Liquid Silicone Rubber (LSR) parts are used extensively in a multitude of fields in the medical industry because it is inert and bio-compatible — plus, it offers excellent compression characteristics. Ophthalmology is one of the medical fields where LSR is widely used and preferred.
Liquid Silicone Rubber (LSR) is the ideal material for parts with skin contact that need to meet hygiene, comfort, and biocompatibility requirements. Because it is also flexible and inert, it is the preferred choice for a wide variety of applications.
Mothers have high standards for the items they use to take care of their children, and so does the Food and Drug Administration (FDA) last updated in May 2019 in a guidance to provide additional information on how to prepare Food Contact Notifications (FCNs) for food contact substances that will come into contact with infant formula and/or human (breast) milk. Mother and child care products require materials that are hypoallergenic, durable, smooth and comfortable, and easy to clean. For these characteristics, liquid silicone rubber (LSR) has emerged as the material of choice.
Silicone rubber is recognized for being inherently biocompatible with human tissues, resistant to bacteria, and it does not degrade in the presence of fluids like blood, saliva, and others. This material is used more and more in medical applications, but increasingly strict requirements make it necessary to modify the silicone in order to use it. Additives are a common option for increasing mechanical and physical properties, but silicone can also be combined with other materials such as thermoplastics, thermosets, thermoplastic elastomers, ceramics, and metals to comply with application requests. In the industrial processing of materials, the challenge is always to create high-performance products in the shortest time with the least amount of the components. There are two options for that: (i) select the best material that fits with all the requirements of the final application; in some cases, this can be almost impossible since it is common that application requests are opposing, for example, rigid in one area but flexible in another area of the part. There is also option (ii): design a single part made with multiple materials that fulfill the application requirements, which is manufactured using co-injection or over-molding, otherwise called two-shot or multi-shot injection molding; this process offers extended functionality, better appearance, and high quality of the product. In this special process, critical variables include mold temperature, shrinkage, and deformation of the second injected material, and they must be analyzed carefully because the right choice will determine the success of the product.