Radiation protection on polysaccharide solutions and gels
, PhD thesis, University of Salford.
The effects of ionizing radiation on solutions of (1) sodium alginate, (2) alginate gels (wet
and dry), (3) xanthan gum, (4), locust bean gum (LBG) and (5) carboxymethyl cellulose
(CMC), have been investigated.
Problems arise in the radiation sterilization of these gums (either as a solution or gel) due
to reduction in their viscosity and the gel strength, caused by the high doses (25kGy)
commonly used for the purpose of sterilization.
The alginates used here were manugel DMB, manugel DPB and manucol DMF. The
irradiations were carried out using 'Co-ry-source and the gels and solutions were analysed
by measurement of their apparent viscosities using a Brookfield viscometer L.V.T.
The data shows that 2% solutions of the sodium salt of the three alginates used here are all
There is a rapid decrease in viscosity of solutions irradiated up to a dose of 0.5kGy, and the
initial rate of viscosity decrease is unaffected by the presence or absence of air. Inclusion
of mannitol at high concentration (15%) could, at least partially, protect the alginate solutions
degradation by scavenging -OH radicals.
The possibility of using 60Co-7-radiation to sterilize alginate gels (wet gels) was also studied.
Gels of this type have potential use of wound care. Those prepared here could bend easily.
Irradiated to 25 kGy, the gels readily crack by becoming more brittle, are easily squashed
and lose water. Inclusion of mannitol improved the quality of the gels and again indicates its protective role in these systems.
When alginate solutions containing mannitol and the gelling agents 5-gluconolactone and
calcium orthophosphate were irradiated separately and then mixed, gels were formed,
indicating that pre-sterilization of the components by irradiation is a feasible method of
preparation of sterile gels.
Gels that were concentrated (dry) by water evaporation were more stable to radiation (25
kGy). The gels that had the greatest capability to take up saline and to be manipulated most
easily (both before and after irradiation) were those that contained initially 2% alginate and
5% mannitol, and dried to a quarter of the original weight (ie. the gel now contained 8%
alginate and 20% mannitol). These gels were clear and pliable and after irradiation to 30
kGy remain stable in saline for up to 24 hours.
The effect of ionizing radiation on xanthan and LBG solutions are also studied. The initial
studies indicated that these solutions were also pseudoplastic. Irradiation of xanthan gum
solutions caused a rapid initial decrease in apparent viscosity. t-Butanol had some protective
effect on xanthan-LBG and xanthan-NaC1 solutions. Addition of mannitol (20%) to xanthan
gum solutions again only partially protects the solutions. The solutions with highest apparent
viscosity were those prepared by mixing equal volumes of solutions of LBG 1%, mannitol
(20%) and ascorbic acid (10" mol dm') and solutions of xanthan gum (1%), mannitol (20%)
and ascorbic acid (10' mol dm'). The viscosity of this solution falls from 300,000 cps to
250,000 (shear rate 0.07s4), after irradiation to 25 kGy. Therefore, whereas xanthan gum
solutions containing readily depolymerized by irradiation, very high viscosity irradiated
xanthan solutions containing thickening agents (LBG) and radiation protectors (mannitol - ascorbic acid) can be prepared. Solutions of CMC are also pseudoplastic. Irradiation to 25
kGy resulted in a decrease in the apparent viscosity of solutions of CMC/mannitol/ascorbic
acid from — 180,000cps to 8,000cps, whereas for solutions of CMC alone and for
CMC/mannitol solutions the viscosity was less than 500cps. This further illustrates the
protective effect of ascorbic acid as was observed for xanthan solutions and also suggests that
mannitol radicals cause depolymerization of CMC.
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