Synthetic Non-Biodegradable Polymers

Synthetic Non-Biodegradable Polymers:

Synthetic polymers have been widely used in making various medical devices, such as disposable supplies, implants, drug delivery systems and tissue engineering scaffolds. The advantages of using polymers, as biomaterials, are their manufacturability. Polymers are easy to fabricate into various sizes and shapes compared to metals and ceramics. They are also light in weight and with a wide range of mechanical properties for different applications.

1- Polyethylene:

There are three type of polyethylene: linear high density polyethylene
(HDPE), branched low density polyethylene (LDPE) and ultrahigh molecular weight polyethylene (UHMWPE). HDPE and UHMWPE are frequently used as biomaterials.

1.1 High Density Polyethylene:

High density polyethylene (HDPE) is a very inert material with very low tissue reactivity. It has been used as bone and cartilage substitutes since 1940s. More than 30 years of follow-up results showed favorable response to these HDPE implants. Therefore, HDPE has become a standard reference material for biocompatibility testing. Histological examination of HD implants reveals a lack of minimal inflammatory and foreign body reactions.
When HDPE was fabricated into porous scaffolds, it has the added advantages of allowing fibrous tissue ingrowth into the implant. The ingrowth of the fibrous tissue will provide adequate stabilization in a non-load-bearing environment. MedPor is a porous HDPE product fabricated by sintering HDPE microbeads in a mold to create implants with interconnected porous structure. The average pore size in this material is greater than 100 µm and the pore volume is in the 50% range. These materials are readily available in a variety of preformed shapes and can be customized with a scalpel easily.
The pore size and porosity is very important for tissue ingrowth. Studies have shown that pore size larger than 100 µm encourages tissue ingrowth. The tissue ingrowth results in firm attachment and integration of the implant to the surrounding tissue leading to decreased migration of the implant, thus obviating the need for screw or suture fixation in some cases.