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Small fortune: How to achieve bioabsorbable micro moulding success

Lindsay Mann, MTD Micro Molding, examines micro moulding bioabsorbable polymers. What impacts quality, performance, cost-effectiveness, and speed-to-market? And why aren’t they your average thermoplastic?

The market for less invasive micro medical devices continues to grow worldwide. In fact, the medical device industry leaps ahead almost daily, with constant demand for newer, smaller, never-before-seen micro medical devices. For the past 15 years, MTD Micro Molding has partnered with medical OEMs who came to MTD with an idea they weren’t sure could be made – looking for a solution. By refining its micro design for improved manufacturability and consulting on materials, its team of engineers helps brings these new products to market.

In addition to less invasive devices, novel uses of bioabsorbable technology are constantly evolving as well. And MTD has developed expertise in micro moulding bioabsorbable, implantable applications.

While bioabsorbables seem like a new trend, MTD has been micro moulding bioabsorbable medical components for 15 years and has worked with numerous types of bioabsorbable polymers.

Successful bioabsorbable micro moulding projects will meet the following criteria:

Here are just a few ways MTD helps medical device companies achieve bioabsorbable micro moulding success:

Runner optimisation

MTD’s MicroRunner tool has a ratcheting runner system that varies in diameter and aids in determining the minimum runner size required to fill the volume of your part with the goal of sizing a runner system to adequately mould a product without sacrificing material. This is extremely important for bioabsorbable materials, given that they are so expensive. This important step can result in an annual savings of over $250K in material for the medical OEM.

Robust validation

Validating a bioabsorbable part requires more steps than a non-bioabsorbable part, but with good planning and exact execution, the timeline to get to production is far from daunting. One MTD customer said it best: “We assumed that the smallest component in our device would be the hardest to validate, being that it was bioabsorbable, the most intricate, and critical-to-function. However, it turned out to be the smoothest validation process out of all the [larger, simpler] components in the device”. With a collaborative approach, MTD fully documents and customises its validation processes for each client and project. It stores each part’s quality score with all the process data, providing a high level of traceability for all our micro medical device parts.

Caption: Validating a bioabsorbable part requires more steps than a non-bioabsorbable part, meticulous planning, and exact execution

In-house testing

Many micro moulders need to outsource their testing for Inherent Viscosity (IV) and Differential Scanning Calorimetry (DSC), which can add weeks or months to the project timeframe. MTD has the in-house capability for real-time, continuous testing. This allows us to monitor, optimise, and report IV loss throughout the development and validation processes of a product as well as verify post-mould IV to release every production lot to the customer. In-house testing capabilities saves weeks in a bioabsorbable parts’ development process.

Minimal and consistent IV loss

What’s important to keep in mind is that post-mould inherent viscosity (IV) loss is dependent on the micro moulder and the material. Even if a micro moulder has the equipment to work with a particular material, they may have trouble delivering consistent product with controlled IV loss for each moulding run if they are not familiar with the complexities of the material. On-site IV and DSC testing capability enables the impact of process variables on these outputs to be determined and adjusted immediately, allowing for a better optimised moulding process, minimal and consistent IV loss, and improved capability.

One of MTD’s high volume production lines, having zero product returns with over 15 million components produced, has a historical post-mould IV variation of less than 2%.

Controlled handling and packaging

Storage of bioabsorbable and sensitive materials and moulded inventory in temperature controlled environments is critical. At MTD, temperature is monitored, logged, with alert limits if critical settings are exceeded. All manufacturing occurs in environmentally controlled ISO Class 8 cleanrooms and specialised shipping procedures for sensitive materials are in place.

Customised, specialised equipment

At MTD, specialised micro molding equipment is in place to control critical bioabsorbable processing factors like residence time, shear and degradation rate of material. MTD creates customised screws in-house, specialty drying media and procedures – not only is it investing in specialised equipment, it customises it completely once it arrives.

High volume bioabsorbable micro component production

When OEMs prepare to increase production volume of a micro moulded component, many focus on multi-cavitation tooling as a strategy to reduce piece part price. While increasing cavitation may be a cost-effective approach for higher volumes of simple thermoplastic parts, it is typically not the best approach for micro moulded parts, especially those that are bioabsorbable or made from other high dollar value materials. This may initially seem counter-intuitive.

Material waste

Figure 1 shows an example of optimised micro runner system designs that can be utilised for any material. You can see that the inherent material waste is in simple surface area. With expensive materials like bioabsorbable resins, which can cost $5-10 per gram, it’s easy to see how this amount of waste results in a non-cost savings situation. In micro moulding, it’s estimated that a runner-to-part ratio for an optimised 1-cavity design is about 80:1. For an 8-cavity, it’s an estimated 800:1. An 80:1 ratio may seem like the runner is big and wasteful, but the reality is the majority of the material will always live in the sprue and runner, because the micro parts they are feeding are extremely small in comparison.

(Figure 1)

Increased cycle time

When increasing from a 4-cavity to an 8-cavity runner system design, one may assume that you’d double the yield. But in reality it takes longer for the moulding process to create an 8-cavity shot — about 10–15% longer cycle than a 4-cavity version.

Mould & automation issues

Complex, tightly-toleranced micro designs lend themselves best to smaller cavitation tooling. With hundreds of variables to control in micro moulding, introducing higher cavitation can further expose the moulding process to risk. And risk is expensive. Hidden costs of high cavitation micro moulds are a result of significantly more time and resources being spent on hard-to-avoid issues like more frequent repairs, maintenance and downtime. The automation complexity increases with more cavities as well. Having a robot successfully and accurately remove a tiny, fragile part from a 1-cavity mold, present the part to multiple camera systems, and dispense the part into a custom packaging solution is a feat in itself in micro moulding. That challenge gets compounded significantly with more cavities.

How to ramp up production while decreasing piece part price

With high cavitation tooling not being an ideal cost-savings option for micro moulding, and especially for bioabsorbable products, how can piece part pricing effectively be reduced with production volume ramp up? We recommend focusing on the following four areas to bring the piece part down for bioabsorbable products:

Runner sizing: Use runner optimisation to pinpoint the minimal amount of material required for the runner system to be successful.

Production optimisation: Having a successful moulding optimisation period during early production helps with planning and efficiency, which can result in cost savings down the line.

Accurate forecasting, steady ordering: Accurate forecasting, blanket purchase orders, and steady ordering can allow the moulder and material provider to be more efficient with their processes, resulting in less manufacturing costs and piece part cost savings passed down to the customer.

(For example, MTD was able to reduce a bioabsorbable piece part price with steady ordering and accurate growth forecasts by 40% over a five-year span.)

Risk mitigation strategy: Designing the validation protocol to validate the widest range of bioabsorbable material IV lots available is a risk mitigation approach that could result in cost savings for the product.

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