Polymers and plastics in biomedical applications

Polymers and plastics in biomedical applicationsIntroductionPolymers atomic number 18 increasingly be used to fabricate biomedical materials for tissue engineering and provoke pr for each oneing applications, as well as for drug delivery. For tissue engineering and wound treatment applications, the automatonlike properties of the polymeric material wee to be matched to the particular proposition application. An example of tissue engineering is the use of bioresorbable polymeric orthopedic materials for tusk regeneration applications. The degradable material supports the growth and adhesion of new lift cubicles (chondrocytes) and is holey so as to provide a large, continuous surface for cell proliferation through stunned the matrix. The degradable material serves to maintain mechanical integrity while the b one heals itself. The materials ar designed to degrade in a time adapted for the particular application, but may be on the order of vi months to twenty-four months.An example of an external wound treatment application is contrived skin, where the polymeric material provides protection as new growth develops. new(prenominal) materials are used internally to separate organs after surgical procedures. In tissue engineering and wound treatment applications the mechanical properties of the materials consecrate to meet requirements specific to the application. In this experiment you will determine how the pliant properties of studys of plasticized biopolymers depend on the chemical formulation of the material. Such applications are ground on the polymer materials being degradable as well as biocompatible. Other applications powerfulness require materials that are biocompatible and nondegradable, such as long-term polyethylene implants.PolymersPolymers ignore be synthetic or biological. Synthetic polymers are almost eer made from nonrenewable fossil feedstocks, mainly petroleum. Examples are polyethylene, polystyrene, poly(vinyl chloride), and polypropylene, all of which are polyolefins. Poly(ethylene terephthalate) PET is a synthetic polyester. None of the above-named polymers are degradable, the main precedent being that the polymer backbones contain only carbon-carbon single bonds. Examples of biodegradable polymers derived from petroleum are poly(vinyl alcohol) a polyalcohol, poly(ethylene glycol)a polyether, and the polyesters polycaprolactone and poly(glycolic acid). Polymers with heteroatoms in their backbones are generally biodegradable, although there are exceptions.Biological polymers (biopolymers) are found in nature they are intrinsically biodegradable. Abundant biopolymers embroil plant polysaccharides such as starch (composed of amylose and amylopectin), cellulose, agarose, and carrageenan, and animal polysaccharides such as chitin and the glycosaminoglycans. Abundant proteins include gelatin(denatured/hydrolyzed collagen), casein, keratin, and fibroin.Poly(lactic acid) (PLA) is an example of a synthetic commercial polymer in which the monomer, lactic acid, is produced in large amounts through fermentation the polymer is thencece synthesized by conventional methods. PLA is biodegradable.Mechanical PropertiesIn implant and wound healing applications, the mechanical properties of the materials are of critical importance. In this experiment you will carry out waxy trialstests in which specimens are placed between twain clamps (grips) and drawn. The dick measures and vaunts the force being applied (the load) and the resulting increase in the length of the sampling (elongation, also called extension).From the dimensions of the take in specimen (largeness and thickness), the instrument software product calculates and displays the tensile straining (), equal to the load (F) per unit area of cross section (A = width x thickness). It also calculates the (tensile) strain (), equal to the elongation (extension) divided by the original length of that portion of the specimen being measure d (called the crapper length). In our experiment, the gage length is simply the separation of the grips securing the specimen. The instrument will display percent elongation, which is the strain multiplied by 100.As the tensile test proceeds, the instrument generates and displays a tensile stress-strain curve, which is a diagram that displays values of tensile stress (in MPa) plotted against tensile strain (%). The test continues until the specimen breaks. From the stress-strain curve, the software determines, and reports the following results in table form(1) Tensile strength at break (or ultimate strength), which is the tensile stress at break. (2) Elongation at break, as a percentage. (3) Youngs modulus (also known as elastic modulus or modulus of cracking or sometimes simply as modulus).It is calculated as the sign slope of the stress-strain curve, which is usually observed to be linear with plastic fools. This initial region reflects the elastic deformation of the specimen, in which the stress varies linearly with strain, same to Hookes law for the expansion of a spring. Beyond the linear region, the behavior is termed steamy polymers and plastics are said to be viscoelastic materials. Modulus is a measure of the harshness of the polymer or plastic. Table 1. Typical tensile properties of materialsMaterial t.s.(MPa) elong.(%) modulus(MPa) polyethylene, low absorption 10 620 166 polycaprolactone 26 600-1000 435 polypropylene 36 1380 poly(lactic acid), biaxially oriented film one hundred ten/145 160/100 3310/3860 keratin(human hair) 526 46 6700 copper, annealed 240 30 100,000-130,000 steel 380-700 200,000-250,000 rubbish 2160-4830 50,000-70,000 Encyclopedia of Chemistry, 4th ed. Handbook of Physics, 2nd ed.Experimental Procedure 1. require holdingPrepare the following cast films of plasticized biopolymers.Sample 1 spatial relation 32 mL of 2%(v/v) aqueous glycerol solution in a 200 mL beaker. Add 88 mL urine and 2.40 g starch and 4.8 g agar. Heat with stirring to about 85-95 C or until the polymer is in solution do non boil. Slowly pullulate the solution into the big petri dish on a flat train surface. Try to drive all imperfections (bubbles) from the surface. Sample 2. Repeat use 32 mL glycerol solution, 88 mL water, and 1.20 g starch and 3.6 g agar.Sample 3. Repeat development 48 mL glycerol solution, 72 mL water, and 1.20 g starch and 3.0 g agar.Sample 4. Repeat using 48 mL glycerol solution, 72 mL water, and 2.40 g starch and 3.5 g agar.Allow the solutions to set for approximately one hour then place the petri dish in the drying oven. Label all petri dishes.2. Film instruct After the agar films have been in the drying oven for about 24 hours, remove the petri dishes from the oven and place them in the large relative-humidity conditioning box (maintained at approximately 50% relative humidity) for 24-48 hours.3. Preparing test specimens After conditioning, the films are ready to have test specimens prepared f rom them. Working with one sample at a time, remove the petri dish from the conditioning box. Slowly and carefully remove the film from the petri dish by first peeling one corner and then applying fairly equal pressure to the entire width of the film as it comes off the petri dish lengthwise.Place the sample on a human beings of cardboard. Using the 1/4 wide aluminum template as a straight edge, and the rotateting knife, cut a rectangle approximately 3.5 x 3 from the center of the film, so as not to include twain edges, as they are often not as uniform in thickness as the center. Align the sample on the cardboard as follows Place the 1/4 wide aluminum template vertically near one of the edges. Using the cutting tool, cut on both sides of the template to produce a specimen 3.5 long and 1/4 wide. Cut as cleanly as possible so as not to notch or tear the specimen. Cut six or seven additional strips, but do not use the molybdenum cut of the previous specimen as the first edge of th e nigh make two new cuts to produce each specimen. Place the cut specimens on a piece of filter paper and transfer them into the dessicator primed(p) next to the Instron instrument. Similarly prepare specimens from the other three film samples.4. bill mechanical properties of test specimens During the laboratory you will measure the mechanical properties of the fours cast films. Measure at least five specimens for each of the four film samples. As you remove each specimen from the dessicator, you will be bar the thickness of the specimen with a digital caliper. 5. Operating the Instron Testing puppetRefer instrument manual.6. Laboratory Report1. Express the compositions of the four film samples in terms of the weight percent of each component to two significant figures (excluding water) i.e. % agar, % glycerol (the density of glycerol is 1.26) and, if present, % starch.2. Prepare a stocky table of results showing the mean values of tensile strength (Mpa) (to 3 sig. figs.) and its amount deviation, elongation (%) (to 2 sig. figs.) and its standard deviation, and elastic modulus (MPa) (to 3 sig.figs.) and its standard deviation. ASTM specifies these numbers of significant figures a smaller number of significant figures would differently be justified given the observed standard deviations.3. For the three agar-glycerol films what correlativity do you observe between the effect of glycerol on one property and its effect on the others? Prepare a graph for each of the properties showing variation with composition. In Excel you can show a standard error for each point separately by using a separate data series for each point. Do not show a trend line and do not campaign to connect the data points.