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Polymer Solution Casting Thin Layering Process Overcomes Multilayer Tubing Challenges

Wed, 04/02/2014 - 2:47pm
Paul Schmeling, Director of Operations, Avalon Labs

Medical device manufacturers are demanding polymer tubing that offers increased functionality for market competitive demands while remaining cost-effective or reducing manufacturing costs. Co-extrusions or multilayer tubing is commonly used to adjust the properties of a device through the combination of multiple layers of resins with different properties (such as lubricity and flexibility) on the I.D. and O.D. of the tube to attain performance characteristics.

As tubing designs become more complex, medical tubing production has had to adapt to accomplish all of the requirements and typically with several different manufacturing steps and bonds necessary. To meet performance needs extrusion technology utilizes multi-layer extrusion, or reflow. Multi-layer technology is used to improve functionality or to combine a weldable OD material with additional materials that add performance properties.

Avalon’s polymer solution casting technology utilizes a liquid polymer layering process to create an all in one piece continuous construction with no bonded joints and increased design flexibility. The polymer solution casting seamlessly offers the ability to add multiple components, varying wall thickness or diameter along the length of the device. It is the ultimate multi-layering approach offering pinpoint delivery performance where needed.

Similar materials are used in both approaches to achieve essential device operational requirements. Both options can provide lubricious inner and outer surfaces or radiopaque materials. A wire-reinforced layer is also available with both manufacturing approaches for added stability and strength as needed.

Polymer Solution Casting manufacturing offers no bonded joints, single piece construction, with availability of changes in diameter, wall thickness or material properties along the length. With polymer solution casting the process provides the ability to embed components in virtually any configuration. As an example polymer solution casting works effectively with laser cut hypotubes gaining interest for the ability to add flexibility and strength seamlessly along the length of the shaft. It offers the optimal approach for complex medical devices.

With Extruded Tubing bondable materials need to be located either on the OD or ID for ease of assembly of complex medical devices. It’s a several step process to achieve the desired outcomes with some extruders offering up to three/four materials on an extrusion run and then multiple pass options. Many times materials aren’t compatible requiring a tie-layer or lamination processing steps.

Bonding two incompatible materials using a tie layer is commonly how extruded tubing bonds these materials. The tie layer provides no mechanical function beyond bonding inner and outer desired layers. It is optimal to have the tie layer as thin as possible to maintain ID and OD specifications with a ± 10% achievable wall thickness. There is also variance and difficulty with keeping concentricity and is provided with a minimum of 85 - 90% concentricity.

Typically it’s desired to minimize the impact of the additional layer on the overall size of the tube, the tie layer is frequently applied as thinly as possible and ODs may have to compensate for the incorporation of a tie layer.

Polymer Solution Casting excels at multi-layering as it is a thin layering process with the ability to offer different wall thickness down the length of the device or different materials along the length and embedded reinforcement features for optimal pinpoint function. Wall thickness varies dependent upon material which correlates to device duration of use and biocompatibility. Dependent upon material the thin layering process can range from .004 - .040” and with single coating layers to 0.00018 to 0.00025”. Additional layering can be applied to the proximal end for strength and thinner layering to the distal end for flexibility. This approach is optimal when specific function is required such as inner lubricious layer and/or biocompatible outer layer with thin layers of material placed for most effective operation.

Development costs can be relatively less with polymer solution casting as the molds are economical and manufacturing is easily scalable as needed. Polymer solution casting offers highly-customized shaft performance characteristics without the assembly costs and weak bonded joints associated with traditional extrusion methods.

As medical devices become more complex standard extrusion technology pushes its limits and polymer solution casting can offer a cost-effective alternative with feature-rich options and device design flexibility.

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