Biomedical Engineering Reference
In-Depth Information
12. The glass beaker used for sonication should be of a suitable size to
achieve satisfactory size reduction. If a large beaker is used, parti-
cles near the walls might not experience enough sonication and
will remain as larger-sized particles, increasing the polydispersity.
13. It has been observed that when the probe touches the glass
walls, it gives rise to particle impurities in the final product.
Hence it is advisable to use a wide mouthed container for
sonication and care should be taken that the probe does not
touch the glass walls during sonication.
14. The Tg for
L
-PLA is around 55-60
C and Tg for
DL
-PLGA
(Resomer
®
RG 503H) is in the range of 44-48
C. Therefore,
the heat generated during probe sonication can degrade these
polymers. Hence sonication is done on ice using prechilled
preparations to prevent heat generation and thermal degrada-
tion of thermolabile actives and the polymer.
15. The quality of the probe controls the quality of the nanoparticles
formed. A new good quality probe with a high power input yields
monodisperse small-sized particles as compared to an old probe.
16. Sonication of the primary emulsion after it has been added to
2 % w/v PVA ensures a further reduction in the droplet size of
the emulsion.
17. Organic solvent removal method would largely depend on the
type of the solvent employed. The most common approach for
removing the solvent is a rotary evaporator placed in a hood,
which uses heat to force the liquid solvent into a gaseous state
and simultaneously applies vacuum to remove the solvent
gases. Rotary evaporator can be used for removal of most of
the solvents. Stirring at room temperature in a hood to remove
the organic solvent can be a good alternative method for drugs
that are sensitive to temperature or vacuum pressure. However,
stirring at room temperature mandates the use of a low boiling
point solvent like DCM (B.P. 40
C).
18. The temperature of the water bath in the rotary evaporator
should not exceed glass transition temperature (Tg) of the
polymer being used. Temperature of the bath is generally set
at 40
C (Buchi Heat Bath B490) if DCM is used as the solvent.
19. Organic solvent removal is a critical step in particle preparation
because the rate of solvent removal influences the particle size
and drug entrapment efficiency [
51
]. Fast rate of solvent
removal has been reported to decrease the particle size and
increase the drug loading [
51
]. Faster removal decreases the
aggregation of nanoparticles, thereby promoting formation of
smaller-sized particles. The rate of polymer precipitation dur-
ing solvent evaporation step influences drug partitioning into
the external phase and subsequently affects the amount of drug
entrapped. Slow rate of solvent removal can lead to polymer
