Biomaterials 1 – Biomedical engineering
Lecture 2 – Condensation polymers for biomaterials
Summary of reading assignments:
Section I: 2.2A, 2.6
Section II: 4.1-4.3, 5.16D
Introduction: the diversity and versatility of biomaterials
When biomaterial devices and systems are exposed to the biologic environment, it is their
surfaces that first encounter biological species such as proteins, which usually deposit a
monolayer of protein. Subsequently, cells interact with the adsorbed protein monolayers on the
surfaces of the biomaterials. Therefore, it is the fundamental compositions and “nanotextures” of
those biomaterials surfaces that are expected to strongly influence the overall responses of the
biological environment to the materials.
From WW2 to early 1960s, a few pioneering surgeons were taking commercially available
polymers and metals, fabricating implants and components of medical devices from them, and
applying them clinically. Whilst the first devices and implants were successful there were also
some dramatic failures often due to poor choice or improper fabrication of biomaterial
components. This led to the collaboration of surgeons, physical, biological and material
scientists and engineers giving rise to the earliest bioengineering.
Polymers: basic principles
Polymer materials possess an array of unique properties which make them useful in a wide
variety of biomaterial applications such as orthopedics, dental, hard and soft tissue
replacements, and cardiovascular devices. The central idea is structure-property relationships,
which means molecular characteristics such as molecular architecture, molecular weight, and
chemical composition are directly related to the physical and chemical properties of the
macroscopic material. Polymer scientists have been able to exploit structure-property
relationships to create non-stick coatings, pressure sensitive adhesives, and the penetration-
resistant materials used in bullet-proof vests.
Molecular structure of single polymer molecules
The simplest shaped polymer is the linear chain where there is a single molecular backbone.
When linear chains of two different composition polymers (e.g. A and B) are linked together, the
resultant polymer is called an A-B block polymer. If another chain is added to the second chain,
it may be called an A-B-C triblock copolymer, or more simply an A-B-C block copolymer.
Branched structures are also possible where a central polymer backbone has smaller side
chains extending from it. Branches can occur due to undersized side reactions during synthesis,
or can be purposefully incorporated into the molecular structure. If this is repeated many times
you would eventually link all of the polymer chains together into one very large network polymer.
