Alginate Fibres

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Chapter: Pharmacognosy and Phytochemistry : Fibres, Sutures and Surgical Dressings

An aqueous solution of sodium alginate is pumped through a spinneret which is immersed in a bath containing acidic calcium chloride solution.




Alginate fibres are composed of calcium alginate.




An aqueous solution of sodium alginate is pumped through a spinneret which is immersed in a bath containing acidic calcium chloride solution. In the bath sodium cations are substituted with calcium cations and the insoluble calcium alginate is precipitated as continuous filaments. The filaments are collected, washed, and dried for surgical purposes

The filaments are cut up to give stable form of length 1–8 inches for preparing calcium alginate wool or a fabric. Trace amounts of substances are added to the calcium alginate to inhibit mould and bacterial growth.




Alginate fibres are fairly lustrous and pale cream coloured. The fibres may be processed into absorbable, haemostatic dressings. They give general tests for vegetable fibres. They are soluble in ammonical copper nitrate and 5% sodium citrate solution.




Alginic acid is composed of polymers of both mannuronic and glucuronic acids. The properties of the two are variable and alginates of different origin have different compositions and properties. Kalostat haemostatic dressing is derived from the seaweed Laminaria hyperborea collected off the Norwegian coast and yields an alginate with a glucuronic-mannuronic ratio of 2:1. Other dressing is prepared from Laminaria and Ascophyllumspecies collected off the west coast of Scotland and gives an alginate with a glucuronic-mannuronic acid ratio of about 1:2. On a wound surface the α-linkages of the glucuronic acid polymer are not easily broken so that fibre strength is retained and a strong gel is formed on contact with the wound exudates. A high ratio of mannuronic acid polymer (β-linkages) yields a product giving a weaker gel and less retention of fibre strength. The Kalostat dressing can be removed from the wound with forceps and Sorbsan is removed by irrigation with sodium citrate solution.

Calcium alginate fibres of commerce contain substantial traces of substances used to inhibit mould and bacterial growth in the sodium alginate spinning solution. Spinning lubricants such as lauryl or cetyl pyridinium bromide (anti-bacterial) are also applied to the filaments. These substances must not be used in the case of bacteriological swabs.


Before use as an absorbable haemostatic dressing some calcium alginate dressing must be immersed in sodium chloride to give a fibre of the calcium alginate covered by sodium alginate. The degree of conversion is conditioned to give the desired rate of absorption when in use; the greater the proportion of sodium alginate the faster the absorption rate.


Alginate filaments are composed of salts of the long-chain molecules of alginic acid, and there is little cross-linking between the chains in the fibre.


Chemical Tests

1.     The fibre burns in a flame and goes out when removed from flame.


2.     With (N/50) iodine and sulphuric acid, a brownish-red colour is produced, the filaments swell and dissolve to leave a strand of insoluble alginic acid.


3.     In ammoniacal copper nitrate solution they swell and dissolve.


4.     The fibres are insoluble in 60% w/w sulphuric acid.


5.     The fibres are insoluble in warm (40°C) hydrochloric acid.


6.     The fibres are insoluble in boiling 5% KOH (swell and acquire a yellow tint).


7.     The fibres are soluble in 5% sodium citrate solution.


8.     Fibre, 0.1 g, boiled with 5 ml of water remains insoluble but dissolves when 1 ml 20% w/v sodium carbon-ate solution is added and boiled for 1 min. A white precipitate of calcium carbonate is formed, depending on the proportion of original calcium alginate present. When centrifuged and the clear supernatant acidified, a gelatinous precipitate of alginic acid is produced. The precipitate will give a purple colour after solution in NaOH and addition of an acid solution of ferric sulphate.


9.     Shirla stain A gives a reddish-brown colour.


10. Alginate haemostatic fibres are invisible in polarized light with crossed Nicols.



The alginate absorbable haemostatic dressings are nontoxic and nonirritant. They have advantages over oxidized cellulose, which include selective rate of absorption, sterilization (and resterilization) by autoclaving or dry heat and compatibility with antibiotics such as penicillin. They are used internally in neurosurgery, endural and dental surgery to be subsequently absorbed. Externally, they are used (e.g. for burns or sites from which skin grafts have been taken) to arrest bleeding and form a protective dressing which may be left or later removed in a manner appropriate to the type of dressing employed. Protective films of calcium alginate may also be used by painting the injured surface with sodium alginate solution and then spraying it with calcium chloride solution.

Calcium alginate wool as a swab for pathological work or bacterial examination of such things as food processing equipment and tableware permits release of all the organisms by disintegration and solution of the swab in, for example, Ringer’s solution containing sodium hexametaphosphate.

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