mid term exam sample biomaterials

8/18/2019 Mid Term Exam Sample biomaterials

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Mid-term Exam

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1. Discuss the evolutionary trends in biomaterials science. (Score: 10)

The trend of biomaterial development has gone from using implantable devices,as the as the Chinese and Aztecs did with gold teeth more than 2000 years ago;

to creation of regenerative medicine, such as the use of plastics and stainless in

hip replacement, or engineered composite scaffolds to replace cartilage and

heart valves; to the development of nanotechnology for diagnostics and drugdelivery.

The evolution of biomaterials science can be broken into 3 generations, going

from structural implants, to soft tissue replacements, to functional, engineeredmaterials.

To begin with, the 1st-generation can be characterized as one of ad-hoc implants.Physicians used commonly available materials to accomplish their goals, andsuccess was often accidental. The use of gold fillings for dentistry, steel for bone

plates, glass for eyes, and Dacron vascular grafts all exemplify this ad-hoc use of

common materials for implants. These materials did not interact with tissue andwere inactive.The 2nd generation of biomaterials science can be characterized as one of

collaborative, engineered implants. While common and borrowed materialswere still being used, biomaterials scientists were using advances from otherfields to develop their own field and physicians collaborated with engineers to

engineer materials. The implants were now being deliberately designed basedon new knowledge from 1st-generation experience, other fields, andcollaborative work. Some examples from this generation are the titanium dental

and bone implants, UHMWPE in hip joints, and mechanically engineered heart

valves.

The 3rd generation of biomaterials, which is now in development, is one offunctional, bioengineered implants. Bioengineering implants are now made with

Course: Biomaterials

bioengineered materials. New tissue implants can regrow tissue instead of

replacing it, bone cements can be resorbed, and artificial skin is being developed.

2. What is the definition of “Biomaterials”? What are the essential biomaterials characteristics for blood vessel stents? (Score: 15)

A biomaterial is a material, synthetic or natural, that is incorporated with

biological systems, in order to diagnose, treat, restore, or replace tissue, organs, or bodily functions. A blood vessel stent is used to restore or improve blood flow through arteries.

Course: Biomaterials

Instructor: Yunqing Kang

Date: 3/04/2016


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One essential characteristic of the stent is that it must not degrade over time,

because it is a long-term implantation. Another important characteristic is that the stent must be treated so that blood does not clot on its surface, as this would impede blood flow. The stent should also be flexible and elastic to be able to

expand to f it the artery. It should feature strong corrosion resistance as it will be

in contact with blood flow. Finally, the stent should be strong enough to

withstand the implantation process, compression from the arterial wall, and variable pressure from blood pr essure.

3. Discuss the differences between ionic and covalent structure, and also

discuss the differences between crystalline and amorphous states. (Score:

15)

An ionic bond is generally made up of a metal and non-metal and involves the

transfer of electrons from the metal to the non-metal. When the valence

electrons are transfered, the atoms become charged and are attracted by electrostatic force. Ionic bonds have a defined structure and direction, and the

ions form crystals. Ionic bonds are very strong, so compounds have high boiling

and melting points. In a solid state, compounds cannot conduct electricity, because the electrons are locked into their bonds; however, in their liquid or

dissolved forms, the compounds are good conductors.

Unlike ionic bonds, covalent bonding involes non-metals only, not a metal and non-metal. Valence electron pairs are shared between these atoms, not

transfered, and while ionic bonding has an electronegativity greater than 2, covalent bonding is less than 2. Covalent compounds do not form crystals but

instead stay as separate molecules. The bonds are weak, and so compounds have low boiling and melting points. Covalent compounds are not good

conductors of electricity in any state and are not as soluble in water as ionic compounds. Covalent compounds also mostly exist in liquid or gas states. Crystalline solids have a long-range order and melt and boil at specific points.

Their properties are generally anisotropic. Crystalline solids are also generally very rigid. Amorphous solids have short-range order and their melting and

boiling points are not as well-defined. Their properties are isotropic, due to the random arrangement of the molecules.

4. Discuss the overall host response to biodegradable biomaterials with

different scale size? (Score: 20)

Biomaterials can exist on a macroscale, microscale, or nanonscale level. At each

scale size, the host has different responses.

At a macroscale level, the process of mechanotransduction will create a response

from the cell to force transmission, through protein conformation and cytoskeleton change. This can result in host responses like osteoporosis, fibrosis, and hemolysis. The elasticity of the material will also send mechanical

signals to stem cells, which affect how they develop. The host response at a macroscale level is also dictated by chemical reactions

with the biomaterial. Integrin receptors on the cell membrance control cell

binding and cell response after adhesion. When a cell binds to a biomaterial, the release of impurities, free radicals, or additives from the material can begin cell signaling that can lead to necrosis, hyperplasia, or phenotype change.


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Microscale biomaterials lead to different responses in the host body. The

microparticle can be consumed by a macrophage through phagocytosis, and the particle will degrade inside the cell. This leads to no effect on the tissue. Needle-shaped particles can interfere with phagocytocis and lead to fibrosis. If a giant

cell tries to remove the microparticle, it can lead to inflammation and fibrosis.

Particles within joints can lead to bone resorption.

At a nanoscale level, cells will uptake nanoparticles. The particles can affect the mitochondria or nucleus, leading to cell death, or the particles are transferred between

endosomes until they are degraded.

5. Discuss the reasons why synthetic materials are intrinsically incompatible

with mammalian physiological systems. (Score: 20)

Synthetic materials are intrinsically incompatible with mammalian physiological

systems because those systems have highly sensitive mechanisms to identify

foreign objects, such as synthetic materials. Once these foreign objects have been detected, the physiological systems deploy defense systems which have

also evolved to destroy foreign objects. Because of the body's ability to detect

and defend against any foreign object, an attempt to put a synthetic material in contact with physiological systems results in resistance and incompatibility.

6. What factors control the surface reactivity of biomaterials? (Score: 20)

The surface reactivity of biomaterials is controlled by the surface energy, chemistry, and topography. The surface energy of a material is higher than the

energy of atoms in the bulk; this higher free energy encourages adsorption from the environment to bring about an energy balance. The chemistry of the surface

is controlled by many factors, including the material's readiness to be oxidized and to adsorb contaminants; the orientation, flexibility, and mobility of polymer side groups; the density of the charge at the surface; and the diffusion from of

additives and other conatimants from the bulk of the material to the surface. The topography, such as smoothness and roughness, of the surface can also affect

surface reactivity

mid term exam sample biomaterials

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