Resin Eases Molding of Drug-Delivery Device

A specialty resin replaces polycarbonate in a device designed with complex snaps and undercuts.

Duoject�s Inter-Vial consists of two parts made from K-Resin BK15 SBC: The syringe socket, which houses the glass cartridge, and the vial socket into which the drug vial is snapped.

Duoject Medical Systems Inc. markets all-in-one drug-delivery systems for reconstituting powdered drugs. The Duoject Inter-Vial and the Inter-Vial Plus are two such products, which are simple to use and provide accurate dosing. Duoject licenses its technology to drug companies that use Duoject�s outside molders to produce and assemble the components for its drug-maker clients. In addition, Duoject handles between five and 10 specialty on-request projects each year for major biotech and pharmaceutical companies.

�The mission of our company,� explains Dave Reynolds, Duoject�s founder and president, �is to develop systems that are simple to fill by drug companies and safe to use by patients and caregivers.� In 1987, Reynolds received a patent for the Vari-Vial system and licensed the technology to several major drug manufacturers.

�I don�t really know how we came up with the idea,� Reynolds says. �While talking with a customer at his plant about filling syringes and watching his vial filling line, we wondered whether syringes could be filled on his existing vial equipment. So, we took a standard drug vial, cut the bottom off, and replaced it with a rubber piston. Then, we extended the height of the modified glass vial.� A key benefit of Reynolds� design is that it can be processed on existing vial packaging machinery, reducing revalidation time and investment in a dedicated syringe-filling line. 

For the Inter-Vial units, Duoject relied on the toolmaking expertise of Harry L. Braun (Crystal Lake, IL). The company reviewed the blueprints for the tools and provided valuable recommendations for refining the molds. It also contributed input on material selection. High-melt flow, clarity, gloss, and the ability of the material to accurately injection-mold parts with close tolerances for a secure fit were just some of the criteria.

�To meet our aesthetic and performance needs, our immediate thought for a clear, tough polymer was to go with polycarbonate,� says Daniel MacDonald, director of engineering services. MacDonald leads Duoject�s R&D team. �Braun, however, suggested K-Resin SBC mainly because of its mold-flow characteristics. We and our clients have found it to be a pharmaceutically elegant material that communicates a professional, high-quality medical device.� K-Resin SBC is produced by Chevron Phillips Chemical Co. (The Woodlands, TX).

Another reason for replacing polycarbonate with a grade of K-Resin SBC was the intricate nature of the product�s design. �There is a strong need for flexibility in our device, which polycarbonate did not offer. The clarity was there, but not the flexibility for the numerous snaps, latches, and grooves we have in our system,� MacDonald explains. �Polycarbonate just couldn�t provide the flexibility needed to adequately mold specific undercut and snap fits, whereas K-Resin SBC did. We also tried a clear ABS resin in the same molds, but it would turn slightly yellow when subjected to gamma sterilization. The gamma sterilization resistance wasn�t as good as that of K-Resin SBC.�

The two components of the Inter-Vial are screwed together. Once the system is activated, a fluid path is created, and mixing of the diluent and powdered drug can take place.

Chuck Kelley, medical market director for K-Resin SBC, says that K-Resin can work with other sterilization methods, too. �K-Resin SBC and K-Resin SBC/general-purpose polystyrene blends are essentially unaffected by either single or multiple EtO gas exposures. For that reason, K-Resin SBC is an even more attractive alternative for a wide range of medical applications where part sterilization is required.�

�Mold flow was another prime reason K-Resin SBC was suggested to us,� MacDonald says. �Our molder likes an easy resin to work with�you can more easily strip snaps and undercuts with K-Resin SBC than with polycarbonate. The K-Resin BK15 SBC formulation also provides good scratch resistance.�

Two parts of the Inter-Vial units are made from K-Resin BK15 SBC: the syringe socket, which houses the glass cartridge, and the vial socket into which the drug vial is snapped. These two components are screwed together.

The barrel holds a transfer needle assembly consisting of a spike at one end and a detachable needle at the other. Once the system is activated, a fluid path is created between the wet and dry compartments so mixing between the diluent and powdered drug can take place. When detaching the syringe portion of the device from the vial socket, the transfer needle used during the reconstitution process is captured by the vial socket and safely discarded along with the empty drug vial.

�In order to make this design a reality, we had to find a mold maker like Harry L. Braun, who specializes in building tools with lots of complex actions that come together cleanly,� MacDonald says.

According to the maker of the production tooling, Tom Braun of Harry L. Braun, �For these parts, we knew we�d pushed the limits of flow, so we incorporated hot nozzles and a cold runner system. K-Resin SBC did amazingly well with the parts that have a low taper, low draft, and long cores. It works best in the hot nozzle and cold runner system.�

According to Kelley, the BK15 grade has properties and characteristics ideally suited for this project. �Duoject�s Inter-Vial products have fine threads and fittings along with a five-stage barrel assembly that has to fit perfectly,� he said. �BK15 grade gives parts excellent detail on fast production cycles. Its high-melt flow rate improves cycle time by up to 20% when compared with similar materials at the same temperatures and clamping force.�

With a 200% elongation rate, K-Resin BK15 SBC provides the required flexibility. Its melt flow rate of 15 g/10 min permits molding with the higher length-to-thickness ratio needed to fill the cavity for injection-molding these components or any long, thin part. Molds for the Inter-Vial units incorporate a cam and actuator system plus hot nozzles and cold runners. Braun used three tools, each with a floating �A� plate. 

�The barrel assembly screws together,� says Braun. �With threads on one end and undercuts on the other, we really had to push the limits of the material. The female thread also has a series of four fingers with cliptails. We had to be especially careful with the unscrewing action in order to achieve this. A side unscrewing action with a nonrotating center core forms the four prongs, with a stripper plate on the �B� side.

�The K-Resin SBC material did amazingly well pulling the low tapered part out of low-draft long cores,� Braun continues. �The longer of the two molds has a floating �A� plate with a slide at the top that pulls the part out and also has double gating to maintain and help material flow through the core.�

The R&D work continues at Duoject. Two new products based on the successful Duoject principle of safe, precise, and simple drug reconstitution are planned for introduction this year. The Smart-Rod and E-Z-Link systems further extend Duoject�s drug reconstitution technologies to include integration with auto-injectors and pharmaceutical pen systems. �As long as there are challenges in the injectable drug transfer and delivery market, we look forward to providing viable solutions,� Reynolds says. 

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