TITANIUM MATERIALS

Kekuatan tinggi, bobot ringan, serta ketahanan korosi luar biasa yang dimiliki oleh titanium dan paduannya telah menghasilkan berbagai aplikasi sukses yang luas dan beragam. Hal ini menuntut tingkat performa handal yang tinggi di bidang bedah dan medis, sebagaimana halnya di industri kedirgantaraan, otomotif, pabrik kimia, pembangkit listrik, ekstraksi minyak dan gas, olahraga, serta industri utama lainnya.

Lebih dari 1.000 ton (2,2 juta pon) perangkat titanium dengan segala jenis deskripsi dan fungsi ditanamkan pada pasien di seluruh dunia setiap tahunnya. Kebutuhan untuk penggantian sendi terus meningkat seiring bertambahnya usia harapan hidup manusia, atau akibat cedera saat berolahraga berat dan joging, maupun cedera serius dalam lalu lintas jalan raya dan kecelakaan lainnya. Ringan, kuat, dan sepenuhnya biokompatibel, titanium adalah satu dari sedikit material yang secara alami memenuhi persyaratan untuk implantasi dalam tubuh manusia.

Paduan titanium tingkat medis memiliki rasio kekuatan-terhadap-berat yang jauh lebih tinggi dibandingkan baja tahan karat (stainless steel) pesaingnya. Rentang paduan titanium yang tersedia memungkinkan desainer spesialis medis untuk memilih material dan bentuk yang disesuaikan secara cermat dengan kebutuhan aplikasi tersebut. Rentang lengkap paduannya mencakup mulai dari titanium murni komersial dengan daktilitas tinggi yang digunakan saat kemampuan bentukan ekstrem sangat penting, hingga paduan yang dapat diberi perlakuan panas sepenuhnya dengan kekuatan di atas 1300 MPa (190 KSI). Paduan pengingat bentuk (shape-memory alloys) berbasis titanium memperluas lebih jauh rentang sifat dan aplikasi yang berguna. Kombinasi dari proses penempaan atau pengecoran, permesinan, dan fabrikasi merupakan rute proses yang digunakan untuk produk medis. Rekayasa permukaan sering kali memainkan peran penting, memperluas performa titanium hingga beberapa kali lipat melampaui kemampuan alaminya.

Titanium Performance in Medical Applications:

‘Fit and forget’, is an essential requirement where equipment in critical applications, once installed, cannot readily be maintained or replaced. There is no more challenging use in this respect than implants in the human body. Here, the effectiveness and reliability of implants, and medical and surgical instruments and devices is an essential factor in saving lives and in the long term relief of suffering and pain. Implantation represents a potential assault on the chemical, physiological and mechanical structure of the human body. There is nothing comparable to a metallic implant in living tissue. Most metals in body fluids and tissue are found in stable organic complexes. Corrosion of implanted metal by body fluids, results in the release of unwanted metallic ions, with likely interference in the processes of life. Corrosion resistance is not sufficient of itself to suppress the body’s reaction to cell toxic metals or allergenic elements such as nickel, and even in very small concentrations from a minimum level of corrosion, these may initiate rejection reactions. Titanium is judged to be completely inert and immune to corrosion by all body fluids and tissue and is thus wholly bio-compatible.

The natural selection of titanium for implantation is determined by a combination of most favorable characteristics including immunity to corrosion, bio-compatibility, strength, low modulus and density and the capacity for joining with bone and other tissue – osseointegration. The mechanical and physical properties of titanium alloys combine to provide implants which are highly damage tolerant. The human anatomy naturally limits the shape and allowable volume of implants. The lower modulus of titanium alloys compared to steel is a positive factor in reducing bone resorption. Two further parameters define the usefulness of the implantable alloy, the notch sensitivity, – the ratio of tensile strength in the notched vs un-notched condition, and the resistance to crack propagation, or fracture toughness. Titanium scores well in both cases. Typical NS/TS ratios for titanium and its alloys are 1.4 – 1.7 (1.1 is a minimum for an acceptable implant material). Fracture toughness of all high strength implantable alloys is above 50MPam-1/2 with critical crack lengths well above the minimum for detection by standard methods of non-destructive testing.

Titanium Medical Specifications:

Forms and material specifications are detailed in a number of international and domestic specifications, including ASTM and BS7252/ ISO 5832 examples below:

Bone and Joint Replacement:

About one million patients worldwide are treated annually for total replacement of arthritic hips and knee joints. The prostheses come in many shapes and sizes. Hip joints normally have a metallic femoral stem and head which locates into an ultrahigh molecular weight low friction polyethylene socket, both secured in position with polymethyl methacrylate bone cement. Some designs, including cement less joints, use roughened bio active surfaces (including hydroxyapatite) to stimulate osseointegration, limit resorption and thus increase the implant lifetime for younger recipients. Internal and external bone-fracture fixation provides a further major application for titanium as spinal fusion devices, pins, bone-plates, screws, intramedullary nails, and external fixators.

Dental Implants:

A major change in restorative dental practice worldwide has been possible through the use of titanium implants. A titanium ‘root’ is introduced into the jaw bone with time subsequently allowed for osseointegration. The superstructure of the tooth is then built onto the implant to give an effective replacement.
Maxillo and Cranio/facial treatments:
Surgery to repair facial damage using the patients own tissue cannot always obtain the desired results. Artificial parts may be required to restore the ability to speak or eat as well as for cosmetic appearance, to replace facial features lost through damage or disease. Osseointegrated titanium implants meeting all the requirements of bio-compatibility and strength have made possible unprecedented advances in surgery, for the successful treatment of patients with large defects and hitherto highly problematic conditions.

Cardiovascular devices:

Titanium is regularly used for pacemaker cases and defibrillators, as the carrier structure for replacement heart valves, and for intra-vascular stents.

External Prostheses:

Titanium is suitable for both temporary and long term external fixations and devices as well as for ortho calipers and artificial limbs, both of which use titanium extensively for its light weight, toughness and corrosion resistance.

Surgical Instruments:

A wide range of surgical instruments are made in titanium. The metal’s lightness is a positive aid to reducing any fatigue of the surgeon. Instruments are frequently anodized to provide a non reflecting surface, essential in micro surgical operations, for example in eye surgery. Titanium instruments withstand repeat sterilization without compromise to edge or surface quality, corrosion resistance or strength. Titanium is non magnetic, so therefore no threat of damage to small and sensitive implants.