Crystallisation in Confinement - A Biological Perspective

Lead Research Organisation: University of Leeds
Department Name: Sch of Chemistry

Abstract

The organisation and function of biological systems is based on compartmentalisation, where processes occur within small volumes rather in bulk solution. A simple example of a biological compartment is a cell, which itself can contain many smaller compartments. It is becoming increasingly obvious that confining reactions in this way can dramatically affect the mechanisms and products of biological and chemical reactions by changing the way that molecules interact with each other and their environment.This project will focus on one very important category of biological processes - biomineralisation - which is the formation of mineral-based structures such as seashells, bones and teeth. There is considerable interest in understanding how Nature controls crystallisation to produce materials of this type. Although biominerals are produced under mild reaction conditions, they often exhibit properties which can not only equal but actually surpass those of engineering materials such as concrete. The research in this proposal will investigate how confinement affects crystallisation, and how Nature exploits this to produce such remarkable materials. To-date, research directed towards understanding how Nature controls the formation of minerals has concentrated on the role of organic macromolecules. Further, although biomineralisation invariably occurs within restricted volumes, experiments aiming to mimic these processes are typically carried out in bulk solution. While organic molecules are certainly important, it is very likely that confinement also has a significant affect on these crystallisation processes. Indeed, there are many biogenic crystallisation phenomena, such as the precipitation of calcium phosphate crystals in collagen fibres during bone formation, which cannot be adequately described in terms of crystallisation from bulk solution. Initial work will focus on the precipitation of calcium carbonate and calcium phosphate in small volumes. The research programme will then be extended to investigate the effect of confinement on the crystallisation of a range of other minerals. While it is clear that confinement over a wide range of length scales can strongly affect crystal nucleation and growth, with the exception of freezing phenomena, these effects are poorly understood and as yet unpredictable. The research conducted will lead to a greater understanding of crystallisation in restricted volumes, and will therefore enable us to use confinement to control crystallisation, and to profit from it in synthetic systems. Indeed, there are many technological applications which rely upon crystal growth within constrained volumes such as the fabrication of nano-materials including nanowires and nanotube arrays, general templating processes, drug delivery systems and implants. Crystallisation in confinement is also widespread in Nature, and in addition to biomineralisation processes, includes events such as weathering and frost heave - which occur with great cost to civil engineering the environment and technology. The proposed research is clearly of great relevance to both fundamental research and technology across many disciplines.

Publications

10 25 50
 
Description We have demonstrated that:

(1) Confinement has significant effects on crystallization and can be used to control crystal nucleation and growth.

(2) Confinement, even at surprisingly large length scales (up to the micron level) typically results in stabilisation of metastable phases.

(3) Confinement can be used to control crystal orientation, morphology and single crystal/ polycrystalline character. It is therefore highly likely that biology uses confinement as a way to control the formation of biominerals (such as bones and teeth) and that this is a strategy that can be translated to synthetic systems.

(4) Confinement provides an effective route to identifying new crystallization mechanisms, and we have used this to identify new amorphous precursor phases.

(5) The alignment of hydroxyapatite crystals seen in collagen in bone can be achieved by confinement alone. No structural correspondence between the collagen and crystal lattice is required. This contradicts the majority ideas about bone mineralization.

This project has also profited from microfluidic devices to study crystallization within well-defined environments.

(1) We have developed a novel screening platform, which when guided using genetic algorithms, can be used to optimise droplet interfaces for specific interfaces. This has been used to identify oil/surfactant combinations that promote mineralisation. Such mineralised droplets exhibit enhanced stability and can be used to support in vitro protein expression.

(2) We have developed novel microfluidic devices termed a "crystal hotel" to study crystallization mechanisms. This can be used to investigate the pathway of crystallization, and we have used this to show that additives only affect crystal morphologies at later stages of growth.

(3) Further functionalization of the hotel room with an array of posts can be used to generate single crystals with complex morphologies.

(4) We have designed novel chips that will allow us to study crystallization mechanisms on chip using synchrotron XRD.

Work has also been conducted to investigate the internal structures of single crystals of calcite using Bragg Coherent Diffraction Imaging (BCDI).

(1) We have demonstrated for the first time that BCDI can be used to visualise in 3D the dislocations present within individual crystals.

(2) Investigation of calcite crystals precipitated on self-assembled monolayers using BCDI demonstrated the presence of a single dislocation look at the crystal base. This provides new insight into how organic matrices control the growth of inorganic crystals, and shows that strain relief also governs the morphological development of the crystals.

Finally, we have performed a number of studies investigating crystallization mechanisms in bulk solution.

(1) We have investigated the crystallization mechanism of amorphous calcium carbonate (ACC) in aqueous solution and in the solid state and have demonstrated that the transformation occurs by the same mechanism in both environments. Further, we have shown that the barrier to nucleation of a crystalline phase is so high that initial nucleation must occur by particle dissolution/ reprecipitation.

(2) We have investigated the effect of additives on the crystallization of ACC in solution and demonstrated a Janus effect. While small additives retard crystallization in both environments, large additives retard crystallisation in solution while accelerating it in the solid state. As crystallization of ACC in biology occurs within confinement, this has important implications for additive-directed crystallization in biology.

(3) There has been significant interest in the formation of calcium carbonate mesocrystals, where these are defined as crystals comprised of aligned nanoparticle subunits. By carrying out rigorous analyses of a range of calcium carbonate mesocrystals; we have shown that the existing literature is incorrect, and that these crystals are actually single crystals with rough surfaces.
Exploitation Route (1) Confinement can now be used as an effective route to controlling crystallization.

(2) Confinement can be used to determine crystallization mechanisms and to identify new, metastable crystal phases.

(3) Biomineralization mechanisms (including bone and tooth formation) needs to be considered in light of confinement effects and not simply traditional ideas of organic matrix directed crystallization.

(4) Our novel screening approach and combinatorial methods guided by genetic algorithms can be used to construct emulsion droplets with target properties. This approach can also be extended to materials science in general.

(5) Study of crystallization in microfluidic devices opens the door to temporal and spatial control of crystallization.

(6) Our synchrotron powder XRD studies of crystallization on-chip will enable high through study of crystallization mechanisms.

(7) The scientific community needs to re-evaluate existing publications on mesocrystals, as many are based on data which has been incorrectly analysed.

(8) BCDI can be used to study the influence of external stimuli on the movement and interaction of a network of dislocations within single crystals.
Sectors Agriculture

Food and Drink

Construction

Energy

Environment

Healthcare

Pharmaceuticals and Medical Biotechnology

URL http://www1.chem.leeds.ac.uk/FCM/
 
Description Platform Grant
Amount £1,408,821 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2015 
End 11/2020
 
Description Programme Grant
Amount £5,436,236 (GBP)
Funding ID EP/R018820/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2018 
End 02/2023
 
Description Responsive mode
Amount £824,035 (GBP)
Funding ID EP/M003027/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2014 
End 12/2017
 
Description Responsive mode
Amount £819,881 (GBP)
Funding ID EP/L015005/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 08/2014 
End 09/2017
 
Description Bristol Festival of Nature 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact 6 members of the research group participated in the 2-day "Bristol festival of nature" where they manned a stand that showcased demonstrations about crystallisation processes.
Year(s) Of Engagement Activity 2015
 
Description Directed Assembly Summer school 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Presented a seminar as part of the Directed Assembly Summer School
Year(s) Of Engagement Activity 2015
 
Description exhibition of images 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact We exhibited scientific images (of crystals) at the North Bar, Leeds over a period of 3 months.

none
Year(s) Of Engagement Activity 2013
 
Description superposition 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact I presented as part of "Superposition" which is a regular series of events aimed at causing mixing between artists and scientists

None
Year(s) Of Engagement Activity 2012