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properties and chemistry shelf life. As well as one or more surfactants, sequestrants can be added to addresses the negative effects of hard water or aid in cleaning of proteins. Other inert ingredients are added to significantly enhance performance and give the formulation their classification name - enzymatic, alkaline and neutral.
Cleaning chemistry types Enzymatic formulations also contain enzymes. Enzymes are bio-organic molecules designed to break down larger molecules into smaller, more water-soluble ones. They are very selective and only target specific soil components and will have negligible effects on other molecules. The formulation is typically neutral pH in order to prevent breakdown to these enzyme proteins. Enzymes are typically named after the substances they help to break down; proteases break down protein, amylases break down starch, lipases break down fats/lipids and cellulases break down cellulose. Only proteases are considered useful in medical device cleaning formulations due to protein being prevalent in clinical soils. Different proteases can be combined to broaden pH or temperature effectiveness, but using a higher concentration of the same enzyme will not necessarily increase efficacy. Alkaline formulations also contain alkalis. They form a solution in water greater than pH 10; they typically contain sodium hydroxide (NaOH) or potassium hydroxide (KOH). The alkali causes hydrolysis of proteins and lipids, breaking them into smaller water- soluble pieces. They are more effective at higher temperatures (greater than 60˚C), but high pH and high temperature can have material compatibility issues (i.e. alkaline corrosion), dependent upon the concentration used. Alkaline detergents have been shown to be capable of the inactivation of prion proteins. Neutral formulations form a solution in water that is between 6 to 8. They can be used as a two-part clean – an enzymatic detergent is
Fig 3
used, followed by a neutral detergent. They are used as an alternative to alkaline detergents where material compatibility could be an issue; as well as being less aggressive than alkaline detergents, there can be an increased cycle time and a need for a higher temperature for equivalent cleaning efficacy. Sequestrants and chelating agents can be
used to address the negative effects of hard water metal ions. These chemicals are known as sequestrants, having a chemical structure that allows them to bond with metal ions. A specific form of sequestrant is known as a chelating agent; these agents have a claw-like structure which can bind the free metal ions thus enhancing the effects of the detergent. Chelates prevent chemical deposition onto instruments and can also inhibit scale formation and remove scale deposits. Soils typically encountered on reusable medical devices after use may be organic, inorganic or both in nature. Organic soils may be comprised of muscle, skin, connective tissue, fat, grease, proteins and carbohydrates. Inorganic soils may consist of rust, hard water deposits and residues from cleaners and medical solutions (iodine, saline, skin preparations). Combination (organic and inorganic) soils may originate from substances such as bone. Protection of medical devices by the cleaning
chemistry formulation can prevent rust or pitting corrosion sometimes found on medical devices containing iron (which includes stainless steel). Soft metals, such as aluminium, may also exhibit corrosion due to water and or harsh conditions. Cleaning chemistries can be formulated with corrosion inhibitors to prevent this corrosion.
Fig 2: Richard Bancroft, BSc (Hons), Senior Director, Scientific at STERIS
Choosing a cleaning chemistry There is much more to a cleaning chemistry than just a surfactant in aqueous solution, with the additional components in the formulation
making a significant difference to its cleaning efficacy. Selecting the highest performing cleaning chemistry requires an appreciation of all of these attributes. Through a process of scientific studies and washer validation, a number of high-level conclusions can be drawn: l Alkaline cleaning chemistries are generally better at rendering surfaces non-infectious than enzymatic detergents
l Alkaline and enzymatic cleaning can be effective at inactivating transmissible spongiform encephalopathies (TSEs)
l The precise formulation may be more important than whether the cleaning chemistry is classified as alkaline or enzymatic
l The suitability and effectiveness of a given cleaning chemistry depends on water quality
l Cleaning chemistries should be formulated to be low foaming and have the ability to defoam soils
l Have high performance against clinically relevant soils such as proteins
l Protect surgical instruments from corrosion and staining
l Reduce maintenance costs by minimising pump cavitation
l Be biodegradable, non-toxic to aquatic life, free from environment-damaging chemicals and be provided in minimal packaging by concentrating the formulation.
Email:
uksales@steris.com Web:
www.steris.com
STERIS UK August 2024 I
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