Implantable medical devices are implanted into the body for various reasons including orthopedic applications (e.g., hip replacement, spinal procedures, knee replacement, bone fracture repair, etc). In view of the structural integrity required by such devices, materials of fabrication are limited and generally consist of metal, plastic and composites.
The benefits derived from these devices are often offset by infection which in some cases can lead to sepsis and death. The most common organisms causing infections are Staphylococcus epidermidis and Staphylococcus aureus. Staphylococcus epidermidis is a major component of the normal bacterial flora of human skin and mucous membranes. It is a common pathogen that often colonizes patients in hospital settings who have surgical implants due to the microbes' ability to adhere to medical devices and form a biofilm. Additionally, methicillin-resistant Staphylococcus aureus (MRSA) is a type of staphylococcus bacteria that is resistant to many antibiotics is therefore of particular concern. Other gram-positive bacteria, gram-negative bacteria and fungal organisms also are causative organisms that may be problematic.
As microorganisms come in close proximity to the surface of the medical device, they will either be attracted or repelled by it depending on the sum of the different non-specific interactions. In biological systems, hydrophobic/hydrophilic interactions play an important role in the pathogenesis of a wide range of microbial infections.
Many bacteria can form multicellular coatings, or biofilms, on bioengineered implants. Biofilms facilitate the proliferation and transmission of microorganisms by providing a stable and protective environment for their growth. These biofilms may often result in a broad systemic infection.
In many instances, when implants are seeded by organisms which are protected by tenacious biofilms, the implant must be removed and the patient must be treated with a prolonged course of one or more antibiotics in an effort to cure the infection, after which time a new implant is then reimplanted. This process not only subjects the patient to additional trauma and pain but is also extremely expensive.
Not surprising, a great deal of research has been devoted toward preventing the colonization of the surfaces of orthopedic implants by bacterial and fungal organisms with the use of antimicrobial agents such as antibiotics which may be bound to the surface of these devices.
Thermoplastic resins including polyetherketoneketone (PEKK) and polyetheretherketone (PEEK) have been found to be a useful material for these implants. PEEK is particularly suitable because its modulus of elasticity closely matches that of bone. However, PEEK is a hydrophobic material and bacteria tend to adhere easily to these types of surfaces. It is also an organic material which does not carry significant surface charges. Consequently, it may be desirable to develop a medical implant composed of one or more thermoplastic resins that has reduced hydrophobic properties, and/or that has a net negative charge, particularly at an exposed surface when implanted.