REVIEW : LECTURE 17 NANOMECHANICS AND BIOCOMPATIBILITY : PROTEIN-BIOMATERIAL INTERACTIONS.EXAMPLE OF A BIOMATERIAL : VASCULAR GRAFTS- Other design considerations : proper mechanical properties (modulus, strength), to avoid bursting, kinking, leaking, avoid fraying easy manipulation during surgery2nd EXAMPLE OF A BIOMATERIAL : ENDOTRACHEAL TUBE (ETT)KINETICS OF PROTEIN ADSORPTIONUSE OF STERIC REPULSION TO INHIBIT PROTEIN ADSORPTIONTHERMAL MOTION OF POLYMER BRUSHES : MOVIES(left) : (J. Marko (Cornell U) : http://www.lassp.cornell.edu/marko/thinlayer.html)POLY(ETHYLENE OXIDE) AS A BIOINERT COATINGBLOOD VESSELS The outer component of a cell surface; usually contains strongly acidic sugars, hence it carries a negative electric charge. A thick endothelial glycocalyx provides the endothelial surface with a nonadherent shield, during inflammation, it reduced in size to allow adhesion of leukocytes.3.052 Nanomechanics of Materials and Biomaterials Tuesday 04/24/07 Prof. C. Ortiz, MIT-DMSEILECTURE 18: NANOMECHANICS AND BIOCOMPATIBILITY :PROTEIN-BIOMATERIAL INTERACTIONS 2 Outline :REVIEW LECTURE #17 : BASICS OF BIOCOMPATIBILITY.....................................................................2EXAMPLE OF A BIOMATERIAL : VASCULAR GRAFTS...........................................................................32nd EXAMPLE OF A BIOMATERIAL : ENDOTRACHEAL TUBE..............................................................4 KINETICS OF PROTEIN ADSORPTION..................................................................................................5 USE OF STERIC REPULSION TO INHIBIT PROTEIN ADSORPTION.....................................................6THERMAL MOTION OF POLYMER BRUSHES : MOVIES........................................................................7POLY(ETHYLENE GLYCOL) AS A BIOINERT COATING..........................................................................8BLOOD VESSEL STRUCTURE................................................................................................................9 Objectives: To establish a fundamental qualitative and quantitative scientific foundation in understanding the biocompatibility of biomaterials implanted in vivoReadings: Course Reader Documents 29, 30 Multimedia : Polymer Brush Demos (posted on stellar)13.052 Nanomechanics of Materials and Biomaterials Tuesday 04/24/07 Prof. C. Ortiz, MIT-DMSEREVIEW : LECTURE 17 NANOMECHANICS AND BIOCOMPATIBILITY : PROTEIN-BIOMATERIAL INTERACTIONS Definitions : biocompatibility, bioinert, bioactive, bioadhesion, biofilm→ example of biomaterialsTemporal biological response to materials implanted in vivo; Host effects vs. Biomaterial Effects• living materials respond rapidly to foreign materials ( <1 s ), new layer of protein coats (isolates) biomaterial surface ( minutes ), attachment of platelets, bacteria, yeasts, and additional proteins to surface ( minutes-hours ), alteration in cell and tissue behavior ( minutes-years )Blood Compositions and Solution Conditions :pH7.15 - 7.35, IS=0.15 M, Temperature ~37°C -cells and platelets (~45 wt.%)-The liquid portion of the blood, the plasma or serum (55wt. %), is a complex solution containing more than 90%wate- 6-8 wt.% proteins in plasma (over 3,000 different types),including :58% albumins, 38% globulins, 4% fibrinogens-The majority of blood plasma proteins are net negativelycharged. Each has its' own heterogeneous surfacechemistry and unique intermolecular potential withbiomaterial surface that changes and evolves with time invivo.→ want bioinert surface....23.052 Nanomechanics of Materials and Biomaterials Tuesday 04/24/07 Prof. C. Ortiz, MIT-DMSEEXAMPLE OF A BIOMATERIAL : VASCULAR GRAFTSVascular graft : prosthetic tube that acts either a permanent or resorbable artificial replacement for a segment of a damaged blood vessel (e.g. from athersclerosis, aneurysms, organ transplant, cancer, arteriovenous fistula, diabetes) : $200 million market worldwide• expanded polytetrafluoroethylene (Gore-Tex, ePTFE)-fibrillated, open cell, microporous (pore size 0.5-30 mm), 70% air, nonbiodegradable, chemically stable, used for 26 yrs, hydrophobic/ nonpolar, flexible • polyethylene terephthalate (Dacron, PET)-multifilamentous yarn fabricated by weaving/knitting, amphiphilic, smaller pores than ePTFE• polyurethane derivatives• bovine collagen -fibrous, hydrophilic- Other design considerations : proper mechanical properties (modulus, strength), to avoid bursting, kinking, leaking, avoid fraying easy manipulation during surgeryZhang, et al. J. Biomed. Mtls. Res.60(3), 2002, 502.www.vascutek.com33.052 Nanomechanics of Materials and Biomaterials Tuesday 04/24/07 Prof. C. Ortiz, MIT-DMSE2nd EXAMPLE OF A BIOMATERIAL : ENDOTRACHEAL TUBE (ETT)-ETT is a polymeric conduit between the lungs and a ventilator and is used to form a closed system of pulmonary ventilation necessary to maintain optimal respiration, as well as protect the lungs from any foreign material that may be aspirated into the trachea. Most often used in critical intensive care situations to allow the delivery of air to the patient. Insertion of the tube is called Intubation, most often used in critical intensive care situations.-Intubation usually requires general anesthesia and muscle relaxation but can be achieved in the awake patient with local anaesthesia or in an emergency without any anaesthesia, although this is extremely uncomfortable and generally avoided in other circumstances.-In 2002, there were 30 million intubations.ETTs are made of Poly(vinyl chloride) + 30-40 wt. % of low molecular weight plasticizers, di-ethylhexyl phthalate (DEHP), also referred to as di-octylphthalate (DOP). -vinyl monomers and DEHP potential carcinogens, irritant of mucus membranes (DEHP leaches out), damage to trachea begins immediatelyhttp://www.mallinckrodt.com/Respiratory/resp/Product/HiLoEvac/HiLoMini.html43.052 Nanomechanics of Materials and Biomaterials Tuesday 04/24/07 Prof. C. Ortiz, MIT-DMSEKINETICS OF PROTEIN ADSORPTIONMolecules can be brought to the surface by diffusion; (I. Szleifer, Purdue University)22protein proteinprotein;� �=� �� ��= +� � �1 4 2 4 3r rr22C CD C = concentration, D = diffusion coefficient, z = distance, t = timet z(z,t) (z,t)D (t z zIdeal