Haemorrhoidal haemodynamic changes in patients with haemorrhoids treated using Doppler-guided dearterialization.

BACKGROUND: Arterial hyperflow to haemorrhoids has been implicated as a possible pathophysiological co-factor in haemorrhoidal disease. The purpose of this study was to investigate how transanal haemorrhoidal dearterialization (THD) can influence haemodynamic parameters at the level of the haemorrhoidal piles. METHODS: Patients with grade III haemorrhoids selected for THD between July and December 2018 were evaluated using endoanal ultrasonography and colour Doppler imaging at the level of internal haemorrhoids before and 1 year after the surgical procedure. Peak systolic velocity, pulsatility index, resistivity index, acceleration time, and end-diastolic velocity were measured, and preoperative and postoperative values compared. Symptom severity was measured using a symptom-based questionnaire (score range 0-20). RESULTS: Of 21 patients treated, 17 completed the study. Compared with preoperative values, postoperative peak systolic velocity (mean(s.d.) 18.7(1.1) versus 10.3(0.4) cm/s; P < 0.05), pulsatility index (5.5(0.3) versus 2.8(0.4); P < 0.050), and resistivity index (1.0(0.2) versus 0.8(0.5); P < 0.050) decreased significantly, whereas acceleration time increased significantly (65.6(3.6) versus 83.3(4.7) cm/s2; P < 0.050); end-diastolic velocity did not change (1.9(0.2) versus 2.0(0.4); P = 0.753). Symptoms disappeared or had improved significantly in all patients by 1 year after surgery. The mean(s.d.) total symptom severity score decreased from 15.8(1.1) to 1.2(1.6) (P < 0.001). CONCLUSION: THD affects the main haemodynamic parameters at the level of internal haemorrhoids and is associated with a decrease in arterial hyperflow.

Spiramyin-loaded PLGA implants for the treatment of ocular toxoplasmosis: development, characterization, biocompatibility, and anti-toxoplasma activity.

Ocular toxoplasmosis is the major cause of infectious posterior uveitis worldwide, inducing visual field defect and/or blindness. Despite the severity of this disease, an effective treatment is still lacking. In this study, spiramycin-loaded PLGA implants were developed aiming at the treatment of ocular toxoplasmosis. Implants were manufactured by a hot-molding technique, characterized by Fourier Transform Infrared Spectroscopy, X-Ray Diffraction, Differential Scanning Calorimetry, Scanning Electron Microscopy; evaluated in terms of ocular biocompatibility by immunofluorescence, flow cytometry, cell migration, Hen's egg test-chorioallantoic membrane (HET-CAM) irritation test; and investigated in terms of in vitro efficacy against Toxoplasma gondii . Characterization techniques indicated that spiramycin was dispersed into the polymeric chains and both substances preserved their physical structures in implants. The HET-CAM test indicated that implants did not induce hemorrhage or coagulation, being non-irritant to the CAM. ARPE-19 cells showed viability by MTT assay, and normality in cell cycle kinetics and morphology, without stimulating cell death by apoptosis. Finally, they were highly effective against intracellular parasites without inducing human retinal pigment epithelial cell death. In conclusion, spiramycin-loaded PLGA implants represent a promising therapeutic alternative for the local treatment of ocular toxoplasmosis.

Simple fistula-in-ano: is it all simple? A systematic review.

BACKGROUND: Simple anal fistula is one of the most common causes of proctological surgery and fistulotomy is considered the gold standard. This procedure, however, may cause complications. The aim of this systematic review was to assess the surgical treatment of simple anal fistula with traditional and sphincter-sparing techniques. METHODS: A literature research was performed using PubMed, Cochrane, and Google Scholar to identify studies on the surgical treatment of simple anal fistulas. Observational studies and randomized clinical trials were included. We assessed the risk of bias of included studies using the Jadad scale for randomized controlled trials, and the MINORS Scale for the remaining studies. RESULTS: The search returned 456 records, and 66 studies were found to be eligible. The quality of the studies was generally low. A total of 4883 patients with a simple anal fistula underwent a sphincter-cutting procedure, mainly fistulotomy, with a weighted average healing rate of 93.7%, while any postoperative continence impairment was reported in 12.7% of patients. Sphincter-sparing techniques were adopted to treat 602 patients affected by simple anal fistula, reaching a weighted average success rate of 77.7%, with no study reporting a significant postoperative incontinence rate. The postoperative onset of fecal incontinence and the recurrence of the disease reduced patients' quality of life and satisfaction. CONCLUSIONS: Surgical treatment of simple anal fistulas with sphincter-cutting procedures provides excellent cure rates, even if postoperative fecal incontinence is not a negligible risk. A sphincter-sparing procedure could be useful in selected patients.

Immunology and the immunological response in pregnancy.

The immune system in humans is a complex system capable of discriminating self from non-self, and mounting appropriate allogenic immune responses to protect themselves from foreign organisms. This system is made up of two arms of defense: the first one is a non-specific arm (innate), in which humans are born with and do not require antigenic recognition. The second one is specific arm (humoral) involving B and T cells that are capable of mounting responses to particular antigen with immense specificity. Both of these systems importantly interact with each other to protect humans in the most effective and efficient manner. Defects or malfunctions in these systems can result in a variety of illnesses and conditions. The immunology of pregnancy is a very unique, highly controlled system, which allows for survival of a fetus (semi-allograft), whilst simultaneously protecting a pregnant woman. There are immune shifts in pregnancy, which are well established to facilitate maternal-fetal tolerance. This promotes the concept that the immune system is not suppressed, but instead modulated to facilitate a pregnancy and explain the differential response to various pathogens in pregnancy. During pregnancy, the development of a fetal immunological system also occurs with intricate interaction between the maternal and fetal interface. The mechanism is preterm and term birth is poorly understood, but the immunological response has been well documented for both the pathological and physiological scenarios.

Management of hemorrhoidal disease: new generation of oral and topical treatments.

Hemorrhoidal disease is a widespread proctologic clinical entity. Even if surgical excision is an effective treatment, it only represents the standard procedure for patients with high-grade hemorrhoids. Considering that most cases are grade I or II hemorrhoids, oral or topical therapies are widely used despite, currently, there are no satisfactory options for these kinds of treatments. The pathology involves the degeneration of the supporting tissue of the anal cushions, causing venous dilation, blood stagnation, formation of edematous venous plexus covered by mucosa and inflammation. An effective treatment must, therefore, be multi-targeted and capable of acting on all the pathological mechanisms simultaneously. During the 8th National Congress of the Italian Association of Colorectal Surgery (SICCR), some clinical evidence of hemorrhoidal disease has been discussed along with new opportunities in oral and topical treatment options. Among these, the effectiveness and the safety of two innovative products, a sublingual nanoemulsion and a liquid bandage, has been reported.

Efficacy of Sphinkeeper™ implant in treating faecal incontinence.

The primary aim of this prospective study was to assess the efficacy of Sphinkeeper™ (SK) implantation in patients with faecal incontinence. Forty-two patients with faecal incontinence (14 with sphincter defects) underwent SK implantation and were followed up for a mean(s.d.) of 15·9(8·6) months. SK implantation was a safe and effective method that improved patients' quality of life. Implants and incontinence.

Fistulotomy and primary sphincteroplasty for anal fistula: long-term data on continence and patient satisfaction.

BACKGROUND: The aim of this study was to evaluate the safety and long-term efficacy of fistulotomy and primary sphincteroplasty (FIPS). Secondary endpoints were its impact on postoperative continence status and patients' satisfaction. METHODS: A retrospective study was conducted on patients with cryptoglandular anal fistula (AF) who had FIPS between June 2006 and May 2017. Patients were evaluated with standardized telephone interviews and clinical/instrumental assessment. Main outcome measures included fistula healing rate, continence status, and patient satisfaction. Incontinence was defined as an inability to hold either gas, liquid, or solid stools, as well as postdefecation soiling, and was measured by the Cleveland Clinic fecal incontinence score. Patient satisfaction was evaluated by an 11-point numeric rating scale. RESULTS: There were 203 patients (139 males; mean age: 48.7 years) who had FIPS. The overall healing rate was 93% (188 patients) with a mean follow-up period of 56 ± 31 months. Half of the total cohort (51%) had a complex fistula. Preoperatively, 8 (4%) patients complained of postdefecation soiling and 2 (1%) of gas incontinence. Postoperatively, 26 (13%) patients had continence impairment (de novo n = 24), mainly consisting of postdefecation soiling (10%). In univariate analysis, patients with recurrent (RR 6.153 95% CI 2.097-18.048; p = 0.002) or complex (RR 3.005 95% CI 1.203-7.506; p = 0.012) AF and those with secondary tracts (RR 8.190 95% CI 2.188-30.654; p = 0.004) or previous set on drainage (RR 5.286 95% CI 2.235-12.503; p = 0.0001) were at higher risk of incontinence. In multivariate analysis, no significant predictors were found, although fistula complexity approached statistical significance (RR 5.464 95% CI 0.944-31.623; p = 0.050). The mean patient satisfaction numeric rating scale was 9.3 ± 1.6. Lower satisfaction rates were found in patients with transphincteric (p = 0.011) or complex (p = 0.0001) AF, with secondary tracts (p = 0.041) or previous seton drainage (p = 0.008), and in those with postoperative continence impairment (p = 0.0001). Postoperative onset of incontinence was the only significant factor in multivariate analysis (p = 0.0001). CONCLUSIONS: FIPS should be considered a valid therapeutic option for selected AF. However, the risk of postoperative minor fecal incontinence exists, and should be discussed during preoperative patient counselling.

Antiangiogenic activity of a bevacizumab-loaded polyurethane device in animal neovascularization models.

PURPOSE: To evaluate the antiangiogenic activity of bevacizumab-loaded polyurethane using two animal models of neovascularization. METHODS: The percentage of blood vessels was evaluated in a chicken chorioallantoic membrane model (n=42) and in the rabbit cornea (n=24) with neovascularization induced by alkali injury. In each model, the animals were randomly divided into the groups treated with the bevacizumab-loaded polyurethane device, phosphate-buffered-saline (negative control) and bevacizumab commercial solution (positive control). Clinical examination, as well as histopathological and immunohistochemical evaluation, were performed in the rabbit eyes. Microvascular density in hot spot areas was determined in semi-thin sections of corneal tissue by hematoxylin-eosin staining and factor VIII immunohistochemistry. Immunohistochemical analysis was also performed to evaluate VEGF expression. RESULTS: In the evaluated models, the use of bevacizumab (Avastin®) and the bevacizumab-loaded polyurethane device led to similar results with regard to inhibition of neovascularization. In the chorioallantoic membrane model, the bevacizumab-loaded polyurethane device reduced angiogenesis by 50.27% when compared to the negative control group. In the rabbit model of corneal neovascularization, the mean density of vessels/field was reduced by 46.87% on analysis of factor VIII immunohistochemistry photos in the bevacizumab-loaded polyurethane device group as compared to the negative control (PBS) sections. In both models, no significant difference could be identified between the bevacizumab-loaded polyurethane device and the positive control group, leading to similar results with regard to inhibition of neovascularization. CONCLUSIONS: The present study shows that the bevacizumab-loaded polyurethane device may release bevacizumab and inhibit neovascularization similarly to commercial bevacizumab solution in the short-term.

Papain wound dressings obtained from poly(vinyl alcohol)/calcium alginate blends as new pharmaceutical dosage form: Preparation and preliminary evaluation.

Transparent, soft, flexible, mechanically resistant films, which are ideal for use as wound dressings were prepared in the presence of 2% papain, a proteolytic enzyme that can play a role in the chemical debridement of the skin and can accelerate the healing process. The films, based on poly(vinyl alcohol):calcium alginate blends with increasing concentrations of polysaccharide (10, 20, and 30% v/v), were obtained by casting method. FTIR and DSC analyses were performed to assess the composition and miscibility of blends. Mechanical properties such as tensile strength, elasticity modulus, and elongation at breakpoint were evaluated. The influence of different concentrations of calcium alginate on physical attributes of films like wettability, swelling capacity and mechanical properties was determined. The stability of papain in the films was assessed indirectly by hemolytic activity assay employing direct contact method and confirmed by technique based on blood agar diffusion. Preliminary cytotoxicity was evaluated with the XTT method. The results showed that at the polymer concentrations tested, the blends were miscible. The increase in the content of the calcium alginate increased the wettability and swelling capacity of the films, which is desirable in wound dressings. On the other hand, mechanical resistance decreased without causing breakage of the films during the swelling tests. The hemolytic activity of the films was maintained during the studied period, suggesting the stability of papain in the proposed formulations. Cellular viability indicated that the films were non-toxic. The analysis of the results showed that it is possible to prepare interactive and bioactive wound dressing containing papain from blends of PVA and calcium alginate polymers.

IFPA meeting 2015 workshop report II: mechanistic role of the placenta in fetal programming; biomarkers of placental function and complications of pregnancy.

Workshops are an integral component of the annual International Federation of Placenta Association (IFPA) meeting, allowing for networking and focused discussion related to specialized topics on the placenta. At the 2015 IFPA meeting (Brisbane, Australia) twelve themed workshops were held, three of which are summarized in this report. These workshops focused on various aspects of placental function, particularly in cases of placenta-mediated disease. Collectively, these inter-connected workshops highlighted the role of the placenta in fetal programming, the use of various biomarkers to monitor placental function across pregnancy, and the clinical impact of novel diagnostic and surveillance modalities in instances of late onset fetal growth restriction (FGR).

Design, characterization and preliminary in vitro evaluation of a mucoadhesive polymer based on modified pectin and acrylic monomers with potential use as a pharmaceutical excipient.

Bio-based polymers have been reported to have applications in biomedical and pharmaceutical areas. Polysaccharides, especially prepared from plant sources, have served a variety of uses. This work aims to prepare a polymer for use as a pharmaceutical excipient containing a functionalized carbohydrate (pectin) and acrylic monomers (methyl methacrylate, butyl methacrylate and ethyl acrylate) via an emulsion polymerization technique. Carbon double bonds were incorporated into the pectin by reacting this natural polymer with glycidyl methacrylate. The methacrylated pectin was then polymerized with acrylic monomers by emulsion polymerization. The mucoadhesive performance of the materials was investigated by in vitro preliminary assays based on viscometric studies, texture analysis and film wettability. The obtained results showed that the synergistic viscosity increase with greater concentrations of modified pectin. The contact angle decreased, suggesting an increase in the wettability for polymers with large amounts of methacrylated pectin. The addition of mucin in lattices caused an increase in the intermolecular forces and in the work of adhesion. This corroborates the use of pectin as a mucoadhesive excipient for mucoadhesive drug delivery systems.

The effect of light-curing access and different resin cements on apical bond strength of fiber posts.

PURPOSE: This study evaluated the effect of light-curing access on the bond strength of fiber glass posts to the apical area of bovine roots using self-adhesive cement or dual-cured cement with an etch-and-rinse adhesive system. MATERIALS AND METHODS: The root canals of 60 bovine teeth were endodontically treated and filled. A 15-mm-length post space was prepared and roots were randomly divided into three groups, simulating the levels of light-curing access: coronal (C), with 15-mm post space; middle (M), in which the coronal thirds of roots were cut out, leaving a 10-mm post space; and apical (A), in which the coronal and middle thirds of roots were cut out, leaving a 5-mm post space. Fiber glass posts (Reforpost # 3, Angelus) were cemented with RelyX U100 (3M ESPE) or RelyX ARC/Scotchbond Multi Purpose Plus (SBMP) (3M ESPE) (n=10) and light-cured. After 24 hours, the apical thirds of roots were sectioned perpendicularly to the long axis and submitted to a push-out test (0.5 mm/min, 200 N). The Kruskal-Wallis test compared the three levels of light-curing access, and the Mann-Whitney test compared the cements. RESULTS: The bond strength was significantly higher in the groups C (p=0.028) and M (p=0.016) when U100 was used, whereas it was similar for both cements in group A. The bond strengths of posts cemented with ARC/SBMP were significantly higher in group A compared to group C (p=0.031). CONCLUSIONS: The type of cement used and the light-curing access level influenced the bond strength between glass fiber posts and root canals. The bond strength of the RelyX ARC/SBMP cement proved to be more dependent on photoactivation than was the RelyX U100 cement. The light-curing access level did not influence the apical bond strength of RelyX U100.

Design of prolonged release tablets using new solid acrylic excipients for direct compression.

The design of new excipients that extend the release of drugs from tablets over prolonged periods is essential in reaching enhanced therapeutic performances. In this sense, the objective of this study was to develop new excipients, based on acrylic monomers (ethyl acrylate, methyl methacrylate, and butyl methacrylate) for use in direct compression (DC). The polymeric excipients were prepared by suspension and emulsion polymerization reactions and were characterized by FTIR to confirm the polymerization reaction. For the success of direct compression, excipients must present good flow and compactability properties. Therefore, excipients were submitted to analysis of morphology (SEM), particle size and size distribution by laser diffraction, and powder density (bulk density and tapped density). The Carr index, Hausner ratio, flow ratio, and cotangent of the angle α were determined. Thereafter, the polymeric excipients were used to prepare inert matrices by DC using propranolol hydrochloride (PHCl) as a model drug. The tablets were evaluated for average weight, breaking force, and friability tests. The release profiles were determined, and the dissolution kinetics was studied. The results indicated that matrices prepared from excipients obtained by suspension polymerization (NWCB and PECB) presented a release of PHCl for a period exceeding 12h, most likely due to the higher micromeritic properties. The results suggested that the increase in the percentage of polymers, as well as in the compression time, resulted in a higher hardness of the matrix with a reduced rate release of the PHCl. Finally, in vitro preliminary tests showed that the polymeric excipients produced were non-toxic for the gingival fibroblasts.

In vivo tests of a novel wound dressing based on biomaterials with tissue adhesion controlled through external stimuli.

The high incidence of wounds by second intention and the high costs associated with their treatment give rise to the need for the development of wound dressings that protect not only the wounds themselves but that are also able to promote cell proliferation and skin regeneration. Moreover, it is also very important that no damage to the new regenerated tissue is generated while removing the dressing. In this work, a novel wound dressing, which would be able to favor tissue repair and be removed at an appropriate scheduled moment by means of an external stimulus without promoting extensive damage to the new tissue, was produced and tested. Polyurethane membranes were modified by grafting polymers based on poly(n-isopropylacrylamide) (P-N-IPAAm). P-N-IPAAm undergoes a phase transition at approximately 32°C, which changes its behavior from hydrophilic (below 32°C) to hydrophobic. It was hypothesized that, by reducing the temperature near the wound dressing to values lower than 32°C, the detachment of the dressing would become more effective. The wound dressings containing P-N-IPAAm grafts were tested in vivo by covering excisional wounds produced in mice. The produced dressings were placed in direct contact with the lesions for 3 days. Results showed that the hypothermia due to anesthesia required to remove the dressings from mice lowered the local temperature to 28°C and favored the detachment of the wound dressings containing P-N-IPAAm grafts. Histological analyses showed that lesions covered by dressings presented less intense inflammatory events and denser connective tissue than did the wounds without dressings. The wounds covered by polyurethane membranes with P-N-IPAAm grafts showed signs of more intense re-epithelization and angiogenesis than did the lesions covered by polyurethane without grafts.

Pharmaceutical acrylic beads obtained by suspension polymerization containing cellulose nanowhiskers as excipient for drug delivery.

Direct compression is one of the most popular techniques to prepare tablets but only a few commercial excipients are well adapted for this process into controlled release formulations. In the last years, the introduction of new materials for drug delivery matrix tablets has become more important. This paper evaluated the physicochemical and flow properties of new polymeric excipient of ethyl acrylate, methyl methacrylate and butyl metacrylate, synthesized by suspension polymerization using cellulose nanowhiskers as co-stabilizer, to be used as direct compression for modified release tablets. Infrared spectroscopy (FTIR) confirmed the success of the copolymerization reaction. Scanning electron microscopy (SEM) showed that excipient was obtained how spherical beads. Thermal properties of the beads were characterized by thermogravimetric (TG) analysis. Particle size analysis of the beads with cellulose nanowhiskers (CNWB) indicated that the presence of the nanowhiskers led to a reduction of particle size and to a narrower size distribution. In vitro test showed that the nanowhiskers and beads produced are nontoxic. Parameters such as Hausner ratio, Carr's index and cotangent of angle α were employed to characterize the flow properties of CNWB beads. Furthermore, the beads are used to produce tablets by direct compression contained propranolol hydrochloride as model drug. Dissolution tests performed suggested that beads could be used as excipient in matrix tablets with a potential use in drug controlled release.

Contrast-enhanced ultrasound assessment of arterial vascularization of small nodules arising in the cirrhotic liver.

BACKGROUND AND AIM: Aim of this study was to compare contrast-enhanced ultrasound and multi-detector row computed tomography in detecting arterial hypervascularity in small cirrhotic nodules. PATIENTS AND METHODS: Sixty-two nodules (41 measuring 1.0-2.0 cm, 21 measuring 2.1-3.0 cm) found in 55 cirrhotic patients were examined with both methods. Lesions displaying arterial hypervascularity with washout in the portal/venous phase on both studies were considered hepatocellular carcinomas and treated; all other nodules were subjected to ultrasound-guided fine-needle biopsy. RESULTS: The larger nodules (2.1-3.0 cm) included 19 hepatocellular carcinomas (90%), 1 macroregenerative nodule type I and 1 macroregenerative nodule type II; 35 (87%) of the smaller nodules were hepatocellular carcinomas, 2 were macroregenerative nodules type I, 2 macroregenerative nodules type II and 2 hemangiomas. The two studies yielded concordant findings for 54 nodules (87%), including 46 hypervascular on both examinations and 8 that were consistently hypovascular. Two of the latter nodules were hepatocellular carcinomas. The other eight nodules displayed arterial hypervascularity on only one of the studies. Six of these (75%) were hepatocellular carcinomas, including five that were negative in the contrast-enhanced ultrasound study. CONCLUSION: Computed tomography and contrast-enhanced ultrasound show high agreement in the vascular classification of small nodules detected by ultrasound in cirrhotic livers, although the former technique was slightly more sensitive in the detection of arterial hypervascularization.

Biomaterial with chemically engineered surface for protein immobilization.

The last 3 decades have been a revolution in the area of sol-gel-derived materials. They can be used to encapsulate biomolecules such as enzymes, antibodies, hormones, and proteins retaining their functional state. Proteins can be immobilized in many ways but it is crucial that they retain their native conformational structure and, therefore, bioactivity. Porous silica gel matrixes with modified surfaces offer unlimited possibilities to control the protein-solid interaction behavior. The bioimmobilization process on sol-gel biomaterials with chemically engineered surface has driven applications on solid-phase materials, affinity chromatography, biosensors and many others. In the present work, we have aimed to produce surface-modified silica glass materials obtained via sol-gel route to be used as solid support on drug delivery systems and as solid-phase in immunodiagnostic. The functionalization process was carried out by reacting alkoxysilanes with 5 different silane surface modifying chemical groups: tetraethoxysilane (TEOS), 3-mercaptopropyltrimethoxysilane (MPTMS) and 3-aminopropyltriethoxysilane (APTES), 3-glycidoxypropyltrimethoxysilane (GPTMS) and 3-isocyanatopropyltriethoxysilane (ICPES). The bioactivity assays were based on two main tests: (a) An in vivo bioresponse of rats with sol-gel disk implants with insulin protein incorporated. In vivo tests with adult male rats were used to verify the immobilized insulin bioactivity after implantation of different biomaterial with functionalized surfaces. All surface modified materials have presented hypoglycemic peak response associated with the insulin bioactivity. (b) The produced solid-phase sol-gel disks with protein substrates were tested through Enzyme Linked Immuno Sorbent Assay (ELISA). The immunoassay results have showed that glasses with chemically functionalized surfaces regulated the extent of bioimmobilization of protein. The amine, thiol and hydroxyl terminated porous gels have showed significant interaction with the antibody-antigen, during the coupling process. We believe that it is due to balance of forces associated with Van der Waals interaction, hydrophilic and hydrophobic forces and steric hindrance acting at the surface. Therefore, such novel biomaterial could be advantageously used in drug delivery systems and in immunoassays of diagnostic kits.

Influence of the power density on the kinetics of photopolymerization and properties of dental composites.

Polymer shrinkage during photopolymerization of dimethacrylate monomers, used for many years to produce materials for dental restoration, can induce either the formation of tooth-restoration gaps or the production of residual stress depending on the quality of adhesion between tooth and dental composites. In this work, the effect of the power density, used to photopolymerize three commercial dental composites (Fill Magic, Supra Fill, and Z100), on the kinetics of the reaction was investigated to determine processing conditions in which the generation of residual stress would be reduced by allowing polymer chains and macromers to flow before freezing during gelation of the polymer network. The kinetics of photopolymerization of the dental composites was monitored by real-time infrared (FTIR) spectroscopy. Polymer shrinkage and mechanical properties were also investigated by using, respectively, density and microhardness measurements. Results showed that the final conversion (after 200 s), volumetric shrinkage, and microhardness values were not affected by different power densities, mainly because the amount of energy used during photopolymerization was set constant by using different irradiation times. Lower power densities were able to reduce the maximum polymerization rate and delay the formation of a rigid network. Conversion before the formation of the rigid network was also enhanced by using a lower power density. Considering that too premature gelation can lead to residual stress during shrinkage, the results of this work indicated that the use of a lower power density can be effective in terms of delaying the onset of the formation of a rigid network, providing then conditions for macromolecules to flow and relieve stress during shrinkage.

Preparation of bioactive glass-polyvinyl alcohol hybrid foams by the sol-gel method.

A new class of materials based on inorganic and organic species combined at a nanoscale level has received large attention recently. In this work the idea of producing hybrid materials with controllable properties is applied to obtain foams to be used as scaffolds for tissue engineering. Hybrids were synthesized by reacting poly(vinyl alcohol) in acidic solution with tetraethylorthosilicate. The inorganic phase was also modified by incorporating a calcium compound. Hydrated calcium chloride was used as precursor. A surfactant was added and a foam was produced by vigorous agitation, which was cast just before the gel point. Hydrofluoric acid solution was added in order to catalyze the gelation. The foamed hybrids were aged at 40 degrees C and vacuum dried at 40 degrees C. The hybrid foams were analyzed by Scanning Electron Microscopy, Mercury Porosimetry, Nitrogen Adsorption, X-ray Diffraction and Infra-red Spectroscopy. The mechanical behavior was evaluated by compression tests. The foams obtained had a high porosity varying from 60 to 90% and the macropore diameter ranged from 30 to 500 microm. The modal macropore diameter varied with the inorganic phase composition and with the polymer content in the hybrid. The surface area and mesopore volume decreased as polymer concentration increased in the hybrids. The strain at fracture of the hybrid foams was substantially greater than pure gel-glass foams.