When it comes to balloon catheters — pushability, trackability, and crossability — are easy to define, yet challenging to design. Intravascular procedural performance such as angioplasty requires the ability to transmit force along the length of the catheter shaft so that the catheter can be pushed (pushability) through the patient's vasculature. In addition to the pushability it needs to offer sufficient flexibility to allow the catheter to track (trackability) over a guide wire through tortuous anatomy. The catheter also needs to cross (crossability) stenosed areas of the patient anatomy.

Many organizations are using hydrophilic, hydrophobic, silicone or other surface coating techniques and formulations for reduced friction force. This is an end-user and procedural design consideration and it is important to the ultimate market success of the balloon catheter.

Multiple hurdles

There are many design challenges when it comes to achieving the right combination of physical properties for balloon catheters. One requirement is to provide a soft distal tip to prevent or minimize injury to arterial vessels during catheter advancement. An inherent difficulty exists in forming a connection between the soft tip and the catheter that is strong enough to prevent disengagement of the soft tip or kinking between the tip and catheter shaft junction. It is necessary to balance the strength of the connection between tip and catheter shaft with the need to minimize the stiffness of the distal end of the catheter.

Another challenge involves designing the balloon catheter in such a way that it will guide smoothly over a guide wire in the clinical setting. The inner lumen of a coaxial design or the guide-wire lumen of a multi-lumen shaft is an important clinical factor. It will determine the guide wires used, and it is dependent upon anatomical considerations, such as arterial access. The size of the sheath and guiding catheter used is also dependent on arterial access and will limit the outer lumen dimensions, which affects inner lumen sizing. This can put constraints on the catheter design along with considerations on guide wire standard sizing and availability.

Ergonomics also plays a key role when it comes to the design of the luer hub, which connects the balloon catheter to air pressure for inflation and deflation of the balloon in the clinical setting. For ease of handling and gripping, luer hub designs are contoured and incorporate wing grips. The interior of the hub is tapered for easy insertion of the guide wire. And threads are well-defined so as to eliminate any possibility of cross-threading concern. The luer hub must also comply to ISO-594 (for lock fittings).

Materials selection

Newer markets emerge everyday along with ever-increasing technology demands including ultra low profile and higher burst pressure capability. Primary materials used to achieve these attributes for the balloon and catheter shaft include advanced performance nylon tubing with engineered nylon resins such as nylon 12 and polyether block amide (PEBA) in multiple durometers (e.g. 6333, 7033, and 7233). Other materials used in balloon and catheter development include polyethylene terephthalate (PET) and polyurethane.

Careful consideration of balloon materials and characteristics start with the need for specialty balloon tubing with consistent lot-to-lot characteristics, a critical factor for driving yield improvement in medical balloon manufacturing. It is a key process for achieving precise tubing dimensions. High-quality specialized balloon tubing can improve balloon yields and functional requirements.

Custom molds and balloon-forming equipment are necessary for accomplishing a final balloon design and product. The balloon-development process is simplified when working with a contract manufacturing organization that has in-house capabilities to offer a multitude of custom molds and end plugs. Balloon development must also take into consideration aging, shrinking, and annealing processes. An experienced balloon development company can provide rapid prototyping and study requirements expertise potentially shortening product deliverables and time-to-market.

Focus on FDA

Design engineers must keep in mind that the FDA or proper regulatory agency will require data that indicates biocompatibility testing, design controls, and product specification testing has been completed and that the devices are safe for the intended use of the catheter. The FDA and worldwide regulatory agencies do not approve materials. It is the manufacturer's responsibility to show that a device incorporating a material is safe and effective for its intended use. Outside suppliers or contract manufacturing resources can benefit the design process by providing physical and biocompatibility testing and analysis data for submission, ultimately resulting in potential time and cost savings.

The overall process to develop a balloon catheter product for manufacturability starts with concept development involving dimensions and physical properties, then full prototyping, feasibility verification and validation, and finally, full-scale production after meeting regulatory and clinical requirements. An experienced balloon catheter manufacturing supplier can accomplish this while reducing time-to-market.

For continuous R&D updates, read the Medical Edge e-newsletter

For your free subscription, visit http://medicaldesign.com/subscribe/newsletters/