Precipitation casting of polycaprolactone for applications in tissue engineering and drug delivery

In vitro and in vivo evaluation of the effects of demineralized bone matrix or calcium sulfate addition to polycaprolactone-bioglass composites

The objective of this study was to improve the efficacy of polycaprolactone/bioglass (PCL/BG) bone substitute using demineralized bone matrix (DBM) or calcium sulfate (CS) as a third component. Composite discs involving either DBM or CS were prepared by compression moulding. Bioactivity of discs was evaluated by energy dispersive X-ray spectroscopy (ESCA) and scanning electron microscopy (SEM) following simulated body fluid incubation. The closest Calcium/Phosphate ratio to that of hydroxyl carbonate apatite crystals was observed for PCL/ BG/DBM group (1.53) after 15 day incubation. Addition of fillers increased microhardness and compressive modulus of discs. However, after 4 and 6-week PBS incubations, PCL/BG/DBM discs showed significant decrease in modulus (from 266.23 to 54.04 and 33.45 MPa, respectively) in parallel with its highest water uptakes (36.3 and 34.7%). Discs preserved their integrity with only considerable weight loss (7.5-14.5%) in PCL/BG/DBM group. In vitro cytotoxicity tests showed that all discs were biocompatible.

Characterization and release behaviors of porous PCL/Eudragit RS microcapsules containing tulobuterol

In this work, porous poly(epsilon-caprolactone) (PCL)/Eudragit RS 100 (ERS-100) microcapsules containing tulobuterol base as a model drug were prepared by a solvent evaporation method and the effect of the quaternary ammonium groups of ERS-100 on the release behaviors of the microcapsules was investigated. The microcapsules prepared with PCL alone showed a stable and smooth surface, whereas porous microcapsules were formed with the addition of ERS-100. Drug loading and encapsulation efficiency of the microcapsules were slightly decreased with an increase of ERS-100 content, resulting from an increase in the porosity of the microcapsules. In an acidic release medium, PCL microcapsules showed slow drug release, whereas PCL/ERS-100 microcapsules showed a faster release rate with an increasing ERS-100 content. These behaviors are likely due to an increase in the diffusion rate of the drugs stemming from an increased hydration of the microcapsules, which results from the interaction between the carboxyl group of the release medium and the quaternary ammonium group of ERS-100.

Bacterial adhesion, cell adhesion and biocompatibility of Nafion films

We investigated bioadhesion (bacterial and cell adhesion) and biocompatibility of poly(tetrafluoroethylene-co-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acid) (Nafion) and compared the results with those obtained with poly(vinylidene fluoride-co-hexafluoropropylene) (PVFHFP). When incubated with bacteria for 4 h to 7 days, Nafion film exhibited scarce bacterial adhesion at 6 h, after which the adhesion gradually increasing to relatively low levels. In contrast, significant bacterial adhesion to PVFHFP film was observed at 4 h, and much higher adhesion levels were shown thereafter. Although HEp-2 human cells adhered normally to both films, reaching confluence in 7-8 days, the cells adhered to Nafion appeared more lively and stable than those to PVFHFP. Subcutaneous implantation in mice revealed that Nafion elicited a mild acute inflammatory reaction without chronic inflammation or tissue necrosis, indicating excellent biocompatibility in mice. PVFHFP, however, provoked a moderate and prolonged acute inflammatory response. These differences in the biological characteristics of Nafion and PVFHFP films may be attributable to the differences in the chemical and physical natures of these polymer films. Nafion film provided a sufficiently solid support, expressing a high surface charge density and good water-wettability. In summary, Nafion is suitable for use in biomedical applications that require biocompatibility with a reduced possibility of post-operative infections.

Multifunctional protein-encapsulated polycaprolactone scaffolds: fabrication and in vitro assessment for tissue engineering

Here we demonstrate the use of a twin screw extrusion/spiral winding (TSESW) process to generate protein-encapsulated tissue engineering scaffolds. Bovine serum albumin (BSA) was distributed into PCL matrix using both wet and hot melt extrusion methods. The encapsulation efficiency and the time-dependent release rate, as well as the tertiary structure of BSA (via circular dichroism), were investigated as a function of processing method and conditions. Within the relatively narrow processing window of this demonstration study it was determined that the wet extrusion method gave rise to greater stability of the BSA on the basis of circular dichroism data. The rate of proliferation of human fetal osteoblast (hFOB) cells and the rate of mineral deposition were found to be greater for wet extruded scaffolds, presumably due to the important differences in surface topographies (smoother scaffold surfaces upon wet extrusion). Overall, these findings suggest that the twin screw extrusion/spiral winding (TSESW) process offers significant advantages and flexibility in generating a wide variety of non-cytotoxic tissue engineering scaffolds with controllable distributions of porosity, physical and chemical properties and protein concentrations that can be tailored for the specific requirements of each tissue engineering application.

Immobilization of biomolecules on the surface of electrospun polycaprolactone fibrous scaffolds for tissue engineering

To make polycaprolactone (PCL) more suitable for tissue engineering, PCL in the form of electrospun fibrous scaffolds was first modified with 1,6-hexamethylenediamine to introduce amino groups on their surface. Various biomolecules, i.e., collagen, chitosan, and Gly-Arg-Gly-Asp-Ser (GRGDS) peptide, were then immobilized on their surface, with N,N'-disuccinimidylcarbonate being used as the coupling agent. Dynamic water contact angle measurement indicated that the scaffold surface became more hydrophilic after the aminolytic treatment and the subsequent immobilization of the biomolecules. The appropriateness of these PCL fibrous scaffolds for the tissue/cell culture was evaluated in vitro with three different cell lines, e.g., mouse fibroblasts (L929), human epidermal keratinocytes (HEK001), and mouse calvaria-derived preosteoblastic cells (MC3T3-E1). Both the neat and the modified PCL fibrous scaffolds released no substances in the levels that were harmful to these cells. Among the various biomolecule-immobilized PCL fibrous scaffolds, the ones that had been immobilized with type I collagen, a Arg-Gly-Asp-containing protein, showed the greatest ability to support both the attachment and the proliferation of all of the investigated cell types, followed by those that had been immobilized with GRGDS peptide.

Customizing the degradation and load-bearing profile of 3D polycaprolactone-tricalcium phosphate scaffolds under enzymatic and hydrolytic conditions

The degradation of polycaprolactone-20% tricalcium phosphate (PCL-TCP) scaffolds was customized for dentoalveolar augmentation applications, where 5-6 months period is optimal. The scaffolds were treated with either 3M sodium hydroxide (NaOH) or 0.1% lipase solution for a total of 108 h. A greater degree of degradation and reduction in the physical properties of the scaffolds was observed in the lipase treated when compared with NaOH-treated scaffolds. After 108 h, increases in weight loss and average porosity of the scaffolds in the lipase-treated group measured 90.6% and 22.9%, respectively, when compared with 52.8% and 11.8% in the NaOH-treated group. The mechanical testing results revealed a similar trend, with a complete loss of compressive strength and modulus measured as early as 60 h in the lipase-treated group. The honeycomblike architecture was well preserved throughout the experiment only for the NaOH-treated scaffolds in addition to a favorable surface roughness ideal for bone-regeneration applications. In conclusion, pretreatment with NaOH demonstrates a simple approach for tailoring the physical properties and degradation rate of PCL-TCP scaffolds for the potential use as biomaterials targeted for dentoalveolar bone-regeneration procedures.

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(epsilon-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 microm 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.

The synergic effect of polylactide fiber and calcium phosphate particle reinforcement in poly epsilon-caprolactone-based composite scaffolds

In this work, three-dimensional porous composite scaffolds, based on poly(epsilon-caprolactone) (PCL), were fabricated through the combination of a filament winding technique and a phase inversion/salt leaching process. Sodium chloride crystals were used as the porogen agent, and poly(lactic acid) (PLA) fibers and calcium phosphates as reinforcement. The aim of the current work is to assess the effective synergistic role of bioactive particles (i.e. alpha-tricalcium phosphates (alpha-TCP)) and PLA fibers on the morphology and mechanical response of the final scaffold. Morphological investigations performed on fiber-reinforced composite scaffolds with different PCL/alpha-TCP volume ratios (0%, 13%, 20% and 26%) show a high porosity degree (ca. 80%), pore interconnection and a homogeneous distribution of pores within the scaffold. More specifically, a bimodal pore size distribution was observed. This comprised microporosity (pores with radii ranging from 0.1 to 10 microm, which were strictly related to solvent extraction) and macroporosity (pores with radii from 10 to 300 microm, which were ascribable to the leaching of porogen elements). Static compressive tests showed that the effect of alpha-TCP on the mechanical response was to increase the elastic modulus up to a maximum value of 2.21+/-0.24 MPa, depending on the concentration of alpha-TCP added. This effect may be explained through the interaction of calcium-deficient hydroxyapatite crystals, formed as a consequence of a hydrolysis reaction of alpha-TCP, and the fiber-reinforced polymer matrix. The correct balance between chemical composition and spatial organization of reinforcement systems allows the attainment of an ideal compromise between mechanical response and bioactive potential, facilitating the development of composite scaffolds for bone tissue engineering applications.

Preparation and characterization of a novel bioactive restorative composite based on covalently coupled polyurethane-nanohydroxyapatite fibres

Nanohydroxyapatite (n-HAp) was prepared using a sol-gel method. n-HAp powder was obtained from the gel form by heat treatment followed by grinding using ball milling. A novel polyurethane composite material was prepared by chemically binding the hydroxyapatite to the diisocyanate component in the polyurethane backbone through solvent polymerization. The procedure involved the stepwise addition of monomeric units of the polyurethane and optimizing the reagent concentrations. The resultant composite material was electrospun to form fibre mats. The fibres were less than 1mum in thickness and contained no beads or irregularities. Chemical structural characterization of both the ceramics and the novel polymers were carried out by Fourier transform infrared and Raman spectroscopy. X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy and Brunauer-Emmett-Teller surface area analysis were also employed to observe the crystal lattice and size and surface area of the n-HAp. Further characterization (by energy-dispersive X-ray analysis and SEM) of the spun fibres revealed the presence of elements associated with hydroxyapatite and polyurethane without the presence of any loose particles of hydroxyapatite, indicating the formation of the covalent bond between the ceramics and the polymer backbone.

Effect of sterilisation by gamma irradiation on the ability of polycaprolactone (PCL) to act as a scaffold material

This paper investigates the effect of sterilisation by gamma irradiation (dose 2.5Mrad) on the following properties of polycaprolactone (PCL): (1) degradation rate (catalysed by lipase), (2) mechanical properties, (3) the ability of cells to attach and subsequently grow on its surface. Gel permeation chromatography (GPC) was used to determine the effects of gamma irradiation of weight average (M(w)) and number average (M(n)) molecular weights. Gamma irradiation significantly decreased the rate of degradation, although the rates depended on the initial mass of polymer; it also affected the appearance of the degraded specimens when they were examined by scanning electron microscopy. Irradiation also significantly increased the mechanical yield stress but not the failure stress of PCL. It caused a significant increase in M(w) and decrease in M(n) that could be attributed to chain scission and cross-linking. Chondrocyte attachment and growth on PCL was not significantly affected by gamma irradiation.

Effect of biomimetic conditions on mechanical and structural integrity of PGA/P4HB and electrospun PCL scaffolds

The selection of an appropriate scaffold represents one major key to success in tissue engineering. In cardiovascular applications, where a load-bearing structure is required, scaffolds need to demonstrate sufficient mechanical properties and importantly, reliable retention of these properties during the developmental phase of the tissue engineered construct. The effect of in vitro culture conditions, time and mechanical loading on the retention of mechanical properties of two scaffold types was investigated. First candidate tested was a poly-glycolic acid non-woven fiber mesh, coated with poly-4-hydroxybutyrate (PGA/P4HB), the standard scaffold used successfully in cardiovascular tissue engineering applications. As an alternative, an electrospun poly-epsilon-caprolactone (PCL) scaffold was used. A 15-day dynamic loading protocol was applied to the scaffolds. Additionally, control scaffolds were incubated statically. All studies were performed in a simulated physiological environment (phosphate-buffered saline solution, T=37 degrees C). PGA/P4HB scaffolds showed a dramatic decrease in mechanical properties as a function of incubation time and straining. Mechanical loading had a significant effect on PCL scaffold properties. Degradation as well as fiber fatigue caused by loading promote loss of mechanical properties in PGA/P4HB scaffolds. For PCL, fiber reorganization due to straining seems to be the main reason behind the brittle behavior that was pronounced in these scaffolds. It is suggested that those changes in scaffolds' mechanical properties must be considered at the application of in vitro tissue engineering protocols and should ideally be taken over by tissue formation to maintain mechanically stable tissue constructs.

Controlling protein release from scaffolds using polymer blends and composites

We report the development of three protein loaded polymer blend and composite materials that modify the release kinetics of the protein from poly(dl-lactic acid) (P(dl)LA) scaffolds. P(dl)LA has been combined with either poly(ethylene glycol) (PEG), poly(caprolactone) (PCL) microparticles or calcium alginate fibres using supercritical CO(2) (scCO(2)) processing to form single and dual protein release scaffolds. P(dl)LA was blended with the hydrophilic polymer PEG using scCO(2) to increase the water uptake of the resultant scaffold and modify the release kinetics of an encapsulated protein. This was demonstrated by the more rapid release of the protein when compared to the release rate from P(dl)LA only scaffolds. For the P(dl)LA/alginate scaffolds, the protein loaded alginate fibres were processed into porous protein loaded P(dl)LA scaffolds using scCO(2) to produce dual release kinetics from the scaffolds. Protein release from the hydrophilic alginate fibres was more rapid in the initial stages, complementing the slower release from the slower degrading P(dl)LA scaffolds. In contrast, when protein loaded PCL particles were loaded into P(dl)LA scaffolds, the rate of protein release was retarded from the slow degrading PCL phase.

Physical characterization of polycaprolactone scaffolds

Films and sponges were prepared from a solution of Poly(epsilon-caprolactone) (PCL) in tetrahydrofuran (THF). The porosity, crystallinity, and mechanical properties of the samples were studied. Porosity of around 15% was obtained for the films produced by evaporation of THF at room temperature. A much more porous structure (50-70%) was found for the sponges obtained by cooling the solution at -30 degrees C and subsequently eliminating the solvent by freeze drying. The porosity of the samples was also observed by scanning electron microscopy (SEM). The crystallinity of the samples was studied by the calorimetric technique (DSC) before and after the compression scans. The mechanical properties of the different samples were determined by compression test, and were compared to those corresponding to the PCL in bulk. The compression scans did not affect the crystallinity of the samples. The variations observed in the results of the different scans were attributed to the differences in porosities and crystallinity.

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.

Electroactive Oligoaniline-Containing Self-Assembled Monolayers for Tissue Engineering Applications

A novel electroactive silsesquioxane precursor, N-(4-aminophenyl)-N'-(4'-(3-triethoxysilyl-propyl-ureido) phenyl-1,4-quinonenediimine) (ATQD), was successfully synthesized from the emeraldine form of amino-capped aniline trimers via a one-step coupling reaction and subsequent purification by column chromatography. The physicochemical properties of ATQD were characterized using mass spectrometry as well as by nuclear magnetic resonance and UV-vis spectroscopy. Analysis by cyclic voltammetry confirmed that the intrinsic electroactivity of ATQD was maintained upon protonic acid doping, exhibiting two distinct reversible oxidative states, similar to polyaniline. The aromatic amine terminals of self-assembled monolayers (SAMs) of ATQD on glass substrates were covalently modified with an adhesive oligopeptide, cyclic Arg-Gly-Asp (RGD) (ATQD-RGD). The mean height of the monolayer coating on the surfaces was approximately 3 nm, as measured by atomic force microscopy. The biocompatibility of the novel electroactive substrates was evaluated using PC12 pheochromocytoma cells, an established cell line of neural origin. The bioactive, derivatized electroactive scaffold material, ATQD-RGD, supported PC12 cell adhesion and proliferation, similar to control tissue-culture-treated polystyrene surfaces. Importantly, electroactive surfaces stimulated spontaneous neuritogenesis in PC12 cells, in the absence of neurotrophic growth factors, such as nerve growth factor (NGF). As expected, NGF significantly enhanced neurite extension on both control and electroactive surfaces. Taken together, our results suggest that the newly electroactive SAMs grafted with bioactive peptides, such as RGD, could be promising biomaterials for tissue engineering.

Synthesis of novel cholic acid functionalized branched oligo/poly(ɛ-caprolactone)s for biomedical applications

Novel cholic acid functionalized branched oligo/poly(epsilon-caprolactone)s were synthesized through the ring-opening polymerization of epsilon-caprolactone initiated by cholic acid with hydroxyl groups. The molecular weight of the branched polymers can be adjusted by controlling the feed ratio of the initiator cholic acid to the monomer epsilon-caprolactone. Comparing with linear homopolymer poly(epsilon-caprolactone) (PCL), these branched oligo/poly(epsilon-caprolactone)s show much faster hydrolytic degradation rates, implies that our approach provides a convenient and effective strategy to accelerate degradation of the biodegradable polymers with slow degradation rates such as PCL. The cell culture experiment indicates the incorporation of cholic acid moiety to the polymer chain can improve both cell adherence and proliferation obviously.

Molar mass dependent growth of poly(epsilon-caprolactone) crystals in Langmuir films

Poly(epsilon-caprolactone) (PCL) samples with number average molar masses (Mn) ranging from 3.5 to 36 kg.mol-1 exhibit molar mass dependent nucleation and growth of crystals, crystal morphologies, and melting properties at a temperature of 22.5 degrees C in Langmuir films at the air/water (A/W) interface. At surface area per monomer, A, greater than approximately 0.37 nm2.monomer-1, surface pressure, Pi, and surface elasticity exhibit molar mass independent behavior that is consistent with a semidilute PCL monolayer. In this regime, the scaling exponent indicates that the A/W interface is a good solvent for the liquid-expanded PCL monolayers. Pi-A isotherms show molar mass dependent behavior in the vicinity of the collapse transition, i.e., the supersaturated monolayer state, corresponding to the onset of the nucleation of crystals. Molar mass dependent morphological features for PCL crystals and their subsequent crystal melting are studied by in situ Brewster angle microscopy during hysteresis experiments. The competition between lower segmental mobility and a greater degree of undercooling with increasing molar mass produces a maximum average growth rate at intermediate molar mass. This behavior is analogous to spherulitic growth in bulk PCL melts. The plateau regions in the expansion isotherms represent the melting process, where the polymer chains continuously return to the monolayer state. The magnitude of Pi for the plateau during expansion decreases with increasing molar mass, indicating that the melting process is strongly molar mass dependent.

Microhardness of starch based biomaterials in simulated physiological conditions

In this work the variation of the surface mechanical properties of starch-based biomaterials with immersion time was followed using microhardness measurements. Two blends with very distinct water uptake capabilities, starch/cellulose acetate (SCA) and starch/poly(epsilon-caprolactone) (SPCL), were immersed in a phosphate buffer solution (PBS) at 37.5 degrees C for various times. The microhardness of the blends decreased significantly ( approximately 50% for SPCL and approximately 94% for SCA), within a time period of 30 days of immersion, reflecting the different hydrophilic character of the synthetic components of the blends. The dependence of microhardness on the applied loading time and load was also analysed and showed a power law dependency for SCA. Water uptake and weight loss measurements were performed for the same immersion times used in the microhardness experiments. The different swelling/degradation behaviour presented by the blends was related to the respective variation in microhardness. Moreover, complementary characterization of the mechanical properties of SCA and SPCL was accomplished by dynamic mechanical analysis (DMA) and creep measurements. Microhardness measurements proved to be a useful technique for characterizing the mechanical behaviour near the surface of polymeric biomaterials, including in simulated physiological conditions.

Development of a new calcium sulphate-based composite using alginate and chemically modified chitosan for bone regeneration

In this work we developed a novel calcium sulphate-based composite in which the hemihydrate calcium sulphate (CHS) can be encapsulated in a polymeric biodegradable and biocompatible matrix, in order to retain the structural integrity and decrease the bioresorption rate in bone regeneration applications. Two polymers were employed to realize this system: chitosan (Ch) and sodium alginate (Alg), both already widely used in biotechnological and biomedical applications. Chitosan was modified in order to obtain a water soluble polymer, the N-succinylchitosan (sCh). The reaction was performed with succinic anhydride in presence of pyridine and confirmed by FT-IR and NMR analyses. Finely ground Alg and sCh powders were mixed in different compositions with CHS and by adding water to the powder mixture it was obtained a mouldable paste that sets in few hours. Thermogravimetric analyses coupled with solvent extraction performed on the composite proved the alginate crosslinking in the presence of CHS. Mechanical studies carried out on composites of different compositions demonstrated that the blend of the two polymeric components causes a substantial synergistic reinforcement of composites. The presence of carboxylic groups on sCh chain in addition to those of alginate could enhance the chelating power of polysaccharide mixture. The results obtained with morphological analyses (SEM) further confirmed the hypotesis of the synergistic effect between alginate and N-succinylchitosan in presence of calcium sulphate. In vitro cytotoxicity tests proved that the developed system was not cytotoxic.

Human bone marrow stromal cells: In vitro expansion and differentiation for bone engineering

Stromal cells from marrow hold a great promise for bone regeneration. Even if they are already being exploited in many clinical settings, the biological basis for the source and maintenance of their proliferation/differentiation potential after in vitro isolation and expansion needs further investigation. Most studies on osteogenic differentiation of marrow stromal cells (MSC) have been performed using bone marrow from the iliac crest. In this study, MSC were derived from spare femoral bone marrow obtained during hip replacement surgery from 20 adult donors. After in vitro isolation the cells were grown in osteogenic medium, and their proliferation and differentiation analysed during in vitro expansion. We found that MSC isolated from the femur of adult patients consistently maintain an osteogenic potential. Using biochemical signals, these cells turn to fully differentiated osteoblasts with a predictable set of molecular and phenotypic events of in vitro bone deposition. When seeded on polycaprolactone-based scaffold or surfaces, the proliferation and mineralization of femur-derived MSC were modulated by the surface chemistry/topography. Despite remarkable differences between individual colony-forming ability, alkaline phosphatase production, and mineralization ability, these cells are a potential source for bone engineering, either by direct autologous reimplantation or by ex vivo expansion and reimplantation combined to a proper scaffold.

Stem cell-based tissue engineering with silk biomaterials

Silks are naturally occurring polymers that have been used clinically as sutures for centuries. When naturally extruded from insects or worms, silk is composed of a filament core protein, termed fibroin, and a glue-like coating consisting of sericin proteins. In recent years, silk fibroin has been increasingly studied for new biomedical applications due to the biocompatibility, slow degradability and remarkable mechanical properties of the material. In addition, the ability to now control molecular structure and morphology through versatile processability and surface modification options have expanded the utility for this protein in a range of biomaterial and tissue-engineering applications. Silk fibroin in various formats (films, fibers, nets, meshes, membranes, yarns, and sponges) has been shown to support stem cell adhesion, proliferation, and differentiation in vitro and promote tissue repair in vivo. In particular, stem cell-based tissue engineering using 3D silk fibroin scaffolds has expanded the use of silk-based biomaterials as promising scaffolds for engineering a range of skeletal tissues like bone, ligament, and cartilage, as well as connective tissues like skin. To date fibroin from Bombyx mori silkworm has been the dominant source for silk-based biomaterials studied. However, silk fibroins from spiders and those formed via genetic engineering or the modification of native silk fibroin sequence chemistries are beginning to provide new options to further expand the utility of silk fibroin-based materials for medical applications.

Experimental investigation of interfaces in hydroxyapatite/polyacrylic acid/polycaprolactone composites using photoacoustic FTIR spectroscopy

Molecular interactions in hydroxyapatite (HAP) polymer composites have been studied using photoacoustic spectroscopy. HAP is mineralized by wet precipitation under two conditions: first is in the absence of polyacrylic acid (PAAc) (ex-situ HAP) and second in the presence of PAAc (in-situ HAP). Porous and solid composites of ex-situ and in-situ HAP with polycaprolactone (PCL) have also been made to evaluate their applicability as bone scaffolds. Photoacoustic Fourier transform infrared (PA-FTIR) spectroscopy studies indicate that both in-situ and ex-situ HAP have HPO4 (2-) in their structure, which leads to Ca2+ deficiency. During crystallization of in-situ HAP, PAAc dissociates to form carboxylate ions, which binds to calcium ions and act as suitable site for nucleation for HAP crystallization. PA-FTIR spectra of porous and solid composites indicate that porous composites adsorb more water, which is hydrogen bonded with carbonyl of PCL. Mechanical tests on solid samples indicate that ex-situ HAP/PCL composites have higher elastic modulus than in-situ HAP/PCL composites. However, in case of porous composites, in-situ HAP/PCL composites are found to have higher elastic modulus. In-situ HAP is chemically and structurally different from ex-situ HAP. This modified HAP causes variation in microstructure of porous composite and hence alteration of its load transfer mechanisms and hence mechanical properties.

Blending chitosan with polycaprolactone: effects on physicochemical and antibacterial properties

Chitosan is a well sought-after polysaccharide in biomedical applications and has been blended with various macromolecules to mitigate undesirable properties. However, the effects of blending on the unique antibacterial activity of chitosan as well as changes in fatigue and degradation properties are not well understood. The aim of this work was to evaluate the anti-bacterial properties and changes in physicochemical properties of chitosan upon blending with synthetic polyester poly(epsilon-caprolactone) (PCL). Chitosan and PCL were homogeneously dissolved in varying mass ratios in a unique 77% acetic acid in water mixture and processed into uniform membranes. When subjected to uniaxial cyclical loading in wet conditions, these membranes sustained 10 cycles of predetermined loads up to 1 MPa without break. Chitosan was anti-adhesive to Gram-positive Streptococcus mutans and Gram-negative Actinobacillus actinomycetemcomitans bacteria. Presence of PCL compromised the antibacterial property of chitosan. Four-week degradation studies in PBS/lysozyme at 37 degrees C showed initial weight loss due to chitosan after which no significant changes were observed. Molecular interactions between chitosan and PCL were investigated using Fourier transform infrared spectroscopy (FTIR) which showed no chemical bond formations in the prepared blends. Investigation by wide-angle X-ray diffraction (WAXD) indicated that the crystal structure of individual polymers was unchanged in the blends. Dynamic mechanical and thermal analysis (DMTA) indicated that the crystallinity of PCL was suppressed and its storage modulus increased with the addition of chitosan. Analysis of surface topography by atomic force microscopy (AFM) showed a significant increase in roughness of all blends relative to chitosan. Observed differences in biological and anti-bacterial properties of blends could be primarily attributed to surface topographical changes.

Poly(epsilon-caprolactone) biomaterial sterilized by E-beam irradiation

The effects of ionizing radiation (electron beam) on poly(epsilon-caprolactone) (PCL) were studied by analyzing changes in viscosity-average and weight-average molecular weight and radius of gyration, and by performing sol-gel analysis and swelling tests. Samples were irradiated under various conditions: solid and molten PCL in the presence or absence of air. The overall efficiency of crosslinking is higher for samples irradiated in the molten state than in the solid state, and is reduced in the presence of oxygen. Based on three kinds of experiments (molecular weight dependence on the dose in the pre-gelation region, sol-gel analysis, and swelling study), radiation-chemical yields of intermolecular crosslinking and scission were determined and are discussed in terms of the mechanism of radiation-induced reactions in PCL. Properties of the gels formed by high-dose irradiation and mechanical properties of irradiated PCL were analyzed. Irradiation causes an increase in the compression modulus of PCL. This process occurs at the pre-gelation stage and continues in the gel-containing system. We have demonstrated, for the first time, that irradiation of solid PCL is accompanied by a pronounced post-effect, which manifests itself by changes in the average molecular weight. EPR data indicate that this effect, at least in part, is caused by the presence of long-lived radicals trapped in the crystalline regions. Irradiation with the sterilizing dose does not cause a statistically significant change in the biocompatibility of PCL after subsequent storage for 79 d, as determined by preliminary osteoblast vitality tests.

Degradação acelerada de suportes de poli(épsilon-caprolactona) e poli(D,L-ácido láctico-co-ácido glicólico) em meio alcalino

O estudo da degradação in vitro de polímeros bioreabsorvíveis em soluções alcalinas vem sendo proposto nos últimos anos como alternativa aos estudos tradicionais feitos em tampão fosfato. Este trabalho descreve a degradação acelerada de poli(épsilon-caprolactona) (PCL) e poli(D,L-ácido láctico-co-ácido glicólico) (50/50) (PLGA50), polímeros biodegradáveis e bioreabsorvíveis, amplamente estudados em aplicações biomédicas. Amostras foram preparadas pelo método de fusão seguido de injeção em molde cilíndrico (2 mm diâmetro), a 160 ºC, e submetidas à degradação em soluções de NaOH em pH 12, 13 e 13,7 a 37 ºC. Por meio da caracterização da variação da massa, morfologia e propriedades térmicas, por calorimetria exploratória diferencial, os resultados mostraram que as amostras de PCL são mais estáveis quando comparadas às de PLGA50. Pela taxa de variação das propriedades térmicas foi possível extrapolá-las em função do tempo em pH fisiológico, 7,4. Validado, o estudo da degradação acelerada em meio alcalino mostrou-se como uma técnica útil e de baixo custo para avaliar o comportamento em curtos períodos de degradação.

Poly-epsilon-caprolactone/hydroxyapatite composites for bone regeneration: in vitro characterization and human osteoblast response

Polycaprolactone (PCL), a semicrystalline linear resorbable aliphatic polyester, is a good candidate as a scaffold for bone tissue engineering, due to its biocompatibility and biodegradability. However, the poor mechanical properties of PCL impair its use as scaffold for hard tissue regeneration, unless mechanical reinforcement is provided. To enhance mechanical properties and promote osteoconductivity, hydroxyapatite (HA) particles were added to the PCL matrix: three PCL-based composites with different volume ratio of HA (13%, 20%, and 32%) were studied. Mechanical properties and structure were analysed, along with biocompatibility and osteoconductivity. The addition of HA particles (in particular in the range of 20% and 32%) led to a significant improvement in mechanical performance (e.g., elastic modulus) of scaffold. Saos-2 cells and osteoblasts from human trabecular bone (hOB) retrieved during total hip replacement surgery were seeded onto 3D PCL samples for 1-4 weeks. Following the assessment of cell viability, proliferation, morphology, and ALP release, HA-loaded PCL was found to improve osteoconduction compared to the PCL alone. The results indicated that PCL represents a potential candidate as an efficient substrate for bone substitution through an accurate balance between structural/ mechanical properties of polymer and biological activities.

Alkaline-treated poly(ε-caprolactone) films: Degradation in the presence or absence of fibroblasts

In the first stage, we observed the study of the degradation behavior of alkaline-treated poly(epsilon-caprolactone) (PCL) in two biologically-related media: phosphate buffered saline (PBS) and Dulbecco's modified Eagle's medium (DMEM) for 18 months, finding a much accelerated degradation in the last one. As expected, the degradation in the presence of cells is much pronounced even considering that the study is limited to 6 months. The characterization of the degraded substrates by chemiluminescence (CL) allows to explain the modifications of the substrate and their relations with transitory oxidative stress phenomena described in the fibroblasts seeded onto the PCL membranes.