Biological systems and processes
have had, and continue to have, important
implications and applications in
materials extraction, processing, and
performance. This paper illustrates
some interdisciplinary, biological issues
in materials science and engineering.
These include metal extraction involving
bacterial catalysis, galvanic couples,
bacterial-assisted corrosion and degradation
of materials, biosorption and
bioremediation of toxic and other heavy
metals, metal and material implants
and prostheses and related dental
and medical biomaterials developments
and applications, nanomaterials
health benefits and toxicity issues, and
biomimetics and biologically inspired
materials developments. These and
other examples provide compelling
evidence and arguments for emphasizing
biological sciences in materials
science and engineering curricula and
the implementation of a bio-materials
paradigm to facilitate the emergence of
innovative interdisciplinarity involving
the biological sciences and materials
sciences and engineering.
In 1969, the National Colloquy on the Field of Materials was held on the campus of Pennsylvania State University to assess and examine the emergence of materials science and engineering as a “new synthesis of disciplines.”1 After only a decade of development, materials science and engineering, while still in some degree of disciplinary uncertainty, was emerging as a model for interdisciplinarity and multidisciplinarity which prominently linked to various engineering
disciplines, chemistry, physics, and mathematics. Its continued evolution along the lines of emergence of biophysics, combining biology and physics, or geochemistry, combining geology and chemistry, was questioned, but neither biomaterials nor bio-materials (the spectrum of biological sciences and materials sciences interdisciplinarity) was a prominent issue.
By the end of the 1980s, a further assessment of the progress of materials science and engineering was made in the context of an effort “to conduct a comprehensive materials research and technology assessment for the next decade.” The result was a publication titled Materials Science and Engineering for the 1990’s: Maintaining Competitiveness in the Age of Materials.2 Here, inherently interdisciplinary areas included biomaterials prominently, but the true interdisciplinary issues of bio-materials education and research were not prominent, despite the fact that the synergistic elements which now defined materials science and engineering—structure, properties, synthesis/processing, and performance of materials—could find clear examples of bio-materials: prostheses, artificial organs, biosensors, drug delivery, wound management, and a plethora of medical equipment and devices. In addition, bioleaching and related biomaterials processing and processes were emerging along with biomimetics applied to materials-related innovations.
"By the end of the 1990s, nanotechnology and nanomaterials became the emerging science and engineering initiatives worldwide, and more recent evolution of these concepts has touted convergent new technologies: the synergistic combination of nanotechnology, biotechnology, information technology, and cognitive sciences"
By the end of the 1990s, nanotechnology and nanomaterials became the emerging science and engineering initiatives worldwide, and more recent evolution of these concepts has touted convergent new technologies: the synergistic combination of nanotechnology, biotechnology, information technology, and cognitive sciences.3 These convergences elicit additional and imperative interdisciplinarity involving public health and the environmental sciences and engineering, especially as these relate to the manufacture and proliferation of nanomaterials, and in particular nanoparticulate materials. Here the biological and especially bio-materials implications bode prominently.
This paper will review a few research examples—or case histories—of biological issues and interdisciplinary applications in materials sciences and engineering. These examples span more than three decades, including novel biomimetic materials developments and the development of systematic if not systemic assays to evaluate the cytotoxic potential for emerging nanoparticulate materials applications.
In addition to demonstrating the applications of fundamental biological phenomena in materials extraction, processing, and performance (as related, for example, to degradation [biodegradation] or corrosion), this article will illustrate the characterization of biological and biomaterials microstructures as these relate to properties, processes, and performance. These examples and applications involving biological materials sciences will provide the basis for a bio-materials paradigm and the emphasis of the biological sciences in materials science and engineering curricula.
IN MATERIALS PROCESSING
Copper Leaching: in Dumps, In-Situ, in Vats
The presence of copper was observed in mine waters around 1000 BC4 while the leaching of copper and its recovery from solution was not accomplished until around 1670 AD.5 The first evidence of microorganisms having some role in the leaching of copper in particular was documented around 1922,6 but systematic bioleaching did not become popular until the 1960s and 1970s, nearly a decade after the discovery and characterization of the chemolithotrophic, iron-oxidizing bacterium, Thiobacillus ferrooxidans, or T. ferrooxidans.7,8 T. ferrooxidans is a motile, single-pole flagellated, non-spore-forming, aerobic, chemi-autotrophic, rod-shaped, gram-negative bacterium. Figure 1a, c, e, and f illustrates a variety of electron microscope views of this microorganism which utilizes CO2 as a carbon source, and which requires sources of N2 as well as phosphates for chemosynthesis and growth through energy derived from the catalytic oxidation of ferrous iron (Fe2+), insoluble metal sulfides (iron, copper, zinc, etc.), or elemental sulfur.
Figure 1b and d also shows for comparison a higher temperature (thermophilic) Sulfolobus-like microorganism capable of catalytic activity at temperatures as high as 80°C and at pH values from 1 to 6 in contrast to the T. ferrooxidans, which becomes nonviable above about 40°C.9 Sulfolobus acidocaldarius and other thermophilic microorganisms have been isolated from acidic hot springs10,11 and other extreme environments. Microorganisms found in a variety of extreme environments (for example, temperatures well below freezing to near the boiling point) have become known as “extremophiles.”
The role of bacteria, especially the synergistic or symbiotic catalysis of those illustrated in Figure 1 for heap, dump, or in-situ leaching of copper, is shown in Equations 1, 2, and 3, respectively, for pyritic porphyry copper waste or deposits. (All equations are presented in the Equations table.)
FeS2 + 3.5O2 + H20 bacteria FeSO4 + H2SO4
2CuFeS2 + 8.5O2 + H2SO4 bacteria 2CuSO4 + Fe2(SO4)3 + H2O
FeS2 + Fe2(SO4)3 → 3FeSO4 + 2S
2S + 3O2 + 2H2O bacteria 2H2SO4
2FeSO4 + 0.5O2 + H2SO4 → Fe2(SO4)3 + H2O
2FeSO4 + 0.5O2 + H2SO4 bacteria Fe2 (SO4)3 + H2O
4 Fe2+ + O2 + 4H+ bacteria 4 Fe3+ + 2 H2O
O2 + 4e– + 4 H+ → 2H2O
CuFeS2 → Cu2+ + Fe2+ + 2S° + 4e–
CuFeS2 + O2 + 4H+ → Cu2+ + Fe2+ + 2S° + 2H2O
M → Mn+ + ne–
MS → Mn+ + S° + ne–
In the presence of bacteria, the elemental
sulfur formed in Equation 3 can be efficiently converted to sulfuric acid as shown in Equation 4. The efficiency of bacterial catalysis in these reactions has been demonstrated generally in the work of Lacey and Lawson,12 who showed that the rate of the reaction (see Equation 5) is nearly one million times faster for Equation 6. The ferrous-to-ferric oxidation in Equation 6 can be expressed generally as Equation 7, and is illustrated in Figure 2 in the context of the structure-function role of the cell envelope in oxidation catalysis. That is, regardless of the microorganism or its range of viability (Figure 1), its structure-function regime remains constant.
The catalytic role of bacteria, including temperature symbiosis for T. ferrooxidans to Sulfolobus-like bacteria, as well as electrochemical cell effects involving the galvanic interaction in the leaching of metal sulfide systems, is illustrated on comparing the data in Figure 3. The metal sulfide particle mixtures (in Figure 3a) involved different size fractions of FeS2 and CuFeS2, producing variations in shake-flask pulp densities (solids/volume). The effects of bacterial catalysis, galvanic conversion, and the combined effects of galvanic conversion and bacterial leaching with both T. ferrooxidans (at 30°C) and the thermophilic Sulfolobus-like microorganism (at 55°C) are illustrated in Figure 3.
Figure 4 illustrates schematically the conversion of chalcopyrite and the passivation of contacting pyrite where the anodic member (CuFeS2) having the lower rest potential (~0.52V) can react vigorously relative to the cathodic FeS2 (where the rest potential is ~0.63V). Similar results have been observed for large, bulk contacting systems as well, and for a variety of galvanic couples including FeS2, CuFeS2, and ZnS.9,13–15 The galvanic interaction between FeS2 and CuFeS2 (Figures 3 and 4) in acid medium can be described as follows.
The interaction on the cathodic pyrite surfaces is shown in Equation 8, and on the anodic chalcopyrite surfaces in Equation 9. The overall, uncatalyzed reaction is observed to be that shown in Equation 10. The elemental sulfur formed in Equation 10 can be aggressively converted to sulfuric acid by bacterial catalysis as shown previously in Equation 4.
and Materials Biodegradation
Electrochemical attack involving electron flow through characteristic anodic and cathodic cells on a metal surface is regarded as the most general mechanism driving corrosion (i.e., an oxidation-reduction half-cell reaction). Equations 8 and 9 are specific examples. For general metals corrosion, metals (M) more reactive to hydrogen (referenced against the standard hydrogen electrode in the electromotive series) are assigned negative potentials and are considered to be anodic to hydrogen, as shown in Equation 11.
For positive potentials, the reaction in Equation 11 is reversed. For a metal sulfide, the anodic reaction is similar, as shown in Equation 12, where n = 2.
Figure 5 illustrates the resulting corrosion
for an exposed (100) single-crystal pyrite surface in non-agitated sulfuric acid-ferric sulfate solution.16 In Figure 5a and b, corresponding to three-weeks and six-weeks exposure, the surface attack or corrosion is considerably less than that for the same lixiviant with the Sulfolobus-like microorganism added. Despite the fact that there is a reaction rate difference for the temperature difference (30°C versus 55°C), there is a clear indication of microbial influence, and of course the overall leaching comparisons in Figure 3 support this conclusion.15
use of microbial cells as biosorbents for heavy metals in particular has been demonstrated to be an effective method for metal decontamination or recovery from a variety of industrial waste streams"
Anaerobic sulfate-reducing bacteria are also important in steel corrosion, especially associated with underground storage tanks and exposed pipes. Other metals are also similarly affected.17,18 Many steel structures as well as other engineering structures are degraded by bacteria and other microorganisms.19 Bacteria can form minerals by passive growth and as a result of metabolic activity. In addition, mineral degradation as a result of various mechanisms of biodegradation can occur. For example, heterotrophic fungi such as Penicillium (P.) simplicissimum are able to dissolve metals from various rocks by growing on sugar-containing substrates,20 which allows them to release citric acid, among other organic acids. The acids react with the mineral matter, dissolving metals through a chelating action. Aluminum dissolution in complex alumino silicates has been studied21 using P. Simplicissimum isolated from weathering basalt rocks.22 A recent publication by Benzerara et al.23 has described nanoscale environments associated with bioweathering of rocks.
Biosorption and Bioremediation
The ability to observe biological
microstructures such as bacteria and
other cell structures as illustrated in
Figure 1c, d, and e for selective staining by heavy metals prompted a number of
innovations nearly three decades ago
to explore the prospects of the removal
of metals from aqueous solutions, particularly
waste streams containing low
concentrations of toxic metals.24–28 The
use of microbial cells (bacteria, microalgae,
yeasts, fungi, etc.) as biosorbents for heavy metals in particular has been demonstrated to be an effective method for metal decontamination or recovery from a variety of industrial waste streams.27,28
Figure 6a illustrates the
accumulation of nanofibrils of uranium
in a 0.2 μm surface cell envelope region of Saccharomyces (S.) cerevisiae.27 The
uranium biosorbed on the cell envelope region in Figure 6a could be removed chemically, and the cells reused as a biosorbent.27 Other microbial cells take
uranium into the cell body.27 In the case
of uranium accumulation, Horikoshiet al.28 demonstrated that the abilities of
microorgansims to accumulate uranium were as follows: actinomycetes > bacteria > yeasts > fungi.
Figure 6b illustrates a more contemporary
example of metal biosorption in
living plants.30 The left portion of Figure
6b shows a low-magnification transmission-electron microscope (TEM) image of an alfalfa shoot embedded in a resin
and microformed to a ~50 nm slice.
The arrows indicate gold nanoparticles formed by the transport of gold atoms from the roots to the shoots. The high resolution
TEM image to the right in Figure 6b illustrates these nanoparticles
to be polyhedral crystals characteristic of metal quantum dots. Figure 6b also represents an example of using plants to extract gold or other heavy metals (such as uranium) from contaminated soil areas, a phenomenon referred to as phytoremediation.31
Silver uptake in alfalfa plants similar
to gold in Figure 6b has also been demonstrated
and these kinds of plant uptake
features have been touted as a possible
innovative process for synthesizing
quantum dots.29 Oat biomass (or dead
plant tissue) has also been demonstrated
to possess the capacity to recover Au3+
ions from aqueous solutions forming
gold nanoparticles as in Figure 6b.29 In
fact, the size of the gold nanoparticles
could be controlled by changing the
pH.32 A range of agricultural byproducts,
or dead biomass materials, have been
demonstrated to have high affinities
for heavy metal ions. These materials
include waste wool33 and tree barks,34
BIOMATERIALS AND BIOCOMPATIBILITY
Biomaterials are among the earliest
materials developments. For example,
silver-tin amalgams as filling materials
for teeth were first used by Chinese
physicians around 700 AD.35 A dental
amalgam containing bismuth, lead, and
tin was introduced in France around 1826
while the contemporary Ag, Sn, Cu, and
Hg amalgams evolved from the mid-1800s, especially in the United States.36
Although mercury has caused some
concerns, dental amalgams continue to
utilize roughly 40% mercury added to a
particulate mix of ~40% Ag, ~28% Sn,
~30% Cu, and ~2% Zn.3,37 While other
dental restorative materials have been
developed,35 it is generally concluded
that mercury-based amalgams will continue
to be the restorative material of
choice when aesthetic concerns are not
Early development work and applications
of titanium and titanium alloys for
a variety of orthopedic and surgical
reconstructive implants evolved from
military and commercial efforts, especially
in aerospace materials research.
The high corrosion resistance and
strength-to-weight ratio properties of
Ti-6Al-4V in particular, along with high
fatigue strength and nonthrombogenic
behavior have made it a biomaterial of
choice for several decades. However,
recent concerns of titanium ion release
as a biocompatibility issue, especially
for long-term implants, have prompted
searches for better biomaterials.39,40
Biocompatibility studies on titanium and
Ti-6Al-4V have also been concerned
with tissue (and cell) adhesion, and
especially the performance of rough
implant surface structure in contrast to
very smooth implant surface structure.
Figure 7 shows a simple comparison of rough versus smooth surface adhesion,
or attachment, for fibroblast cells attaching
to titanium (Figure 7a and b) and
Ti-6Al-4V alloy (Figure 7c and d) in
culture. There is a noticeable advantage
for the rough surface for both materials
in Figure 7.
Over the past few years (especially
since 2000) the field of biomaterials has
grown rapidly. Advanced materials for
diagnosis, drug release, and scaffolds for
tissue engineering are currently being
developed.42 The design and synthesis
of artificial bone-like materials has been
a recent outcome of this research.43
BIOMEDICAL MICROSYSTEMS AND NANOPARTICULATE APPLICATIONS
In recent years the efficiency of aerosol
drug delivery, especially in nasal
respiratory sprays from metered inhaler
devices, has been enhanced by utilizing
inert microcages, some inspired by zeolites
and other confining structures.44,45
Tailored, cage-like silica structures
consisting of micrometer-size particles
with nanopores have been utilized to
transport and control the release of
drugs. Cyclodextrins, dendrimens, and
other protein structures consisting of
nanoscale matrices that form protective
cages around delicate therapeutic
molecules have also been developed
for drug delivery.46,47 So-called “Trojan
horse” proteins “smuggle” therapeutic
molecules into cells using iron storage
proteins like ferritin (a self-assembled
protein cage-like structure) or other
magnetic, iron-coated nanoparticles
forming a bioferrofluid for magnetic drug
delivery. These have been partly inspired
by single-domain magnetic materials
synthesized by magnetotactic bacteria
which contain intracellularly produced
crystals of magnetite (Fe3O4) or greigite
Magnetic materials synthesis based
upon magnetotactic bacteria and studies
relating to bioinspired materials
development represent a wide range
of biomimetic approaches to materials
chemistry, and materials sciences
and engineering.50–52 Silica structures,
especially cage-like silica structures,
represent tailored or tunable size regimes
which are frequently derived from the
natural, biological world. Figure 8 illustrates
a relatively common radiolarion, an
ellipsoidal or spherical-shelled spumellaria;
a marine plankton with a siliceous
(opaline/polycystine) solid skeleton.
Radiolaria are protozoa originating ~600
million years ago.53 Figure 8b shows, in
contrast to Figure 8a, a C60 cage with
pores or openings roughly 105 smaller
than the radiolarian.
The implication that nanocages such
as the C60 molecule in Figure 8b can
act as a therapeutic drug or other agent
transport system must be tempered by
potential adverse effects. For example,
C60 has been described as a potential
generator of singlet oxygen which is
known to be a highly cytotoxic agent.54
In addition, Oberdörster55 has recently
demonstrated that C60 accumulates as a
toxic agent in fish brains, throwing some
caution to the concept of drug transport
in nanocage materials.
Particulate materials, especially
nanoparticle colloids, can have direct
biomedical effects. Silver and its compounds
are particular examples with
known antibacterial effects in antiquity.
Water stored in silver urns was known
not to support pathogens while colloidal
silver in water and other gels or salves has had numerous health benefits for
hundreds of years.56 Recent applications
of nanoparticulate silver have included
open wound and burn treatment, and
preliminary studies have shown that a 20
ppm silver colloidal suspension (~30 nm
diameter) in purified water has a 100%
cure rate for malaria.57
Titanium dioxide, especially as
nanoparticulate anatase, is also an
interesting antibacterial, with notable
photocatalytic behavior. But ultrafine
anatase has also been identified as
cytotoxic, and in-vivo studies have
shown that it can be severely toxic in the
respiratory system.58,59 Figure 9a and b
shows the appearance of commercially
available TiO2 (anatase) and silver
nanoparticulates, respectively, observed
in the TEM.
Figure 9c and d illustrates
the cytotoxic response for anatase and
silver in comparison to black carbon
(BC), chrysotile asbestos nanofibers, and
a commercial multiwall carbon nanotube
aggregate material (MWCNT-R) for a
murine macrophage cell line (Figure
9c) and a human macrophage cell line
(Figure 9d), respectively. Figure 10a and
b shows for comparison soot collected
in a home with natural gas appliances,
and the commercial BC represented in
Figure 9c and d, respectively. Figure 10c
and d shows for comparison MWCNT
aggregates in a kitchen using natural gas
to cook and MWCNT-R represented in
Figure 9c and d, respectively.
The black carbon in Figure 10b and the
MWCNT material in Figure 10d might
be considered to represent surrogate
materials for the anthropogenic samples
shown in Figure 10a and b. These might
be considered to be cytotoxic in the
context of the results shown in Figure 9c
and d.60 The use of chrysotile asbestos
in Figure 9c and d as a positive control
exhibiting a cytotoxic response may
serve as a special caution for nanoparticulate
materials development and their
nanotechnology applications. Chrysotile
asbestos is probably the oldest and most
versatile nanofibrous material, having
achieved nearly 4,000 different product
applications or uses from circa 500 B.C.
to the present time.61 But it was demonstrated
to be a prominent cancer cause in
the late 20th century, after having been
described as a major health problem
as early as 70 A.D. by Pliny the Elder.
Consequently, the emerging prospects
for nanobiotechnology and even broader
nanotechnology and nanomanufacturing
must recognize the complex interactions
of nanoparticulates in biological
BIOMIMETICS AND BIOLOGICALLY INSPIRED MATERIALS INNOVATIONS
Biomimetics is often considered the
abstraction of good designs from nature.
As they apply to materials innovation
and development, biological systems can
exhibit wide arrays of multifunctional materials. Around 1940, Swiss engineer
George deMestral returned from a hike
with his dog and noticed both he and
the dog were covered with burrs. Upon
examining the burrs under a microscope,
deMestral was struck with the idea of
a fabric fastener. Velcro®, the quintessential
biomimetic design example, was
In a more recent example, mollusk
shells, particularly abalone, have been
recognized as hierarchical, structural
composites optimized for toughness,
despite the fact that they are composed
of relatively weak calcium carbonate
plates bound together by an organic
glue, or mortar. For example, the tensile
strength and toughness of the CaCO3
(aragonite) plates (Figure 11) are roughly
30 MPa and < 1 MPa-m1/2, respectively,
while the tensile strength and toughness
of the inner shell (or mother-of-pearl
of the abalone) varies between 100
MPa and 300 MPa, and corresponding
fracture toughness between 3 MPa-m1/2and 7 MPa-m1/2.62–64
As illustrated in
Figure 11, while the inner (nacre) portion
of the abalone shell is composed of
~86% aragonite blocks joined by ~10%
conchiolin or complex fossil protein
(sclero protein) and water, the outer portion
of the shell is composed of calcite
(CaCO3) with an increasing amount of
conchiolin near the outer surface. This
laminate microstructure of aragonite
has inspired a new class of structural
materials called metallic-intermetallic
laminate composites.65 A Ti-Al3Ti
laminate has demonstrated impressive
ballistic performance as a consequence
of high strength and fracture toughness,
and thermal management attributes.65 Of
course in the abalone, the multifunctional
attributes not only include these unusual
mechanical properties, but also a self healing
and translucent, lustrous, colored
pearl material which can be used as the
basis for cultured pearls.
The color of mother-of-pearl is the
result of diffraction from the one dimensional
aragonite lattice illustrated
schematically in Figure 11, and shown in
the scanning-electron microscopy (SEM)
view of a fractured nacre section in Figure
12a and b. The resulting blue-to-orange
color corresponds to spacings from
roughly 400 nm to 600 nm, respectively
(Figure 11). These structural color effects
are also illustrated by tilting a compact
disc (CD) in the light, which alters the
effective track spacings and the incident
angles to diffract all the colors included in
the optical portion of the spectrum (~350
nm to 800 nm wavelengths). Figure 12c
and d shows SEM views for a clean CD
and a CD with digital information written
onto it, respectively. The arrows in
Figure 12c and d provide a directional
reference for the grooves or tracks which
are interrupted in Figure 12d to produce
the digital tracking or data storage.
Color in biology is due to a variety of
optical phenomena including interference,
diffraction, absorption, refraction,
reflection (or scattering), and diffusion.
Diffraction effects, as noted previously,
can occur by reflection from finely ridged
surfaces (Figure 12c) acting as a diffraction
grating. Periodic microstructures
on the scale of color wavelengths create
this optical diffraction grating. Structural
coloration in nature has inspired innovations
in nano-bio-optics, nano-optics,
or photonics.66–69 Photonic crystals or
spatially periodic structures fabricated
from dielectric materials have different
retractive indices. These materials were
first proposed by Yablonovich70,71 and
John72 as optical band gap structures.
Photonic crystals73 or so-called superatom
lattices can be one-, two-, or three-dimensional
(1-D, 2-D, or 3-D) structures,
illustrated schematically in Figure
13a. These structures can be patterned
from two different dielectric materials
or interconnected air spaces or porous
materials. These arrays, especially 3-D
arrays, can produce structural color by
diffraction as illustrated schematically in Figure 13b.
Figure 14 illustrates some common
examples of biological or natural structural
color regimes. Figure 14a to c
illustrates yellow-orange butterfly wing
scales and color-generating scale microstructures.
Figure 14d shows a typical
opal structure, which represents a natural
face-centered cubic SiO2 sphere structure
or 3-D photonic crystal structure. As
the silica (SiO2) sphere size varies, the
diffracted color will correspondingly
In addition to the structural color
generation illustrated in Figures 12 and
14, there is the pigmentation coloring by
organic dyes and particulate pigments,
both microscopic and nanoscopic. Fiber reactive
dyes are formed inside fibers and
produce light and wash “fast” colors,
while dyes such as indigo can become
trapped in nanoporous fibers such as
palygorskite to produce durable color
systems such as Maya blue.74,75 Indigo
is a plant-derived pigment produced in
anaerobic batch processing with Clostidium
bacteria. Common examples
of particulate coloration due to optical
absorption occur in glass where
nanoparticles and nanoclusters produce
a wide range of colors: Co (blue), Mn
(amethyst), Se (red), Ti (yellow), Au
(~10 nm–ruby; < 10 nm–cranberry), and
Fe (green).76 Many biological (natural)
regimes exhibit both structural and pigmentation
coloring. Peacock feathers
are a good example. The blue peacock
feather “eye” results by structural coloring
while the associated red and black
coloring is due to pigmentation.68
Beetles also exhibit structural colors,67
but a recent discovery in Queensland,
Australia, of a green-colored weevil
was the first observation of an opal color
structure in animals. The close-packed
opal lattice on this beetle was found to
consist of hemispherical scales.77,78
Around 2000, biologist Kellar Autumn
at Lewis and Clark College in Oregon
was fascinated by the ability of a gecko
to navigate ceilings and walls with
ease. Together with an undergraduate
research student, Wendy Hansen, it was
discovered that the gecko has closely
packed foot hairs called setae (~100 µm
in length) with pads on their ends called
spatulae (~200 nm in diameter). These
hairs create a van der Waals force of
~200 μN and there are roughly 15,000
setae/nm2 on the gecko foot. Not only
do geckos attach by what is tantamount
to a “dry” adhesive effect, but the hairs
were discovered to be self-cleaning, since
the gecko can attach to dirty surfaces.79
Consequently, a self-cleaning, dry adhesive
material was under development.
Yurdumakan et al.80 have described
synthetic gecko foot hairs configured
from aligned growth of multiwall carbon
nanotubes similar to those illustrated in
Figure 10c and d. One centimeter square
of this synthetic adhesive can support ~1
kg by the combined van der Waals force
THE BIO-MATERIALS PARADIGM
Bio-materials as a paradigm outlined
in this article involves bioleaching and
biomineralization, biologically or microbial-assisted corrosion, biosorption and
bioremediation, bio-nano-photonics and
photonic materials, nano-bio-materials,
functional bio-materials, including multicomposite
materials, and biologically inspired
materials innovations. Since materials in
a broad sense imply materials science
and engineering, bio-materials can be
considered to connect the broad discipline
of biology to an existing multidisciplinary
Interdisciplinarity or interdisciplinary
studies in the context of research
implicit in the examples provided herein
demonstrate a process or processes to
address broad and complex problems not
adequately dealt with by a single discipline
or profession.81,82 Biophysics,
biochemistry, biomolecular nanotechnology,
etc., integrated with materials science
and engineering provide an even
broader context to bio-materials including
cross disciplinarity and transdisciplinarity,
in addition to interdisciplinarity and multidisciplinarity.82
Biophysics, biochemistry, and bioengineering
represent biological issues in
traditional disciplines of physics, chemistry,
and engineering, respectively, while
bio-materials integrates biology with
materials science and engineering—in
a broad sense, not just biomaterials as a
subset of materials types. Materials
engineering, or more broadly materials
science and engineering curricula, need
to re-think the role of chemistry and
physics and the necessity to introduce
biology and the biological sciences as a
part of the basic sciences core in order
to embrace the development of the biomaterials
paradigm as a reconfiguration
of the materials science and engineering
Bio-materials in the context
of engineering interdisciplinarity must
of necessity become more pervasive in
both undergraduate and graduate materials
curricula in support of increasing
emphasis in bio-materials research and
Biological structures, properties,
processes, and their associated performance
mimic the basic tenets of materials
science and engineering. Life constitutes
the ultimate materials, the construct
of living matter. Living cells and
their constituents are the manifestation
of multi-functional, self-organizing (or
the end point and starting
point (alpha and omega) for biomimetics.
Consequently bio-materials is a necessary,
paradigmatic inclusion in contemporary
materials science and engineering
Research incorporated as examples
in this paper has been supported in part
by several projects funded by the Southwest
Consortium for Environmental
Research and Policy and a Mr. and Mrs.
MacIntosh Murchison Endowed Chair.
The help of Micah Baquera, Erika
Esquivel, and others in creating selected
SEM images utilized in this paper is
1. R. Roy, editor, Materials Science and Engineering in
the United States (University Park, PA: Pennsylvania
State University, 1970).
2. Materials Science and Engineering for the 1990’s;
Maintaining Competitiveness in the Age of Materials
(Washington, D.C., National Materials Research
3. M.C. Roco, “The Emergence and Policy Implications
of Converging New Technologies Integrated from
the Nanoscale,” J. Nanoparticle Res., 7 (2005), pp.
4. G. Agricola, De Re metallica (translated from the
first Latin edition of 1556 by H.C. and L.H. Hoover)
(New York: Dover Publications, 1950).
5. J.H. Taylor and P.F. Whelan, “The Leaching of
Cupreous Pyrites and the Precipitation of Copper
at Rio Tinto, Spain,” Trans. Inst. Min. Metall., 52
(1942/1943), pp. 35–71.
6. W. Rudolfs and A. Helbronner, “Oxidation of Zinc
Sulfides by Micro-Organisms,” Soil Sci., 14 (1922), pp.
7. A.R. Colmer, K.L. Temple, and M.E. Hinkle, “An
Iron Oxidizing Bacterium from the Acid Drainage
of Bituminous Coal Mines,” J. Bact., 59 (1950), pp.
8. K.L. Temple and A.R. Colmer, “The Autotrophic
Oxidation of Iron by a New Bacterium, Thiobacillos
ferrooxidans,” J. Bact., 62 (1951), pp. 605–611.
9. L.E. Murr, “Theory and Practice of Copper Sulfide
Leaching in Sumps and In-Situ,” Minerals Sci. Engrg.,
12 (3) (1980), pp. 121–189.
10. T.D. Brock et al., “Microbial Growth under Extreme
Conditions,” Symp. Soc. General Microbiol., 19 (1969),
11. B.B. Bohlool, “Occurrence of Sulfolobus
acidocaldarius, an Extremely Thermophilic Acidophilic
Bacterium, in New Zealand Hot Springs. Isolation
and Immunofluorescence Characterization,” Arch.
Microbiol., 106 (1975), pp. 171–186.
12. D.T. Lacey and F. Lawson, “Kinetics of the Liquid
Phase Oxidation of Acid Ferrous Sulfate by the
Bacterium Triobacillus ferrooxidans,” Biotechnol.
Bioengrg., 12 (1970), pp. 29–38.
13. V.K. Berry, L.E. Murr, and J.B. Hiskey, “Galvanic
Interaction between Chalcopyrite and Pyrite during
Bacterial Leaching of Low-Grade Waste,” Hydromet.,
3 (1978), pp. 309–326.
14. A.P. Mehta and L.E. Murr, “Kinetic Study of
Sulfide Leaching by Galvanic Interaction between
Chalcopyrite, Pyrite, and Sphalerite in the Presence
of T. ferrooxidans (30°C) and a Thermophilic
Microorganism (55°C),” Biotechnol. Bioengng., 24
(1982), pp. 919–940.
15. A.P. Mehta and L.E. Murr, “Fundamental Studies
of the Contribution of Galvanic Interaction to Acid-
Bacterial Leaching of Mixed Metal Sulfides,” Hydromet.,
9 (1983), pp. 235–256.
16. L. Keller and L.E. Murr, “Lixiviant Alteration by
Fungal Adsorption of Iron during Acid-Bacterial
Leaching of Pure Pyrite,” Metall. Trans. B, 11 (1980),
17. R. Vaidya et al., “Protection of Be Metal Against
Microbial Influenced Corrosion Using Silane Self-
Assembled Monolayers,” Metall. Mater. Trans. A, 30
(1999), pp. 2129–2136.
18. I.B. Beech, “Sulfide-Reducing Bacteria in Biofilms
on Metallic Materials and Corrosion,” Microbiol. Today,
30 (2003), pp. 115–117.
19. P. Howsam, editor, Microbiology in Civil Engineering (London: E&F. N. Spon, 1990).
20. V.B.D. Skierman, “A Guide to the Identification of
the Genera of Bacteria,” (Baltimore, MD: Williams and
21. A.P. Mehta, A.E. Torma, and L.E. Murr, “Effect
of Environmental Parameters on the Efficiency of
Biodegeneration of Basalt Rock by Fungi,” Biotechnol.
Bioengng., 21 (1979), pp. 875–885.
22. M.P. Silverman and E.F. Munoz, “Penicillium
simplicissimum Recovery from Weathering Basalt
Rocks,” Science, 169 (1970), pp. 985–987.
23. K. Benzerara et al., “Nanoscale Environments
Associated with Bioweathering of a Mg-Fe-Pyroxene,”
Proc. Natl. Acad. Sci., 102 (4) (2005), pp. 979–982.
24. T.J. Beveridge, “The Response of Cell Walls of
Bacillus subtilis to Metals and to Electron Microscopic
Stains,” Can. J. Microbiol., 24 (1978), pp. 89–104.
25. T.J. Beveridge and R.G.E. Murray, “Sites of Metal
Deposition in the Cell Wall of Bacillus subtilis,” J.
Bacteriol., 141 (1980), pp. 876–887.
26. S.E. Shumate II et al., “Separation of Heavy
Metals from Aqueous Solutions using ‘Biosorbents’—
Development of Contacting Devices for Uranium
Removal,” Biotechnol. Bioengng. Symp., 10 (1980),
27. G.W. Strandberg, S.E. Shumate, and J.R. Parrott,
Jr., “Microbial Cells as Biosorbents for Heavy Metals:
Accumulation of Uranium by Saccharomyces
cerevisiae and Pseudomonas aeruginosa,” Appl.
Environ. Microbiol., 41 (1) (1981), pp. 237–245.
28. T. Horikoshi, A. Nakajima, and T. Sakaguchi, “Studies on the Accumulation of Heavy Metal Elements
in Biological Systems,” European J. Appl. Microbiol.
Biotechnol., 12 (1981), pp. 84–89.
29. J.L. Gardea-Torresdey et al., “Alfalfa Sprouts:
A Natural Source for the Synthesis of Silver
Nanoparticles,” Langmuir, 19 (2003), pp. 1357–1361.
30. J.L. Gardea-Torresdey et al., “Formation and
Growth of Au Nanoparticles Inside Live Alfalfa Plants,”
Nanolett., 2 (4) (2002), pp. 397–401.
31. E.L. Arthur et al., “Phytoremediation—An Overview,”
Crit. Rev. Plant Sci., 24 (2) (2005), pp. 109–144.
32. V. Armendariz et al., “Size Controlled Gold
Nanoparticle Formation by Avena Satira Biomass: Use
of Plants in Nanobiotechnology,” J. Nanoparticle Res.,
6 (2004), pp. 377–382.
33. M.S. Masri and M. Friedman, “Removal of Heavy
Metal Ions by Waste Wool,” J. Appl. Polymer. Sci., 18
(1974), pp. 2367–2377.
34. J.M. Randall et al., “Removal of Heavy Metal Ions
from Solution by Tree Bark,” Forest Prod. J., 24 (1974),
35. E. Greener, J. Harcourt, E. Lautenschlager,
Materials in Dentistry (Baltimore, MD: Williams & Wilkens Co., 1972).
36. W. McGehee, H. True, and E. Inskipp, A Textbook of
Operative Dentistry (New York: McGraw-Hill Book Co.,
37. J.A. Marquez, L.E. Murr, and V. Aguero, “A Study
of Alternative Metal Particle Structures and Mixtures
of Dental Amalgams Based on Mercury Additions,” J.
Mater. Sci., 11 (2000), pp. 469–479.
38. T.G. Berry et al., “Dental Amalgam,” J. Amer. Dental
Assoc., 129 (1998), pp. 1547–1558.
39. J. Karrholm et al., “Increased Metal Release from
Cemented Femoral Components,” Trans. Orthop. Res.
Soc., 18 (1993), pp. 507–517.
40. E.A. Trillo et al., “Evaluation of Mechanical and
Corrosion Biocompatibility of TiTa Alloys,” J. Mater. Sci.:
Mater in Medicine, 12 (2001), pp. 283–292.
41. R. Villa et al., “In Vitro Biocompatibility Studies of
Fibroblast Cells on Ti-Ta Alloys,” Mater. Trans. (Japan
Inst. Metals), 49 (4) (2003), pp. 2991–2999.
42. B. Palsson et al., editors, Tissue Engineering (Boca
Raton, FL: CRC Press, 2003).
43. W. Bonfield, “From Concept to Patient—Materials
Solutions for Bone Replacement,” Acta Biomater.,
(2006) (in press).
44. H. Bisgaard, C. O’Callaghan, and G.C. Smaldone,
editors, Drug Delivery to the Lung (New York: Marcel
Dekker Inc., 2002).
45. H.J. Fan et al., “Growth Mechanism and
Characterization of Zinc Oxide Microcages,” Solid
State Comm., 130 (2004), pp. 517–521.
46. S.L. Tao and T.A. Desai, “Microfabricated Drug
Delivery Systems: from Particles to Pores,” Adv. Drug
Delivery Rev., 55 (2003), pp. 315–328.
47. See “Dendrimers and Protein Cages as
Nanoparticles in Drug Delivery,” Drug Discov. Today, 9
(3) (2004), pp. 111–112.
48. R. Blakemore, “Single Domain Magnetic Materials
Synthesized by Magnetotactic Bacteria,” Science, 190
(1975), pp. 377–379.
49. M.T. Klem, M. Young, and T. Douglas, “Biomimetic
Magnetic Particles,” Mater. Today, 8 (9) (2005), pp.
50. T. Douglas, Biomimetic Synthesis of Nanoscale
Particles in Organized Protein Cages (New York:
Wiley-VCH Publishers, 1996).
51. S. Mann, editor, Biomimetic Materials Chemistry(New York: Wiley-VCH Publishers, 1996).
52. E.L. Mayes and S. Mann, Nanobiotechnology(Weinheim, Germany: VCH Publishers, 2004).
53. R.O. Anderson, Radiolaria (New York: Springer-Verlag, 1983).
54. J.W. Arbogast et al., “Photophysical Properties of
C60,” J. Phys. Chem., 95 (1991), pp. 11–12.
55. E. Oberdörster, “Significance of Particle Parameters
in the Evaluation of Exposure-base Relationships of
Inhaled Particles,” Inhal. Toxicol. (Suppl.), 8 (1996), pp.
56. G. Sykes, Disinfection and Sterilization (Princeton,
NJ: D. Van Nostrand Co., Inc., 1958).
57. A product manufactured by American Biotechnology
Inc. (Baltimore, MD), under the name ASAP.
58. K.-I. Ishibashi et al., “Generation and Deactivation
Processes of Superoxide Formed on TiO2 Film
Illuminated by Very Weak UV Light in Air or Water,” J.
Phys. Chem. B, 104 (2000), pp. 4934–4938.
59. G. Oberdörster, “Pulmonary Effects of Inhaled
Ultrafine Particles,” Int. Arch. Occup. Environ. Health,
74 (2001), pp. 1–8.
60. L.E. Murr et al., “Combustion-Generated
Nanoparticulates in the El Paso, TX, Juarez, Mexico
Metroplex: Their Comparative Characterization and
Potential for Adverse Health Effects,” Int. J. Environ.
Res. & Public Health, 2006 3 (1) (2006), pp. 45–63.
61. J.E. Alleman and B.T. Mossman, “Asbestos
Revisited,” Sci. Amer. (July 1997), pp. 70–75.
62. M. Sarikaya, “An Introduction to Biomimetics: A
Structural Viewpoint,” Microsc. Res. Tech., 27 (1994),
63. B.J.J. Zelinsky et al., editors, Better Ceramics
through Chemistry IV (Warrendale, PA: Materials
Research Society, 1990).
64. A. Lin and M.A. Meyers, “Growth and Structure in
Abalone Shell,” Mater. Sci. Engng., 390 (2005), pp.
65. K.S. Vecchio, “Synthetic Multifunctional Metallic-
Intermetallic Laminate Composites,” JOM, 57 (3)
(2005), pp. 25–29.
66. H. Ghiradella, “Structural Coloration,” Microscopy
Anal. Invet., 11 (1998), pp. 257–263.
67. M. Srinivasarao, “Nano-Optics in the Biological
World: Beetles, Butterflies, Birds and Moths,” Chem.
Rev., 99 (7) (1999), pp. 1935–1961.
68. K. Phillips, “Feathers Reveal Their True Colors,” J.
Exp. Biol., 205 (2002), pp. 1402–1411.
69. P. Vokosic and J.R. Sambles, “Photonic Structures
in Biology,” Nature, 424 (2003), pp. 852–855.
70. E. Yablonovich, “Inhibited Spontaneous Mission in
Solid-State Physics and Electronics,” Phys. Rev. Lett.,58 (1987), pp. 2059–2062.
71. E. Yablonovich, “Photonic Crystals: Semiconductors
of Light,” Sci. Amer. (December 2001), pp. 47–55.
72. S. John, “Localization of Light,” Physics Today (May
1991), pp. 32–34.
73. Y. Xia, K. Kamata, and Y. Lu, “Photonic Crystals:
Chap. 20,” Introduction to Nanoscale Science and
Technology, M. Di Ventra, S. Evoy, and J.R. Hetling, Jr.,
editors (Boston, MA: Kluwer Academic Publishers,
Inc., 2004), pp. 505–527.
74. L.A. Polette et al., “Maya Blue: Application of XAS
and HRTEM to Materials Science in Art and
Archaeology,” Microchem. J., 71 (2002), pp. 167–174.
75. E.V. Esquivel et al., “TEM Observations of a 30
Million Year Old Mountain Leather Nanofi ber Mineral
Composite,” Mater. Characterization, 54 (2005), pp.
76. K. Nassace, The Physics and Chemistry of Color:
The Fifteen Causes of Color (New York: J. Wiley & Sons Inc., 1983).
77. A.R. Panker et al., “Structural Color: Opal Analogue
Discovered in a Weevil,” Nature, 426 (2003), pp. 786–787.
78. J. Roach, “Bejeweled Weevil May Inspire Synthetic
Gem,” Natl. Geographic News (12 January 2004).
79. W.R. Hansen and K. Autumn, “Evidence for Self-
Cleaning in Gecko Setae,” Proc. Natl. Acad. Sci., 102
(2005), pp. 385–389.
80. B. Yurdumakan et al., “Synthetic Gecko Foot-Hairs
from Multiwalled Carbon Nanotubes,” Chem. Comm.,
30 (2005), pp. 3799–3801.
81. J.T. Klein and W.H. Newell, “Advancing
Interdisciplinary Studies,” Interdisciplinarity: Essays
from the Literature, ed. W.H. Newell (New York: College
Entrance Examination Board, 1998), p. 3.
82. J.T. Klein, Humanity, Culture, and Interdisciplinarity:
The Changing American Culture (New York: State
University of New York Press, 2005).
L.E. Murr is a professor in the Department of
Metallurgical and Materials Engineering at The
University of Texas at El Paso.
For more information, contact L.E. Murr, The
University of Texas at El Paso, Department of
Metallurgical and Materials Engineering, 500 West
University Avenue, El Paso, TX 79968, USA; (915)
747-6929; fax (915) 747-8036; e-mail firstname.lastname@example.org.