PubMed · 3545924
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P Claney. Alginate impression procedures.. https://pubmed.ncbi.nlm.nih.gov/3545924/
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The flow properties of liquid calcium alginate injections were investigated for application in endovascular embolization. Alginate shear properties were assessed with a rheometer and a controlled injection system. The experimental results were used to model the flow properties and predict alginate's flow characteristics within various medical microcatheter delivery systems. The results suggest that alginates undergo shear-thinning effects with increasing shear. A flow comparison of 2.0 wt % alginate and a Newtonian fluid (82 cP) injected from the same microcatheter had similar flow rates at low injection pressure (100 kPa). However, at high injection pressure (2100 kPa), the alginate was injectable at a flow rate 100% higher than was the Newtonian fluid. Further analysis of injections through microcatheters resulted in a flow model for predicting viscosity changes, flow rates, and injection pressures of liquid alginate at medium-to-high shear rates. The predicted injection pressures and flow rates had an average variance of less than 15% from that of the experimental flow data. This study indicates that calcium alginate has the requisite flow properties for successful delivery to vascular lesions via endovascular injection. Possible uses of alginates include treating arteriovenous malformations (AVMs), aneurysms, blood flow to tumors, and vascular hemorrhages.
Oral immunization is the most effective way of inducing immune responses in the intestinal tract. Biodegradable microspheres have been used extensively for the delivery of antigens to the Peyer's patches (PPs) within the gut-associated lymphoid tissue (GALT). We evaluated various formulations of alginate microspheres for their capacity to induce mucosal immune responses in vivo. Multiple intestinal "loops" each containing a single PP, were surgically prepared in lambs. We have previously showed that PP in individual intestinal loops function as independent sites for the induction of immune responses. This animal model provides a system for directly comparing different antigen formulations within the same animal. Individual intestinal loops were injected with a model antigen, porcine serum albumin (PSA) encapsulated in three different formulations of alginate micropsheres. Three weeks after immunization, PSA-specific immune responses were assayed with antibody secreting cell (ASC) ELISPOT, lymphocyte proliferative responses (LPRs), IFN-gamma production and antibody secreted into intestinal loops. PSA encapsulated in alginate micropsheres or in saline induced humoral immune responses as indicated by the presence of numerous ASC. However, PSA-specific T-cell responses (LPR and IFN-gamma production) were not induced.
The high-pressure freezing (HPF) technique was applied to the cryo-immobilization of alginate gels and the quality of the freezing analyzed on a TEM by comparison of the segregation pattern of samples of decreasing thickness. Dynamic simulations of heat transfer within an idealized slab of pure water surrounded by two walls of aluminium were performed to illustrate the effect of the heat-transfer coefficient by convection on the cooling rate of the sample. Heat-transfer coefficients in liquid nitrogen and liquid propane at ambient pressure were measured using a carefully characterized thermocouple and the values incorporated as parameters in heat-transfer simulations to compare the efficiency of the plunge-freezing technique with the high-pressure freezing technique. Values of the heat-transfer coefficient in liquid nitrogen and liquid propane, calculated between 273 K and 173 K were 670 and 18420 W/m(2)/K, respectively. Based on TEM observations and the results of heat-transfer simulations, the HPF technique was adapted to the cryo-fixation of 50-microm-thick alginate gels. The occurrence of artifacts was rejected because no differences were observed in the pattern of cryo-fixed and freeze-substituted samples of various thickness, with and without ethanol as cryo-protectant. A sample thickness of 50 microm was found to ensure an adequate preservation of structures as small as a few nanometers, as verified by TEM and SEM observations. Finally, DSC measurements on alginate solutions and alginate beads revealed that under the experimental conditions (0-3%), alginate cannot be considered to be an efficient cryo-protectant.