Component Of Microparticles Research Articles

Tissue Factor and Cardiovascular Disease: Quo Vadis?

The coagulation cascade represents a system of proteases responsible to maintain vascular integrity and to induce rapid clot formation after vessel injury. Tissue factor (TF), the key initiator of the coagulation cascade, binds to factor VIIa and thereby activates factor IX and factor X, resulting in thrombus formation. Different stimuli enhance TF gene expression in endothelial and vascular smooth muscle cells. In addition to these vascular cells, TF has recently been detected in the bloodstream in circulating cells such as leukocytes and platelets, as a component of microparticles, and as a soluble, alternatively spliced form of TF. Various cardiovascular risk factors like hypertension, diabetes, and dyslipidemia, increase levels of TF. In line with this observation, enhanced vascular TF expression occurs during atherogenesis, particularly in patients with acute coronary syndromes. (Circ J 2010; 74: 3 - 12).

Thermal behavior and stability of biodegradable spray-dried microparticles containing triamcinolone

Thermal analysis has been widely used for obtaining information about drug–polymer interactions and for pre-formulation studies of pharmaceutical dosage forms. In this work, biodegradable microparticles of poly (d,l-lactide-co-glycolide) (PLGA) containing triamcinolone (TR) in various drug:polymer ratios were produced by spray drying. The main purpose of this study was to study the effect of the spray-drying process not only on the drug–polymer interactions but also on the stability of microparticles using differential scanning calorimetry (DSC), thermogravimetry (TG) and derivative thermogravimetry (DTG), X-ray analysis (XRD), and infrared spectroscopy (IR). The evaluation of drug–polymer interactions and the pre-formulation studies were assessed using the DSC, TG and DTG, and IR. The quantitative analysis of drugs entrapped in PLGA microparticles was performed by the HPLC method. The results showed high levels of drug-loading efficiency for all used drug:polymer ratio, and the polymorph used for preparing the microparticles was the form B. The DSC and TG/DTG profiles for drug-loaded microparticles were very similar to those for the physical mixtures of the components. Therefore, a correlation between drug content and the structural and thermal properties of drug-loaded PLGA microparticles was established. These data indicate that the spray-drying technique does not affect the physico-chemical stability of the microparticle components. These results are in agreement with the IR analysis demonstrating that no significant chemical interaction occurs between TR and PLGA in both physical mixtures and microparticles. The results of the X-ray analysis are in agreement with the thermal analysis data showing that the amorphous form of TR prevails over a small fraction of crystalline phase of the drug also present in the TR-loaded microparticles. From the pre-formulation studies, we have found that the spray-drying methodology is an efficient process for obtaining TR-loaded PLGA microparticles.

In Situ Gelling Hydrogels Incorporating Microparticles as Drug Delivery Carriers for Regenerative Medicine

Aqueous solutions of blends of biodegradable triblock copolymers, composed of poly(D,L-lactide-co-glycolide) (PLGA) and poly(ethylene glycol) (PEG) with varied D,L-lactide to glycolide ratios, displayed thermosensitivity and formed a gel at body temperature. The gel window of the blend solutions could be tuned by varying the blending ratio between the two components. Furthermore, the storage modulus of the resultant hydrogel from the copolymer blends at body temperature was higher than that of each individual component. Incorporation of poly(D,L-lactide) (PDLLA) microparticles (0.5–40% w/v) within the in situ gelling hydrogel did not change the sol–gel transition temperatures of the polymer solutions, while the mechanical strength of the resultant hydrogels was enhanced when the content of the microparticles was increased up to 30% and 40%. Incorporation of proteins into both the gel and microparticle components resulted in composites that controlled the kinetics of protein release. Protein within the gel phase was released over a 10-day period whilst protein in the microparticles was released over a period of months. This system can be used to deliver two drugs with differing release kinetics and could be used to orchestrate tissue regeneration responses over differing timescales.

Velocity recovery factors of a particle repelled from a solid surface

On the basis of the published experimental data, recovery factors of velocity components of microparticles impacting a target heuristic expression, which are suitable for a wider class of pairs of materials of colliding bodies, have been proposed. The considered range of values of impact velocities is bounded on the side of both low velocities (since the adhesive forces are neglected) and higher velocities (at which irreversible deformation of the particle and/or the target occurs).

Shed Membrane Particles from Preeclamptic Women Generate Vascular Wall Inflammation and Blunt Vascular Contractility

We investigated the role of microparticles in vascular dysfunction of the multisystemic disorder of preeclampsia in women's omental arteries or mouse arteries. Preeclamptic women displayed increased circulating levels of leukocyte- and platelet-derived microparticles compared with healthy pregnant individuals. Microparticles from preeclamptic, but not healthy, pregnant women induced ex vivo vascular hyporeactivity to serotonin in human omental arteries and mouse aortas. Hyporeactivity was reversed by a nitric-oxide (NO) synthase inhibitor and associated with increased NO production. In the presence of a cyclooxygenase (COX)-2 inhibitor, serotonin-mediated contraction was partially reduced in arteries treated with healthy microparticles but was abolished after treatment with preeclamptic microparticles. This was associated with increased 8-isoprostane production. Preeclamptic microparticles induced up-regulation of inducible nitric-oxide synthase and COX-2 expression, evoked nuclear factor-kappaB activation, and enhanced oxidative and nitrosative stress. Interestingly, the microparticles originating most probably from leukocytes were responsible for the COX-2 vasoconstrictor component of preeclamptic microparticles, whereas those of platelet origin were mainly involved in NO release. Moreover, vascular hyporeactivity was observed in arteries taken from mice treated in vivo with preeclamptic microparticles. This study demonstrates pathophysiological relevance and provides a paradoxical effect of preeclamptic microparticles associated with proinflammatory properties on vessels, leading to enhanced NO and superoxide anion levels and counteraction of increased COX-2 metabolites.

Modifizierung der Holzeigenschaften durch Enzyme | Modification of wood properties through enzymes

The addition of phenol oxidising enzyme preparations leads to a change in the fibre structure of lignocellulose products. This means that positive material properties can be selectively put in. In the production of materials the use of activated ownfibre binding forces only makes sense when the production process ensures that fibres are as close to one another as possible. This can be accomplished by fine tuning the density of the material to the method in question. Material densities of over 600 kg/m3 are necessary for dry method approaches. With wet methods, on the other hand, the properties of material can be improved starting from a density of 160 kg/m3. A good distribution and the use of additionally created hydro-bridge builders are responsible for this. The employment of charge carriers during the processing with a wet method also has a positive influence on the physical properties. The suspended particles that become detached from the fibre in the process bind together and are concentrated on the surface of the fibre. To improve the steering of the process with the wet method further enzymatic treatment steps in lignocellulose can be carried out with micro- and nano-particle systems. This can be done via combinations of cationic starch or cationic polyacrylamide. With these systems the cationic polymer is added to the fibre suspension first, followed by the micro-particle components. Both the levels of additives used and the required incubation times can thereby be markedly reduced. Here for the first time we succeeded in using enzymes in processing technically relevant dimensions and were therefore able to renounce the addition of synthetic binding means without impairing the properties of the material.

Tissue factor activity in whole blood

AbstractTissue factor (TF) is an integral membrane protein essential for hemostasis. During the past several years, a number of studies have suggested that physiologically active TF circulates in blood at concentrations greater than 30 pM either as a component of blood cells and microparticles or as a soluble plasma protein. In our studies using contact pathway–inhibited blood or plasma containing activated platelets, typically no clot is observed for 20 minutes in the absence of exogenous TF. An inhibitory anti-TF antibody also has no effect on the clotting time in the absence of exogenous TF. The addition of TF to whole blood at a concentration as low as 16 to 20 fM results in pronounced acceleration of clot formation. The presence of potential platelet TF activity was evaluated using ionophore-treated platelets and employing functional and immunoassays. No detectable TF activity or antigen was observed on quiescent or ionophore-stimulated platelets. Similarly, no TF antigen was detected on mononuclear cells in nonstimulated whole blood, whereas in lipopolysaccharide (LPS)–stimulated blood a significant fraction of monocytes express TF. Our data indicate that the concentration of physiologically active TF in non–cytokine-stimulated blood from healthy individuals cannot exceed and is probably lower than 20 fM.

Active tissue factor in blood?

Following mechanical or chemical damage of the vessel or monocyte stimulation, tissue factor is exposed to the blood and binds plasma factor VIIa (FVIIa) forming the FVIIa–tissue factor enzyme complex. During the last several years, a number of studies have reported that physiologically active tissue factor is found circulating in blood of healthy individuals either as a component of blood cells and microparticles or as a soluble plasma protein1. Reports of the presence, source and activity of tissue factor in blood are controversial, with reported concentrations of physiologically active tissue factor varying from undetectable (<60 fM) in whole blood2 to as high as 37 pM in the plasma of healthy individuals3. Blood or plasma activated with (sub)picomolar concentrations of functional tissue factor clots within several minutes (Fig. 1), suggesting that such concentrations of functional tissue factor cannot be present in blood or plasma in vivo.

Transforming growth factor-β1 release from oligo(poly(ethylene glycol) fumarate) hydrogels in conditions that model the cartilage wound healing environment

This research demonstrates that controlled material degradation and transforming growth factor-β1 (TGF-β1) release can be achieved by encapsulation of TGF-β1-loaded gelatin microparticles within the biodegradable polymer oligo(poly(ethylene glycol) fumarate) (OPF), so that these microparticles function as both a digestible porogen and a delivery vehicle. Release studies performed with non-encapsulated microparticles confirmed that at normal physiological pH, TGF-β1 complexes with acidic gelatin, resulting in slow release rates. At pH 4.0, this complexation no longer persists, and TGF-β1 release is enhanced. However, by encapsulating TGF-β1-loaded microparticles in a network of OPF, release at either pH can be diffusionally controlled. For instance, after 28 days of incubation at pH 4.0, final cumulative release from non-encapsulated microparticles crosslinked in 10 and 40 mM glutaraldehyde (GA) was 75.4±1.6% and 76.6±1.1%, respectively. However, when either microparticle formulation was encapsulated in an OPF hydrogel (noted as OPF-10 mM and OPF-40 mM, respectively), these values were reduced to 44.7±14.6% and 47.4±4.7%. More interestingly, release studies, in conditions that model the expected collagenase concentration of injured cartilage, demonstrated that by altering the microparticle crosslinking extent and loading within OPF hydrogels, TGF-β1 release, composite swelling, and polymer loss could be systematically altered. Composites encapsulating less crosslinked microparticles (OPF-10 mM) exhibited 100% release after only 18 days and were completely degraded by day 24 in collagenase-containing phosphate-buffered saline (PBS). Hydrogels encapsulating 40 mM GA microparticles did not exhibit 100% release or polymer loss until day 28. Hydrogels with no microparticle component demonstrated only 79.3±9.2% release and 89.2±3.4% polymer loss after 28 days in enzyme-containing PBS. Accordingly, these studies confirm that the rate of TGF-β1 release and material degradation can be controlled by altering key parameters of these novel, in situ crosslinkable biomaterials, so that TGF-β1 release and scaffold degradation may be tailored to optimize cartilage repair.

In vitro release of transforming growth factor-β1 from gelatin microparticles encapsulated in biodegradable, injectable oligo(poly(ethylene glycol) fumarate) hydrogels

This research investigates the in vitro release of transforming growth factor-β1 (TGF-β1) from novel, injectable hydrogels based on the polymer oligo(poly(ethylene glycol) fumarate) (OPF). These hydrogels can be used to encapsulate TGF-β1-loaded-gelatin microparticles and can be crosslinked at physiological conditions within a clinically relevant time period. Experiments revealed that OPF formulation and crosslinking time may be adjusted to influence the equilibrium swelling ratio, elastic modulus, strain at fracture, and mesh size of these hydrogels. Studies with OPF–gelatin microparticle composites revealed that OPF formulation and crosslinking time, as well as microparticle loading and crosslinking extent, influence composite swelling. In vitro TGF-β1 release studies demonstrated that burst release from OPF hydrogels with a mesh size of 136 Å was approximately 53%, while burst release from hydrogels with a mesh size of 93 Å was only 34%. For hydrogels with a large mesh size (136 Å), encapsulation of loaded gelatin microparticles allowed burst release to be reduced to 29–32%, depending on microparticle loading. Likewise, final cumulative release after 28 days was reduced from 71% to 48–66% by encapsulation of loaded microparticles. However, inclusion of gelatin microparticles within OPF hydrogels of smaller mesh size (93 Å) was seen to increase TGF-β1 release rates. The equilibrium swelling ratio of the microparticle component of these composites was shown to be greater than the equilibrium swelling ratio of the OPF component. Therefore, increased release rates are the result of disruption of the polymer network during swelling. These combined results indicate that the kinetics of TGF-β1 release can be controlled by adjusting OPF formulation and microparticle loading, factors affecting the swelling behavior these composites. By systematically altering these parameters, in vitro release rates from hydrogels and composites loaded with TGF-β1 at concentrations of 200 ng/ml can be varied from 13 to 170 pg TGF-β1/day for days 1–3 and from 7 to 47 pg TGF-β1/day for days 6–21. Therefore, these studies demonstrate the potential of these novel hydrogels and composites in the sustained delivery of low dosages of TGF-β1 to articular cartilage defects.