Drying is an important part of the process for any product made of hygroscopic (meaning affinity for moisture) thermoplastic. For medical implants made of bioabsorbable polymers, dryness is particularly critical. Inadequate drying can produce a variety of problematic results. These include: lack of tensile properties and impact resistance, as well as varying flow characteristics.
Bioresins, much like other hygroscopic thermoplastic resins, can suffer three types (or a combination of these three types) of degradation: thermal, mechanical or hydrolytic. In most thermoplastics these types of degradation occur chiefly during the molding process. With bioresins such as the PLA, PLG , and PGA families, hydrolytic degradation also occurs before and after the molding process.
An implantable device must decay or degrade in the body as part of the absorption process. Different materials and part designs have different rates of degradation in the body (where it is in a moist environment). The rate of degradation and retention of mechanical properties is affected in no small degree by the way the resin was dried and how the dried resin and finished part were handled.
If a bioresin grocery bag degrades quicker than it was designed to, the results can be the bottom falling out and groceries on the ground. If an implantable device degrades quicker (or slower) than designed to, the results can be harmful to the patient. The degradation process of the implant is key to resorption in the body.
Run of the mill dryers are generally not sufficient to control the moisture as well or reach the super-low moisture levels desired for absorbable implants. Many implant molders opt for vacuum dryers or compressed air with membrane dryers. Since most implants are small, vacuum ovens designed for lab use is another option for resin drying. In any case, the drying schedule and temperatures provided by the resin manufacturer must be strictly followed.
In many cases, the resins must be dried to less than 0.02% (200 ppm) and the resin and finished product must be maintained dry. This requirement mandates an inert gas such as nitrogen atmosphere in any non-vacuum dryer hopper, humidity controlled atmosphere in the cleanroom, vacuum packing with a desiccant and nitrogen, and refrigerated storage of the resin prior to drying.
It is not enough to strictly follow the drying and handling procedure, the resin dryness must be well tested, documented, and controlled. The dryness data is so important because it must be correlated with part degradation data to be able to predict implant device performance and absorption in the body. Lost weight or halogen type moisture analyzers are relatively economical devices but should be equipped with data acquisition and logging technology.
Drying bioabsorbable resins requires specialized knowledge, methods, and equipment, but is key to successful bioresin implant molding.
Much is published about currency manipulation, unfair trading practices, and low cost offshore labor as primary reasons for the large loss of high paying manufacturing jobs in the USA. One thing rarely mentioned is the concept that the introduction of computer controlled machines and automation have had a significant impact on USA companies need for manual labor. Requirements for labor today are far different than in days past as manufacturers now need higher skilled people, but less of them. Special interest groups often look for easy targets when determining the reasons for job losses, but the bottom line is that in many cases, companies need fewer people to do the same amount of work as before. And as labor costs continue to climb, it’s the first place a manufacturer will look to reduce his overhead expenses.
Back in the early days of moldmaking, the product was the result more of craftsmanship than technology. A crusty old moldmaker with thick glasses, clad in a denim apron would take the project from a block of steel all the way to a finely-fit, fully-functional injection mold. The mold was his masterpiece. He took his time hand-fitting the components, and each mold, even for similar products, was often unique. Some tools took the moldmaker the better part of a year to produce.
Times have changed though, and the necessity of quick time to market and short product lives have shrunk lead time, while demanding resins and complex part geometries have dictated that robust and precise molds be built in much less time than in the past.
These shortened lead times are where technology has really stepped in to help. The crusty moldmaker has been replaced by a technologically savvy leadman, and each stage of the mold building operation is done under the control of specialized operators who are completely versed in the technology of their stage of the operation.
All steps of the mold building operation (design, steel milling, electrode cutting, wire and sinker EDM operation, turning, and grinding) are Computer Numerically Controlled and connected via a local area network. Many of these operations are palletized and robot attended, enabling lights-out operation to further reduce time to delivery of the finished mold. Direct access to 3D design models is available to every operator at every phase of operation. Time-tested standards like prints and setup worksheets are becoming a thing of the past. Even the progress of jobs and tracking records are maintained electronically.
Matrix Tooling, Inc. is now thirty years old. Having seen the mold shops of even twenty years ago, it would have been hard to imagine that today’s machining centers with their brightly colored computer displays, robotic arms, and servo motors have any relationship with the mold shops of the “old days” where craftsmanship was king.
But there’s no doubt craftsmanship still has its place. We’ve spent the last thirty years blending the best aspects of traditional mold making with state-of-the-art technology to produce a precise, top quality and robust injection mold as quickly and economically as possible. The first paragraph of the Matrix Tooling quality policy reflects this: “Matrix Tooling, Inc.’s mission is to combine traditional craftsmanship with state-of-the-art technology in designing and producing the highest quality injection tooling and molded products.”
Our team members have found the key to successful mold building and we take great pride in combining the latest technology with old-time craftsmanship into every build. Though the mold building business has evolved each team member takes the same pride in our end product as the crusty old mold maker with the denim apron.
Brent G. Borgerson
Senior Process Engineer (Older Molder)