BME 312 - Polymers III

synthetic polymers

- produced through chemical rxns
- poly (2-hydroxyethyl methacrylate): contact lenses
- poly (ethylene): orthopedic joint implants
- poly (caprolactone): drug delivery devices, sutures
- poly (propylene): sutures
- produced on large scale (quick, cheap, repeatable)
- designed into complex shapes (molding)
- properties can be chemically manipulated
- not fully biocompatible which can cause inflammatory response

natural polymers

- depends on how it was grown, repeatability is an issue
- alginate: wound dressing
- collagen: orthopedic repair matrices, nerve repair
- elastin: skin repair
- hyaluronic acid: orthopedic repair and dermatology

polyolefins

- plastic resins polymerized from polypropylene (PP) and polyethylene (PE)
- inert inside the body
- hydrophobic
- do not degrade (unless in highly-toxic solution)

polypropylene (PP)

- low density (0.855 amorphous to 0.846 crystalline)
- E is 1300-1800 N/m^2
- melt temp is 130-170 deg C, Tg is -12 deg C
- avg MW 2.2 to 7.0 x 10^5 g/mol
- tough and flexible
- medical applications: medical vials, diagnostic devices, petri dishes, IV bottles, specimen bottles, food trays, pans, pill containers, disposable syringes

polyethylene (PE)

- most popular polymer
- doesn't degrade easily
- plastic bags, packaging, bottles
- exists in 5 variants:
1. low density polyethylene (LDPE)
2. high density polyethylene (HDPE)
3. linear low density polyethylene
4. ultrahigh density polyethylene (UHDPE)
5. ultralow density polyethylene (ULDPE)

ultra high MW polyethylene (UHMWPE)

- MW is > 2 x10^6 g/mol (very strong)
- mainly used on sliding surfaces of artificial joints, ortho, cardio, and neuro
- high impact strength
- good biocompatibility
- chemically stable
- release of particles caused by friction (causes implant to fail/infection): crosslinking fixes this issue, or adding vitamin E to lubricate area to combat friction
- orthopedic sutures for soft tissue repair, catheters, stent grafts, heart valves

low density polyethylene (LDPE)

- derived from a high temp (150-300 deg C) and pressures ranging (1000-3000 kg/cm^2) using free radical initiators
- highly branched so flexible
- low crystallinity
- density ranges from 0.915 to 0.935 g/cm^3
- ex is invisalign

polystyrene (PS)

- clear (can be colored sometimes)
- hard and brittle, %EL = 3-4%
- density = 0.96-1.05 g/cm^3
- Tm= 240 deg C
- E = 3000-3600 MPa
- dissolves in acetone but resistant to hydrolysis
- used for plastic cutlery, license plate frames, smoke detector housings
- medical applications: petri dishes, test tubes, microplates

polytetrafluoroethylene (PTFE)

- AKA teflon
- extremely low coefficient of friction
- hydrophobic
- nondegradable
- used in catheters, facial reconstruction, artificial tendons
- also used as a coating for needles and wires
- may produce a mild inflammatory response on the part of the patient
nonstick pans

expanded polytetrafluoroethylene (ePTFE)

- improved mechanical properties (variation of PTFE)
- 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
- more ductile than PTFE so its applications can be expanded

polyvinyl chloride (PVC)

- hydrophobic
- amorphous, rigid
- Tg = 75-105 deg C
- density - 1.4 g/cm^4 (on denser side)
- mech properties depend on what plasticizers used: rigid= 40 MPa, %EL < 15%, flexible= 14 MPa, %EL = 400%
- phthalates: used as stabilizers for PVC, toxic to reproduction
- use in medical application requires special care
- used in tubes, blood bags, catheters
- can degrade from a fungus asperigillus fumigatus

rubbers

- developed for implants
- natural and synthetic rubbers (natural is made from hevea brasiliensis - compatible with blood)
- thermally stable: consistent properties in a wide range of temps
- silicone: developed by Dow Corning, biological stability w/o the need for plasticizing, high usage in ophthalmological applications, information of encapsulation in breast implants, and in intraarticular implants, occurrence of inflammation of the synovial membrane, residues of silicone oil have been associated with hepatic tumors

polymethyl methacrylate (PMMA)

- AKA acrylic
- density 1.18 g.cm^3, Tg= 160 deg C
- transmits light and filters UV light below 300 nm similar to windows
- widely used in ortho as bone cement bc it transfers the load between the implant and bone
- naturally inert biologically, however rxns may occur against its monomer
- used in ophthalmic applications such as eye glasses, contact lenses and intraocular lenses
- used in cosmetic surgery as a filler but has also been reported to used illegally to shape muscles by body builders
- lab-on-a-chip devices

polycarbonate

- density is 1.22 g/cm^3 (heavier,denser)
- Tm = 150 deg C, Tg = 147 deg C, TS = 75 MPa, %EL = 80-150%
- biostable polycarbonate: used in membranes, filaments, nets, and in the manufacture of prototypes for medical equipment
- contain precursor BPA (not good)

polyethylene terephthalate (PET)

- polyester
- hydrophobic
- highly crystalline
- Tm = 265 deg C, density = 1.38 g/cm^3 (due to complex structure)
- PET is used in the manufacturing of textile vascular prostheses, like woven graft, used in treatment of aneurism and occluded blood vessels (artery disease as well)
- sutures, meshes, luer filters, check valves, and catheter housing
- as for degradable polyesters, there are lactic PGA, PLLA, PDLA although they are subject 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

polyether ether ketone (PEEK)

- semi crystalline thermoplastic with excellent thermal, chemical, abrasion, and dynamic fatigue
- Tm =343 deg C, Tg = 143 deg C (HIGH bc of high crystallinity)
- similar E to bone, 3.6 GPa
- high toughness, fatigue strength and biocompatibility
- used as orthopedic implants, heart valves and in the manufacture of implants for the cervical spine

polyamides

- nylon is the most commonly used synthetic polyamide in medical applications
- it is used in suture lines bc of high tensile strength
- a composite material (mixing of materials tg) of nylon and PU within the elasticity thereof and nylon strength is used in the balloons of catheters used in angioplasty

acetal

- synthesized from formaldehyde
- acetal is hard plastic
- high strength
- low coefficient of friction
- used in prototypes of medical equipment and components that are obtained by machining
- bc it is sensitive to the radiation used in sterilization this material becomes brittle and can break
- not used often in medical applications

polyvinyl alcohol (PVA)

- good biocompatibility
- hydrophilic (water soluble): crosslinking affects solubility
- bioadhesion
- excellent properties that support cell adhesion, proliferation, and migration
- can be chemically or physically cross-linked to form hydrogels (bc hydrophilic)
- PVA is often electrospun with natural polymers or other biomolecules to promote tissue regrowth
- used in regenerative medicine

polycaprolactone (PCL)

- most popular/oldest polymer used in biomaterials
- semi-crystalline polyester
- hydrophobic
- high mechanical strength (MW ~ 2000 g/mol)
- biodegradable
- low melt temp: can be mixed with drugs that usually degrade at high temp
- commonly used in fused deposition modeling (FDM) and electrospinning techniques
- due to its excellent chemical/physical properties and versatility, PCL is used in tissue engineering, such as surgical suture anchors and brackets
- very accessible

polylactic acid (PLA)

- hydrophobic aliphatic polyester
- good biocompatibility and mech properties
- can be biodegraded by hydrolysis over time and enzyme activity
- used in suture stents and cellular carrier drug delivery systems, drug-carrying nanoparticles
- PLA is the focus of clinical attention with continuous development and great progress in clinical transformation
- you can alter properties to make it PLLA
- used in our bone scaffold

polyurethanes (PU)

- may exist as a thermoplastic or thermoset
- can exist as a thermally rigid polymer composed of two reactants: a diisocyanate and a diol that form a foam
- different hardness and density according to the type of monomer and additives used, may alter the degree of biocompatibility and biodegradability of the PU
- coating for breast implants, vascular equipment such as aortic balloons and gastric balloons, male contraceptives, and surgical gloves for allergy to latex