The influence of triethylcitrate on the biological properties of poly (L-lactic-co-glycolic acid) membranes.

Biodegradable polymers have a variety of uses in basic and clinical research, as well as important therapeutic applications. The most commonly used are poly (lactic acid), poly (glycolic acid) and their copolymer, poly (L-lactic-co-glycolic acid) or PLGA. The incorporation of a plasticizer into a polymer can be used to obtain a product with specific properties. In this work, we examined the influence of a plasticizer (triethylcitrate) on the properties of PLGA membrane implants for human clinical uses. Membranes with and without plasticizer were dense and compact and contained no pores. The incorporation of 7% plasticizer enhanced the degradation the polymer when compared to polymer without plasticizer. In membranes without plasticizer, the initiation of degradation was very slow and was seen only 60 days after implantation, should allow the use of this material in the repair of damage tissue. In both cases, macroscopic analysis showed that there was no adhesion of the membrane to capsule fibrous, and this adversely affected preservation of the polymer. With time, the adherence of the polymer to surrounding tissue increased. Overall there was little degradation of membranes without plasticizer compared to those containing plasticizer.

Morphometrical analysis of multinucleated giant cells in subdermal implants of poly-lactic acid in rats.

The use of bioabsorbable polymers in (bio)medical applications has increased greatly in recent years, mainly because of their good bioreabsorption and biocompatibility. In this work, we examined the development of foreign body giant cells in intimate contact with porous membranes of poly L-lactic acid containing 7% of plasticizer triethylcitrate implanted in the backs of rats. The membranes were removed 2, 7, 14, 21, 28, 60, 90 and 180 days after implantation, along with a portion of the tissue around the implant. Histological analysis of the implant and tissue revealed the formation of a fibrous capsule from the seventh day of implantation onwards. Foreign body giant cells appeared from the seventh day and increased in number up to the twenty-eighth day and then up to the ninetieth day of implantation, remaining constant up to the end of the study onwards, and increased in number up to the ninetieth day after implantation and then remained constant. The number of nuclei in these cells increased from the seventh day of implantation up to the ninetieth day and then up to the end of the study.

Subdermal implants of poly(L-lactic acid) with plasticizer: an ultrastructural study in rats.

Poly(L-lactic acid) (PLLA) membranes containing 7% triethylcitrate plasticizer were implanted in the subcutaneous tissue of rats, and the cellular reaction was evaluated over a period of 2-180 days. The samples were processed for conventional transmission electron microscopy. Polymorphonuclear-type cells and a fibrin network were seen within membrane pores 2 days after implantation. In subsequent samples, there was cellular infiltration, which consisted mainly of fibroblasts, macrophages and multinuclear giant cells embedded in an abundant extracellular matrix containing a network of collagen fibers and blood vessels. At 90 and 180 days after implantation, a high density of voluminous phagocytic cells with a large number of endocytic polymer fragments within their cytoplasm was seen. These results show that PLLA membranes can support connective tissue proliferation and remodeling, which are important properties for successful bio-protheses.

Use of triethylcitrate plasticizer in the production of poly-L-lactic acid implants with different degradation times.

Bioabsorbable materials have been widely used in the repair of damaged tissue as well as in the controlled release of drugs and as a supports for cultured cells. The degradation time of poly-L-(lactic acid) (PLLA) may be controlled by altering the polymer porosity through the addition of the plasticizer triethylcitrate. This in turn influences the extent cellular infiltration. In this study, we examined the degradation of PLLA membranes containing different concentrations of plasticizer. PLLA discs were implanted subcutaneouly in rats and withdrawn 2, 14 and 60 days after implantation. The samples were processed for light microscopy and scanning electron microscopy (SEM). Polymer degradation was proportional to the concentration of plasticizer, indicating that triethylcitrate could affect the degradation time of the implants, without damaging the polymer biocompatibility.

Synthesis and characterization of poly(L-lactic acid) membranes: studies in vivo and in vitro.

The use of biodegradable polyesters as temporary structural supports in the recuperation of damaged live tissue is a promising area of research. Poly(L-lactic acid) (PLLA) membranes can act as a support for cell fixation and growth or as a barrier against soft tissues invasion in recuperating bone tissues. In this work, five different types of PLLA membranes, which varied in their polymer-solvent ratio and their content of plasticizer were studied. For the study in vivo, 6 mm diameter disks were inserted subcutaneously in the dorsal region of 15 Wistar rats, and the reactions on rats were studied 15 days later. In another series of experiments the samples were immersed in phosphate buffer, pH 7.4 at 37 degrees C, for 30 days. Membranes without plasticizer were morphologically dense and did not allow cell invasion nor tissue adherence, in contrast to membranes with plasticizer. While porosity enhanced cell fixation and growth, it made the membrane more fragile mechanically when compared to membranes without pores.

In vivo interaction of cells on poly L-(lactic acid) membranes containing plasticizer.

The development of biodegradable materials has lead to renewed interest in the study of their interactions with the host organism in order to make the resulting products appropriate for use as temporary materials in protheses. Poly L-(lactic acid)(PLLA)-based biodegradable devices have been used for several purposes. The physical properties of these materials can be modified by the addition of a plasticizer, such as the triethylcitrate, to provide flexibility and porosity to the implants and enhance control of the polymer degradation time. In this work we examined the biological properties of a PLLA porous membrane containing 7% triethylcitrate, by assessing the process of degradation and the interaction with dermal tissue. Samples of skin obtained from female Wistar rats 2-180 days after implantation with PLLA-based membrane were processed for light microscopy and scanning electron microscopy. The membranes became surrounded by a delicate network of connective tissue which gradually invaded the membrane structure. Polymer degradation began with the appearance of radial fractures in the globular units of the biodegradable membrane, especially by 90 and 180 days after implantation.

Phospholipid containing choline histochemistry of mouse uterine epithelia during preimplantation stage.

The physiological role of high lipid content in endometrial cells during pregnancy has not been well established. In the present work we used histochemical techniques to analyze the total lipids and phospholipid containing choline (PCC) in the mouse uterine glandular and luminal epithelia during preimplantation stage. Sudan black histochemistry showed the highest intensity during the second day of pregnancy in both the basal and apical portions of luminal epithelium. Peaks of PCC staining were seen both in the luminal and glandular epithelia at the second and fifth days of pregnancy. Changes in localization and in the amount of lipid in the uterine epithelia suggest high mobility and metabolic rates of this substance, which may be related to morphological and/or functional changes occurring at the same time in the pregnant uterus. The increase and depletion timing of PCC content in the uterine epithelia during preimplantation stage, when uterine prostaglandin is also oscillating, suggest a possible involvement of PCC in prostaglandin biosynthesis. Therefore, the fate of lipid droplets found in the uterine epithelia may be related to critical changes of the pregnant endometrium, rather than the nourishment of developing embryos alone.

A histopathologic study of the mechanism of Evans blue staining of myocardial infarcts in rats.

In a study of the mechanism of Evans blue (EB) staining of experimental infarcts in rats, it has been reported that when the dye was injected iv before left coronary occlusion (LCO) it diffused centripetally from the periphery of the excluded vascular bed region (ExVB), i.e., the myocardial area with circulation interrupted by LCO, to its center. In the present study, we have attempted to identify the mechanism of this phenomenon. The animals were sacrificed at different times after EB injection, i.e., 10, 20, and 30 min and 1, 2.5, 4.5, 6, 16, 24 and 48 h. This phenomenon occurred from 4.5 up to 24 h after LCO and could not be ascribed to either collateral circulation or to venous backflow. We conclude that diffusion from one necrotic cell to another, beginning at the ill-perfused periphery of the ExVB (lateral and endocardial margins of the ExVB), and also at the epicardium (bathed by pericardial effusion rich in EB) is responsible for the production of the so-called "blue infarct".

A histopathologic study of the mechanism of Evans blue staining of myocardial infarcts in rats

In a study of the mechanism of Evans blue (EB) staining of experimental infarcts in rats, it has been reported that when the dye was injected iv before left coronary occlusion (LCO), it diffused centripetally from the periphery of the excluded vascular bed region (ExVB), i. e., the myocardial area with circulation interrupted by LCO, to its center. In the present study, we have attempted to identify the mechanism of this phenomenon. The animals were sacrificed at different times after EB injection, i.e., 10,20, and 30 min and 1,2,5, 4.5, 6, 16, 24 and 48 h. This phenomenon occurred from 4.5 up to 24 h after LCO and could not be ascribed to either collateral circulation or to venous backflow. We conclude that diffusion from one necrotic cell to another, beginning at the ill-perfused periphery of the ExVB (lateral and endocardial margins of the ExVB), and also at the epicardium (bathed by pericardial effusion rich in EB) is responsible for the production of the so-called "blue infarct"

Diameter increase of collagen fibrils of the mouse endometrium during decidualization.

The diameter of collagen fibrils was measured in different regions of the antimesometrial endometrium of mice on days 5, 6, and 7 of pregnancy as well as in the endometrium of virgin mice. The average diameter of fibrils of virgin mice was 39.18 nm (range: 20-80). In the region of fully decidualized cells, the averages and ranges were 45.32 nm (30-170), 89.39 nm (30-270), and 125.88 nm (20-370), respectively, on days 5, 6, and 7 of pregnancy. Thick fibrils larger than 70 nm had irregular profiles. Our results show that the increase in diameter is associated with the decidualization of the mouse endometrium.