Category Archives: Silicone Design

This category contains useful articles on Silicone Design related questions or topics

Barium Loading of Silicone Parts

Implantable silicone materials can be loaded with Barium (BaSO4) for future radiological detection purposes. Both restricted (29 days or less) and unrestricted (29 days and beyond) silicone materials can be loaded with BaSO4. This allows for the silicone part to be detected in future X-Rays and CT Scans.

Typically, the silicone material is loaded with a certain percentage of BaSO4. The loading percentage will depend on the level of contrast needed for the area of the body being viewed. Another common use of Barium loading has been in clinical trials and finished devices for failure detection and assessment since a part failure may be visible. Many of the major silicone suppliers provide Barium loaded materials today in the two implantable grades of silicone. While it is most common for the unrestricted silicone materials to be loaded, some of the restricted grades are as well.

Barium loaded Parts

Barium loading of silicone materials is common for the following applications:

1. Catheters

2. Shunts

3. Stents

4. Toe joints

5. Markers overmolded in silicone to detect and determine placement of devices

Now it is time for some questions for discussion on Barium loading. Have you ever manufactured BaSO4 loaded silicone parts? Did you load and mix the Barium at your company or did you purchase pre-mixed Barium silicone material? What Barium loaded silicone materials did you use?

Albright Technologies can mold your Barium loaded silicone medical devices in our ISO Class 7 hard walled controlled environment room. We can also source Barium loaded silicone material for you. If you need a custom mixed material with a certain percentage of BaSO4, Albright can mix it for you. If you are in need of a quotation for a Barium silicone related project, please visit our RFQ page here.

Compression Molding of Silicone Materials: Pros and Cons

Many Inventors, Engineers and Project Managers believe that injection molding is the best solution for their molded silicone products. However, this is not always the case due to the many variables and constraints of manufacturing silicone parts.

First and foremost, anticipated volume is always a true concern. If you only need to mold 1 to 20,000 pieces then a compression mold is more than suitable. Secondly, do your parts have multiple undercuts or is the geometry highly complex? If so, then a compression mold may be the most viable option.

Compression Molding

During the prototyping phase, a compression tool allows for rapid turnaround time. At Albright Technologies, we will produce a compression mold manufactured out of aluminum, along with engineering samples in 15 business days or less. Now, let’s take a look at the pros and cons of compression molding.

Compression Molding

Pros:

  1. Parts are dimensionally to specification and made with specified materials
  2. Short set-up times, allowing materials and colors to be changed quickly
  3. Flexibility in mold design
  4. Tools with multiple cavities can be made with less concern of balancing
  5. Welding allows for tool modification
  6. Faster mold manufacturing turnaround time
  7. Parts with multiple undercuts can be manufactured
  8. Mold tool cost is lower than injection
  9. Cost of compression molding machines is low
  10. Reduced molding process development time (day(s) not weeks)

Cons:

  1. Slower part production rates
  2. Can be difficult to control flash

Due to the nature of our business as a silicone prototyper and low-volume production molder, compression molding is a great fit. It offers our customers a less expensive, yet rapid option (when compared to injection mold tooling) to turn their product designs into reality. We provide our customers with silicone parts that are molded from complex mold tools with many undercuts as required.

Now, it is time for some questions for discussion. Do you or your company utilize compression mold tools to manufacture silicone parts? How would you rate your overall experience with the compression molding process? How much of your molding business is processed utilizing compression molds?

When turning your design into a silicone prototype, select the World’s Premier Source for Silicone Molded Parts. Get your 3D Models quoted today, visit our RFQ page.

Selecting a Suitable Medical Silicone

Silicone materials can be compounded to create materials that are both, bio-inert and fully compatible with biological systems. Medical silicones are compounded in a similar manner as general purpose silicones to obtain certain characteristics, such as durometer, elongation and tear strength. However, medical silicones undergo additional processing to remove unwanted residuals. This allows for the purest silicones to be manufactured for use in medical devices.

Silicone manufacturers have created systems to determine which materials should be used for a variety of bio-contact applications. These suppliers have created in-house certifications that are based on the positive results of a series of USP (U.S. Pharmacopeial Convention) Tests. There are six separate USP tests, from Level I to Level VI. Materials that meet each of the six tests, are often referred to as “Grade 6″ materials.

To better understand the requirements of each USP test, please see the table below.

table 1

Silicone manufacturers have created several groups in which to place these various medical silicones based on their anticipated use.

  1. Food Grade Silicones: Silicones of this group must meet USP tests, as well as FDA and USDA guidelines and criteria. Materials from this group would commonly be found in food processing equipment in the form of seals or even spatula blades.
  2. Medical Non-Implantable: Silicones of this type do not see use inside the body. Typical applications include tubing and one-time use disposables.
  3. Medical Short Term Implantable: These particular silicones can be implanted into the body for up to 29 days. A few applications include catheters and surgical tools.
  4. Medical Long Term Implantable: Silicones from this group can be implanted for a period greater than 29 days. Typically these materials are used in cardiovascular implants and remain in the body until end of life.
  5. Pharmaceutical: Silicone materials used in the pharmaceutical space, must pass all six USP tests and must be compatible with any drug coming into contact with the part. Drug delivery devices, such as punctal plugs, are typical applications in this group.

Determining which medical grade silicone material is required is based on the function and use of the medical device to be manufactured. Albright’s staff of engineers can assist you in material selection so that your medical application’s requirements are met. Please remember that although many silicone suppliers have conducted USP bio-compatibility tests on their respective materials, all finished medical devices will still need further USP testing. To learn more about medical silicone materials visit our Silicone Material page.

10 Things you Should Know About Silicone Over-Molding

Silicone over-molding is a process that is used to cover, bond or encapsulate an existing part with silicone material. For example, a silicone over-molding process may be used for providing a grip surface to a smooth plastic handle, a flexible septum on a hard plastic surface or for encapsulating an electronics assembly for mounting or protection from the environment.

The motivation for over-molding silicone may include a means of final assembly, enhancing physical surface characteristics and feel, providing a self-healing internal access (ie, an integrated septum), creating the finished product enclosure (such as a key-ring LED light), creating a thermally conductive path for heat-sinking or perhaps applying elastic properties to mounting components.

Important things you should know about silicone over-molding:

1. Over-molding bonding strength typically increases over time.

2. Polymers that are ideal for over-molding include: polycarbonate, nylons and other high temperature resins.

3. In order to have a clean silicone over-mold, the over-molded part must be made with the requisite tight tolerance and part samples of exact size are needed. A stable-dimensioned part is needed to develop and maintain the desired clean over-mold outcome.

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Silicone Adhesives: An Answer to Gentle Skin Adhesion

The goal, when adhering to skin, is to hold the device inplace until it is time to remove it and to not damage the skin, either during wear or at the time of removal. Using methods developed for determining the surface energy of plastics and other materials, the surface energy for human skin has been measured in the low twenties [dynes/cm] – in other words, skin is as difficult to stick to as untreated polyolefins or even fluoropolymers. Low surface energy, as a property of human skin, is generally great for most of the things skin is expected to do, such as easy removal of contaminants with simple soap and water. The downside is that tapes must balance between adequate adhesion levels for the majority of users – the middle of the bell curve – and the ends of that curve. When the adhesion is too low, the device may not stay in place long enough for the full therapeutic effect and if it adheres too well, the tape may cause some mechanical trauma at removal.

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Made In Massachusetts: Creating Jobs In The Bay State

Last month Susan Windham-Bannister, Ph.D., President and CEO of Massachusetts Life Sciences Center, participated In the latest installment of the WBZ NewsRadio 1030 Business Breakfast series. The panelists of business leaders & experts discussed the importance of making products and profits in Massachusetts. The group also discussed how the state’s manufacturing sector is staging an epic turnaround. The event examined and discussed the stories behind manufacturing success and how the state is helping to foster this growth and the beneficial ripple effect it is creating for the Commonwealth and beyond.

Click here to watch the video of the Business Breakfast.

Click here to learn more about Massachusetts Life Sciences Center.

What is the best test to determine the sealing capability of a silicone compound or design?

Two common tests are (1) to put the device or component under pressure using regulated compressed air and then submerging in water or other fluid. The leaks will show as bubbles or (2) use a colored die solution that contrasts with your part colors under pressure and the die will highlight leaks.

Ultimately whenever possible pressure testing of the final assembly under the working load or more, in as close to the final environment as possible can help identify failures caused by condition stack up.

Alternatively for many applications there may be published standard test methods that have been shown to be effective. Medical devices and aerospace both have test standards and you may find some relevant test standards under ASTM.

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Life Expectancy of a Silicone Part

While it depends on the specific application, generally molded silicone parts will have a considerable life expectancy. Once fully cross-linked a silicone rubber part will be virtually inert, meaning it won’t degrade or react chemically with most anything in the environment, aggressive solvents can break silicone down. Compared to thermoplastic elastomers and other rubbers silicone tends to retain its physical properties for much longer periods of time, and over numerous cycles of use, hundreds, thousands, millions (again this is somewhat dependent upon the application).

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