximately 8 times, higher than those without coating. These improvements were attributed mainly to the shielding of framework flaws by a flexible coating layer and partially to the thicker stems (porosity reduction). The dissolution of the coated scaffolds in a phosphate-buffered saline (PBS) solution increased with incubation time. The drug was released sharply within the initial several hours ( approximately 2 h), but the rate decreased further, showing a sustained release. The release amount was well controlled via coating-cycle and initial drug loading amount, suggesting the effectiveness of the coating-scaffold design as a drug-delivery system.     

Effect of calcium salt content in the poly(epsilon-caprolactone)/silica nanocomposite on the nucleation and growth behavior of apatite layer

The effect of calcium salt content in the poly(epsilon-caprolactone) (PCL)/silica nanocomposite on the nucleation and growth behavior of apatite layer in simulated body fluid (SBF) was investigated. The specimens were prepared with low (L) and high (H) concentrations of calcium nitrate tetrahydrate through a sol-gel method. After soaking in the SBF at 36.5 degrees C for 1 week, a densely packed apatite layer that had a smooth surface and a Ca/P ratio similar to bone was formed on specimens containing a low concentration of calcium salt while a loosely packed apatite layer with a rugged surface and a higher Ca/P ratio than that of bone occurred on specimens containing a high concentration of calcium salt. The results are explained in terms of the degree of supersaturation of apatite in the SBF, as determined by the concentrations of constituent ions of apatite and pH. The practical implication of the results is that a dense and bone-like apatite layer on the PCL/silica nanocomposite in vitro, and perhaps in vivo, can be achieved by adopting an appropriate calcium salt content.     

Embedded silica nanoparticles in poly(caprolactone) nanofibrous scaffolds enhanced osteogenic potential for bone tissue engineering

Poly(caprolactone) (PCL) has been frequently considered for bone tissue engineering because of its excellent biocompatibility. A drawback, however, of PCL is its inadequate mechanical strength for bone tissue engineering and its inadequate bioactivity to promote bone tissue regeneration from mesenchymal stem cells. To correct this deficiency, this work investigates the addition of nanoparticles of silica (nSiO(2)) to the scaffold to take advantage of the known bioactivity of silica as an osteogenic material and also to improve the mechanical properties through nanoscale reinforcement of the PCL fibers. The nanocomposite scaffolds and the pristine PCL scaffolds were evaluated physicochemically, mechanically, and biologically in the presence of human mesenchymal stem cells (hMSCs). The results indicated that, when the nanoparticles of size approximately 10?nm (concentrations of 0.5% and 1% w/v) were embedded within, or attached to, the PCL nanofibers, there was a substantial increase in scaffold strength, protein adsorption, and osteogenic differentiation of hMSCs. These nSiO(2) nanoparticles, when directly added to the cells evidently pointed to ingestion of these particles by the cells followed by cell death. The polymer nanofibers appeared to protect the cells by preventing ingestion of the silica nanoparticles, while at the same time adequately exposing them on fiber surfaces for their desired bioactivity.     

Hydrophilized polycaprolactone nanofiber mesh-embedded poly(glycolic-co-lactic acid) membrane for effective guided bone regeneration

A novel guided bone regeneration (GBR) membrane was fabricated by an immersion precipitation of poly (glycolic-co-lactic acid) (PLGA)/Pluronic F127 solution impregnated in an electrospun polycaprolactone (PCL)/Tween 80 nanofiber mesh. The prepared PCL/Tween 80 nanofiber mesh-embedded PLGA/Pluronic F127 membrane (hydrophilized PCL/PLGA hybrid membrane) had nano-size pores on the top side (which can prevent from fibrous connective tissue infiltration but allow permeation of oxygen and nutrients) and micro-size pores on the bottom side (which can improve adhesiveness with bone). From the comparisons of mechanical properties (tensile and suture pullout strengths), model nutrient (FITC-labeled bovine serum albumin) permeability, and bone regeneration behavior using a rat model (skull bone defect) of the hybrid membrane with those of PLGA/Pluronic F127 membrane (asymmetrically porous, hydrophilized PLGA membrane), PCL/Tween 80 nanofiber mesh (electrospun, hydrophilized PCL nanofiber mesh), and a commercialized GBR membrane, Bio-Gide (collagen type I/III membrane), it was observed that the PCL/PLGA hybrid membrane seems to be highly desirable as a GBR membrane for the selective permeability caused by its unique morphology and osteoconductivity provided by several tens micro-size pores of the bottom side as well as the excellent mechanical strengths by the hybridization of porous PLGA membrane and PCL nanofiber mesh.     

Preparation and characterization of bioactive calcium silicate and poly(epsilon-caprolactone) nanocomposite for bone tissue regeneration

A novel biocomposite of nanosized calcium silicate (n-CS) and poly(epsilon-caprolactone) (PCL) was successfully fabricated directly using n-CS slurry, not dried n-CS powder, in a solvent-casting method. The in vitro bioactivity of the composite was evaluated by investigating the apatite-forming ability in simulated body fluid. A proliferation assay with mouse L929 fibroblasts was used to test the in vitro biocompatibility. The composition, hydrophilicity, and mechanical properties were also evaluated. Results suggest that the incorporation of n-CS could significantly improve the hydrophilicity, compressive strength, and elastic modulus of n-CS/PCL composites, with the enhancements mainly dependent on n-CS content. The n-CS/PCL composites exhibit excellent in vitro bioactivity, with surface apatite formation for 40% (w/w) n-CS (C40) exceeding that of 20% (w/w) n-CS (C20) at 7 and 14 days. The Ca/P ratios of apatite formed on C20 and C40 surfaces were 1.58 and 1.61, respectively, indicating nonstoichiometric apatite with defective structure. Composites demonstrated significantly better cell attachment and proliferation than that of PCL alone, with C40 demonstrating the best bioactivity. The apatite layers that formed on the composite surfaces facilitated cell attachment (4 h) and proliferation during the early stages (1 and 4 days). Collectively, these results suggest that the incorporation of n-CS produces biocomposites with enhanced bioactivity and biocompatibility.     

Morphology and properties of organic-inorganic hybrid materials involving TiO2 and poly(epsilon-caprolactone), a biodegradable aliphatic polyester

The novel biodegradable poly(epsilon-caprolactone)/titanium dioxide hybrid materials were prepared via in situ sol-gel process of tetrabutyl titanate (TBT) as inorganic precursor in the presence of PCL. The relationships between morphology, microphase separation, crystalline structure, and properties were investigated by means of XPS, SEM, XRD, DSC, and in vitro degradation test. The microstructures of the bulk hybrids display two-phase microscopic separation on the nanometer scale, which domain is 20-80 nm. The surface morphology and intermolecular bonding interaction are significantly dependent on inorganic component. The relative crystalline degrees of PCL/TiO(2) hybrid nanocomposite materials were controlled by both inorganic component and hydrogen bonding special interaction. The hybrid nanocomposite materials with TiO(2) showed faster biodegradation rate than that of pure PCL itself, and the transparency corresponding to microstructure increase with increase of inorganic component content.     

The mechanical properties and bioactivity of poly(methyl methacrylate)/SiO2–CaO nanocomposite

The mechanical properties and bioactivity of poly(methyl methacrylate)/SiO₂–CaO nanocomposite were investigated using dimethyldiethoxysilane (DMDES) and tetraethoxysilane (TEOS), which could produce two and four siloxane linkages, respectively, after a sol–gel reaction. Methyl methacrylate was co-polymerized with 3-(trimethoxysilyl)propyl methacrylate and then co-condensed with DMDES (specimen D) and TEOS (specimen T), respectively, with calcium nitrate tetrahydrate under acidic conditions. The fracture toughness of specimen D was much improved compared to that of specimen T, whereas its fracture strength, hardness, and apatite-forming ability in simulated body fluid (SBF) were slightly decreased. The improved fracture toughness of specimen D without losing apatite-forming ability was explained by the decrease of siloxane linkage numbers and the introduction of alkyl groups in silica structure because covalently bonded siloxane linkages produce hard and brittle fracture behavior in the nanocomposite while the alkyl groups help to make the silica as linear chain structure. The practical implication of these results is that this new nanocomposite can be applied to the filler materials for bone cement and dental composite resin because of its good bioactivity and improved mechanical properties.     

Hydroxyapatite/poly(epsilon-caprolactone) composite coatings on hydroxyapatite porous bone scaffold for drug delivery

Hydroxyapatite (HA) porous scaffold was coated with HA and polycaprolactone (PCL) composites, and antibiotic drug tetracycline hydrochloride was entrapped within the coating layer. The HA scaffold obtained by a polymeric reticulate method, possessed high porosity ( approximately 87%) and controlled pore size (150-200 microm). Such a well-developed porous structure facilitated usage in a drug delivery system due to its high surface area and blood circulation efficiency. The PCL polymer, as a coating component, was used to improve the brittleness and low strength of the HA scaffold, as well to effectively entrap the drug. To improve the osteoconductivity and bioactivity of the coating layer, HA powder was hybridized with PCL solution to make the HA-PCL composite coating. With alteration in the coating concentration and HA/PCL ratio, the morphology, mechanical properties, and biodegradation behavior were investigated. Increasing the concentration rendered the stems thicker and some pores to be clogged; as well increasing the HA/PCL ratio made the coating surface be rough due to the large amount of HA particles. However, for all concentrations and compositions, uniform coatings were formed, i.e., with the HA particles being dispersed homogeneously in the PCL sheet. With the composite coating, the mechanical properties, such as compressive strength and elastic modulus were improved by several orders of magnitude. These improvements were more significant with thicker coatings, while little difference was observed with the HA/PCL ratio. The in vitro biodegradation of the composite coatings in the phosphate buffered saline solution increased linearly with incubation time and the rate differed with the coating concentration and the HA/PCL ratio; the higher concentration and HA amount caused the increased biodegradation. At short period (<2 h), about 20-30% drug was released especially due to free drug at the coating surface. However, the release rate was sustained for prolonged periods and was highly dependent on the degree of coating dissolution, suggesting the possibility of a controlled drug release in the porous scaffold with HA+PCL coating.     

Compressive properties and degradability of poly(epsilon-caprolatone)/hydroxyapatite composites under accelerated hydrolytic degradation

Hydroxyapatite (HA) was incorporated as filler into polycaprolactone (PCL) matrix to improve the bioactivity as well as the compressive properties of the polymer composites that can be typically used in tissue engineering scaffolds. The compressive properties of five PCL/HA composites of different compositions were investigated in conjunction with the study of their rate of degradation. As PCL has a slow degradation rate, the experiment was conducted in a concentrated 5M sodium hydroxide medium to accelerate the degradation process. The compressive strength and modulus of all PCL/HA compositions were observed to decrease as the degradation experiment progressed, with samples having high HA content degraded most significantly as compared with samples with lower HA content. Pure PCL samples, however, were found to retain their mechanical properties comparatively well in the same degradation experiments. Although the addition of HA as filler into the PCL matrix was shown to have improved mechanical properties and bioactivity initially, these results do raise concerns of material properties being compromise during hydrolytic degradation.     

Chitosan/poly(epsilon-caprolactone) blend scaffolds for cartilage repair

Chitosan (CHT)/poly(?-caprolactone) (PCL) blend 3D fiber-mesh scaffolds were studied as possible support structures for articular cartilage tissue (ACT) repair. Micro-fibers were obtained by wet-spinning of three different polymeric solutions: 100:0 (100CHT), 75:25 (75CHT) and 50:50 (50CHT) wt.% CHT/PCL, using a common solvent solution of 100 vol.% of formic acid. Scanning electron microscopy (SEM) analysis showed a homogeneous surface distribution of PCL. PCL was well dispersed throughout the CHT phase as analyzed by differential scanning calorimetry and Fourier transform infrared spectroscopy. The fibers were folded into cylindrical moulds and underwent a thermal treatment to obtain the scaffolds. μCT analysis revealed an adequate porosity, pore size and interconnectivity for tissue engineering applications. The PCL component led to a higher fiber surface roughness, decreased the scaffolds swelling ratio and increased their compressive mechanical properties. Biological assays were performed after culturing bovine articular chondrocytes up to 21 days. SEM analysis, live-dead and metabolic activity assays showed that cells attached, proliferated, and were metabolically active over all scaffolds formulations. Cartilaginous extracellular matrix (ECM) formation was observed in all formulations. The 75CHT scaffolds supported the most neo-cartilage formation, as demonstrated by an increase in glycosaminoglycan production. In contrast to 100CHT scaffolds, ECM was homogenously deposited on the 75CHT and 50CHT scaffolds. Although mechanical properties of the 50CHT scaffold were better, the 75CHT scaffold facilitated better neo-cartilage formation.     

Development of perforated microthin poly(epsilon-caprolactone) films as matrices for membrane tissue engineering

The design and fabrication of thin films based on bioresorbable polymers such as poly(epsilon-caprolactone) (PCL) has been the focus of a part of current biomedical research, especially as matrices for membrane tissue engineering. We have successfully developed perforated microthin PCL membrane for this purpose. Two critical issues are the control of moisture permeability and understanding the degradation of PCL microthin film. In order to increase the moisture permeability. PCL films were biaxially stretched to a thickness of 10 +/- 3 microm and perforated with uniform array of holes (180-275 microm) using a Sony Robotic system. After perforation, the water vapour transmission rate was increased by 50% to a value of 47.6 +/- 2.7 g/h per m2. Accelerated hydrolytic degradations were performed in 5 M NaOH. The degraded samples were characterised for changes in weight, surface morphology, mechanical properties, crystallinity and molecular weight. Hydrolytic degradation commenced with random chain scission of backbone ester bonds on the film surface and followed by loss of material due to surface erosion. In general, the perforated films degraded faster than the unperforated microthin films. Scanning electron microscopic images showed that surface erosion led to extensive formation of micropores, microcracks and increased in surface roughness.     

Electrospun poly(epsilon-caprolactone)/gelatin nanofibrous scaffolds for nerve tissue engineering

Nerve tissue engineering is one of the most promising methods to restore nerve systems in human health care. Scaffold design has pivotal role in nerve tissue engineering. Polymer blending is one of the most effective methods for providing new, desirable biocomposites for tissue-engineering applications. Random and aligned PCL/gelatin biocomposite scaffolds were fabricated by varying the ratios of PCL and gelatin concentrations. Chemical and mechanical properties of PCL/gelatin nanofibrous scaffolds were measured by FTIR, porometry, contact angle and tensile measurements, while the in vitro biodegradability of the different nanofibrous scaffolds were evaluated too. PCL/gelatin 70:30 nanofiber was found to exhibit the most balanced properties to meet all the required specifications for nerve tissue and was used for in vitro culture of nerve stem cells (C17.2 cells). MTS assay and SEM results showed that the biocomposite of PCL/gelatin 70:30 nanofibrous scaffolds enhanced the nerve differentiation and proliferation compared to PCL nanofibrous scaffolds and acted as a positive cue to support neurite outgrowth. It was found that the direction of nerve cell elongation and neurite outgrowth on aligned nanofibrous scaffolds is parallel to the direction of fibers. PCL/gelatin 70:30 nanofibrous scaffolds proved to be a promising biomaterial suitable for nerve regeneration.     

Comparative study of the in vitro apatite-forming ability of poly(epsilon-caprolactone)-silica sol-gels using three osteoconductivity tests (static, dynamic, and alternate soaking process)

The in vitro apatite-forming ability of poly(epsilon-caprolactone) (70 wt %)-silica sol-gels, with hydroxyl and triethoxysilane end-groups with potential use in bone repair have been assessed using static and dynamic osteoconductivity tests. Diffuse reflectance infrared spectroscopy, scanning electron microscopy, and microanalysis techniques were used to observe and characterize precipitates formed on the material's surface. An apatite layer was observed to form on both of the composites' surface. However, variations were observed according to the test method used, in accordance with other studies on bioactive ceramics. A third method, the "alternate soaking process" (ASP) was developed to provide rapid results and quantify the amount of calcium-containing precipitates formed on the surface of potentially "bioactive" materials. The results presented here show that for a material to be bioactive and have the ability to form a precipitate containing calcium and phosphate ions, levels of calcium ions measured by a complexometric assay should be significantly higher than the level of 5 microg/cm(2). This level of calcium ions was obtained after 20 ASP cycles for the hydroxyl and triethoxysilane end-capped poly(epsilon-caprolactone) samples that did not form precipitates on their surfaces even after >50 ASP cycles. For the two sol-gel silica composites containing approximately 70% hydroxyl and triethoxysilane poly(epsilon-caprolactone), there was no significant difference in the amount of calcium-containing precipitate as observed using the in vitro apatite-forming ability tests suggesting that polymer end-group modification is not detrimental to the apatite-forming ability of such composites.     

Simple surface modification of poly(epsilon-caprolactone) to induce its apatite-forming ability

A biodegradable polymer coated with a bone-like apatite layer on its surface is useful as a scaffold for bone tissue regeneration. In this work, a poly(epsilon-caprolactone) (PCL) surface was modified by an O2 plasma surface treatment to form oxygen-containing functional groups. The plasma-treated samples were subsequently dipped alternately in an alcoholic solution containing calcium ions and one containing phosphate ions to deposit apatite precursors on the surface. The surface-modified PCL samples formed a dense and uniform surface bone-like apatite layer after immersion for 24 h in a simulated body fluid with ion concentrations approximately equal to those of human blood plasma. This surface-modification process is applicable to two-dimensional PCL plates and three-dimensional PCL meshes. In the resulting apatite-PCL composite, the apatite layer strongly adhered to the PCL surface and remained intact after a tape-detachment test. Therefore, this type of composite material will be a useful scaffold for bone tissue engineering.     

Degradation and cell culture studies on block copolymers prepared by ring opening polymerization of epsilon-caprolactone in the presence of poly(ethylene glycol)

Poly(epsilon-caprolactone) (PCL) and its block copolymers with poly(ethylene glycol) (PEG) were prepared by ring-opening polymerization of epsilon-caprolactone in the presence of ethylene glycol or PEG, using zinc metal as catalyst. The resulting polymers were characterized by various analytical techniques such as (1)H NMR, SEC, DSC, IR, X-ray, ESEM, and CZE. PCL/PEG copolymers with long PCL chains presented the same crystalline structure as PCL homopolymer, whereas PEG-bearing short PCL blocks retained the crystalline structure of PEG and exhibited an amphiphilic behavior in aqueous solutions. Degradation of PCL and PCL/PEG diblock and triblock copolymers was realized in a 0.13 M, pH 7.4 phosphate buffer at 37 degrees C. The results indicated that the copolymers exhibited higher hydrophilicity and degradability compared with the PCL homopolymer. Large amounts of PEG were released from the bulk after 60 weeks' degradation. In vitro cell culture studies were conducted on scaffolds manufactured via solid free form fabrication by using primary human and rat bone marrow derived stromal cells (hMSC, rMSC). Light, scanning electron, and confocal laser microscopy, as well as immunocytochemistry, showed cell attachment, proliferation, and extracellular matrix production on the surface, as well as inside the scaffold architecture. Copolymers showed better performance in the cell culture studies than the PCL homopolymer.     

Taxol-loaded block copolymer nanospheres composed of methoxy poly(ethylene glycol) and poly(epsilon-caprolactone) as novel anticancer drug carriers

We prepared the methoxy poly(ethylene glycol) (MePEG)/poly(epsilon-caprolactone) (PCL) amphiphilic block copolymeric nanospheres containing taxol which has promising anticancer activity. MePEG/PCL block copolymeric nanospheres (MEP50) showed a narrow size distribution and an average diameter of less than 100 nm. When the initial weight ratio of taxol to polymer was 0.5:1.0, we could obtain the nanospheres having a relatively high drug-loading of more than about 20%. The size of the MePEG/PCL nanospheres also increased according to the taxol loading. However, the nanospheres did not exhibit a significant change in the size distribution and also showed a size of less than 100 nm for even that with drug-loading content (DLC) of about 20%. From the 1H NMR analysis, we identified that the MePEG/PCL nanospheres prepared by dialysis procedure have core-shell structure consisting of the hydrophilic outer shell of MePEG and the hydrophobic inner core of PCL. We confirmed the low toxicity of MePEG/PCL nanospheres (MEP70) in the acute toxicity study using male ICR mice. In addition, considering the extremely lipophilic characteristics of taxol, this MePEG/PCL, nanosphere system with high taxol loading content and suspended properties in water could be useful for the delivery of taxol.     

Material model measurements and predictions for a random pore poly(epsilon-caprolactone) scaffold

We investigated material models for a polymeric scaffold used for bone. The material was made by co-extruding poly(epsilon-caprolactone) (PCL), a biodegradable polyester, and poly(ethylene oxide) (PEO). The water soluble PEO was removed resulting in a porous scaffold. The stress-strain curve in compression was fit with a phenomenological model in hyperbolic form. This material model will be useful for designers for quasi-static analysis as it provides a simple form that can easily be used in finite element models. The ASTM D-1621 standard recommends using a secant modulus based on 10% strain. The resulting modulus has a smaller scatter in its value compared with the coefficients of the hyperbolic model, and it is therefore easier to compare differences in material processing and ensure quality of the scaffold. A prediction of the small-strain elastic modulus was constructed from images of the microstructure. Each pixel of the micrographs was represented with a brick finite element and assigned the Young's modulus of bulk PCL or a value of 0 for a pore. A compressive strain was imposed on the model and the resulting stresses were calculated. The elastic constants of the scaffold were then computed with Hooke's law for a linear-elastic isotropic material. The model was able to predict the small-strain elastic modulus measured in the experiments to within one standard deviation. Thus, by knowing the microstructure of the scaffold, its bulk properties can be predicted from the material properties of the constituents.