Background

M.M.A.TECH Ltd was founded in July 2001 as a Start-up company within the framework of a Technological Incubator.

Orthopedic implantation is possibly the greatest advance in the past century. The concept of introducing an artificial joint was impossible until new materials and fixation methods were developed and applied by successful collaboration of materials scientists, engineers and surgeons. A joint replacement has the great advantage of providing pain free movement for the patients.

Plastics hold an important position in the field of medicine as structural materials implanted in the body and as surgical aids. Plastic materials are preferred over metals and ceramics due to their low specific weight, high mechanical strength (on a strength-to-weight basis), chemical stability and non-corrosivity.

Plastic materials are also easily shaped and machined and commercially available in diverse forms and structures.

The majority of total hip prosthesis implanted currently consists of hard metal, or ceramic femoral head against ultra-high-molecular weight-polyethylene (UHMWPE) acetabular cup with or without cement fixation. Currently around 900,000 artificial hips are implanted in USA and Europe per year. The low-friction, low-wear UHMWPE was considered for the last two decades as the best solution for total artificial hip implants. Despite the success, over the last 10 years these prostheses showed frequent failures due to late aseptic loosening, migration, and inflammation resulting in the need to be revised. No implant survived more than 25 years, while most of the implants lasted only between 10 to 15 years. The increasing need to implant hip prosthesis in younger, more active patients demands the developing of new artificial hip joints using alternative more advanced materials. This research, aiming at extended lifetime of the artificial implants, becomes the major issue within the orthopedic community these days.

The material chosen for an implant should withstand the different loads (tensile, compression and shear), resist friction and wear of the human hip or knee joints. UHMWPE(3-5) -promotes bone lysis (Periprosthetic Osteolysis) due to release of tiny sub-microns size debris into the human cells and surrounding soft tissues as a result of wear. The body reacts by releasing agents (macrophages) that attack the bone implant interface causing loosening and infection. The UHMWPE implant degrades in the body, chips off, exposes the base metal and releases from the cemented fixation. There are 20-30 % cases within 5-7 years of implantation.

UHMWPE -Crosslinked(2) – shows 50% less wear than UHMWPE ,thus longer term of stability, but still has a risk of wear debris stimulated osteolysis. There is a risk of oxidation of the UHMWPE by the Gamma radiation during the cross-linking process releasing free radicals. This oxidation weakens the material and causeembrittlement during aging.

CERAMIC implants(6) are composed of Alumina and Zirconia and are mostly used in Europe. Ceramic has excellent biocompatibility (highly oxidized), good lubrication, friction and low wear, high hardness, and smooth surface finish. The drawbacks of ceramic implants are low fracture toughness and brittleness causing fragmentation, wear scars and cracking of the implants. Failures include femoral head fractures and catastrophic breakage of ceramic sockets. Impact strength is low too. Improved performance is dependent on careful operation techniques with correct positioning of the prosthesis. Massive wear and osteolysis occur between the femoral neck and the rim of the acetabular cup. Small sharp edged particles (5 µm) and smaller granular debris (0.4 µm) have been found in macrophages near the surface of the implant. Zirconia wear debris are more frequent than alumina. Osteolysis appeared after a mean implantation time of 92 months. Loosening and migration of acetabular components were also found which demanded revision. The ceramic wear debris stimulate a foreign body response. Other disadvantages of ceramics are the high specific density (causing elevated weight of the implant compared to UHMWPE) and water hydrolysis causing crack formation in wet environment and fracture. At present, there is insufficient data to compare ceramics with other implants.

Metal implants(5-7) consist today mostly of CoCrMo alloy which exhibits low wear (40-100 times lower than UHMWPE), good surface finish and high mechanical properties. The drawbacks of metals are metallic electrochemical corrosion risk (biocompatibility issue) caused by the salty body fluids and oxygen environment, formation of chemically active degradation products, and production of wear particles. The wear particles are very small (mostly 10-25 nm) but the numbers of particles exceed those of UHMWPE (13 to 500 times more). The small size and large number of the particles raise a new issue of remote distribution in the human body and the biologically affecting various cells and tissues. Some particles may corrode or dissolve in the lymphatic vessels. The hematological spread of the metal particles may access any tissue in the body even the brain. Metal debris in the lymph nodes cause structural changes including necrosis and fibrosis. There is an increased risk for development of tumors of the lymphatic system (carcinogenic potential). Metal hyper-sensitivity of the body to metal ions release is another problem. Metal ions may bind to body proteins when they are released from the metal implant. Metal ions bound to proteins induce T lymphocyte response leading to hyper sensitivity reactions. Another problem is the toxicity of the metal ions (Co and Cr). Co and Cr ions reduce cell viability even at low concentrations, are toxic to osteoblast cells by inhibiting their differentiation. Compared to UHMWPE metal prosthesis have elevated weight. Titanium is a much lighter metal but is a poor bearing material. It wears fourfold more than CoCr and is toxic as well. It activates macrophages and causes osteolysis. The level of inflammation depends on the amount, size and shape of the debris. The new suggested polymeric material is aimed to solve these problems.

Our solution:

MMATECH developed a new advanced material from the Polyimide family, MP-1™, which can replace metal, UHMWPE or ceramic in articulating joint implants. MP-1™ polymer is a high performance biomaterial providing advanced solutions for implant manufacturers. MP-1™ is safe, biocompatible and durable polymer.

Polyimide MP-1™ polymer, originated from Jet engine bearings balls, exhibits a superior combination of strength, toughness, wear, creep and fatigue resistance, together with extensive biocompatibility which makes it suitable for medical device applications. MP-1™ was first examined to replace the liner as part of the hip implant as well as the femoral head. MP-1™ can be processed by conventional techniques such as compression molding to blocks and rods followed by machining, or near net shape compression molding in specific designed mold allowing a broad design and manufacturing flexibility.

We declare that our new polymeric material can withstand the natural properties of the joint and may last in the body at least 25-30 years.