Biomineralization seems an odd sort of word. How can you combine biology and minerals? However, a quick look around brings to light many familiar objects that are examples of biominerals. Most dramatic are the coral reefs and sea shells of the marine environment (calcium carbonate) and human bone and teeth (calcium hydroxyapatite) but there are many other examples. In the past 10 years, an increasing number of biominerals has been reported (Table 1). Interest in the biological and chemical processes that lead to biomineralization, howeyer, has only developed rather recently. Early observations were made by paleontologists who were interested in the preservation, through geological time, of the hard parts of organisms such as shells and skeletons but only in 1989 did the field really come of age with the almost simultaneous publication of three monographs covering current knowledge of the biological, biochemical, chemical and taxonomic aspects of biomineralization (Mann et al. 1989; Lowenstam & Weiner 1989; Simkiss & Wilbur 1989)

Evans, L.A.

Macey, D.J.

St Pierre, T.G.

Webb, J.

English

Research Repository

Biominerals - Source and Inspiration for Novel Advanced Materials J. Webb, L  A. Evans and T. G. St. Pierre School of Mathematical and Physical Sciences, Murdoch University, Murdoch, WA 6150 O. J. Macey School of Biological and Environmental Sciences, Murdoch University, Murdoch, WA 6150 iomineralization seems an odd sort of word. How can you combine biology and minerals? However, a quick look around brings to light many familiar ob-jects that are examples of biominerals. Most dramatic are the  coral  reefs  and sea shells of the marine environment (calcium  carbonate) and human bone and teeth (calcium twdroxyapatite) but there are many other examples. In the past  10  years,  an  increasing number of biominerals has been  reported  (Table  1).  Interest  in the biological and chemical  processes  that lead to biomineralization, how-eyer,  has  only developed rather recently. Early observa-tions were made by paleontologists who were interested in the preservation, through geological time, of the hard parts of organisms such as shells and skeletons but only in 1989 did the field  really come of age with the almost simultane-ous  publication  of three  monographs  covering  current of the biological,  biochemical, chemical and aspects of biomineralization (Mann et al.  1989; & Weiner 1989; Simkiss &  Wilbur 1989). But  there  is  much more to biomineralization than just interest  in the biological materials 'because they are there'.  Biominerals exhibit a wide variety of functions and unuerstctnding how biominerals perform these functions is \  :1 major new frontier in interdisciplinary scientific research. ,  Much  of the current interest derives from the inspiration to he found  in biominerals for the design of novel materi-als.  Biomineral  phases can be crystalline,  amorphous or rart~y crystalline/partly amorphous. They contain individ-lom1l1eral deposits that are generally less than 1 11 and lllay be'  11  '  ,as sma  as  10 nm. Such nanospace materials are of , to emerging technologies (Birchall 1989). Further-,  111  many biological systems, the biominerals are pre-)knt as  c  f  "  omponents 0  composite materials, where the in-Itf<Janic ,  components are organized together with organic b'  such as proteins or polysaccharides to form the lOlogical  structure. Two established instances will to illustrate the link between the structure of biomin-and the design of novel materials. A third example re-to OUr own studies of the biological mineralization of 1nsom  '  e manne molluscs. natural  I  k  cora  s  eleton is  a porous structure with many and  spaces,  whose dimensions  in certain coral ""';J,rh.1,ll,atch those of human bone. This similarity to, and be U  d  With,  bone has been exploited in that coral Se  as a'  1  h  k  n nul' ant in bone tissue. In France, suc  a treat  nown as  Biocoral® has been prepared by selec-ment  f  o  natural coral and used for some years as a substitute for  bone grafts  and in plastic surgery  (Inoteb 1989). The Australian distributors (3M Company) indi-cate that Biocoral has been approved for use in Australia and already several surgical procedures have been carried out in Sydney and Melbourne. The mechanical properties of Biocoral can be controlled by changing its porosity, giv-ing materials that match or exceed bone in compressive strength and  elasticity.  It  is  the chemistry of the coral preparation that is particularly appropriate for this surgical use.  As noted above, bone is  made of a phosphate salt of calcium,  while  coral  is  a  carbonate salt.  The particular form of CaCOJ  is  aragonite, a metastable form of CaCOJ• This metastable nature means that, when implanted, the CaCOJ gradually dissolves (i.e. is resorbed) and is replaced IiIl FIG. 1  Tablets of crystalline aragonite, CaCO, (approx. 0.5 11m thick) with their proteinaceous matrix in the nacre of the shell of Halialis rufescens (photo courtesy of Professor H. Nakahara). Search, Vol. 22,  No, 4, June 1991  137 TABLE 1  The types and functions of the main inorganic solids found in biological systems Mineral  Formula  Organism/Function Calcium carbonate: Calcite  CaCO/  Algae/exoskeletons Trilobites/eye lens Aragonite  CaC03  Fish/gravity device Molluscs/exoskeleton Vaterite  CaC03  Ascidans/spicules Amorphous  CaC03·nH2O  Plants/Ca store Ca phosphate: Hydroxyapatite  Ca10(P04 )6(OH)2  Vertebrates/endoskeletons teeth Ca Store Octa-calcium  CagH2(P°4)6  Verteb rates/p recu rso r phosphate  phase in bone? Amorphous  ?  Mussels/Ca store Vertebrates/precursor phases in bone? Calcium oxalate: Whewellite  CaC20 4·H2O  Plants/Ca Store Weddellite  CaC204.2H2O  Plants Ca store Group IIA metal sulphates Gypsum  CaS04  Jellyfish larvae gravity device Barite  BaS04  Algae/gravity device Celestite  SrS04  Acantharia/cellular support Silicon dioxide: Silica  Si02·nH2O  Algae/exoskeletons Iron oxides: Magnetite  Fe30 4  Bacteria/magnetotaxis Chitons/teeth Geothite  u-FeOOH  Limpets/teeth Lepidocrocite  y-FeOOH  Chitons (Mollusca) teeth Ferrihydrite  5 Fe20 3.9H2 O  Animals and plants/ Fe storage proteins * A range of magnesium-substituted calcites are also formed. III!  FIG. 2  Scanning electron micrograph ofthe radula of the chiton A. hirtosa. Scale bar = 1  00  ~m. The major lateral teeth are indicated by arrows. 138  Search. Vol. 22, No.4, June 1991 1 ",~~: by newly formed bone, synthesized by that migrate into the porous structure f. d·  b  Th  h  I  Orr,  a  Jacent  one.  e ot  er co~mon  fOtllt~; CaC03,  calcite,  does  not dissolve  und.; these  conditions.  The  implant  mater~~ contains some amino acids but no prot  'ct, etl) and  thus  differs  from  natural bone,  Th' absence of foreign  protei~ however is  part tlcularly attractlve m an Implant since avoids any adverse immunological react Ill!' and hence rejection. In this instance  ", structure and composition of the  ' biomineral, coral, can be used to prepare l highly useful biomaterial for surgery.  . Flexible Concrete The  micro  architecture  of the material  that  is  the  molluscan  shell been  used  to  inspire  the  preparation what at first glance appears to be a diction in terms: flexible concrete, or, accurately, macrodefect-free concrete cha1l1989). Molluscan shells are of microcrystals of CaC03 organized protein-rich organic matrix (Fig.  1). shells have strengths in tension that ate order of magnitude  greater  than that concrete. The  innovative  inclusion of water-soluble polymer in the concrete mulation  was  derived  directly  from analogy  of  the  structural within the shells and proved to be in obtaining a plastic rheology for the crete.  This  novel  concrete  material been used  to fabricate  building and automobile components, including springs,  although not yet on an mass production scale. Chitons and Limpets The biological structure that has our  interest  is  the  radula,  a organ,  of two  kinds  of marine namely,  chitons  and  limpets, widely  distributed  in  intertidal  enviro1lc; ments (Webb et al.  1989,  1990). Chiton jl and limpets have highly mineralized teet$ on the  radula to scrape  from  rocky  sll~i  ."  strates  the  crustose  coralline  algae  Ll~ which  they  feed.  The  organic  matrix~. teeth and mineralizing elements for  subs!,! quent hardening are secreted by  epithel~ cells as  the teeth migrate slowly along  t~ radula  membrane.  This migration  resul~  .  ~*'  from  the  continual wearing  away  ot  ["~ teeth during feeding.  The radula is  th\~~ 'conveyor  belt'  of teeth,  with  the  e~t teeth being soft and unmineralized and d'l fully  mature  teeth  being  hardened  at'): functional  composite  structures  (Fig·:j p The availability of teeth at varying stages of mineralization llowS  us  to study the process of mineralization and the a echanisms  involved,  as  well  as  the products,  i.e.  the ~ominerals tngether with associated organic material. Both chiwns and limpets use iron to harden their teeth, depositing witl;in t~em  a v~riety. of  iro~ oxides. These, to-gether  with otner morgam.c  soitds~  ~emf~rce and ha~den the organic matnx. In the itmpet, slitcon IS  also deposIted, as amorpholls  silica SiOz, while in the chiton, calcium is deposited as crystalline forms of hydroxyapatite. A distinct mineralized layer of magnetite (M in Fig. 3) and as many as ,  other oxides cover the surface of the chiton tooth that the rocky substrate during feeding and the molecu-mechanisms  that lead  to their formation have been Fcl2lntH~a only recently (Kim et al.  1989; Webb et al.  1991). Behind the magnetite layer are densely packed fibres that rope-like  strands of chitin (Evans et al.  1990), their determining whether magnetite is  formed or cal-is mineralized. Most of the protein of the tooth is pre-in the calcified region, suggesting that proteins playa role in initiating and controlling mineralization (Evans 1991). For iron mineralization, this matrix-mediated is less evident and mineralization and its products to be under kinetic control of the flux of iron into tooth  from  the superior  epithelial cells  (Kim et  al. Webb et al.  1991). micro architecture of the chiton tooth can be re-directly to its biological function as a feeding imp  le-Magnetite, with a hardness of 6-6.5 on the Mohs (Le.  harder than apatite but not as  hard as quartz) is packed  as  a surface layer of the tooth cusp that on the substrate during feeding. Behind this layer chitin fibres,  reinforced with hydroxyapatite, that act absorbers' supporting the tooth during the physi-stress  of  feeding.  In  summary,  a  matrix-poor  but region serves as  the cutting edge that is by a matrix-rich calcified region that gives about the biological manipulation of materials ~rrt'lrt,.~pc to perform a function can be used to develop new technologies. At the University of Groningen in The Netherlands, the chiton radula is  being used to develop new designs for dredging machinery. In addition, the con-trol of crystallization in biology is relevant to the problems faced by such emerging industries as  those developing ad-vanced ceramics as  well as  established mineral processing plants. Size and shape of crystals affects how readily the crystals can be filtered,  washed and processed.  Indeed a specific size  range of the particle may be necessary for  its role, such as is the case for the iron oxide particles on mag-netic recording tape. There are many options and challenges derived from the study of biominerals. As Derek Birchall of ICI (UK)'s Ad-vanced Materials Group has put it (Birchall, 1989): Biology  does  not waste  energy manipulating materials  and structures that have no function and it eliminates those that do not function adequately and economically. The structures that we observe 'work' and their form and microstructure have been developed and refined over millions of years. The task of the modern materials technologist is to develop, within a very short timescale, materials the microstructure of which is  such that they perform a function efficiently. It is as well, then, to look for fresh insights to biology at the wisdom encapsulated in the materials it uses. Acknowledgements We acknowledge with gratitude financial support over sev-eral years by the Australian Research Council and Mur-doch University's Special Research Grant. L.  A. Evans is the  recipient  of  an  Australian  Postgraduate  Research Award. References Birchall, ]. D.  (1989) The importance of the study of biominerals to ma-terials technology. In: Biomineralization: Chemical and Biochemical Perspec-tives,  S.  Mann, ].  Webb and  R.  ].  P.  Williams  (eds).  VCH Verlags-gesellschaft, pp. 491-509. Evans, L. A, Macey, D.]. & Webb,]. (1990) Characterization and struc-tural organization of the organic matrix of the radula teeth of the chiton Acanthopleura hirtosa. Phil. Trans.  Roy.  Soc.  Lond. B., 329. Evans, L. A, Macey, D.]. & Webb, J.  (1991) Distribution and composi-tion of matrix protein in the radula teeth of the chiton Acanthopleura hirtosa. Mar.  BioI.  (in press). Inoteb (1989) From coral ...  to biocoral® Inoteb 56920 Noyal-Pontivy, France and references therein. Kim, K-S., Macey, D. J., Webb, J.  &  Mann, S.  (1989) Iron biomineraliz-ation in the radula teeth of the chiton Acanthopleura hirtosa.  Proc.  Roy. Soc.  Lond.  B.  237,335-346.  -Lowenstam,  H.  A.  &  Weiner, S.  (1989)  On Biomineralization.  Oxford University Press. Mann, S., Webb, J. &  Williams, R. J.  P.  (1989) Biomineralization: Chemi-cal and Biochemical Perspectives. VCH Verlagsgesellschaft. Simkiss, K.  &  Wilbur, K.  M.  (1989) Biomineralization. Academic Press. Webb, ]., Macey, D. J. & Mann, S.  (1989) Mineralization of iron in mol-luscan teeth. In:  Biomineralization:  Chemical and Biochemical Perspectives, S.  Mann, J. Webb and R. J.  P. Williams (eds). VCH Verlagsgesellschaft, pp.348-388. Webb, J., St. Pierre, T. G. & Macey, D. J.  (1990) Iron biomineralization in invertebrates. In: Iron  Biominerals, R.  B.  Frankel (ed.). Plenum Press, New York (in press). Webb, J., Evans, L.A, Kim,  K.-S., St. Pierre, T.G. & Macey D.J.  (1991) Controlled deposition and transformation of iron biominerals in chiton radula  teeth.  In:  Biomineralization  '90,  S.  Suga  (ed.).  Springer-Verlag Tokyo. Search, Vol. 22, No.4, June 1991  139 

Biomineralization: Chemical and Biochemical Perspectives.

Characterization and structural organization of the organic matrix of the radula teeth of the chiton Acanthopleura hirtosa.

Controlled deposition and transformation of iron biominerals in chiton radula teeth. In: Biomineralization

Distribution and composition of matrix protein in the radula teeth of the chiton Acanthopleura hirtosa.

From coral ... to biocoral® Inoteb 56920 Noyal-Pontivy, France and references therein.

Iron biomineralization in invertebrates.

Iron biomineralization in the radula teeth of the chiton Acanthopleura hirtosa.

Mineralization of iron in molluscan teeth. In: Biomineralization: Chemical and Biochemical

On Biomineralization.

The importance of the study of biominerals to materials technology. In: Biomineralization: Chemical and Biochemical

Biominerals - source and inspiration for novel advanced materials

http://researchrepository.murdoch.edu.au/7216/

Biominerals - source and inspiration for novel advanced materials

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