The hydrophilic coating on the surface of medical devices is mostly composed of hydrophilic polymers. Common hydrophilic polymers include polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), polyacrylamide (PAM) and natural polysaccharide polymers such as chitosan (CS), hyaluronic acid (HA), etc. Their hydrophilicity comes from the abundant amino, hydroxyl, amide and other functional groups on the polymer chain, which can form hydrogen bonds with water to promote the dissolution of the polymer. Currently, most of the components of hydrophilic lubricating coatings on commercially available medical devices are PVP or PAM.
The water solubility of hydrophilic polymers is related to the molecular weight and structure of the polymer. Linear structured hydrophilic polymers (left in Figure 1), such as PVP and PAM, are soluble in water at lower molecular weights and at appropriate concentrations, and therefore are widely used in food, cosmetics and pharmaceutical fields. As the molecular weight increases, the water solubility of the polymer will decrease. 。When the hydrophilic polymer forms a cross-linked network (right in Figure 1), it can only fully swell in water, but cannot dissolve in water.
Most hydrophilic lubricating coatings on the surface of medical devices are hydrophilic polymers (such as PVP, PAM) or their derivatives that are transformed into a cross-linked network structure of the polymer on the surface of the substrate through specific coating processes (such as dipping, spraying) and curing processes (such as UV curing, thermal curing) and are firmly bonded to the substrate. Therefore, high-quality hydrophilic lubricating coatings can only absorb water and swell, but cannot dissolve in water, so the leach solution will not contain hydrophilic substances released by the coating, resulting in abnormal chemical performance (GB/T14233.1) test results.
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