������������ ������������������������������� �������������������

Classes of Materials used in Medicine

03-01-2011

Classes of Materials used in Medicine

Material Science

Performance/Application

Synthesis+processing

Structure

Properties•Physical•Biological

������������ �����������

A biomaterial must be:� inert or specifically interactive � biocompatible

mechanically and chemically stable or � mechanically and chemically stable or biodegradable

� processable (for manufacturability) � nonthrombogenic (if blood-contacting) � sterilizable

���� �������� �����������

� Metals

� Ceramics

� Polymers (synthetic or natural)

� Composites

����

� closely packed crystal structure; � load bearing implants as well as internal fixation devices

used for orthopedic applications as well as dental implants;� when processed suitably they contribute high tensile,

fatigue and yield strengths; � low reactivity and good ductility to the stems of hip implant

devices; and, � Their properties depend on the processing method and

purity of the metal, however, and the selection of the material must be made appropriate to its intended use.

���� �����

Medical Tubing

Catheters Stents

������ �����������

� The problem with the use of metals in orthopedic applications is the phenomenon of stress shielding;

� In hip implantation, the high strength of the metal in the implant induces it to assume more than its share of responsibility for the load in that region;

� This decreases the load born by the surrounding tissue and therefore shields it from experiencing stress;

� Lack of stress causes bone density to decrease as bone tissue resorbs, eventually causing complications in the implant/tissue interface.

���������� ����������

� Excellent mechanical properties and fair biocompatibility i.e. they do not cause serious toxic reactions in the human body.

� Metals exhibit excellent strength and resistance to fracture.

���������������������

� BCC, ductile & plastic ie more workable

� FCC, ductile & plastic ie workable

� HCP, lack plasticity

�������������� ������������

FCC metals are usually more ductile, i. e. can sustain large plastic deformation without fracture. Thus, FCC metals are used to make dental implants of complex shapes

Polymorphism – Iron, Titanium and Cobalt

Increasing nickel content in SS results in FCC type, instead of BCC type SS

��������

��� �������������

������������������������

� Properties of a metallic material, such as its strength, fracture resistance and corrosion resistance, change with its alloying conditions and its history of heat treatment and deformation during metal formingand deformation during metal forming

� mechanically deforming a titanium alloy at ambient temperature can significantly increase its yield strength and tensile strength

��������� �������

• Manufacturing Techniques ???

���� ���������������

������������������������������

���� ��������������� �����!�����"���#��$����

������%

Rolling

Forging

Casting

Extrusion Drawing

���������� �������������������������������

&������������

'��#�(�������� � �������)����

������

��#��������������� Production of metal powder� Blending and mixing of powder� Compaction � Sintering

Typical heat treatment cycle in sintering process

SinteringBlending Compaction

Production of metal powder

*������������ �����

� Strengthening by Alloying� Strengthening by Work Hardening� Strengthening by Addition of elements

Strengthening by Thermal treatments� Strengthening by Thermal treatments� Full Annealing� Normalization� Quenching� Tempering

������� *�����*������

(a) substitutional and (b) interstitial

� More abundant element is referred to as the solvent and the less abundant element is the solute.

Filling materials: Silver alloys consisting of Ag-Sn-Cu, mixed with Hg

*�������������

� Alloys formed through substitution must have similar crystal structures and atomic size.

+�������������,��������������

Gold-Silver alloy (Type III for crowns & bridges: e.g. 75%Au-11%Ag-9%Cu3.5%Pd)

� 2.882 Å - Gold (Au) FCC : FCC (Ag) Silver - 2.888 ÅSilver-Copper alloy (One of the two types of particles in

'admixed' dental amalgam alloys)'admixed' dental amalgam alloys)� 2.888 Å - Silver (Ag) FCC : FCC (Cu) Copper - 2.556 ÅSilver-Tin alloy (Particles in 'low copper' dental amalgam

alloys)� 2.888 Å - Silver (Ag) FCC : FCC (Sn) Tin - 3.016 Å

&�������������������

� Size of atom becomes the major factor.� Solute atoms must be small in size to fit into the spaces

between the larger solvent atoms.� Important interstitial solute atoms are carbon, hydrogen,

boron, nitrogen, and oxygen.boron, nitrogen, and oxygen.

Example of interstitial solid solution is steel or carbon dissolved in iron