Silicone Life

Date: 31.01.18
Enjoying a 60 year history in the healthcare and medical industry, silicone represents the gold standard for biocompatibility and biostability, being the material of choice for medical devices and equipment, and hospital supplies. With a number of processing options available, silicone is becoming a critical element for device and equipment manufacturers to advance medical procedures and patient care. -By Donna Guinivan

IN SHORT

  • Silicones have long been established as a material of choice in the healthcare & medical industry.
  • With a number of processing options available, silicone is becoming a critical element for device and equipment manufacturers to advance medical procedures and patient care.
  • Trelleborg Sealing Solutions continuously works at the leading edge of process innovation; one area of focus is drug-eluting and combination devices.

SILICONES WERE FIRST USED IN HEALTHCARE AND MEDICAL APPLICATIONS in the 1950’s after extensive usage in the aerospace industry in the previous decade. Within twenty years, a considerable body of work established that silicone oils and cross-linked siloxane systems did not give rise to harmful consequences when performing subcutaneous, intracutaneous, and intramuscular administrations.

In the 1950s, a study reported the cultures of various tissues of warm blooded animals, known to be extraordinarily sensitive to foreign influences, showed no deviation from the usual growth picture on contact with liquid, semisolid, and rubber-like silicone products. Silicones have been characterized as biologically and toxologically inert since then as a result of this work, deemed to be suitable for medical applications, including within and in contact with the body.

Flexible Design

Ursula Nollenberger, Product Director Liquid Silicone Rubber (LSR) Components, says: “Silicone is ideal for medical devices and equipment, not only because it is inert and biostable, and biocompatible but also due to the fact that it can be processed in a multitude of ways from extrusion to molding, casting, coating and immersion; on its own or in combination with other materials and substrates, including API (Active Pharmaceutical Ingredients).

“This gives the designer tremendous flexibility and a myriad of choices to solve application challenges, including an option to combine functions through simple or complex product constructions. Each process tends to lend itself to certain types of applications. Extrusion is perfect for tubing and hoses, for instance, while Liquid Silicone Rubber injection molding can produce intricate moldings that offer significant cost savings as an alternative to an assembly. It is even possible to combine multiple processes principally to achieve lean manufacturing goals.”

SILICONE EXTRUSION

What is it? In the silicone extrusion process, silicone is forced through a shaped die to generate a continuous profile. Most commonly this is a standard or custom profile, such as tubing of specific inner and outer diameters.

Trelleborg Brands: Pharmatube™, PharmaSil™, NutraSil™, Pharmalable™, SilFit™

Trelleborg capabilities include: Production of single- or multi-lumen tube from standard and custom silicone materials in bulk or fabricated to customers’ specific requirements. These can be cut-to-length and incorporate color striping or tinting. Braiding into hose, with either single or double braiding, produced in ply or 4-ply plus wire wrap. Hose assemblies with various fittings are available, and all can be delivered in ready-to-use packaging

Applications: Fluid Management, peristaltic pumps, bioprocessing, medical devices.

CUSTOM-ENGINEERED EXTRUSION

What is it? Trelleborg Sealing Solutions has pioneered the technology of movable die and mandrels allowing the production of tubes with transitional geometries. This results in innovative designs, eliminating secondary operations and thereby increasing product reliability and reducing costs.

Trelleborg Brand: GeoTrans®

Trelleborg capabilities include: Production of single- or multi-lumen, thick- or thin-walled tubing down to below 5 millimeters / 0.02 inches. These can be ribbed, perforated and split, as well as be supplied with a varied inside or outside diameter and wall thickness. Any formed extrusion profile is possible, including with ends, coils or pigtails in single or multiple planes, as well as kinkresistant tubing.

The GeoTrans® process can be used to achieve hosing and tubing with in-built features.

  •  Balloons can be formed in a single extrusion step as an integral part of a catheter shaft
  • A single lumen tube can transition into a multi-lumen tube
  • Geo-Trans® Stop Lumen Tubing incorporates one or more stops, or restarts can be extruded into a single or multi-lumen
  • Bump or Tapered GeoTrans® tubing combines a variable outer diameter with either a constant or variable inner diameter

Applications:

Pacemakers and other implants, catheters, drug delivery, wound drains, medical cuffs, feeding tubes

LSR INJECTION MOLDING

What is it? Liquid Silicone Rubber (LSR) can be processed in a liquid injection molding (LIM) process. The liquid raw material is mixed from two separate components in a ratio of 1:1 and injected via a cold-runner-system into a hot mold. Curing of the parts in the mold takes place within seconds, therefore offering the advantage of fast cycling and production of large quantities quickly.

Trelleborg capabilities include: As one of the pioneers and true experts in LSR injection molding, Trelleborg Sealing Solutions uses a holistic approach to the engineering of component, tooling and overall process to take advantage of the full capabilities that highly viscous, fastcuring silicone offers. Whether madeto-print or beginning with a black box design, high precision in-house LSR tool making and optimum process automation are the foundation of high precision, high quality components that provide the lowest cost of ownership for the customer.

The Trelleborg Sealing Solutions automated approach to LSR processing is unique and the tooling design, from stage one, is developed not just to optimize the function of a component in the application, but also to maximize the effectiveness of automated operations. Flash-less part and tool design, waste-less process, in-process quality checks, batching by cavity and packaging are considerations that are always made.

In particular, Trelleborg excels in:

  • Micro- and Nano-sized components below 10 milligrams in weight produced using special needlepoint injection technology
  • Thin sections of 0.10 millimeters of less and delicate parts
  • Virtually flash-free manufacturing without secondary deflashing and demonstrating high dimensional stability
  • Forming of blind sections and undercuts reliably
  • For components requiring a HCR silicone material, Trelleborg equally employs compression, injection, or transfer molding technologies from prototype to multi-cavity serial production tools

Applications:

LSR injection molding is ideal for production of complex geometries and to consolidate various functional features into a single part in highvolumes. This gives significant advantages in terms of product reliability and total cost of ownership. Applications range from drug delivery such as primary drug packaging or wearable smart drug pump systems, fluid management, diagnostics, to biotechnology.

2C LSR INJECTION MOLDING

What is it? The simultaneous injection of Liquid Silicone Rubber (LSR) in combination with technical thermoplastics, dissimilar LSR, or other material allows the creation of hard-soft or soft-soft product combinations. This is commonly also referred to as 2K, 2shot, multicomponent injection molding, or coinjection.

Trelleborg capabilities include: Trelleborg Sealing Solution has the ability to combine two, three or more individual materials into one fully bonded, robust component. This is challenging in terms of tool making and process engineering, including automation, due to the differing process requirements of LSR and thermoplastics. Trelleborg Sealing Solutions is considered an expert in this field with the ability to develop and implement high cavitation tooling concepts for high-volume production.

Applications: 2C LSR injection molding allows the consolidation of assemblies and functions, combining a number of components of different materials into a single part, adding greater latitude and robustness in design. This gives significant advantages in terms of product reliability and total cost of ownership for the customer, with applications increasingly, for example, in personalized drug delivery systems and other types of smart medical devices.

2C LSR OVERMOLDING
What is it? A finished component of a different material, usually a thermoplastic or metal substrate, is overmolded with LSR in a liquid injection molding process in either a semi-automated or fully automated process. This method of production lends itself to smaller production quantities or to cases where, due to the substrates, an extra step is necessary to apply bonding technology.

Trelleborg capabilities include: Fully-bonded components are available in a variety of hardsoft or soft-soft combinations. For components requiring a HCR silicone material Trelleborg employs compression, injection, or transfer molding technologies from prototype to multi-cavity serial production tools.

Applications: 2C LSR overmolding allows the consolidation of individual parts and functions, combining a number of components of different materials into a single part, adding greater latitude and robustness in design. This gives significant advantages in terms of product reliability and total cost of ownership for the customer with applications ranging from hospital and home care equipment and devices, biotechnology, and fluid management.

DIPPING

What is it? There are two variants of dipping. One is dip-molding, whereby a mandrel is dipped into a silicone dispersion. Once fully cured, the mandrel is removed and the finished product is a shell or balloon. The second option is to dip components into a silicone dispersion to coat them to achieve specific functions.

Trelleborg capabilities include: Trelleborg Sealing Solutions is an expert in silicone dipping with unique material and process engineering experience developed over decades.

Applications: Products and devices such as catheter balloons, tissue expander shells, breast implant shells, electrosurgical blades or other surgical tools.

SILICONE SHEETING

What is it? High Consistency Rubber (HCR) may be formed into continuous sheeting of uniform thickness in a specialized calendering process that compresses silicone material through a pair of polished steel hydraulic rollers to intended product specifications. Another means of producing individual sheets is through molding of LSR or HCR.

Trelleborg Brand: PharmaElast™

Trelleborg capabilities include: A variety of calendared and molded sheeting options, vulcanized, unvulcanized, reinforced, or non-reinforced in either rolls or cut to purpose, is available. Calendared sheeting may be pigmented and a number of surface finishes are possible with thicknesses available as low as 0.5 millimeters/ 0.02 inches. PharmaElast™ is available in sheet sizes of either 150 millimeters by 200 millimeters/ 6 inches by 8 inches or 300 millimeters/ 12 inches square.

Applications: Silicone sheeting is a key component in various types of valve assemblies. Mesh-reinforced sheeting is, for example, integrated as sewing rings on artificial heart valves, while laminated sheeting containing both vulcanized and unvulcanized layers, for example, can be used to seal tissue expanders and mammary devices.

SILICONE FILM

What is it? In this process, LSR is spread by a vertical blade across a carrier belt into a high precision, thin-film continuous sheet and cured in line. The cured sheeting may then be processed further from simple die-cutting to multi-layer composite structures, or simply spooled as finished product.

Trelleborg capabilities include: The knife coating capabilities of Trelleborg Sealing Solutions are unique. Compared to traditional methods, the process significantly reduces the risk of particulate contamination due to environmental exposure and larger batch sizes can be produced at lower cost. In addition, sheeting thickness is more precise, accurate and reproducible down to film thicknesses of as little as 0.025 millimeters/ 0.00098 inches.

Applications: Applications involving wound management and scar reduction, such as custom dermal adhesive gel products.

DRUG-ELUTING DEVICES

What is it? Silicone is used to produce drugeluting devices. Due to the material's favorable porous nature, Active Pharmaceutical Ingredients (API) can be integrated into a silicone matrix, so that these drugs are eluted into the human body at specific doses over time.

Trelleborg capabilities include: Two methods of adding API to silicone for drug delivery devices exist. The established method is the addition of API to raw silicone. The alternative and more recent development is the impregnation of API into vulcanized silicone by immersion. Trelleborg Sealing Solutions is established in the addition method to produce combination products and at the forefront of the new immersion technology.

Applications: Hormone regulation, autoimmune conditions, diabetes, oncology, pain management, abuse deterrence and Central Nervous System (CNS) disorder treatment.

Further Reading: Whitepapers

Trelleborg Sealing Solutions continuously works at the leading edge of process innovation to support advanced products and applications in the healthcare and medical industry. One area of focus is drug-eluting devices and combination products. For designers and engineers in these fields, two new whitepapers are now available
exploring these subjects.

Supporting the advancement of drug-eluting devices

Presenting alternative methods for addition of API to silicone components for drug-eluting medical devices

Over the past years there has been a stepped change in the treatment and control of medical conditions. Pills and injections can be viewed as imprecise, irregular and inconsistent in their delivery of drugs. Hence the rapid growth and development of drug device combination products, in particular those that elute regular controlled doses of drugs precisely and consistently to a treatment area.

To the extent that combination products can successfully be developed for manufacture in volume and to consistently meet drug efficacy as well as regulatory requirements, the demand for these products will undoubtedly grow. This will be driven by trends in the market, such as an aging population, increasing chronic disease, and global healthcare concerns related to obesity, diabetes and infectious diseases combined with the benefits that drug device combination products can offer.

Drug device combination products, defined as a device integrated with drugs, can be produced in and by a variety of materials and processes. One of the most successful materials for production of combination products, in particular implantable ones, is silicone. Two methods of adding Active Pharmaceutical Ingredients (API) to silicone, the addition of API to raw silicone and the impregnation of vulcanized silicone with API by immersion, are discussed in the whitepaper.

The traditional method of adding API to raw silicone is proven and effective. However, it is limited to API that are resistant to a vulcanization process and exposure to heat. A newer method of impregnation of vulcanized silicone by API, potentially broadens the APIs that can be used in drug-eluting silicone devices. This whitepaper presents test results that prove that this method works, potentially opening drug-eluting devices to delivery of a wider range of API.

Download whitepaper

Fighting Hospital Acquired Infection

Exploring methods of combining silicone tubing with APIs

Healthcare-Associated Infections (HAI) are a major, yet often preventable threat to patient safety. If they are controlled, it can have a significant impact on the survival rate of patients that undergo procedures and treatments, so the minimization of these infections is an important focus globally.

There is evidence of a decrease in hospital-acquired infections, however, they still remain a significant issue. In particular, catheter-associated infections are difficult to prevent on catheters and tubing due to its inherent positioning part in and part out of the body, even when products are made of biocompatible silicone.

Silicone is usually used for the catheter tubes and though the material is biocompatible and biostable, it is not immune to bacterial colonization. Techniques exist that can reduce this colonization including coating, addition of antibiotic Active Pharmaceutical Ingredients (API) to raw silicone and the impregnation of vulcanized silicone with API through immersion. In this whitepaper the three techniques are evaluated.

Download whitepaper