Time-Resolved Cryo-TEM Study on the Formation of Iron Hydroxides in a Collagen Matrix

Bernette M. Oosterlaken, Mark M.J. van Rijt, Rick R.M. Joosten, Paul H.H. Bomans, Heiner Friedrich, Gijsbertus de With (Corresponding author)

Research output: Contribution to journalArticleAcademicpeer-review

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The mineralization of collagen via synthetic procedures has been extensively investigated for hydroxyapatite as well as for silica and calcium carbonate. From a fundamental point of view, it is interesting to investigate whether collagen could serve as a generic mineralization template for other minerals, like iron oxides. Here, bio-inspired coprecipitation reaction, generally leading to the formation of magnetite, is used to mineralize collagen with iron hydroxides. Platelet-shaped green rust crystals form outside the collagen matrix, while inside the collagen, nanoparticles with a size of 2.6 nm are formed, which are hypothesized to be iron (III) hydroxide. Mineralization with nanoparticles inside the collagen solely occurs in the presence of poly(aspartic acid) (pAsp). In the absence of pAsp, magnetite particles are formed around the collagen. Time-resolved cryo-TEM shows that during the coprecipitation reaction, initially a beam-sensitive phase is formed, possibly an Fe3+-pAsp complex. This beam-sensitive phase transforms into nanoparticles. In a later stage, sheet-like crystals are also found. After 48 h of mineralization, ordering of the nanoparticles around one of the collagen sub-bands (the a-band) is observed. This is very similar to the collagen-hydroxyapatite system, indicating that mineralization with iron hydroxides inside collagen is possible and proceeds via a similar mechanism as hydroxyapatite mineralization.

Original languageEnglish
Pages (from-to)3123–3131
Number of pages9
JournalACS Biomaterials Science and Engineering
Issue number7
Publication statusPublished - 12 Jul 2021

Bibliographical note

Funding Information:
The work of B.M.O. and M.M.J.v.R. was supported by a TopPunt grant (Bi-Hy, 718.016.003) of the Netherlands Organisation for Scientific Research (NWO).


  • biomineralization
  • collagen
  • electron tomography
  • Iron hydroxides


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