Published on MATSE 81: Materials In Today's World (https://www.e-education.psu.edu/matse81)

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Lesson 11: Biomaterials and Smart Materials

Overview

The environment can have a large deteriorative effect on materials over time, including corrosion and degradation. For biomaterials, the materials have the additional condition for the use of having to be able to survive the unique environment of biological systems. In this lesson, we explore issues around biomaterials including structural requirements, functional requirements, biocompatibility, and ethical concerns. 

Learning Objectives

By the end of this lesson, you should be able to:

  • Distinguish between biological, biomaterials, bio-based materials, and biomimetic materials.
  • Explain the differences between structural and functional biomaterials.
  • List and discuss several examples of structural biomaterials applications.
  • List and discuss several examples of functional biomaterials applications.
  • Identify moral and societal issues involved in the usage of biomaterials.
  • Explain the connection between smart materials and biological systems.

Lesson Roadmap

Lesson 11 will take us one week to complete. Please refer to Canvas for specific due dates.

Lesson Roadmap
To Read Read the Biomaterials pages in Canvas under Lesson 11, plus the few pages included here.
To Watch Making Stuff: Smarter
To Do Lesson 11 Quiz

Questions?

If you have general questions about the course content or structure, please post them to the General Questions and Discussion forum in Canvas. If your question is of a more personal nature, feel free to send a message to all faculty and TAs through Canvas email. We will check daily to respond.

Introduction to Biomaterials

Before beginning a discussion of biomaterials there are several different terms that we should define. One way of classifying biomaterials is to use the following four materials classifications: biological materials, biomaterials, bio-based materials, and biomimetic materials.

Biological materials are materials that are produced by living organisms, such as, blood, bone, proteins, muscle, and other organic material. Biomaterials, on the other hand, are materials which are created specifically to be used for biological applications. These applications can include bone replacement, skin replacement, membranes for dialysis, artificial limbs, etc. Bio-based materials are materials that are derived from living organisms but are repurposed for other applications. One example of a bio-based material would be enzymes mass-produced by microbes to be used in the synthesis of drugs. Biomimetic materials are materials that are physically or chemically similar to materials produced by living organisms.

In the textbook reading for this lesson, materials will be classified as structural or functional and then the natural biological material will be compared and contrasted with the biomaterials designed to replace or interact with it.

Structural biomaterials, as the name implies, have as their primary function physical support and structure. Structural biomaterials are sometimes referred to as inert biomaterials. Functional biomaterials (also known as active biomaterials) have a non-structural application as their primary function. An example of a functional biomaterial would be membranes used during dialysis to filter impurities from blood. 

An example of a structural biomaterial would be a titanium steel implant with a ball and socket being used as a hip replacement. Two other terms that might be helpful to define before the reading are immune response and biocompatibility. During the body’s immune response, the body sends white blood cells to attack and destroy foreign material. Biocompatible materials are those biomaterials which typically do not elicit the body’s immune response during the operational lifetime of the biomaterial in the body.

Stainless steel hip replacement, ball is white, the rest is silver and pointed
Stainless steel and ultra high molecular weight polyethylene hip replacement.
Credit: Science Museum London / Science and Society Picture Library via Wikimedia Commons [1]

Now that we have covered a few basic terms please continue to the next section and begin the reading for this lesson.

Reading Assignment

Things to consider...

When you read this chapter, use the following questions to guide your reading. Remember to keep the learning objectives listed on the previous page in mind as you learn from this text.

  • What is the difference between biological, biomaterials, bio-based materials, and biomimetic materials?
  • What are structural biomaterials and where are they currently being used in the body?
  • What are functional biomaterials and where are they currently being used in the body?
  • Many biomaterials are available on a limited basis, who decides who gets them and why?

Reading Assignment

Read the Biomaterials pages in Canvas under Lesson 11, plus the few pages included here.

Ethics of Biomaterials

Ethical issues raised by the use of biological materials are numerous and so complex that an entire field of study known as bioethics has been created. 

Will the biomaterial be safe or potentially be harmful to the body in the near term and long term? Will data obtained during testing on animals justify the suffering and sacrifice of living creatures? Will professional and financial interests by researchers result in conflicts of interest which could taint trial data? Should supply and demand, and profit, allow biomaterials companies to charge "what the market will bear"? When evaluating a new biomaterial product what should be the balance between sustaining life versus quality of life issues? What should be the role of regulatory agencies? Should access to biomaterials be determined by medical need or ability to pay? How does society ensure that humans living in the Third World have access to current advances in biomaterial applications? How does society balance scientific advancements in the area of biomaterials with religious doctrines, which are sometimes at odds with those advancements?

Clearly, we could spend another course just on the topic of ethics in biomaterials. Hopefully, the reading in the lesson and on the website has made you aware, if you were not already, of this important subject. In the next section of our website, we will be looking at a biomaterial which is also a smart material.

Nitinol

In the lesson reading this week vascular stents were covered, including the revolutionary nitinol stents. When the body heats up this smart material ‘remembers’ its initial programmed shape. So, in addition to being a biomaterial, nitinol is a smart material as well. What are smart materials? Smart materials are materials that are designed to mimic biological behavior. They are materials that, like biological systems, ‘respond to stimuli.' More smart materials will be presented in the video for this lesson, but right now please watch this short video (1:27) on the amazing nitinol.

To Watch

WTF Paperclip!? (Nitinol)
Click for transcript

This is no ordinary paper clip. In fact, it's made from nitinol and it has some unique qualities. Let's bend it into a completely different shape. Okay, I think that should do. Now watch what happens when I drop this into some hot water. Now that is pretty darn cool. Nitinol is also known as memory metal and once it reaches a certain heat the atoms become locked into the previous arrangement that they were forged in. This is also the same material that magicians use to bend spoons. Sorry to ruin the magic. So there we have it. Nitinol. Don't forget to check out my Facebook and Twitter the links are below and as always I will see you next time. Thanks for watching.

Credit:Andy Elliott

Now proceed to the next section to watch the video for this lesson. As you watch this lesson, see if you can answer the following for each of the smart materials presented: what is the stimulus and what is the response?

Video Assignment

Now that you have read the text and thought about the questions I posed, take some time to watch this 54-minute video about one type of advanced materials (smart materials) that sense their environment and, in some cases, can even adapt to their environment. As you watch this video see if you can find the following:

  1. Smart materials are defined by their ability to sense and respond and not by the materials properties (chemistry and atomic structure) that we use for classical materials classification. Another way of stating this is, smart materials are defined by their function, not by their materials properties. As you watch this video attempt to separate the function from the materials properties by classifying the materials (metal, ceramic, polymer, composite, semiconductor, biomaterial, nanomaterial) that are utilized in the smart material examples of this video.
  2. Some materials applications are heavily dependent not only on the materials that compose their parts but also the physical structure of their parts. Hook and loop fasteners, e.g., Velcro™ tape, is an example of this. Hook and loop fasteners are composed of two parts that are typically constructed of the same synthetic polymer. However, it is the physical structure of the two parts that make hook and loop fasteners so widely used today. One side is composed of hooks, while the other is composed of loops, which combined with the material properties of polymers make hook and loop fasteners the go-to fastener where temporary bonds are required. Some of the smart materials highlighted in this video depend on the physical structure to properly function. See if you can spot which smart materials these are.

Video Assignment

Go to Lesson 11 in Canvas and watch NOVA's Making Stuff: Smarter Video. You will be quizzed on the content of this video.

Summary and Final Tasks

Summary

Biomaterials and smart materials are two of the four advanced materials that we discussed in Lesson 1 of this course. Unlike the classical classifications of materials (metals, ceramics, polymers, and composites), advanced materials are defined by their function, i.e., what role that they serve. Biomaterials can be metals, ceramics, polymers, composites, or combinations of these, that are used inside the body. They can serve structural and/or functional purposes within the body. Of course, an important consideration is how bio-compatible the material is, which determines whether the material can be used, where in the body, and the useful lifetime of the material. Smart materials can be metals, ceramics, polymers, composites, or combinations of these, that mimic life. These materials 'respond to stimuli'.

Reminder - Complete all of the Lesson 11 tasks!

You have reached the end of Lesson 11! Double-check the to-do list on the Overview page to make sure you have completed all of the activities listed there before you begin Lesson 12.


Source URL:https://www.e-education.psu.edu/matse81/node/2181

Links
[1] https://commons.wikimedia.org/wiki/File:Stainless_steel_and_ultra_high_molecular_weight_polythene_hip_replacement_(9672239334).jpg