All stages of the manufacturing process are important to obtain the soft skin adhesive or wound contact layer that meets both the manufacturer’s productivity targets and the customers’ quality requirements. Teamwork among the silicone supplier, the manufacturer and the final product designer is key to ensure success.
Clément des Courières, Elkem Silicones
The proven biocompatibility and tissue-preserving properties of silicone soft skin adhesives (SSA) have made them a material of choice for modern wound treatment. The gradual switch to silicones for over-the-counter (OTC) applications has made it more important for wound-care companies to be efficient when manufacturing and supplying their silicone dressings to medical professionals and consumers.
Silicones have a unique set of properties that distinguish them from traditional, acrylic-based adhesives. They are highly biocompatible, hypoallergenic, comfortable, resist bacteria and offer easy and gentle removal from the skin. These superior properties also make silicones different to use.
SSAs are made up of two-component, low-to-medium-viscosity silicones. One component contains the platinum catalyst, while the other contains the crosslinker. Both parts should be mixed homogeneously, typically in a 1:1 ratio, before being applied by direct or indirect coating onto the chosen substrates and cured in an oven.
Here are some processing considerations and tips for manufacturers seeking to obtain the perfect skin adhesive or wound contact layer using silicone.
Choose the right silicone adhesive product
Silicone suppliers will offer a wide range of SSAs to choose from. However, each product is different and developed for a different purpose. Two main parameters will help you make a decision. The material’s viscosity should be adapted to your equipment and process. And the level of adhesion to the skin should be suitable for your application. In case of doubt, ask your silicone supplier to make a recommendation.
Combine the SSA with the correct substrate as a backing layer
Backing substrates for skin adhesive applications should be both very flexible and breathable, which makes polyurethane films and open fabrics like non-wovens outstanding for use in this field. When coating most silicones directly onto a polyurethane film, no chemical adhesion will be formed, and therefore there is a risk of delamination that could lead to residues being left on the skin.
The silicone supplier can recommend several options, including film treatment or using a specific primer. On open substrates, the challenge is to avoid penetration by the gel into the fabric. For this application, a high-viscosity silicone (at least 50.000 mPa.s) is preferred.
Make sure the silicone is fully cured on time
Once the silicone is correctly applied, it should be cured, typically in an in-line oven. Two parameters will affect the cure: temperature and time. While silicones can easily withstand high temperatures (up to 180°C), the substrates mentioned above do not, and will dictate the maximum temperature limit.
The length of dwell time in the oven will depend greatly on the temperature and the silicone chosen (namely its kinetic profile) but should be in the range of a few minutes. Silicone suppliers will be able to provide support to help determine the optimal cure time and improve the overall productivity.
Use a relevant test method to assess the coating’s performance
Due to its 3D structure and the great variations between individuals, skin is one of the most challenging surfaces to stick to. Traditional methods for self-adhesives include measuring the peeling force from steel or polycarbonate, but they fail to differentiate soft adhesives and to represent skin. Other materials like structured paper or artificial leather can be much more relevant. In any case, great care should be taken when trying to predict the performance of an adhesive on the skin. Nothing will replace actual wear tests.
Clément des Courières is business development manager for skin adhesives at Elkem Silicones. He works closely with skin-adhesive and wound-care companies to provide the best solutions for their needs.
The opinions expressed in this blog post are the author’s only and do not necessarily reflect those of Medical Design and Outsourcing or its employees.