Pure water is a vital ingredient, packaging component and process aid in the manufacture of contact lenses. To meet new demand, lens producer CooperVision has added a fourth Orion Purified Water system. Rod Musson at ELGA Process Water explains how it works.
Contact lenses have come a long way since German ophthalmologist Adolf Fick inserted a glass scleral lens into his eye back in 1888. Glass gave way to Perspex and then, just a century after Fick’s pioneering work, the development of oxygen permeable hydrogels meant that contact lenses could be more comfortable and worn for longer periods. Also they could be disposable. Today, there is a huge range of lens materials that can correct most eye conditions, including toric lenses for astigmatism and varifocals for presbyopia.
CooperVision is one of the world’s largest contact lens manufacturers, and a leading producer of toric lenses. Its manufacturing facility in Hamble-le-Rice near Southampton, UK, produces some of the most technically advanced lenses on the market including naturally wettable silicone hydrogel lenses featuring its Aquaform technology.
Contact lenses are manufactured via a cast moulding process. Liquid monomer is filled into a two-part mould. The monomer is polymerised to produce a hard lens that is removed by splitting the two halves of the mould. The next stage is extraction-hydration in which the lens is immersed in purified water. Unconverted monomer and other impurities are washed from the lens, which also absorbs water, swelling by up to 35%.
The resulting soft lens is then immersed in a weak saline solution, similar in composition to that of tears, which stabilises the lens to its final dimensions before packaging in saline solution-filled blister packs. It is the water content of the lens that allows oxygen to diffuse through it to the surface of the eye.
Water is a raw material in the manufacturing process, an ingredient in the saline solution in which the product is packaged and is also used for cleaning-in-place of production equipment. The quality of that water is critical to the excellence of the product. Chemical purity is essential for the extraction and hydration process and microbiological purity is equally vital for sterile packaging of a product that will come into intimate contact with the user’s eyes.
CooperVision’s Proclear one-day lenses are the only daily disposable contacts that the US Food & Drug Administration (FDA) has approved with a supporting statement that they may help improve dry eyes, and this is a factor in setting water quality standards.
With manufacturing facilities in three continents, all of which produce lenses that could enter the US market, compliance with FDA requirements is essential. For this reason, CooperVision has globally adopted the US Pharmacopoeia standard for purified water.
With considerable breadth and depth in its product range, CooperVision produces many lenses and that means a great deal of purified water. With demand for lenses increasing, the company needed to increase its purified water production and the Elga Process Water Orion purification plant was at its maximum capacity. To meet its immediate needs and provide some spare capacity for future expansion, the company decided to replace the plant with a new 4000 l/h Orion.
The water system uses a combination of technologies to produce high purity water from the Southampton mains water. First the water passes through a combined water softener and activated carbon filter. This removes calcium and magnesium salts, which would cause scaling, and free chlorine that causes oxidative attack on the downstream reverse osmosis and CDI membranes/resins.
The softened water is purified by reverse osmosis using low pressure membranes that remove 95% of dissolved salts and 99% of organic contaminants, producing a permeate of conductivity about 10µS/cm. The permeate then feeds a continuous electro-deionisation unit, a membrane and resin-based process that polishes the treated water to high purity standards. The resulting high purity water is delivered into two 7000 litre stainless steel storage tanks from which it is pumped round a ring main to the points of use, with unused water returning to the tank.
The purified water system, storage tank and ring main are all constructed using hygienic 316L stainless steel and the system’s intermediate tank is fitted with a heater to allow the water system to be periodically sanitised by circulating water at 85°C. Routine sanitisation is automatic and ensures that the microbiological quality of the purified water is maintained. Table 1 summarises the water quality demanded by the US Pharmacopoeia and that produced by the Orion.
| Table 1 – Water quality criteria | ||||||
| Parameter | Units | USP | Orion | |||
| Conductivity at 25°C | μS/cm | 1.3 | 0.2 | |||
| Total Organic Carbon | μg/l | 500 | 250 | |||
| Total Viable Bacteria Count | cfu/ml | 100 | 10 | |||
There are other ways of producing purified water of this quality, so why did CooperVision opt for the Orion system? Martin Frost, principal facilities engineer at Hamble-le-Rice, explains: “We originally had ion exchange plants – actually Elga Duo 2 units – and they used hydrochloric acid and caustic soda for regeneration,” he says. “That became a health and safety issue: we wanted to minimise the storage and handling of hazardous chemicals on site.” The Orion uses almost no chemicals – even sanitisation uses hot water rather than peracetic acid or similar chemicals – so it is both safe and environmentally friendly. It was also developed for the pharma industry to meet USP water quality and FDA regulations, so it ticked all of CooperVision’s boxes.
The changes at CooperVision follow a trend in the contact lens industry that Jim Keary, Elga Process Water’s technical manager, has observed: “Fifteen years ago water for contact lens manufacturing was almost invariably produced by ion exchange deionisers, and distribution systems consisted of PVCU or ABS pipework with numerous deadlegs,” he recalls. “The result was more frequent biofilm growth and microbiological contamination of the product.”
The industry has learned a great deal from pharmaceutical guidelines and has generally adopted the Baseline Pharmaceutical Engineering Guide on Water and Steam Systems produced by the International Society for Pharmaceutical Engineering (ISPE). As a result, reverse osmosis has largely replaced ion exchange because of its ability to remove not only dissolved ionic impurities but also organics, particles and bacteria, which ion exchange leaves behind. But perhaps the biggest change is in distribution system design. New systems are designed to minimise deadlegs where bacteria flourish and plastic pipes whose joints and fittings harbour bacteria have given way to orbitally-welded hygienic stainless steel.
Another feature of the water system is that it is completely skid-mounted, including a control panel with a PLC and password protected HMI, reducing on-site installation time. It also means that Elga Process Water, a Veolia Water Solutions & Technologies company, can provide a full, standardised, Good Automated Manufacturing Practice (GAMP) compliant documentation package covering installation qualification (IQ) and operational qualification (OQ).
“I am responsible for all the water system validations and pre-validation of the Orion meant that we didn’t need to worry about IQ and OQ, so we could go straight to performance qualification (PQ) and get the plant up and running much sooner,” says Frost. “This is our fourth Orion so we know the system well and we have been very satisfied with its reliability and with the support service provided.”
Although site work and validation was minimised by the skid-mounted package, the removal of the old Orion and installation of the new one would, inevitably, mean that the purified water supply would be lost for about three months. To ensure that there was no disruption to production, Elga Process Water provided a mobile Quattro 3000 unit from its Aquamove range to provide continuity of water supply. The Quattro 3000 was pre-validated, GAMP compliant and ready to be connected to a mains water supply and the CooperVision distribution ring main.
There is a last bonus for Frost from the project: during 2011 he is relocating the old Orion to replace his last ageing ion exchange plant and eliminating one more of his health and safety concerns.
Aquaform, ORION and Quattro 3000 are registered trademarks