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Q & A
What is silicone?Any of a class of synthetic materials that are polymers with a chemical structure based on chains of alternate silicon and oxygen atoms, with organic groups attached to the silicon atoms. Such compounds are typically resistant to chemical attack and insensitive to temperature changes and are used to make rubber, plastics, polishes and lubricants. (source : Google Search)
What is liquid silicone?Liquid silicone is a high purity platinum cured silicone with low compression set, great stability and ability to resist extreme temperatures of heat and cold ideally suitable for production of parts, where high quality is a must. Due to the thermosetting nature of the material, liquid silicone injection molding requires special treatment, such as intensive distributive mixing, while maintaining the material at a low temperature before it is pushed into the heated cavity and vulcanized. (source : Wikipedia)
What is Liquid Injection Moulding system (LIMs)?Injection molding of liquid silicone rubber (LSR) is a process to produce pliable, durable parts in high volume. LIMs is mainly comprises injection unit, mixer unit and raw material bay unit. Raw materials are shipped in two separate containers (known in the industry as a kit) identified as "A" and B" compounds, with the "B" side usually containing the catalyst, but may vary based on the brand of silicone used. The two (A and B) compounds are then mixed in the mixer unit. Once the two components come together the curing process begins immediately. A colour pigment can be added via a colour injector used in conjunction with the material pump before the material enters the mixer unit. A chiller supplying cold water to jacketed fittings is typically used to retard the curing process prior to the materials being pumped into the injection unit.In the injection unit, mixed compunds are pumped through cooled sprue and runner systems into heated mould where the vulcanization takes place to form the desired silicone components/parts. Moulds and toolings are varying in design, execution and cost.
PVC vs Silicone for use in medical devicesPVC is durable, inexpensive and easily manufactured. However, the use of PVC in medical device manufacturing requires the addition of plasticizers to make the material more pliable. Bis(2-ethylhexyl) phthalate, commonly abbreviated DEHP is the most often used plasticizer in PVC products. DEHP has a low vapour pressure but the temperatures for processing PVC material are often high, leading to "contaimination" of the PVC material. The "contaminated" PVC may leech DEHP substance into liquid that comes in contact with the PVC plastic. Hence, the use of PVC in medical devices has been raising concerns about health risks to patients. Among the health risks:- Adverse effects to the sexual development of male human Toxicity effects Obesity efffects Cardio-toxicity effects A more detailed DEPH effects on environment and living organisms can be found at Wikipedia site. Silicone as alternative. Among the properties of silicone are:- Chemically inert Superior compatibility with human tissue and body fluids Odourless and tasteless Does not support bacteria growth Will not stain or corrode other materials Why use Silicone in medical devices? Low compression set Wide range of durometers : 5 to 85 shore Wide temperature range : -75°F to 600°F (-60°C to 315°C) High tear strength : up to 250 ppi (45 N/mm) High tensile strength : up to 1500 psi (10 MPa) Good elongation : up to 1250% Flexibility and... due to the chemical properties of silicone itself! Application examples of silicone in medical devices Minimal Invasive Surgery ie Laparoscopic, Thoracospic and/or Ophthalmic Advanced drug delivery Vascular devices Catheter components IV therapy
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