Fluoropolymers VS Polymer Materials PTFE/PFA/FEP/ETFE /PI/ PA/ PU in Minimally Invasive Interventional Medical Devices!

The polymer materials commonly used in minimally invasive interventional medicine are a crucial part of the treatment process, and high-performance interventional medical equipment can affect the safety of surgery and the comfort level of patients. Therefore, such medical materials should have characteristics such as good biocompatibility, easy processing, high mechanical strength, and corrosion resistance. Polymer materials are widely used in minimally invasive medical devices, such as stents, membrane materials, catheters, etc.
The development, production, processing, and application of minimally invasive medical device materials involve many biomedical materials, which can be mainly divided into input polymer materials and implantable polymer materials. Both of them play an extremely important role in the field of minimally invasive intervention medicine.

Polymer materials for conveyors

In minimally invasive medical devices, commonly used ones include stents, covered stents, etc. These instruments and conveyors constitute a complete interventional medical device. After transportation, the conveyor also needs to complete the disposal process of being placed and removed from the body, so it is usually a disposable item. However, the performance of the transporter directly affects the smoothness of the surgical process and the recovery process after surgery. More importantly, it affects whether the treatment equipment can be stably and accurately placed in the designated area

During the treatment process, it is necessary to choose a vein or superficial artery approach that is easy to puncture, and it is also necessary to transport the treatment equipment to the lesion site through tortuous blood vessels. This requires the transporter to have good tracking performance, flexibility, and torsion control. Various types of polymer materials with different properties provide various directions for conveyor materials, such as polyether block amide copolymers, fluorine polymer materials, etc.

1. Polyetheramide block copolymer (Pebax)

Pebax produces different hardness products by combining different types and proportions of hard segment linear polyamide segments and soft segment polyether segments. The polyether soft segment provides ductility and flexibility, while the polyamide hard segment provides physical crosslinking. Not only does Pebax material have a wide range of hardness, but it also has good mechanical properties, biocompatibility, and ease of processing, thus receiving widespread attention.

Pebax catheter

Due to the good compatibility and hot welding strength between different models of Pebax, different Pebax materials are used as different parts as needed to obtain a catheter with gradually increasing hardness and better fit when used as a minimally invasive interventional treatment instrument material. For example, the curved blood vessels in the front end of the human body need to be softer to reach the affected area; And the backend requires a certain level of hardness to maintain sufficient support; During the transition, it is required to be smooth and have good connection strength to reduce the puncture and resistance to the advancement of blood vessels during use, while maintaining integrity during treatment. From this, it can be seen that Pebax materials are very important in minimally invasive interventional treatment devices.

2. Fluorine polymer materials

Fluorinated polymers have attracted widespread attention in minimally invasive medical device materials due to their low friction coefficient and excellent biocompatibility. Among them, polytetrafluoroethylene (PTFE) has the smallest coefficient of friction, making it one of the most commonly used materials in minimally invasive interventional treatment instruments, as it can be directly used as a delivery tube

However, PTFE belongs to non-polar polymer materials and cannot be directly subjected to adhesive or hot welding processing. Therefore, it can only be connected by mechanical methods; In addition, the modulus of PTFE is relatively low, and it is prone to elongation and deformation during use due to frictional resistance and tension, which limits the direct application of pure PTFE as various conduits. Usually, it needs to be made into composite materials during use.

Polyvinylidene fluoride (PVDF) and perfluoroethylene propylene copolymer (FEP) have the lowest melting point, making them easier to heat weld or perform adhesive processing. Therefore, they are used when minimally invasive medical device materials have high requirements for friction coefficient and processing.

When using fluorinated polymers as catheters or conveyors, it can reduce the resistance of therapeutic instruments and improve the controllability and accuracy of their release. In addition, fluoropolymer materials can also be used as materials for coating the outer surface of metal conduits to reduce resistance in the human body.

3. Polyamide material (PA)

Compared to the previous types of materials, polyamide polymer materials (PA) have the characteristics of moderate friction coefficient, easy processing, and high strength, and can also be used as catheters for minimally invasive intervention therapy. In addition, PA and its copolymer polymer materials have high wear resistance and modulus, and can also be used as the primary material for preparing balloons.
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For example, the FXminiRAIL double wire balloon dilation catheter contains PA in the balloon portion and outer layer of the catheter trunk, and a water-based coating composed of polyethylene pyrrolidone and polyacrylonitrile is applied on the outer surface of the catheter. Therefore, it is widely used in improving coronary arteries. The balloon of another type of MissouriPTCA balloon dilation catheter is also composed of PI, and its proximal tube is supported by stainless steel material coated with PFTE coating.

4. Polyimide material (PI)

Polyimide (PI) has stable chemical properties, the best overall performance, and can withstand high temperatures up to 400 ℃ or above. It also has advantages such as corrosion resistance, no obvious melting point, poor water absorption, mechanical strength (1 × 106 Psi), and modulus (42 × 105 Psi). Its high strength and low extensibility can be used as a delivery material in minimally invasive interventional treatment instruments with thin tube walls (0.03-0.05 mm), minimizing the cross-sectional area of the delivery device and minimizing the risk of surgery. The materials made from PI are also suitable for other types of medical devices, such as vascular structures, conveyor sheaths, and other materials.

5. Composite polymer materials

Although each of the above types of materials has excellent characteristics, using them alone as a delivery material usually has many drawbacks. For example, delivery devices made of polyether block amide copolymers are prone to breakage and have a low modulus, which increases the resistance force when entering the human body and releasing medical devices. In some cases, it can lead to sheath stretching and deformation, which increases the risk of minimally invasive intervention surgery. Therefore, it is necessary to synthesize their advantages to prepare composite materials to meet the needs of minimally invasive interventional treatment devices.

Implantable polymer materials

In minimally invasive interventional treatment equipment, the carriers of the release system, such as covered stents, embolic agents, biodegradable stents, and therapeutic drugs, need to be controlled to meet the requirements using polymer materials. And these types of devices usually coexist with the human body for a long time after implantation. Therefore, the polymer materials used should ensure good anti thrombotic properties, excellent compatibility, stable physical and chemical properties, and high mechanical strength.

1. Material of covered stent (PU, PTFE)

The covered stent is divided into two parts: the covered membrane and the stent. The covered membrane (a layer of polymer film) attaches to the surface of the metal stent and is implanted in the human body for a long time with the stent. So the polymer materials used need to have excellent biocompatibility and good mechanical properties, and the film used in the treatment of different diseases usually also needs to have specific functions. Currently, polyurethane (PU) and expanded polytetrafluoroethylene (ePTFE) materials are the most widely used.
PU film covered bracket
PU has high mechanical strength, anti-aging, corrosion resistance, stable chemical properties, strong support and can be fully developed. On the other hand, the preparation process of PU is relatively simple. Suitable solvents can be used to dissolve polyurethane resin into liquid, and then it can be attached to the bracket for drying.

Expanded polytetrafluoroethylene (ePTFE) coated bracket

For ePTFE, the PTFE tube can be expanded and formed under controlled conditions during its preparation process. The structure of the prepared ePTFE will produce many small pores, which can be further modified to give it more specific functions (such as breathability, multi porous structure, chemical stability, low friction coefficient, etc.). In recent decades of observation, ePTFE has been found to be non allergenic, non-toxic, and non carcinogenic. Vascular tissue or other tissue cells in the human body can grow on the scaffold through a microporous structure, without forming fibrous cysts or exhibiting rejection behavior with the human environmental tissues.

2. Polymer materials for embolic agents (PVA)

Embolism therapy plays an important role in minimally invasive interventional therapy, usually applied in tumor treatment, bleeding control, and elimination of organ function. When passing through intravenous catheters or arteries, it is often necessary to artificially inject the plug into the supply vessel or site of the lesion, which requires occlusion of the blood vessel or interruption of the supply of embolic agents. This requires embolic agents to ensure the duration of embolization (days to weeks) without affecting human activity. Commonly used embolic agents include absorbent solid embolic agent materials, permanent solid embolic agent materials, micro spring coil embolic agent materials, etc.

Gelatin sponge is the most prominent material among absorbable solid embolic agents due to its excellent water swelling, compressibility, antigenicity, low cost, and no obvious biological toxicity. However, gelatin sponge embolic agents can only temporarily act as occlusive agents after entering the human body. It is commonly used for embolization and hemostasis before tumor resection, as well as embolization of small artery bleeding.

PVA particle embolic agent

The commonly used material for permanent embolization is polyvinyl alcohol particles, which are insoluble in water and do not degrade in vivo, while possessing excellent biocompatibility. When it accumulates in the blood vessels, it will block the blood vessels and form a thrombus, which will then hinder the collateral circulation established during embolization treatment.

However, polyvinyl alcohol is prone to producing sticky tubes, which can cause pain and complications for patients. Microspring coil embolization material is a type of mechanical embolization material. During the treatment process, it will ligate damaged blood vessels in the body while protecting normal body tissues through microcatheters under the traction of guide wires.

3. Degradable polymer scaffold (PLLA)

In recent years, scaffold materials made from biodegradable polymer materials have attracted widespread attention. Among them, polylactic acid material (PLLA) stands out. It has advantages such as in vivo solubility, high tensile strength, high modulus, and mechanical properties.

Polylactic acid scaffold

The mechanical strength of PLLA stent is similar to that of metal stent, so it can be directly used for the preparation of minimally invasive intervention therapy stent. After implanting a bioabsorbable stent into the human body, the support force is equivalent to that of a metal stent within one year, completing the task of supporting blood vessels and helping with reconstruction. Around 2-3 years, it will gradually degrade into water and carbon dioxide, which will be completely absorbed by the body and there will be no more foreign objects in the body.

Due to the need for direct contact with patients during the medical process, the performance requirements for medical polymer materials are very strict, which must simultaneously meet the characteristics of good biocompatibility and strong mechanical properties. Especially when in direct contact with the patient’s skin, blood, or body fluids, these medical devices containing polymer materials, whether long or short, will be implanted or placed in the patient’s body.

With the advancement of technology and the development of the times, medical methods are gradually inclined towards fast, stable, healthy and reliable, and minimally invasive intervention medicine will play a crucial role in the future. By promoting the research and application of biopharmaceutical polymer materials in medical devices, the role of minimally invasive intervention medical devices and polymer materials in medical services will be fully utilized.