BME 312 Exam 2
Natural Polymers - Chitosan Wound Healing
1. Hemostasis: coagulation system is activated after blood vessels constrict and platelets aggregate. Fibrinogen is transformed into insoluble fibrin that forms clots to stop hemorrhaging - chitosan promotes the platelet aggregation. 2. Inflammation: bacteria and necrotic tissue are cleared by inflammatory cells. 3. Proliferation: epithelial cells proliferate and migrate to form epithelial tissue to cover the wound in the proliferation stage. 4. Skin Remodeling: fresh epidermis and dermis will regenerate to finish the skin repair procedure
Polymers - Manufacturing (Inkjet Bioprinting)
A hydrogren pre-polymer solution with encapsulated cells (Bioink) is stored in the ink cartridge. The cartridge is then connected to a printer head and acts as the bioink source during the electronically controlled printing process. During printing, the printer heads are deformed by a thermal or piezoelectric actuator and squeezed to generate droplets of a controlled size. Advantages: Low cost due to a similar structure with commercial printers, High printing speed conferred by the ability of the printer heads to support parallel work mode, Relatively high cell viability (usually from 80% to 90%)
Natual Polymer - Chitosan
A linear polymer that consists of repeating units of N-acetylglucosamine and glucosamine monomers linked by glyosidic bonds. Derived from chitin. Degree of deacetylation and molecular weight are both known to significantly affect the properties of derived materials. Characterized by degree of deacetylation. Processing stages in producing chitosan from shells -1. Deproteination 2. Demineralization 3. Discoloration 4. Deacetylation (NaOH)
Polymers - Manufacturing (Electrospinning)
A technique that is used to develop nanofibers. Advantages are due to its simplicity, low cost, and scalability (Extruding a polymer solution or melt through a syringe which ejects a continuous flow of the material, The material is exposed to a voltage source that induces the fibers emerging from the top of the electrospinning to accelerate toward a collector of an opposite polarity, The expelled polymer from the electrospinning head is altered from a round sphere to a Taylor then to a nanofiber when the surface tension of the liquid is exceeded). Controlling it: several parameters are central to controlling the structure and morphology of an electro spun fiber - 1. Solubility of the polymer 2. Concentration of the polymer in the solution 3. Number of channels in the spinneret die 4. Shape of the needle tip 5. Applied voltage- high voltages will increase the electrical field and reduce the diameter of the fibers 6. Polymer flow rate 7. Working distance- distance between the tip
Polymers
Ability to degrade, properties can be easily adjusted (can mimic native tissues), large spectrum of mechanical properties, inexpensive, alter physical appearance (like color), manufactured in large quantities quickly
Polymethyl Methacrylate (PMMA)
Acrylic. Used in orthopedic applications (bone cement)/ PMMA transfers the load between the implant and the bone. Naturally inert biologically. Reactions occur against its monomer. Used in ophthalmic applications like eye glasses, contact lenses and intraocular lenses. Used in cosmetic surgery as a filler but has also been reported to be used illegally to shape muscles by body builders.
Polymer Synthesis
Addition / Chain Polymerizations: This is a process by which monomer units are attached one at a time in a chainlike fashion to form a linear macromolecule. The composition of the resultant product molecule is an exact multiple of that of the original monomer (like paper clips). Condensation (step) polymerization: Starts with 2 monomers, and you'll get a combination of the two, and get some sort of biproduct (most commonly ends up being water). During polymerization processes, not all polymers will grow at the same length.
Properties of Bioceramics - Porosity
Advantageous Allows for movement of nutrients and removal of wastes Promotes tissue growth Large surface to volume ratio
Polymers - Manufacturing (Blow Molding)
Air is blown into a molten balloon within a mold, thereby forcing the plastic into a desired shape
Polymers - Manufacturing (Thermoforming)
Air or mechanical forces are applied to thermoplastic sheets until they take the shape of the mold
Naturally Derived Polymers
Alginate - wound dressing. Collagen - orthopedic repair matrices, nerve repair. Elastin - skin repair. Hyaluronic Acid - orthopedic repair and dermatological.
Natural Polymers - Chitosan pt.2
Antimicrobial Activity: Inhibition of the mRNA and protein synthesis via penetration of chitosan into the nuclei if the microorganism and the formation of an external barrier which deprives bacterial from nutrients and growth. Anti-tumor Activity: Low-molecular-weight water-soluble chitosan's and oligochotsans can be useful in preventing tumor growth, partly through enhancing cytoxic activity against tumors as an immunodulator, degradation products are nontoxic. Chelation is the ability to absorb metal ions Chitosan has highest chelating ability than other natural polymers. This phenomena has been used for H2O filtration and other environmental applications. Absorption and selectivity can be enhanced -Chemical and physical modification of both the amine and hydroxyl groups (Ag- Disinfectant or bactericide, bullet fragments in surgery, change the pH to effect absorption) Chitosan and metal ions (Zn, Zr, and Ag) have the properties of disinfection and bactericide.
Polymers - Manufacturing (Solvent Casting)
Applications: drug delivery films, and scaffolds. Pore size can be controlled by the particle size or by adding more particles. Advantage: quick and easy method Disadvantage: hard to control.
Additives to Polymer
Filters- added to polymers to improve tensile and compressive strengths, abrasion resistance, toughness, dimensional thermal stability, and other properties (Particle sizes range from 10nm to macroscopic dimensions. Decreases cost. Ex: carbon black, silica gel, wood flour, glass, limestone, talc, etc.). Plasticizers- used in polymers that are brittle to improve flexibility, ductility and toughness (Liquids with low vapor pressure and low Molecular weight Commonly added to PVC- otherwise its brittle). Stabilizers- counteract deteriorative processes such as UV or oxidation. Lubricants- added to allow easier processing, polymer 'slides' through dies easier (ex: sodium stearate). Colorants- depending on the application, this may be needed. Flame Retardants- reduce combustibility; typically contain fluorine, chlorine and boron.
Physically Measuring Polymer's Molecular Weight
Gel Permeation: Chromatography Determines MW by size exclusion, places the material in a solvent and separates the material based on the size
Manufacturing Ceramics - Glass Forming Techniques
Glass is amorphous and no grains are present. Heat treatment of glass does not impact their mechanical properties. Softening Point (temperature of glass is when its viscosity is 4x10^-7 P - Max temperature at which the piece can be handled without significant change in shape). Working Point (temperature when its viscosity is 10^4 P - glass can be easily deformed). Glass can be pressed (similar to forging), blown, and drawn Drawing: Analogous to metals drawing process, Molten glass is poured over rollers to form long sheets or tubing, May also be drawn to small offices to form glass fibers.
Polyvinyl Alcohol (PVA)
Good biocompatibility, hydrophilic (water soluble), and bioadhesion. Excellent properties that support cell adhesion, proliferation and migration. PVA can be chemically or physically cross-linked to form hydrogels (The chemical cross-linking method by using chemicals (glutaraldehyde, methanol, ethanol, acetone) to crosslink hydrogels with radiation or aldehydes is inexpensive and efficient). PVA is often electro spun with natural polymers or other biomolecules. Used in regenerative medicine
Polylactic Acid (PLA)
Hydrophobic aliphatic polyester, good biocompatibility and mechanical properties, can be biodegraded by hydrolysis and enzyme activity. Used in a variety of applications, such as suture stents and cellular carrier drug delivery systems. PLA can be used as drug carriers for drug-carrying nanoparticles, such as liposome polymers, nanoparticles, dendrimers, and micelles, and for drug delivery in packaging machines. PLA is also the focus of clinical attention, with continuous development and great progress in clinical transformation.
Polyvinyl Chloride (PVC)
Hydrophobic. Amorphous, rigid. Mechanical properties dependent upon plasticizers used. The use of PVC in medical applications requires special care. The use of stabilizing and plasticizing elements induces undesired toxicity (Phthalates are the most common type of plasticizers that have been banned in Europe (carcinogenic and toxic to reproduction)). Used in tubes, blood bags, and catheters. Can degrade from a fungus Asperigillus Fumigatus.
Polypropylene (PP)
Tough and flexible, Medical applications include medical vials, diagnostic devices, petri dishes, intravenous bottles, specimen bottle, foot trays, pans, pill containers, and disposable syringed
Temperature in Polymers - Tm (Melt Temperature)
Transformation of a solid material having an ordered structure of aligned molecular chains to a viscous liquid in which the structure is highly random. Polymer melt temperatures differ between ceramic and metals (Happens over a range of temperatures. It also depends on the history of the material, (plasticizers added)). The precense of double bonds and aromatic groups in the polymer backbone lowers chain flexibility and causes an increase in Tm. The precense of polar groups (Cl, OH, and CN) even though not excessively large, leads to significant intermolecular bonding forces and relativley high Tm
When Designing with Ceramics
Understand the application (analysis of usage, function of the device (dental, bond fixation, joint replacement). Biocompatibility. Mechanical Considerations (Theyre very brittle, design must account for their mechanical properties to prevent fractures. This might involve optimizing the shape, thickness, and stress distribution). Surface Finish (Surface roughness and finish are crucial for biocompatibility and wear resistance, proper polishing or coating techniques might be necessary). Manufacturing Processes (Each method had its advantages and disadvantages). Quality Control (Implement stringent quality control measures to ensure the final product meets required standards). Mechanical Testing (Conduct tests to assess the device's strength, hardness, and wear resistance under realistic conditions).
Manufacturing Ceramics - Powder Processing
Used for crystalline materials. A powdered ceramic and small amount of water and/or binding agent are pressed into a desired shape and the part is subjected to sintering. Process occurs below the melt temperature. Results in a reduction of porosity as the individual crystals will ionically bond to each other
Polyurethanes
May exist as either thermoplastic or thermoset or as a thermally rigid polymer that is composed of 2 reactants, a diisocyanate and a diol that form a foam with different hardness and density according to the type of monomer and additives used which may even alter the degree of biocompatibility and biodegradability. Coating for breast implants, vascular equipment such as aortic balloons and gastric balloons, male contraceptives, and surgical gloves for allergy to latex among other application.
Structure of a Polymer
Means many monomers. Nanoparticles for Drug Delivery (having long polymer chains can impact the synthesis of material and application, Hydrolysis is a process that can be used to decrease molecular weight of the polymer)
Polymers - Manufacturing (Compression Molding)
Used with thermosetting plastics. The material is placed into a hot mold and the mold is closed by a hydraulic press. Ex: Polymer/drug mixtures compressed into water.
Polymers - Manufacturing (Injecting Molding)
Molten plastic under pressure is forced through a nozzle into the mold. When ram retracts, plastic pellets drop from a hopper into a barrel. Ram forces plastic into the heating chamber (around the spreader) where the plastic melts as it moves. Molten plastic is forced under pressure (injected) into the mold cavity where it assumes the shape of the mold.
Natural Polymer- Chitin
Most important constituent of the exoskeleton of crustaceans and insects, cell walls of some bacteria and fungi as mushrooms. Often considered as a derivative of cellulose (Similar to cellulose, it is also a glucose-based unbranched polysaccharide; the difference is that in chitin instead of hydroxyl group). Disadvantage- insolubility in the common solvents generally available, which causes difficulty with processing, whereas chitosan is a lot easier to dissolve. Lobster, crab, and shrimp are result in the availability of substantial quantities of crustacean waste materials. These wastes (tons) consist of mainly of shells and heads that can be processed to yield chitin. Chitin Structure Highly crystalline structure Strong, rigid, linear structure Has trouble dissolving in common organic solvents.
Polyethylene (PE)
Most popular polymer. Plastic bags, packaging, bottles. 5 Variants: Low-density polyethylene (LDPE), High-density polyethylene (HDPE), Linear-low density polyethylene, Ultrahigh density polyethylene (UHDPE), Ultra low density polyethylene (ULDPE)
Ceramics - Calcium Phosphates
Most widely used Used in bone grafting and tissue engineering due to their similarity to the mineral components of bones. At body temperature and pH < 4.2 - dicalcium phosphate. At body temperature and pH > 4.2 - tricalcium phosphate
Natural Polymers - Polysaccharides
Mostly found in plants. 75% of all organic material on earth are in the form of a polysaccharide. Long polymer chains composed of monosaccharide units bound together by glyosidic linkages. Range in structure from linear to highly branches Glucose is a simple sugar and is the most abundant monosaccharide - (Found in blood as sugar Mainly made by plants and algae). Insoluble in cold water, hygroscopic (absorbs moisture from the air). Used in bone replacement implants, bone cements, drug delivery, and tissue scaffolds. Various types include: Chitin
Ceramics - Hydroxyapatie (HA)
Naturally occurring mineral form of calcium apatite, and it is the main component of tooth enamel and bone. Low solubility. Synthetic. hydroxyapatite is widely used in orthopedic and dental applications, such as bone grafts, coatings for dental implants, and bone tissue engineering scaffolds
Ceramics - Zirconia (ZrO2)
Near inert (solid state sintered ceramic). Known for exceptional mechanical strength and biocompatility. Commonly used in dental crowns, bridges, and implants due to tooth-like color and durability
Polyamides
Nylon is the most commonly used synthetic polyamide in medical applications. It is used in suture lines because of its high tensile strength. A composite material of nylon with PU with the elasticity thereof and nylon strength is used in the balloons of the catheters used in angioplasty.
Manufacturing Ceramics - Firing
Once a part is shaped and dried, the piece is then exposed to temperatures between 900C and 1400C (burns out the binding agent, increases the density). Different materials can be developed based on the temperature and duration of firing (can impact the mechanical properties similar to annealing in metals). Vitrification: gradual formation of soft glass that flows around the particles to fill some of the void areas, these materials are created when powdered ceramics are fired and held at a temperature below the melting point.
Polyether Ether Ketone (PEEK)
PEEK is a semi crystalline thermoplastic. Excellent thermal, chemical, abrasion, dynamic fatigue, High toughness, fatigue strength and highly biocompatible. Used in orthopedic implants, heart valves and in the manufacture of implants for cervical cancer.
Polymers - Manufacturing : Extrustion (Thermoplastics)
Plastic pellets drop from the hopper into the turning screw. Plastic pellets melt as the turning screw pushes them forward by the heaters. The molten polymer is forced under pressure through the shaping die to form the final product (extrudate). Medical Devices: Catheters, Tubing, Sutures, Rings. EVA and Tetracycline HCL Fibers for Periodontal Applications. Twin Screw Extrusion: is used extensively for mixing, and compounding
Polyolefins
Plastic resins polymerized from polypropylene (PP) and polyethylene (PE), Inert, Hydrophobic, Do not degrade.
Synthetic Polymers
Poly (2-hydroxyethyl methacrylate) - contact lenses. Poly (ethylene) - orthopedic joint implants. Poly (caprolactone) - drug delivery devices, sutures. Poly (propylene) - sutures. Advantages: They can be produced on a large scale, Can be designed into complex shapes, Properties can be chemically manipulated to alter mechanical properties, Repeatable results when produced. Disadvantages: Not fully biocompatible which can result in inflammatory responses
Polyethylene Terephthalate (PET)
Polyester, Hydrophobic, Highly crystalline. PET is used in the manufacturing of textile vascular prostheses, like woven graft, used in the treatment of aneurism and occluded blood vessels (Although problems related to graft failure have been reported, this is still most reliable option for an artery disease). Sutures, meshes, luer filters, check valves and catheter housing. As for degradable polyesters, there are lactic PGA, PLLA, PDLA although they are subjected to restrictions as to the quantity allowed since they are acidic in their base, they are used as biomaterials in vascular stents and networks for pharmacological coatings.
Polymers - Atomic Bondings
Polymers are held together by covalent bonds (share valence electrons). Mechanical behaviors of covalent bonds (Some are relativley strong, others are weak. Some fail in a brittle manner, whereas others experience significant amounts of deformation before failure. Difficult to predict the mechanical properties of covalently bonded materials on the basis of their bonding characteristics). Covalent compounds usually have lower melting and boiling points than ionic compounds, are softer, and are electrical insulators. Secondary Bonding (Van der Waals is the attractive force between dipoles and Hydrogen Bonding)
Ceramics Primary Applications
joint replacement, fillings, bone grafts / cements, eye (excellent wear, mechanical properties, corrosion resistance)
Bioceramics
used for the repair and reconstruction of diseased or damaged tissue. Can be classified into 3 large groups based on tissue response - Bioinert Ceramics: stable in vivo, do not react with the body (Aluminum oxide and zirconia). Bioactive Ceramics: can bond to bone and promote bone growth (Hydroxyapatite and Tricalcium Phosphate). Bioresorbable Ceramics: dissolve in the body and promote tissue regeneration (Calcium Sulfate, Calcium Phosphate-based ceramics).
Natural Polymers - Pullulan
Pullulan is a linear homopolysaccharide of glucose that is often described as secreted primarily by strains of the fungus Aureobasidium pullulans (Allows it to be flexible, allows for fiber forming and distinct films, these films and fibers resemble synthetic polymers). Hydrophilic; dissolves in water (water can be used as a solvent): Non-hydroscopic. Adhesive properties, O2 impermeable properties. Odorless, tasteless, and edible (used as a filler in beverages and sauces). Low viscosity (stable to heating, high temperature, changed in pH). Methods to alter properties of pullulan - You can reduce its water solubility by esterification or etherification, hydrogenation increases the stability of pullulan, Carboxylation enhances solubility in cold water, Copolymerization can change its function and ability. Clinical Applications: Pharmaceutical coatings (Sustained release) - Drug Delivery, Wound Healing, Vaccines, Tissue Engineering. Limitations: Price, cost of production has limited its
Polymers - Polydispersity Index
Ratio of Mw / Mn International standards have established that PDI values < 0.05 are more common to monodisperse samples, while values > 0.07 are common to a broad size distbribution of particles
Ceramics Crystal Structure
Relative size of ions: formation of stable structures (maximize # of oppositely charged ions) Maintenance of Charge Neutrality: net charge in ceramics should be zero (shown in chemical formulas) - AmXp (A is cation while X in anion)
Polytetrafluoroethylene (PTFE)
Also known as Teflon. Extremely low coefficient of friction. Hydrophobic. Nondegradable. Used in catheters, facial reconstructions, artificial tendons, and coating for needles and wires. May produce a mild inflammatory response on the part of the patient.
Natural Polymers - Chitosan Properties
Anti-thrombogenic, Antioxidant, Hemostatic, Immunity enhancing, Antimicrobial, Biocompatible and biodegradable, Shortens the time of wound healing and the rebuilding of connective tissue, Minimal reactions, Water soluble (almost), Exhibits low toxicity, Chitosan is used as an intraocular lens material because of its oxygen permeability, and it has been found to expedite blood clotting.
Polycarbonate
Biostable polycarbonate: Commonly used in membranes, filaments, nets and in the manufacture of prototypes for medical equipment
Properties of Bioceramics - Failure
Breakdown of ceramics is known as degradations. Ceramics are more stable then metals due to their strong ionic bonds (needs a lot of energy tp break them). Environment and design are 2 contributing factors that contribute to ceramic failure (tension can cause stress induced degradation). Porosity is big in degradation (more surface area with the environment): Increase the formation of cracks or rate of propagation
Ceramics Mechanical Properties
Brittle: Consider deformation (in highly ionic solids, motion is difficult, and resistance to motion of ions like charge past one another). Since theyre so brittle- flexural tests determine strength and mechanical behavior. Difficult to shear or plastically deform (non-ductile) Fractures in the elastic region. Low tensile vs. compressive strength. Flexural Tests - Measurement of Elastic Modulus (Room T behavior is usually elastic, with brittle failure and 3-point blend test is used -Tensile tests are difficult for brittle materials)
Biodegradable Bioceramics
Calcium Phosphates. Bioactive glasses with undergo a reaction at their surface (exchange of ions with the physiological fluid) - Creates a silica (rich layer that affects protein and cell interactions with the material over weeks to months). Erosion Mechanism: erode under physiological conditions due to pH conditions. Rate of erosion is dependent on: Chemical Susceptibility of the material, amount of crystallinity, amount of media (water) available, material surface area to volume ratio
Ceramics Atomic Bonding
Can be ionic or covalent
Polymers - What Affects Tm and Tg
Chain stiffness increased by precense of - 1. Bulky Side Groups 2. Polar Groups or side groups 3. Chain double bonds and aromatic chain groups. Both Tm and Tg increase with increasing chain stiffness. Regularity of repeat unit arrangements (affects Tm only). Side Branches (affects Tg only) - (Long chain aliphatic groups, either linkages promote flexibility into the polymers and lower the glass transition temperature (Tg), To increase the Tg, aromatic structures are large and rigid).
Polystyrene (PS)
Clear (can be colored). Hard and brittle. Dissolves in acetone but resistant to hydrolysis. Used for plastic cutlery, license plate frames, smoke detector housings. Medical applications: petri dishes, test tubes, microplates.
Degree of Polymerization
DP = average # of repeat units per chain. DP=Mn/m (where m= average molecular weight of repeat units for copolymers that is found by m=Efm)
Polymers - Degree of Crystallinity
Degree of crystallinity expressed as %crystallinity (some physical properties depend on the % and heat treating causes crystalline regions to grow and % to increase). Aging can change the degree. Rate of crystallization on cooling from the melt depends on the Annealing and Quenching (Rate of nucleation and Rate of crystallization growth). Increasing the crystallinity of a polymer generally enhances its strength and the material becomes more brittle (For semi crystalline polymers, tensile modulus increases significantly with degree of crystallinity) The degree of crystallinity affects mechanical properties such as hardness. The higher the degree, the higher the modulus. Longer the chains, the hard it is for a polymer to be crystallized. Some branched polymers can not be easily crystallized due to steric hinderances which then causes a semi-crystalline structure. Structure contains ordered and disordered regions
Rubbers
Developed for implants. Natural and synthetic rubbers (Natural rubber is made from latex Hevea Brasiliensis (compatible with blood)). Thermally Stable- consistent properties in a wide range of temperatures. Silicone: Biological stability without the need for plasticizing It has high usage in ophthalmological applications, the formation of encapsulation in breast implants, and in intra-articular implants, Occurrence of inflammation of the synovial membrane, Residues of silicone oil have been associated with hepatic tumors.
Deformation in Polymers (Drawing)
Drawing (Ex: monofilament fishline): stretched the polymer prior to use, and aligns chains in the stretching direction. Results: increases the elastic modulus ( E ) in the stretching direction, increases the tensile strength (TS) in the stretching direction, decreases ductility (%EL). Annealing after drawing: decreases chain alignment, reverses effects or drawing (reduces E and TS, while it enhances %EL). Contrasts to the effects of cold working.
Ceramics - Bioglass (Calcium Sodium Phosphosilicate)
Theyre bioactive- bond with living tissues, making them suitable for bone repair and tissue engineering applications. Non-crystalline (similar to HA). Modifications to their surface allow them to bond with tissue. Often added to other ceramics to improve their performance. Bone grafts, cranial and maxillofacial repair, nerve repair
Ceramics - Al2O3
Excellent biocompatibility. Polycrystalline powder with uses in pharmaceutical, artificial joints, and dental applications. Used as a coating over metals. High density, high wear resistance. Made by solid state sintering (particles are joined together). Impurities degrade the mechanical properties and increase wear
General Properties of Bioceramics
Hard & Brittle, High Melt Temperatures, Biocompatible, Excellent Wear Resistance
Low Density Plyethylene (LDPE)
Highly branched, Low crystallinity
Expanded Polytetrafluoroethylene (ePTFE)
Improved mechanical properties. Can be shaped into membranes, tubes, rods, or other geometries according to the desired function. It has been used in vascular graft applications and as soft tissue filler.
Improving Ceramics Mechanical Properties
Impurities / Alloying Heat Treatment (Annealing, Quenching) Increasing Density of the Ceramic
Polymers - Effects of Temperature Results
Increasing the temperature results in 1. A decrease in elastic modulus 2. A reduction in tensile strength 3. An enhancement of ductility (at 40F the material is totally brittle, whereas there is a considerable plastic deformation at both 122 and 140F
Polymeric Structure
Linear polymers that are made up of identical units repeated (flexible, low melt temperature). Branched- composed of a main chain with one or substituents side chains branched (more rigid, higher melt temperature). Cross-linked (very rigid, very high melt temperature) - Physical: Temperature, pH, electrostatic interaction Chemical: crosslinker molecules; photoinitiators, Enzymatic. Large molecules (macromolecules) like polymers have very different properties than small molecules (Chain entanglement: long polymer chains get entangled with eachother). When the polymer is molten, the chains can flow past each other. Polymer Theoretical Density (Small changes in the number of side branches can cause significant differences in material properties (like: modulus, creep resistant, toughness, and degradation)). Copolymers: Two or more monomers that are polymerized together (Random: A and B are randomly positioned along chain, Alternating: A and B alternate in polymer chain, Block: large bloc
Molecular Weight of Polymers
MW = multiple amount by the weight of one - and add all together (EXAMPLE: 5C8H - 5(12g/mol) + 8(1g/mol) = blah). Molecular weight isnt just one value, its the distribution of values. The higher the MW, the lesser the mobility of the chains - higher strength, greater thermal stability. Number average of molecular weight- Mn: the total weight of the polymer divided by the # of polymer molecules, total weight of polymer/total # of molecules
Ultra High Molecular Weight Polyethylene (UHMWPE)
Mainly used on sliding surfaces of artificial joints, orthopedic, cardiovascular and neurology. High impact strength. Good biocompatibility. Chemically stable. Release of particles caused by friction (crosslinking used to relieve this problem, adding vitamin E in the material). Orthopedic sutures for soft tissue repair, catheters, stent grafts, heart valves
Manufacturing Ceramics - Casting
Preferred for crystalline rather than amorphous structures. Ceramics particles are mixed with water and an organic binder, poured and pressed into a mold. The piece is then left to dry as the water evaporates. The ceramic will shrink away from the walls of the mold (which aids in an easy removal). Further drying removes excess water (must be monitored that the structure of the ceramic could crack).
Ceramics Defects in Crystal Structure
Schottky Defect- where there are vacancies in both cations and anions in the correct ratio to maintain neutrality. Frenkel Defect- a vacancy and interstitial pair is created to maintain electroneutrality; only occurs with cations. Impurities (similar to metal impurities): Solute anions form mainly substitutional solutions since they are too large to fit easily in the interstitial space, in contrast, cations readily form both types of solutions.
Polycaprolactone (PCL)
Semi-crystalline polyester, hydrophobic, high mechanical strength, biodegradable. Commonly used in fused deposition modeling (FDM) and electrospinning techniques. Due to its excellent chemical/physical properties and versatility, PCL is widely used in tissue engineering, such as surgical suture anchors and brackets
Polymers - X-Ray DIffractions
Shows pattern of polymers that can both sharp and well defused bands, sharp bands correspond to crystalline regions and defused bands correspond to amorphous regions. A full x-ray circle shows amphorous samples with sharp arcs and a cut up circle shows a highly crystalline sample with scattered rays.
Polymers - Manufacturing (Bioprinting)
Simultaneous wiring of living cells and biomaterials with a prescribed layer-by-layer stacking organization using a computer-aided transfer process for fabrication of bioengineered constructs. Great leaps in pharmaceutical use because it does not entail any regulatory approvals and there is currently an emerging bioprinting market for tissue fabrication for drug testing and high-throughput assays. Inclusion of multiple cell types and facilitating a complex heterocellular physiological environment, bio printed tissue models (Liver) have been used in drug screening. Recently used in cancer research to investigate cancer pathology, growth and metastasis in a physiologically relevant microenvironment (Agriculture, Food)
Altering Polymers Crystallinity
Slow cooling (Annealing) increases the amount of crystallinity, and decreases the free volume and increases density -> a more brittle material. Quenching with cause less crystallization and the material will become more ductile
Acetal
Synthesized from formaldehyde. Acetal is a hard plastic. High strength and low coefficient of friction. It is used in prototypes of medical equipment and components that are obtained by machining because it is sensitive to the radiation used in sterilization this material becomes brittle and can break.
Polymer Crystallinity
The packaging of molecular chains to produce an ordered atomic array. Any chain disorder or misalignment will result in an amorphous region, The density of a crystalline polymer will be greater than an amorphous one of the same material and weight due to chains being closely packed together.
Temperature in Polymers - Tg (Glass Transition)
The temperature at which the polymer experiences the transition from rubbery to rigid state. The temperature at which the polymer experiences the transition from rubbery to rigid states is glass transition temperature.
Polymers - Thermoplastics vs Thermosets
Thermoplastics: Little crosslinking, ductile, soften w/heating (Ex: polyethylene, polypropylene, polycarbonate, polystyrene) Influence of Strain Rate: increasing the strain rate has the same effect of decreasing T. Thermosets: Significant crosslinking (10% to 50% repeat units), hard and brittle, do NOT soften w/heating, (Ex: vulcanized rubber, epoxies, polyester resin, phenolic resin).
Ceramics Point Defects
Vacancies (exist in ceramics for cations and anions). Interstitials (exist for cations, are not normally observed for anions because anions are large relative to the interstitial sites.
Deformation in Polymers (Simple Shear Deformation)
Viscosity: a property that represents the internal resistance of a fluid to motion or the to "fluidity." The behavior of a fluid in a laminar flow between two parallel plates when the upper plate moves with a constant velocity. (You will have a shear stress and shear force, Viscosity shear stress/strain rate; slope of shear stress vs. strain rate curve, Linear Newtonian fluid, Pseudoplastic- "Shear thinning" Dilatant- "Shear thickening").
Ceramics
synthesized, inorganic, solid, crystalline materials excluding metals, (glass is one but differs in structure)
