OPHTHALMIC NANOPARTICLES DRUG DELIVERY SYSTEMS (Ezine Ready)
In orthopedics, PMMA bone cement is used to affix implants and to remodel lost bone. It is supplied as a powder with liquid methyl methacrylate (MMA). Although PMMA is biologically compatible, MMA is considered to be an irritant and a possible carcinogen. PMMA has also been linked to cardiopulmonary events in the operating room due to hypotension. Bone cement acts like a grout and not so much like a glue in arthroplasty. Although sticky, it does not bond to either the bone or the implant, it primarily fills the spaces between the prosthesis and the bone preventing motion. Dentures are often made of PMMA, and can be colour-matched to the patient's teeth & gum tissue. In cosmetic surgery, tiny PMMA microspheres suspended in some biological fluid are injected under the skin to reduce wrinkles or scars permanently.ADVANTAGES AND LIMITATIONS Advantages1. Material is very hard. 2. Material is clear and can be coloured in any colour from opaque to translucent. 3. Good weathering resistance 4. Good optical properties. 5. High gloss. 6. Scratch resistant (but not as good as glass because it does scratch - this is why car wind screens are not made from PMMA).Limitations 1. Brittle under impact conditions and failure is by shattering. 2. Difficult to mould thin walled products because of poor flow properties. 3. Poor hot-melt strength limits processing methods. 4. Flow properties make processing slow compared to other materials. 5. Does not have significant elastic deformation before failure i.e. goes straight to brittle fracture. REFERENCES Alonso MJ, Snchez A.Pages: 1 2 3 4 5 [6] 7 8 9 10 11 12 13 14
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01.02.2010
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