Duesseldorf, Germany—New applications for liquid silicone rubber offer the potential to avoid invasive surgery. But development of the in-situ cure implant technology will take time.
That's according to Anthony Feng, vice president for biomaterials at NuSil Technology L.L.C., a Carpinteria, Calif.-based silicone materials producer.
"Application potentials are vast. But it takes time, also as we have to be responsible and do enough tests to support and encourage it," Feng said.
NuSil launched the LSR in-situ curing implant technology at the 2017 Compamed trade fair in Duesseldorf. At the 2018 show, Feng talked about progress for the material.
"I think if you look at in-situ cure, even though it is a year on now, I still think there are a lot of noninvasive surgery applications that are not known yet, where this material can be used. We have, meanwhile, a couple of new formulations for in-situ cure," he said.
Feng pointed out that the in-situ implant cure solution means the potential to avoid invasive surgery for medical devices.
"You can just inject the material and let it cure inside the body. But one of the biggest challenges is that when you get the material into the body, it needs to be sterilized and the type of packaging (syringe cartridges)we offer to deliver it allows ethylene oxide sterilization of the uncured material as it enters the body, allowing it to be safe in the body," Feng said.
He said NuSil customizes in-situ cure LSR for customers in terms of viscosity, cure profile and cured material physical properties.
"So that is a lot of collaborative work we do with our customers," Feng said. "A lot of tailoring, because it depends where in the body it is going, what function it plays and the time within which it should cure. All of this determines how we formulate the LSR for particular uses and for each particular customer."
As Feng admitted, there is great caution when it comes to putting silicone elastomers inside human bodies, and despite negative press on silicone breast implant problems in France, NuSil sees it less as a threat and more of an opportunity for the company to emphasize "how we make large investments in our resources to ensure we are compliant with the regulatory landscape."
Feng also gave an update on NuSil's involvement in drug-releasing vaginal rings, which LSR World covered in February 2017.
NusSil's Trelyst LLC medial silicone applications subsidiary in Carpinteria has supplied LSR for mixing and dosing at Qpharma AB in Malmoe, Sweden.
"The vaginal ring application is close to becoming finalized. I think it will be available in the market very soon for consumers to use," he said. "Very seldom do we launch something for consumers to use. On the innovation front, we focus very much on customized solutions for our customers."
Anti-HIV or other drugs are introduced into the LSR at the liquid uncured stage and success depends very much on elution rates of drug release from the LSR ring, and that, in turn, varies with different drugs' formulations and active ingredients, as well as being affected by "how you would like to cure the silicone, the type of silicone and how it cures," Feng said.
"So we have to do research with the customers to see if it meets their requirements and then develop an appropriate LSR formulation for them," Feng added.
Another exhibitor at Compamed 2018, Stein am Rhein, Switzerland-based Trelleborg Sealing Solutions A.G., has capability of adding active pharmaceutical ingredients to LSR for drug delivery, by the "established proven and effective" method of addition in powder form to "raw" uncured LSR, but also most recently by impregnation into cured LSR by immersion, a technology area where TSS claims to be in the forefront.
Post-cure impregnation allows for the use of ingredients that cannot withstand cure and/or post-cure heat, according to TSS.
In a September 2018 white paper, TSS says direct controlled drugelution from implantable "combination" silicone devices containing APIs ensures greater patient compliance than today's 50 percent noncompliance and is more effective than conventional injection or pill use. It talks about API addition solutions for hormone regulation, autoimmune conditions, diabetes, oncology, pain management, abuse deterrence and central nervous system disorder treatment.
TSS refers to a Grand View Research Inc. study that predicted the overall drug device combination market should reach a value of $177.7 billion by 2024.
The company maintains LSR is preferable over other nonbiodegradable drug-eluting alternatives of polyethylene-vinyl acetate and thermoplastic polyurethane, "based on extensive testing and proven results in health care and medical applications over decades."
It adds that silicone elastomers are considered to be the gold standard in terms of biocompatibility and that existence of polydimethylsiloxane polymers within these elastomers in a helical formation with weak intermolecular forces between polymer chains "contributes to the high free volume of silicone rubber and to its exceptional permeability" for API absorption and release.
Immersion impregnation of cured LSR requires use of solvent to swell LSR before immersion in drug solutions, according to TSS. Effectiveness is restricted by the presence of some "loose juice"—noncross-linked polymer chains in fully cured LSR—as these can be extracted from LSR by organic solvent exposure. The result can be drug diffusion from a solvent into LSR being offset by greater noncross-linked polymers diffusing from the rubber into the solvent, leading to distortion of absorbed drug weight calculations.
TSS suggests this could maybe be overcome by improving drug solubility in the LSR by "modification of the backbone of the LSR polymer or the reinforcing silica filler surface."
Kaiserslautern, Germany-based Freudenberg Medical Europe GmbH has announced the start of development in using low-temperature cure LSR from an unspecified LSR material supplier. This is not foreseen for implants, but for the "combination of silicone and temperature-sensitive plastic, incorporation of heat-sensitive ingredients like pharmaceuticals into silicone and encapsulation of electronic parts or flexible printed circuits," the company announced in January 2018.
FME claims UV-cured silicone "opens the door for new medical device design applications as well as lower costs for customers."
Molding and extrusion trials had been made at the company's Carpinteria, Calif., silicone technology lead center following an approach by one of the company's silicone material suppliers.
Momentive Performance Materials has been talking a lot about this technology in the past few years.
Lincolnshire, Ill.-based contract manufacturer Flexan L.L.C. promoted mold-sourcing capability and molding facilities in Suzhou, China, where it has 65 compression and injection presses with clamping forces ranging between 50-500 tons.
It gave an example of a requirement for Breda, Netherlands-based Polyfluor Plastics BV, a producer of extruded fluroplastics products, to supply 400,000 injection molded LSR in-vitro fertilization parts for an unspecified medical industry OEM, a task that Polyfluor contracted out to Flexan. A follow-on contract could require as many as 3 million parts.
Flexan Suzhou offered fast time to market, as it produced mold tools within five weeks and first molded part samples from the new tools at its clean room molding facilities within five days.
On receiving the samples, the customer expressed a wish for a finer surface feel and Flexan achieved this by adapting mold process conditions and having the molds finely polished.
Flexan's Paderborn, Germany-based European commercial leader Werner Karau remarked: "Of course we can, as always, offer European and U.S. express mold making in Europe, but the customer then has to consider it very carefully, especially if the same quality can be offered at our location in China."
Key to the fast mold delivery time is that Flexan Suzhou "has a large requirement of different injection molding tools and therefore has firm production capacity commitments at a large number of well-qualified mold and toolmakers on which it can rely," Karau said, "and this ensures us overall fast tool building."
Flexan is more geared up in Suzhou to deal with many different tools and relatively simple parts in large production series, but its U.S. plants focus more on complex part production, where downstream processing and assembly operations are often required.
Eric Wetzels, Polyfluor Plastics managing director, is pleased with the Flexan Suzhou project. He had poor experience with Chinese-owned suppliers.
Molding and printing
Cavaillon, France-based Sterne S.AS. added LSR molding to its mold shop in 2014. It now focuses on using a KraussMaffei CX 130-380 two-platen injection press installed in April 2018 for LSR menstruation cups, alongside other LSR applications.
Sterne has 10 LSR and HCR injection molding machines, four of which running in clean rooms.
This is in addition to Si-O Shaping UV-curing LSR 3D printing machines installed since 2016.