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Freeze-Drying: Principles and Practice
Published in Sandeep Nema, John D. Ludwig, Parenteral Medications, 2019
Steven L. Nail, Larry A. Gatlin
A good general rule in developing a formulation of a freeze-dried pharmaceutical product, or any product for that matter, is to keep the formulation as simple as possible, and to not include any component without a clear rationale for doing so along with supporting data. It is important to have a clear idea of the critical quality attributes of the product before beginning. Some attributes, such as sterile, non-pyrogenic, and compliant with compendial requirements for visible and subvisible particulate matter are obvious. Complete recovery of the activity present in the formulation prior to freeze-drying is always desired, but may not always be possible. Vaccines, for example, tend to lose some potency as a result of freeze-drying, but the critical factor here is consistency of activity in the reconstituted solution. Dissolution of the freeze-dried cake should be complete, and the reconstitution time should be as fast as possible. Some quality attributes may, or may not, be critical depending on the intended route of injection. For example, it is always desirable for a formulation to be isotonic (the same osmotic concentration as normal physiological fluid). However, this attribute is only critical for certain routes of administration such as intraspinal, intraocular, or into any part of the brain. The same consideration applies to the pH of the formulation, where it is always desirable to have the formulation pH the same as normal plasma, but the reality is that the pH of injectable formulations varies widely as required to achieve suitable solubility and stability in solution.
Physical properties of the body fluids and the cell membrane
Published in Ronald L. Fournier, Basic Transport Phenomena in Biomedical Engineering, 2017
If a cell is placed within a solution that has a lower concentration of solutes or osmolarity, then the cell is in a hypotonic solution, and establishment of osmotic equilibrium requires the osmosis of water into the cell. This influx of water into the cell results in the swelling of the cell and a subsequent decrease in its osmolarity. On the other hand, if the cell is placed in a solution with a higher concentration of solutes or osmolarity, i.e., hypertonic, then osmotic equilibrium requires osmosis or diffusion of water out of the cell, concentrating the intracellular solution and resulting in shrinkage of the cell. An isotonic solution is a fluid that has the same osmolarity of the cell. When cells are placed in an isotonic solution, there is neither swelling nor shrinkage of the cell. A 0.9 wt% solution of sodium chloride or a 5 wt% solution of glucose is just about isotonic with respect to a cell.
Desalination
Published in Frank R. Spellman, Hydraulic Fracturing Wastewater, 2017
Tonicity is a measure of the effective osmotic pressure gradient (as defined by the water potential of the two solutions) of two solutions separated by a semipermeable membrane. It is important to point out that, unlike osmotic pressure, tonicity is only influenced by solutes that cannot cross this semipermeable membrane, as only these exert an effective osmotic pressure. Solutes able to freely cross do not affect tonicity because they will always be in equal concentrations on both sides of the membrane. There are three classifications of tonicity that one solution can have relative to another (Sperelakis, 2012): Hypertonic refers to a greater concentration. In biology, a hypertonic solution is one with a higher concentration of solutes outside the cell than inside the cell; the cell will lose water by osmosis.Hypotonic refers to a lesser concentration. In biology, a hypotonic solution has a lower concentration of solutes outside the cell than inside the cell; the cell will gain water through osmosis.Isotonic refers to a solution in which the solute and solvent are equally distributed. In biology, a cell normally wants to remain in an isotonic solution, where the concentration of the liquid inside it equals the concentration of liquid outside it; there will be no net movement of water across the cell membrane.
PEGylated microemulsion for dexamethasone delivery to posterior segment of eye
Published in Journal of Biomaterials Science, Polymer Edition, 2020
Figure 4 described results of sterility, isotonicity test, ex vivo corneal irritation study and HET CAM. There was no growth or contamination observed in any of Petri dish even after 7 days. Figure 4(A) indicated that MEs prepared in aseptic conditions restrict any kind of fungal and bacterial growth. Thus these can be utilized for ocular use. Isotonicity test also revealed favourable results as no significant alteration in morphology of RBCs was observed under microscope (Figure 4(B)). Hypotonic solution swell and hypertonic solution rupture/constrict RBCs while isotonic one maintains architecture of RBCs. ND and PD both didn’t disrupt RBCs. Thus, developed MEs were isotonic to ocular fluid. H&E staining and corneal hydration test both revealed non-irritancy of MEs to cornea. Hematoxylin stains the nucleus while eosin stains cytoplasm of cell. As can be seen from Figure 4(C), cornea treated with MEs showed intact nuclei confirming no harmful impact of MEs on treated corneas. Weight variation analysis in corneal hydration test before and after treatment with MEs also didn’t show significant difference eliminating probability of edema. Both corneal hydration and H&E staining are indicators of toxicity to membranous barriers of eye. To determine the toxic effect of instilled dosage on vascular barrier of conjunctiva and other parts, HET-CAM test played vital role. Figure 4(D) showed results of HET-CAM which reaffirmed non-irritancy of ND and PD as blood capillaries were intact throughout exposure of dosages.
Effect of proteins and phosphates on the degradation and repassivation of CoCrMo alloys under tribocorrosion conditions
Published in Tribology - Materials, Surfaces & Interfaces, 2020
M. Bryant, J. Rituerto Sin, N. Emami, A. Neville
The four electrolyte solutions used in this study are listed in Table 1. Isotonic saline solution (0.9% NaCl) and Dulbecco’s phosphate-buffered solution (Sigma-Aldrich, Germany) were the two saline solutions studied in this work. In addition, two serum solutions were prepared using bovine calf serum (Haram Sera-Lab®, UK). The first solution consisted of 25 v% bovine calf serum and 75 v% distilled water. The second solution consisted of 25 v% bovine calf serum and 75 v% phosphate-buffered solution.