3. Materiali polimerici o plastiche -...
Transcript of 3. Materiali polimerici o plastiche -...
3. Materiali polimerici o plastiche
Cuore artificiale AbioCor® Acrylic Foldable IOL
Dacron vascular grafts Suture
Tubi e cateteri
Cemento
Sacche raccolta sangue
Classificazione
Volume specifico vs temperatura
Il comportamento caratteristico di polimeri organici termoplastici
o polimeri poco reticolati intermedio tra il comportamento elastico
ed il comportamento di un fluido.
Viscoelasticità
Modi di deformazione
Rilassamento degli sforzi Variazione del carico nel tempo quando al materiale
si impone una deformazione costante.
Scorrimento (Creep) Variazione della deformazione nel tempo per azione di
un carico costante.
OSSERVAZIONE!
I modi di deformazione (ad es. rilassamento e scorrimento) dipendono dal
tempo, mentre i tipi di deformazione (ad es. estensione monoassiale,
taglio semplice, compressione uniforme) dipendono dallo sforzo applicato:
si può applicare qualunque modo di deformazione a qualunque tipo di
deformazione.
rilassamento
degli sforzi
scorrimento
(creep)
Due modi di deformazione in viscoelasticità: (a) rilassamento degli sforzi, (b) scorrimento.
stato vetroso
regime transizione
vetrosa
stato gommoso flusso gommoso
stato viscoso
Polistirene amorfo
Qual è l’origine del comportamento
viscoelastico ?
Poli-aril-eterchetoni (PAEK)
Siliconi
Poliuretani (PU)
Cuore artificiale AbioCor® Acrylic Foldable IOL
Dacron vascular grafts Suture
Tubi e cateteri
Cemento
Sacche raccolta sangue
Polietilene a peso molecolare ultra alto (UHMWPE)
catene polimeriche lineari (i.e. poco ramificate)
il peso molecolare medio è > 2,0106
Struttura semicristallina di UHMWPE
Lamelle cristalline
Zone amorfe
Summary of PAEK Materials Related to Implant Use
Polymer Trade Name Producer Comments
PEEK OPTIMA
(Biomaterial) Invibio (Subsidiary of
Victrex) Thornton-
Cleveleys, UK
Manufacturer and
Supplier of Long Term
Implantable PEEK in
CE and FDA approved
devices since 1998.
PEEK Victrex Victrex, Thornton-
Cleveleys, UK Provides PEEK for
blood/tissue contact less
than 24 hours.
PEEK Gatone Gharda, India No record of supplier
implantation studies.
Discontinued for
medical use when
acquired by Solvay in
December 2005
PEEK Keto-Spire Solvay Advanced
Polymers, LLC Not available for
implant use.
PEKK PEKK DuPont (Wilmington,
DE) Discontinued for
medical use by DuPont
PEKK OXPEKK Oxford Performance
Material (Enfield,
CT)
Implantable Grade
available.
PEKEKK Ultrapek BASF, United States Discontinued in
December 1995
Chemical formula of poly(aryl-ether-ether-ketone), commonly abbreviated as PEEK, and
poly(aryl-ether-ketone-ether-ketone-ketone),
commonly abbreviated as PEKEKK. Image provided courtesy of Exponent, Inc.
(A) Chain conformation of PEEK; (B) Orthorhombic crystal unit cell f
(B) or PEEK. Image provided courtesy of Exponent, Inc.
Posterior dynamic stabilization of the spine using PEEK rods,
image provided courtesy of Medtronic Sofamor Danek.
Bioresorbable polymers
Riassorbimento
Materiali
• Poly (glycolic acid) (PGA)
• Poly (lactic acids) (PLAs)
• Copolymers (PGA-PLA) (i.e. Vicryl, Polyglactin 910)
• Polydioxanone (PDS)
• Polycaprolactone (PCL)
• Polyanhydrides
i.e.
Poly(SA-HDA anhydride)
• Polyhydroxyalkanoates (PHAs)
i.e.
Poly-3-hydroxybutyrate (Poly(3HB))
Poly-4-hydroxybutyrate (Poly(4HB))
Copolymers (Poly3HB-co-4HB, Poly3HB-co-3HV Biopol)
[-CO-(CH2)2-O-CH2-O-]n
[-CO-CH2-O-]n
[-CO-CH(CH3)-O-]n
[-CO-(CH2)5-O-]n
[-CO-(CH2)x-CH(R)-O-]n
[-CO-(CH2)-CH(CH3)-O-]n
[-CO-(CH2)2-CH2)-O-]n
-[-O-CO-(CH2)8-CO-]-[-O-CO-(CH2)14-CO-]-
Current synthetic and natural resorbable polymers
and their applications
• Bone fixation devices
• Drug delivery systems
Gliadel drug delivery wafers in the cavity left by the
removal of a cancerous brain tumor.
MicroFab has obtained paclitaxel-loaded PLGA microspheres
• Suture
Cross-section of Deme Tech polydioxanone suture
and dyed suture attached to needle.
Graph showing strength degredation over time of
synthetic resorbable sutures
(Vicryl, copolymers PGA -PLA)
Sutura a memoria di forma
• Resorbable scaffolds
The first 100% resorbable composite scaffold.
Wedges available in three(3) angle and height
configurations to integrate into the surgical site (see
Dimension Information for angle and height
specifications)
Porous scaffold with mean pore size of 500-600 µm and
75% total porosity for tissue ingrowth
Hydrophilic properties to absorb blood, marrow, cells,
and proteins
Easily trimmed at time of surgery using mechanical
hand instruments
Scaffolding architecture mimics natural bone
Fiber orientation provides improved strength
OsteoCure™ Wedges use PolyGraft® material
technology and are porous, resorbable scaffolds
composed of polylactide-co-glycolide (PLG)
copolymer for providing structure and calcium sulfate
for enhancing bone growth. The copolymer is
amorphous (noncrystalline) and resorbs in four to
eight months. In addition, polyglycolide (PGA) fibers
are incorporated for strength, and surfactant is added
to allow fluids to be easily absorbed into the scaffolds.
Polimeri bioriassorbibili in ortopedia The bioresorbable materials most commonly used in
today’s orthopaedics include polylactic acid (PLA);
polyglycolic acid (PGA); the L–form of PLA: PLLA; the
copolymer of PLA and PGA: PLGA; and the DL–form of
PLA: PDLLA. The degradation process of these
materials in the body involves two steps: hydrolysis
followed by metabolization.The process of hydrolysis
involves the breaking of the polymer chains within the
implant material to produce by-products that include
lactic acid and glycolic acid single molecules. These
degradation products are metabolized in the liver and
produce carbon dioxide as a by-product, which the
body can eliminate.
To date, PLLA has not had sufficiently high strength characteristics for use in the fixation of larger fractures
such as the humerus and femur. Much of the referenced PLLA research has focused on veterinary applications
using rabbits.For injuries such as ligament damage and skeletal fractures, PLLA interference screws and
plates have been used successfully to fixate and heal tissue and bone.
Anterior cruciate ligament reconstructive surgery currently uses titanium, steel, or degradable interference
screws to secure the graft within the femur and tibia. The metallic screws will remain in the patient’s knee for the
rest of his/her life. This can potentially cause problems including stress shielding (the weakening of healing
bone resulting from excessive rigid fixation for prolonged periods of time) and micro-motion (the weakening and
fragmenting of surrounding bone as a result of small movements of the implant within the bone) of the screw
causing the graft to fail. Metallic screws are also nonconducive to tissue regrowth that facilitates complete
healing.This has given rise to the increased use of the bioresorbable interference screws in this application area.
Bioresorbable screws will promote and foster the growth of the surrounding bone tissue, as well as limit stress
shielding and micro-motion.
In many applications, PLLA can perform a function similar to that of a traditional metallic-based device.
However, the unique properties of PLLA implants may provide the clinician with a level of surgical versatility that
Is not found with titanium or stainless-steel devices.9
Advantages of PLLA include
reduced risk of stress shielding
postoperative diagnostic imaging free from the obstruction or artefact caused by metallic implant materials
elimination of the need for secondary surgery to remove metallic implants
better growth of tissue around the implant that will gradually dissipate load to the healing tissue or bone.
Chiusure sternali
Polidiossanone
Resorbable pin and cord