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Welcome Biomaterials Based on Polymers, Fibers, and Textiles ! TXMI 8000 Professor Leonid Ionov College of Engineering, College of Family & Consumer Sciences, The University of Georgia Office: 303 Dawson Hall, 305 Sanford Dr, Athens, GA 30602 Lab: Riverbend Research North, Room 107 110 Riverbend Rd. Athens, GA 30602 Phone: 706-542-4885 E-mail: [email protected] Web: www.ionov-lab.com Office Hours: By appointment via email My group Administrative details • Course Text: Biomaterials Science, An Introduction to Materials in Medicine: Authors: Ratner & Hoffman & Schoen & Lemons, 2012, 3rd Edition, ISBN: 9780123746269. • 26 lectures + 3 midterm tests + 1 day for consultation for preparation to exam • Grading: 25% midterm tests, 25% homework, 50% final exam • Homework: Generally assigned on Thursday and be due on the following Tuesday. • Midterm tests: 3 tests • Final test: May • Lecture notes, problem sets (and answers), supplementary material will be posted on eLearning Commons. Introduction The goal is to improve the quality of life Ancient history of implants and biomaterials. • 3500 - 1800 BC warrior Vishpla, (Rig Veda, Sanskrit) with iron leg • 600 BC Sushruta, a renowned Indian physician,- nose reconstruction using a rotated skin flap • 600 BC Sutures made of vegetable fibers, leather, tendons, • Egypt 4000 years ago - linen sutures • 600 AD – dental implants Modern history of implants and biomaterials. Examples hip replacement knee replacement drug release Examples Increasing Need For Tissue and Organ Replacement 13.000 12.000 And: Waitinglist Organ-Transplantation USA 1990: 20.481 Patients 06/2006: 92.265 Patients 11.000 10.000 9.000 Waitinglist Kidney-Tx Germany UNOS, June 07 2006 8.000 7.000 Kidney - Transplantation in Germany Need ca. 3.500 / Year 2516 in 2003 2478 in 2004 6.000 5.000 4.000 3.000 2.000 1.000 0 1979 '81 '83 '85 '87 '89 '91 Year '93 '95 '97 '99 2001 03 DSO 2006 1970-4 Increasing Need For Tissue and Organ Replacement MEDICAL DEVICE EXAMPLES Sutures (temporary or bioresorbable) Catheters (fluid transport tubes) Blood Bags Contact Lenses Intraocular Lenses Coronary Stents Knee and Hip Prostheses Breast Prostheses (cancer or cosmetic) Dental Implants Renal Dialyzers (patients) Oxygenators/CPB’s (cardiopulmonary bypass system facilitates open heart ANNUAL # (U.S.)* 250 M** 200 M 40 M 30 M 2.5 M 1.2 M*** 0.5 M 0.25 M 0.9 M 0.3 M 0.3 M Vascular Grafts Pacemakers (pulse generators) 0.3 M 0.4 M surgery) Bio…materials Biomaterials do not necessarily have to be natural materials as the name may suggest. Biomaterials are defined by their application, NOT chemical make-up Biomaterials cover all classes of materials – metals, ceramics, polymers In 1974, at the 6th Annual International Biomaterials Symposium held at Clemson University, a biomaterial was defined as … a systemically, pharmacologically inert substance designed for implantation within or incorporation with a living system. In 1986, at a consensus conference of the European Society for Biomaterials, a biomaterial was defined as … a nonviable material used in a medical device, intended to interact with biological Systems definition was provided by Williams … material intended to interface with biological systems to evaluate, treat, augment, or replace any tissue, organ, or function of the body Bio…materials What governs materials choice? Subject One needs to know how body works (chemistry, physics, biology) internal and surface structure of implants (material science) interaction between body and implant = f (body, implant) - mass exchange (transport), - changes in body (immune response), - changes in implant (degradation) Subject • Structure of body, tissues, cells and molecules (overview) • Biomaterials (metals, ceramics, solid polymers, hydrogels, composites, different scale) – chemical and physical properties, structure, • Methods of bulk characterization • Interactions between biomaterials and body (changes in biomaterials, controlled release, active interfaces) • Methods of surface characterization and modification • Applications (drug delivery, implants, scaffolds) Cells • self-organization • regeneration • adaptation Scales Structural Hierarchies 8 Order of magnitude Length scales of structure 1. Primary Chemical Structure (Atomic & Molecular: 0.1–1 nm) Length scale of bonding – strongly dictates biomaterial performance Primary Ionic: e-donor, e-acceptor ceramics, glasses (inorganic) Covalent: e-sharing glasses, polymers Metallic: e-“gas” around lattice of + nuclei Secondary/Intermolecular Electrostatic H-bonding Van der Waals (dipole-dipole, dipole-induced dipole, London dispersion) Hydrophobic Interactions (entropy-driven clustering of nonpolar gps in H2O) Physical Entanglement (high MW polymers) Covalent bonds Covalent bonds : non - polar and polar ( - > dipoles ) ■ covalent bonds , formed by electron pairs , fixed orientation , Relatively high dissociation energy ( 210-840 kJ / mol ) ■ polar bonds , different electronegativity of the atoms , binding electrons unequally distributed , one end of a polar bond has a partial positive charge and the other end is a partial negative charge Non covalent bonds ■ Four main types of non-covalent interactions in biological systems : ionic bonds , Hydrogen bonds , van -der- Waals interactions , hydrophobic interactions. ■ non- covalent interactions between the atoms are much weaker than covalent bonds with bond energy in the range of about 4 - 20 kJ / mol Ionic bonds Kation+ … Anion- Kations : Anions : H+, Na+, K+, Mg2+, Ca2+ Cl-, OH- ionic bonds = electrostatic attractions between the positive and negative charges of the ions. In aqueous solutions, all cations and anions are surrounded by a shell of water molecules bound . Increasing the salt (eg NaCl ) concentration weakens the ionic bonds . Binding energy about 787 kJ / mol ( NaCl ) Metallic bonds Common conduction electrons Metal atoms are good donors of electrons and metallic bonds are characterized by tightly packed positive ions or cores surrounded by electrons Hydrogen bonds • Hydrogen bonds are longer and weaker than covalent bonds between the same atoms . • The hydrogen bond between water molecules ( about 20-40 kJ / mol ) is much weaker than a covalent bond OH ( approximately 460 kJ / mol ) . • The solubility of the neutral substances in an aqueous environment depends on their ability to form hydrogen bonds with water . Van der Waals interactions Nonspecific interactions lead to instantaneous random variations in the distribution of the electrons of an atom = unequal distribution of electrons . Van der Waals interactions are based on interactions of temporary or permanent electrical dipoles . 0.5-5 kJ / mol Hydrophobic interactions „Like dissolves like “ hydrophobic substances • In an aqueous environment , the association of polar or non - polar molecules is brought about by the hydrophobic effect state. • The contact of hydrophobic molecules with water molecules to be reduced . Binding energy 1x100 kJ 1x101 kJ 1x102 kJ 1x103 kJ Examples used for hard tissue replacement e.g., dental implants Ex. 1: alumina Al2O3 – (corundum) Properties: • corrosion resistant • high strength derived from • wear resistant ionic bonding • “biocompatible” derived from ionic bonding Examples Ex. 2: polyethylene oxide (PEO) (CH2CH2O)n Properties: • flexible • hydrolysable • water soluble • bioinert used for protein resistant coatings, hydrogels Derived from primary & secondary bonding 2. Higher Order Structure (1 – 100 nm) Crystals: 3D periodic arrays of atoms or molecules metals, ceramics, polymers (semicrystalline) crystallinity decreases solubility and bioerosion (biogradable polymers & bioresorbable ceramics) Networks exhibit short range order & characteristic lengths Ex. 1: Bioactive Glasses used for hard connective tissue replacement Network formers (~50wt%): SiO2, P2O5 Network modifiers (high! ~50wt%): Na2O, CaO Properties: • partially soluble in vivo (facilitates bone bonding) • easily processed (complex shapes) inorganic glasses, gels Networks Ex. 2: Hydrogels used for contact lenses, drug delivery matrices, synthetic tissues x-linked, swollen polymer network Properties: • shape-retaining • flexible • slow release of entrapped molecules derived from crosslinked network Self-Assemblies aggregates of amphiphilic molecules micelles, lyotropic liquid crystals, block copolymers Ex.: Cationic Liposomes used for gene therapy Properties: • water dispersible • can contain/release DNA • can penetrate cell membrane (-) derived from supramolecular assembly Molecular complementarity Geometry , shape + non-covalent bonds 3. Microstructure (1μm + ) Crystal “grains”: crystallites of varying orientation Ex: Stainless steels Fe-Ni-Cr Spherulites: radially oriented crystallites interspersed w/ amorphous phase semicrystalline polymers, glass-ceramics used for fracture fixation plates,etc., & angioplasty stents Porosity often desirable in biomaterials applications Ex. 1: Porous Bioresorbable Scaffolds polylactide (PLA) Properties: • Penetrable to body fluids, cells • Structurally stable Pore dimensions: 10100 μm derived from pore microstructure used for tissue regeneration