Plastics Reshaping Wearable Medical Devices

Various materials cater to the industry of medical devices. These include metals, composites, and polymers. Early implementation of medical devices for treating humans included materials such as metals and ceramics. Table below shows some of the materials and their applications in the medical industry:

Table below shows a qualitative comparison between various materials used in the industry:

Below are some of the critical properties essential for medical devices:

Polymeric systems find applications in a variety of segments. For example, early 18th century saw the usage of metal catheters which were replaced by disposable catheters in the 1940s. Below is how various polymeric materials have been used in medical applications over the period:

Recent developments in the smart devices enabled bio-medical devices resulted in improved convenience to the consumers/patients. This has led to remote/active diagnosis, therapeutics, and indication.

Chronic conditions such as heart failure may cause immediate death; this is mainly due to lack/failure of detecting/analyzing the symptoms. Heart disease per say is a progressive disease. Symptoms of potential heart failure are:

• Fatigue
• Swelling
• Shoulder pain, and
• Abnormal heart rates

To analyze these conditions visiting a diagnostic center is essential. But, thanks to smart wearable devices, technology grew to a stage where the simplest of temperature/heartbeat could be tested till active drug administration or recommending therapies.

Similar products are already available in the market. Beside is an illustration of 'LifeVest wearable defibrillator' by Zoll technologies¹. This wearable device not only monitors patterns of cardiac conditions, but it also delivers a shock treatment to restore normal heart beat rate.

Similar technologies are being researched for diagnosing/treating various fitness/medical parameters including:

• Heart rate
• BMI calculator
• Arthritis
• Sensing aids
• Pain management
• Temperature
• Body posture
• Glucose monitoring, and
• Digestion monitoring

Various polymeric materials contribute to the useful and inexpensive wearable devices. Here's an indicative list of polymers used in wearable medical devices:

• Polyurethane: Elastomeric/foam made wearable devices.
• Adhesives (Hydrocolloid polymer, epoxy, polyurethane, acrylic): Adhesives for sticking patches.
• Polydimethylsiloxane: Flexible materials where transparency and energy conservation is essential.
• Polyimides/Polyesters: Structural materials where films, non-woven or textiles, used in flexible electronics for example.
• Polypyrrole/polythiopene/Polyaniline: Conducting polymers replacing metals.
• Single-walled nanotubes: Electronic skin.
• Cationic self-assembled polymers: Impact measurement and drug delivery systems.
• Polyethylene glycol gel: Addition of colorants can be used as visual indicators in objects such as diapers.

Other structural polymers include commodity/engineering polymers, such as:

• Polyethylene
• Polypropylene
• Polycarbonate
• Polyamides
• Polyvinyl Chloride
• Polyvinyl Alcohol
• Polyesters, and
• Polyamides

Notable material suppliers include:

1. DuPont: PE872, PE772, PE410, PE773
2. BASF: HyGentic^®, Ultraform^®
3. Dow Chemicals: Health+^™, ASPUN^™, DOWLEX^™
4. INEOS: Eltex^®
5. SABIC: LEXAN^™, ULTEM^™, CYCOLOY^™
6. Covestro: DUREFLEX^™ , PATILON^™
7. Bayer: Makroblend^®, Makrolon^®, Apec^®, Texin^®
8. Henkel: Loctite^®, Indigo^®, Flashcure^®, Nuva-Sil^®

The selection of material depends on the class of medical application, such as:

• Permanent implantation
• Temporary implantation
• Minimal contact with human tissues or fluids

Use of Polymers in Various Wearable Medical Devices

	Companies such as BlackBox Biometrics have developed wearable concussion sensors, which include a printed circuit board covered with plastics/polymers. This sensor is primarily used for measuring traumatic brain injuries of athletes and soldiers.
	Advanced innovative products such as Vitaliti™ are used to monitor more than 15 medical conditions. Vitaliti has been developed by CloudDx. To create such lightweight and safe devices, various polymers are used in components such as body and circuits.
	MIT has developed a cross-linkable silicone-based polymer that can be applied to skin as a cream and is cured via a catalyst liquid. The polymer forms an artificial layer over the skin and can be used for both therapeutic and cosmetic applications.
	Soft-sensing suits are being made from nylon strips, such as Ecoflex® rubbers, which contain sensors made from flexible circuits. This suit can be used to monitor hip, knee, and ankle sagittal plane joint angles.
	Wearable patches/pods are already available in the market and are extensively used for drug delivery in treating conditions such as diabetes, tobacco abuse, and hormonal imbalance. Insulet Corp is a key manufacturer of wearable patches.
	The US FDA has approved wrist bands such as Pulsewave®, which provides real-time non-invasive readings, including heart rate, blood pressure, and respiration rates. These devices use conductive elastic polymers, such as polydimethylsiloxane, and other elastomers.
	Extensive research studies are being carried out for monitoring joints. These studies include monitoring of knee angle and pain sensors for active monitoring. Such devices are either worn as a patch or embedded in a strap made from materials such as nylon.
	Footwear and clothing applications include monitoring of strain and compression patterns. These products are made of materials such as polyurethane, polydiacetylene, and other electrospun polymers.
	Color-changing compositions are being used in diapers and medical dressings; they change color when they come in contact human liquids or blood. Polymer/ co-polymers of olefin-based materials are used in these products.
	Adhesives/sealants play a crucial role in holding medical components near the human body. Gentle adhesives, such as MEDIFIX Solutions™, HydroSoft™ adhesive, and AR SoftWear™, are available in market.

have gained importance over the past in various applications due to their unique properties. Polymeric materials when combined with unique sensing/detecting properties of electronics can be used in advanced applications. One such example is wearable medical devices.

Research has progressed in using polymers in both structural and functional roles. These devices can be used to diagnose, treat, indicate and perform remote monitoring. With increased research focus towards wearable medical devices, it is interesting to observe the latest developments in functional materials.