* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Heterogeneous Nanonucleants - Manuscript - FINAL
Energy applications of nanotechnology wikipedia , lookup
Spinodal decomposition wikipedia , lookup
Strengthening mechanisms of materials wikipedia , lookup
X-ray crystallography wikipedia , lookup
Surface tension wikipedia , lookup
Sessile drop technique wikipedia , lookup
Dislocation wikipedia , lookup
Crystal structure wikipedia , lookup
Ultrahydrophobicity wikipedia , lookup
Low-energy electron diffraction wikipedia , lookup
Tunable metamaterial wikipedia , lookup
Nanofluidic circuitry wikipedia , lookup
Semiconductor device wikipedia , lookup
Sol–gel process wikipedia , lookup
Self-assembled monolayer wikipedia , lookup
Paleostress inversion wikipedia , lookup
Freeze-casting wikipedia , lookup
Nanochemistry wikipedia , lookup
Heterogeneous Nucleants for Crystallogenesis and Bioseparation Umang V. Shaha, Christian Ambergb, Ying Diaoc, Zhongqiang Yangd, Jerry Y. Y. Henga* a Surfaces and Particle Engineering Laboratory (SPEL), Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom. b Engineering Formulation Europe, Syngenta Crop Protection Münchwilen AG, Breitenloh 5, CH-4333 Münchwilen, Switzerland. c Department of Chemical and Biomolecular Engineering, University of Illinois, Urbana, IL 61801, United States of America. d Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China. *Corresponding Author: [email protected] Phone: +44-(0)207-594-0784. Fax: +44-(0)207-594-5700 Web: www.imperial.ac.uk/spel Keywords: nucleation; crystallisation; nanoparticles; bioseparation; proteins Highlights 1. An insight into nucleation mechanism, with brief review of current nucleation theories. 2. Description of selective nucleant approaches for controlling crystallisation. 3. Essential components for successful crystallisation – the Crystallisation Triangle concept. 4. Outlook of crystallisation for biocrystallisation and bioseparation. 5. Emerging approaches to include soft materials. 1 Abstract Crystallisation is a widely used separation step for both isolation and purification of products, for a wide range of chemical processes. Nevertheless, there remains a great challenge in controlling the onset of crystallisation - nucleation. Heterogeneous nucleation has been investigated over the last three decades to determine physico-chemical relationships between nucleant and solute properties, which may be key for controlling nucleation. This can lead to rational design of nucleants facilitating selective crystallisation of particles with desired properties. In this opinion, a review on recent advances in developing mechanistic understanding of the role of interfacial properties, mainly nano-scale surface topography, surface chemistry and the combination of both features, in controlling nucleation is presented. An outlook for the development of next generation nucleants and the potential application areas are presented. 2 Introduction Crystallisation is often considered an essential separation step for many different chemical processes ranging from producing simple compounds such as salt and sugar to large complex macromolecular biotherapeutics such as insulin. Controlling crystallisation has been a topic of interest for many areas of science and technology including environmental sciences [1], pharmaceuticals [2], semiconductors [3], non-linear optics [4], food products [5], neutraceuticals [6], minerals in biological and synthetic systems [7, 8]. Protein crystallisation is often considered more of an art than a science, relying on empirical approaches and hampered by lack of mechanistic understanding [9]. Nucleation is the governing step for controlling crystallisation. However, it is extremely difficult to control nucleation considering that in most practical circumstances, nucleation is initiated on foreign interfaces, i.e. heterogeneous nucleation. Over the last decade, considerable progress has been made in understanding the role of interfacial properties in controlling heterogeneous nucleation [10]. Among the proposed mechanisms, favourable specific molecular interactions for the crystallising molecule and an epitaxial match between the molecule and the substrate have been demonstrated to aid nucleation [11-13]. Furthermore, nucleant surface topography at the nanometre length scale has been reported to affect nucleation [14]. However the contributions from these surface attributes are seldom quantified in isolation, combination of these attributes has been neglected until very recently [15], resulting in a limited mechanistic understanding. Here, recent advances in mechanistic understanding of nucleation and how such advancements have aided the insight into the role of nucleant surface properties in controlling nucleation are presented. Selected literature also highlights mechanisms by which interfacial properties governing heterogeneous nucleation, presenting opportunities for targeted/selective nucleation by specifically designed nucleant, opening up new applications for crystallisation, such as biocrystallisation, bio-separation, water softening, and scale prevention, etc. 3 Insight into nucleation mechanisms Classical Nucleation Theory The fundamental framework used in describing nucleation is known as the Classical Nucleation Theory (CNT). This theory assumes that local concentration fluctuates intermittently form clusters that grow through monomer additions until a critical size is reached. As per CNT, critical cluster size is inversely proportional to the level of supersaturation. It is thus clear that as supersaturation increases, the critical size decreases and the solute is more likely to successfully form nucleus. However, in practice, this expression oversimplifies the nucleation process and fails to account for several aspects of experimental measurements of nucleation rate [16], although is widely applied Two-step Nucleation Model The two-step nucleation model differs fundamentally from the CNT in that solution molecules are not assumed to exchange directly with a cluster. Instead, first an intermediate dense liquid droplet is formed, followed by nucleation of an ordered crystalline structure [17]. At sufficiently high supersaturation and low temperature, the critical nucleus size is unity, such that every molecule in the solution can be a seed. Here, the thermodynamic nucleation barrier is zero and generation of new crystalline phase is only limited by kinetics of cluster growth. Thus, nucleation rate is no longer increased by increasing concentration or lowering temperature, in agreement with experimental nucleation rates [18]. Based on the assumption that formation of crystal nuclei in the dense liquid phase is rate limiting, an improved kinetic rate law was presented [19]. These findings highlight that heterogeneous nucleants do not result in the lowering of the free energy barrier to induce nucleation, but instead in assisting the formation of ordered cluster by influencing the rate of nucleation [20, 21]. The most obvious role for heterogeneous nucleation is the stabilisation of an intermediate en-route to the right crystal structure [22]. This is very similar to the pathway followed by enzymes in stabilising a transition state and not the final products of the enzyme-catalysed reactions. 4 Both theories remain widely adopted. However, the two-step nucleation mechanism not only predicts more realistic nucleation rates, but also provides insight on the nuclei formation from solution [18-20, 22]. Towards developing mechanistic understanding on the role of different surface properties Surface Topography Surface Porosity Nucleants with pore diameter of nanometre length scale were employed for promoting nucleation of biological macromolecules [23, 24], crystallisation of different polymorphs of organic crystals, investigating nucleation kinetics of organic molecules [2], biomineralisation [7, 25] and nucleation of ice [26]. For biological macromolecules, it was hypothesised that a higher local supersaturation within the confinement resulted in a thermodynamic drive for nucleation within the pores. Here, nucleation follows two steps; first, capillary condensation of protein solution in the pores, followed by rapid nucleation. The maximum rate of nucleation was obtained when pore diameter is equivalent to the size of the protein’s critical nucleus [27]. The systematic use of different pore size with narrow size distribution [14], further confirms the existence of such a relationship. Such nanotemplates have the potential of selective nucleation for bioseparation. Surfaces exhibiting topological features have also been applied to controlling crystallisation of organic electronics. Bao’s group reported the use of rough patches of octadecyltriethoxysilane (OTS) functionalized dielectric surfaces (average roughness 10-15nm) for templating single-crystal growth of various organic semiconductors [28, 29]. For morphology control of solution processed solar cells and electronics, Treat et al. applied organic additives to control the nucleation density and domain size [30]. During material processing, these additives crystallise first to provide nanostructured nucleation templates and subsequently induce nucleation. The mechanism of these nanotemplates is probably 5 consistent with the capillary condensation picture discussed above, however, has not been investigated in this light. Crystallisation of organic molecules from a same solvent in nanoscale confinements demonstrated that crystal nucleation and polymorph selectivity are also affected by pore sizes. It was proposed that nanoscale confinement results in stabilising metastable crystal forms by melting point depression and that this effect is more dominant at lower crystal size [31]. Other applications include the use of porous metallic organic framework, modified acrylic copolymer or styrenic copolymer or combination of both [32]. Electrospun cellulose resins with rough surfaces [33] were used for crystallisation of inorganic salts containing calcium and magnesium ions from waters, a “template induced crystallisation” approach for domestic and industrial water softening. Employing Monte Carlo simulations, it was proposed that nucleation rates are theoretically maximum at an angle at which the crystal lattice matches the pore wedge angle [34]. On the basis of experimental evidences, angle-directed nucleation mechanism was proposed where an angle characteristic of the topological feature of the substrate controls nucleation in a minimum strain configuration. This demonstrates the geometrical match between nucleant surface and molecular arrangement in a crystal lattice [35-37]. Epitaxy Epitaxy is a mechanism responsible for nucleation and growth of many organic and inorganic compounds such as semi-conductors [38], pharmaceuticals [39], ice [1] and proteins [40]. It has been demonstrated that if the crystallising molecule is presented with the nucleant having similar unit cell parameters and molecular functionality, nucleant selective polymorphic control can be achieved. The proposed mechanism is that the nucleant stabilises the pre-nucleation aggregates by epitaxial ordering directed by lattice matching and the intermolecular interactions [11, 39, 41]. Recently, the epitaxial 6 effect was incorporated into predictions from crystal energy landscape for selective formation of a metastable polymorph [42]. Surface Chemistry Also relevant in nucleation is the specific chemical interaction between nucleant substrate and crystallising molecule, which may well dominate [43]. In solution phase crystallisation, when both the solute and solvent are polar, the polarisation effect governs the ability of solute molecule to adsorb on the nucleant surface. By adjusting nucleant surface potential, adsorption selectivity can be obtained resulting in surface induced/promoted nucleation phenomenon [44-46]. For organosilane grafted surfaces, the molecular interactions at the polymer-solute interfaces were reported to control nucleation of pure stable form or its nucleant kinetics. The governing surface specific electrostatic interactions involve mainly the hydrogen bonding, dipole moments or acid-base interactions between template surface functional end-groups and solute molecule [37, 47]. Surface chemistry has also played a critical role in controlling the morphology of organic semiconductor thin films, although mechanistic studies have been rare. Gundlach et al. reported crystallisation of fluorinated 5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT) by pentafluorobenzene thiol (PFBT) templated gold electrodes. The templating effect may be guided by the F-S or F-F interactions between diF-TES-ADT and PFBT [48]. Self-assembled monolayers on dielectric surfaces have been extensively used for facilitating the growth of the semiconductor layer [49-52]. The intermolecular interactions are typically non-specific in these cases since the SAM layers used are predominantly aliphatic. Amongst possible templating mechanisms are interfacial free energy matching [51, 53] and in some cases, epitaxy between the 2D lattice formed by crystalline SAM layer and the crystal lattice of the semiconducting layer [49]. Recently, organic small molecules that form an amorphous insulating layer between the semiconductor and the dielectric have been explored for controlling crystallisation of the semiconducting layer as well [54, 55]. 7 Parambil et al. investigated the effect of template surface chemistry and supersaturation on nucleation of organic molecules, reporting a template induced polymorphic occurrence domain (POD). The POD concept highlights the role of template surface chemistry in mediating preferential nucleation [56]. As depicted schematically in Fig 1, the metastable zone width, wherein crystallisation can occur is affected by a combination of i) solution properties [57], such as solvent and salt type, concentration and supersaturation, ii) having a nucleation promoter such as external stimulus (magnetic field, ultrasound, etc) or through surfaces/heteronucleants and iii) process conditions, influenced by hydrodynamics and mass transfer which may also affect rate of achieving supersaturation. Figure X: Crystallisation Triangle Nucleation Promoter Precipitation Controlled Crystallisation Zone Nucleation Promoter Solution Properties Process Conditions Figure 1: A diagram for the “Crystallisation Triangle” concept. 8 Combined Effect of Surface Topography and Surface Chemistry Recently Diao et al. investigated the combination of both surface chemistry and topography by employing different polymeric surfaces for investigating the nucleation kinetics of aspirin. Diao et al. reports that active polymer surfaces with nanoscale porosity were able to increase the nucleation of polar facets of aspirin by an order of magnitude [15]. Different Approaches using Combined Effect of Surface Porosity and Surface Chemistry Selective Nucleant Approach By employing surfaces with narrow pore size distribution and specific surface chemistry as nucleants, Shah et al. reported a selective nucleant approach demonstrating that nucleant with a pore diameter similar to the protein’s hydrodynamic diameter were successful in nucleation of a specific target protein. The selective nucleant approach was employed for crystallisation of a specific protein from a binary protein mixture [58], which is not possible using a nucleant with wide pore size distribution. Selective nucleation provides a means of developing crystallisation for bioseparation – biocrystallisation, potentially as an alternative downstream separation for biopharmaceuticals (Fig. 2). Recent success in crystallising monoclonal antibodies [59], and possibilities of scaling-up, suggests that biocrystallisation may be on the horizon [60]. The selective nucleant is developed on the basis of a relationship between the nucleant and solute surface properties. Mechanism proposed suggests that the functional end-groups on the surface plays a key role in attracting solute molecules to the template surface via electrostatic interaction, forming high dense metastable liquid phase in the close vicinity of the surface [58]. It is envisaged that the design of next generation of selective nucleants for protein crystallisation may include more complex chemistries such as amino-acid, peptides, proteins, in very much a lock and key model for docking specific protein regions (Fig. 3). Such selective nucleant approaches may also be applicable in a wide variety of 9 Figure X:such Outlook of crystallisation process and scale up using application areas, as crystallisation of organic small development molecule polymorphs, prevention of scaling by heterogeneous nucleation for bioseparation inorganic molecules, clathrate hydrate formation, etc. Selective Nucleant as Seeds – crystallising target molecule from protein mixture Developing Crystallisation for Bioseparation using Selective Nucleants 5-25 mL Crystallisation Condition Identification 2-10 mL Testing Condition with Seeds 50 - 500 mL Lab Scale Crystallisation > 5L Pilot & Commercial Scale Crystallisation Crystal Harvesting Figure 2: The development of crystallisation as a downstream separation step. 10 SAM/ organosilane Charged Surfaces #"#"#"#"#"#"#"#"#" +++++++++" Other functional nano-materials with selectivity Potential Approaches Current Approaches DNA Origami Epitaxy Selective Nucleant Soft Nucleant with target amino acids/ligand functionality Soft Templating Approach Figure X: Summary of Current and Potential Approaches for Heterogeneous Nuclean Figure 3: A summary of approaches for controlling nucleation with engineered heterogeneous nucleant. Soft Templating Approaches In contrast to the rigid materials with nanoscopic pores, soft templates have also recently been used to crystallise proteins. Polymer surfaces with porosity and surface functionality is well advanced by Drioli and co-workers [61], and more recently the use of molecularly imprinted polymers (MIPs) have also been used. The MIPs were imprinted with the target protein, which were then extracted from the imprinted polymer creating a cavity. These MIPs have been largely successful, reported to crystallise proteins at lower concentration compared to control glass and further improve diffraction quality of crystals [62]. Diao et al. proposed using polymer “microgels”, a biocompatible material, with tuneable microstructures [63-65]. This approach allows the control of solute concentration within the microgel via 11 thermodynamic partitioning. A composite of hydrogel with organic phase droplets of dissolved API, was shown to enable the control of crystal form, size and shape [66]. It is envisaged that DNA origami structures can also be utilised for the control of protein nucleation. The ability to design a wide variety of biocompatible polymer gel matrix ranging in mesh sizes and surface functionality, and DNA origami structures, holds great promise in de-bottlenecking protein crystallisation. Summary and Outlook In summary, developing heterogeneous nucleants for controlling crystallisation is a work in progress. Recent efforts highlight that the crystallisation community is focused on developing nucleants by rational design adopting the basis of a systematic understanding of target molecule and nucleant properties. While there has also been much progress in developing mechanistic understanding of heterogeneous nucleation, investigations have been mainly focused on small lab scale, with so far limited efforts in scale-up or process development. Interestingly, the application of heterogeneous nucleation is not limited to protein crystallisation, but could include the prevention of scaling in chemical process industries, water softening in domestic supplies, clathrate hydrate crystallisation for flow assurance in the energy sector, to cloud seeding in environmental management. Acknowledgements ZY acknowledges the Royal Academy of Engineering – Research Exchange China and India (RECI) programme (Reference: 1314RECI047). 12 References and Recommended Reading Papers of particular interest, published within the period of review, have been highlighted as: * of special interest ** of outstanding interest 1. Atkinson JD, Murray BJ, Woodhouse MT, Whale TF, Baustian KJ, Carslaw KS, Dobbie S, O'Sullivan D, and Malkin TL: The importance of feldspar for ice nucleation by mineral dust in mixed-phase clouds. Nature 2013, 498: 355-358. 2. Chen J, Sarma B, Evans JMB, and Myerson AS: Pharmaceutical Crystallization. Cryst. Growth Des. 2011, 11: 887-895.* Crystallisation is an essential downstream separation, purification step. This review covers many aspects of pharmaceutical crystallisation, including polymorph screening, process development for selected polymorph, outlook for continuous crystallisation, and challenges. 3. Diao Y, Shaw L, Bao Z, and Mannsfeld SCB: Morphology control strategies for solutionprocessed organic semiconductor thin films. Energy Environ. Sci. 2014, 7: 2145-2159. 4. Ruiz B, Coe BJ, Gianotti R, Gramlich V, Jazbinsek M, and Gunter P: Polymorphism, crystal growth and characterization of an organic nonlinear optical material: DAPSH. CrystEngComm 2007, 9: 772-776. 5. Hartel RW: Advances in Food Crystallization. Annu Rev Food Sci Technol. 2013, 4: 277-292.* This is a recent review, providing details of developments in characterising and controlling crystallisation within the subject area of food processing. 6. Smith AJ, Kavuru P, Arora KK, Kesani S, Tan J, Zaworotko MJ, and Shytle RD: Crystal Engineering of Green Tea Epigallocatechin-3-gallate (EGCg) Cocrystals and Pharmacokinetic Modulation in Rats. Mol. Pharmaceutics 2013, 10: 2948-2961. 7. Wang Y-W, Christenson HK, and Meldrum FC: Confinement Leads to Control over Calcium Sulfate Polymorph. Adv. Funct. Mater. 2013, 23: 5615-5623. 8. Meldrum FC and Cölfen H: Controlling Mineral Morphologies and Structures in Biological and Synthetic Systems. Chem. Rev. 2008, 108: 4332-4432.* This review provides very detailed description of many different approaches and mechanisms, for controlling mineral morphologies and structures in both bio-mineralisation and synthetic systems. Some of these approaches can be adopted by crystallisation of organic molecules and other applications. 9. Chayen NE: Turning protein crystallisation from an art into a science. Curr. Opin. Struct. Biol. 2004, 14: 577-583. 10. Granasy L, Podmaniczky F, Toth GI, Tegze G, and Pusztai T: Heterogeneous nucleation of/on nanoparticles: a density functional study using the phase-field crystal model. Chem. Soc. Rev. 2014, 43: 2159-2173.* 13 A recent review, providing an overview of recent developments in phase-field crystal modelling of heterogeneous nucleation, highlighting recent progress in mechanistic understanding of heterogeneous nucleation on the basis computations studies. 11. Chadwick K, Myerson A, and Trout B: Polymorphic control by heterogeneous nucleation - A new method for selecting crystalline substrates. CrystEngComm 2011, 13: 6625-6627. 12. Hutchins DO, Weidner T, Baio J, Polishak B, Acton O, Cernetic N, Ma H, and Jen AKY: Effects of self-assembled monolayer structural order, surface homogeneity and surface energy on pentacene morphology and thin film transistor device performance. J. Mater. Chem. C 2013, 1: 101-113. 13. McPherson A and Shlichta P: Heterogeneous and Expitaxial Nucleation of Protein Crystals on Mineral Surfaces. Science 1988, 239: 385-387. 14. Shah UV, Williams DR, and Heng JYY: Selective Crystallization of Proteins Using Engineered Nanonucleants. Cryst. Growth Des. 2012, 12: 1362-1369. 15. Diao Y, Myerson AS, Hatton TA, and Trout BL: Surface Design for Controlled Crystallization: The Role of Surface Chemistry and Nanoscale Pores in Heterogeneous Nucleation. Langmuir 2011, 27: 5324-5334. 16. Erdemir D, Lee AY, and Myerson AS: Nucleation of Crystals from Solution: Classical and Two-Step Models. Acc. Chem. Res. 2009, 42: 621-629.* An excellent review of current mechanistic understanding of nucleation, highlighting limitations of classical nucleation theory and why two step nucleation mechanism may provide more insight into kinetics of nucleation. 17. Wolde PRt and Frenkel D: Enhancement of Protein Crystal Nucleation by Critical Density Fluctuations. Science 1997, 277: 1975-1978. 18. Vekilov PG: The two-step mechanism of nucleation of crystals in solution. Nanoscale 2010, 2: 2346-2357.** This is an excellent perspective on two-step nucleation mechanism by one of the pioneers of the theory, who developed and provided experimental evidences of this mechanism. Other publications from this author are also must read to gain an insight to the two-step nucleation mechanism. 19. Vekilov PG: Crystal nucleation: Nucleus in a droplet. Nat. Mater. 2012, 11: 838-840. 20. Harano K, Homma T, Niimi Y, Koshino M, Suenaga K, Leibler L, and Nakamura E: Heterogeneous nucleation of organic crystals mediated by single-molecule templates. Nat. Mater. 2012, 11: 877-881. 21. Dey A, Bomans PHH, Müller FA, Will J, Frederik PM, de With G, and Sommerdijk NAJM: The role of prenucleation clusters in surface-induced calcium phosphate crystallization. Nat. Mater. 2010, 9: 1010-1014.** 14 This paper provides experimental insights to nucleation via prenucleation metastable clusters. The idea of using interfacial properties to induce nucleation of high dense liquid phase or prenucleation cluster, controlling kinetics is presented here. 22. Pouget EM, Bomans PHH, Goos JACM, Frederik PM, de With G, and Sommerdijk NAJM: The Initial Stages of Template-Controlled CaCO3 Formation Revealed by Cryo-TEM. Science 2009, 323: 1455-1458. 23. Khurshid S, Saridakis E, Govada L, and Chayen NE: Porous nucleating agents for protein crystallization. Nat. Protoc. 2014, 9: 1621-1633. 24. Saridakis E and Chayen NE: Towards a 'universal' nucleant for protein crystallization. Trends Biotechnol. 2009, 27: 99-106.** This review discusses heterogeneous nucleant based approaches, providing a historical review for protein nucleation, including epitaxial, charged surfaces, and porous materials, coining concept of ‘universal nucleant’. 25. Stephens CJ, Ladden SF, Meldrum FC, and Christenson HK: Amorphous Calcium Carbonate is Stabilized in Confinement. Adv. Funct. Mater. 2010, 20: 2108-2115. 26. Scherer GW: Crystallization in pores. Cem. Concr. Res. 1999, 29: 1347-1358. 27. van Meel JA, Sear RP, and Frenkel D: Design Principles for Broad-Spectrum Protein-Crystal Nucleants with Nanoscale Pits. Phys. Rev. Lett. 2010, 105: 205501.** The authors have highlighted design principles for porous nucleants, highlighting that highest rate of nucleation can be obtained on the nucleants with pore diameter equal to critical nuclei. 28. Briseno AL, Mannsfeld SCB, Ling MM, Liu S, Tseng RJ, Reese C, Roberts ME, Yang Y, Wudl F, and Bao Z: Patterning organic single-crystal transistor arrays. Nature 2006, 444: 913-917. 29. Mannsfeld SCB, Briseno AL, Liu S, Reese C, Roberts ME, and Bao Z: Selective Nucleation of Organic Single Crystals from Vapor Phase on Nanoscopically Rough Surfaces. Adv. Funct. Mater. 2007, 17: 3545-3553. 30. Treat ND, Nekuda Malik JA, Reid O, Yu L, Shuttle CG, Rumbles G, Hawker CJ, Chabinyc ML, Smith P, and Stingelin N: Microstructure formation in molecular and polymer semiconductors assisted by nucleation agents. Nat. Mater. 2013, 12: 628-633. 31. Ha J-M, Hamilton BD, Hillmyer MA, and Ward MD: Phase Behavior and Polymorphism of Organic Crystals Confined within Nanoscale Chambers. Cryst. Growth Des. 2009, 9: 47664777. 32. Weaver JD, Tang T, and Nguyen PD, Method and System for Servicing a Wellbore, 2014, United States Patent and Trademark Office. p. 15. 33. Rodríguez K, Renneckar S, and Gatenholm P: Biomimetic Calcium Phosphate Crystal Mineralization on Electrospun Cellulose-Based Scaffolds. ACS Appl. Mater. Interfaces 2011, 3: 681-689. 15 34. Page AJ and Sear RP: Crystallization Controlled by the Geometry of a Surface. J. Am. Chem. Soc. 2009, 131: 17550-17551. 35. Diao Y, Harada T, Myerson AS, Alan Hatton T, and Trout BL: The role of nanopore shape in surface-induced crystallization. Nat. Mater. 2011, 10: 867-871. 36. Sear RP: Crystal nucleation: In a tight corner. Nat. Mater. 2011, 10: 809-810. 37. López-Mejías V, Myerson AS, and Trout BL: Geometric Design of Heterogeneous Nucleation Sites on Biocompatible Surfaces. Cryst. Growth Des. 2013, 13: 3835-3841. 38. Cheng SF, Gao L, Woo RL, Pangan A, Malouf G, Goorsky MS, Wang KL, and Hicks RF: Selective area metalorganic vapor-phase epitaxy of gallium arsenide on silicon. J. Cryst. Growth 2008, 310: 562-569. 39. Chadwick K, Chen J, Myerson AS, and Trout BL: Toward the Rational Design of Crystalline Surfaces for Heteroepitaxy: Role of Molecular Functionality. Cryst. Growth Des. 2012. 40. McPherson A and Shlichta PJ: Facilitation of the growth of protein crystals by heterogeneous/epitaxial nucleation. J. Cryst. Growth 1987, 85: 206-214. 41. Quon JL, Chadwick K, Wood GPF, Sheu I, Brettmann BK, Myerson AS, and Trout BL: Templated Nucleation of Acetaminophen on Spherical Excipient Agglomerates. Langmuir 2013, 29: 3292-3300. 42. Arlin J-B, Price LS, Price SL, and Florence AJ: A strategy for producing predicted polymorphs: catemeric carbamazepine form V. Chem. Commun. 2011, 47: 7074-7076. 43. Olmsted BK and Ward MD: The role of chemical interactions and epitaxy during nucleation of organic crystals on crystalline substrates. CrystEngComm 2011, 13: 1070-1073.** The combined effect of nucleant epitaxy and functionality is highlighted to control nucleation of organic crystals. Other publications from Ward et al. also provide insight to polymorph selectivity using nanoscale pits. 44. Kwokal A and Roberts KJ: Direction of the polymorphic form of entacapone using an electrochemical tuneable surface template. CrystEngComm 2014, 16: 3487-3493. 45. Kwokal A, Nguyen TTH, and Roberts KJ: Polymorph-Directing Seeding of Entacapone Crystallization in Aqueous/Acetone Solution Using a Self-Assembled Molecular Layer on Au (100). Cryst. Growth Des. 2009, 9: 4324-4334. 46. Urbanus J, Laven J, Roelands CPM, ter Horst JH, Verdoes D, and Jansens PJ: Template Induced Crystallization: A Relation between Template Properties and Template Performance. Cryst. Growth Des. 2009, 9: 2762-2769. 47. Curcio E, López-Mejías V, Di Profio G, Fontananova E, Drioli E, Trout BL, and Myerson AS: Regulating Nucleation Kinetics through Molecular Interactions at the Polymer–Solute Interface. Cryst. Growth Des. 2013, 14: 678-686. 16 48. Gundlach DJ, Royer JE, Park SK, Subramanian S, Jurchescu OD, Hamadani BH, Moad AJ, Kline RJ, Teague LC, Kirillov O, Richter CA, Kushmerick JG, Richter LJ, Parkin SR, Jackson TN, and Anthony JE: Contact-induced crystallinity for high-performance soluble acenebased transistors and circuits. Nat. Mater. 2008, 7: 216-221. 49. Anokhin DV, Leshanskaya LI, Piryazev AA, Susarova DK, Dremova NN, Shcheglov EV, Ivanov DA, Razumov VF, and Troshin PA: Towards understanding the behavior of indigo thin films in organic field-effect transistors: a template effect of the aliphatic hydrocarbon dielectric on the crystal structure and electrical performance of the semiconductor. Chem. Commun. 2014, 50: 7639-7641. 50. Lee WH, Cho JH, and Cho K: Control of mesoscale and nanoscale ordering of organic semiconductors at the gate dielectric/semiconductor interface for organic transistors. J. Mater. Chem. 2010, 20: 2549-2561. 51. Lee SS, Tang SB, Smilgies D-M, Woll AR, Loth MA, Mativetsky JM, Anthony JE, and Loo YL: Guiding Crystallization around Bends and Sharp Corners. Adv. Mater. 2012, 24: 26922698. 52. Dhagat P, Haverinen HM, Kline RJ, Jung Y, Fischer DA, DeLongchamp DM, and Jabbour GE: Influence of Dielectric Surface Chemistry on the Microstructure and Carrier Mobility of an n-Type Organic Semiconductor. Adv. Funct. Mater. 2009, 19: 2365-2372. 53. Zhang C, Du C, Yan H, Yuan S, and Chi L: Influence of self-assembled monolayers on the growth and crystallization of rubrene films: a molecular dynamics study. RSC Adv. 2013, 3: 15404-15410. 54. Kwon S, Yu K, Kweon K, Kim G, Kim J, Kim H, Jo Y-R, Kim B-J, Kim J, Lee SH, and Lee K: Template-mediated nano-crystallite networks in semiconducting polymers. Nat. Commun. 2014, 5. 55. Li Z, Du J, Tang Q, Wang F, Xu J-B, Yu JC, and Miao Q: Induced Crystallization of Rubrene in Thin-Film Transistors. Adv. Mater. 2010, 22: 3242-3246. 56. Parambil JV, Poornachary SK, Tan RBH, and Heng JYY: Template-induced polymorphic selectivity: the effects of surface chemistry and solute concentration on carbamazepine crystallisation. CrystEngComm 2014, 16: 4927-4930. 57. Tosi G, Fermani S, Falini G, Gavira JA, and Garcia Ruiz JM: Hetero- vs Homogeneous Nucleation of Protein Crystals Discriminated by Supersaturation. Cryst. Growth Des. 2011, 11: 1542-1548.** In addition to employing interfacial interactions to control nucleation, this paper coins an interesting concept (crystallisation mushroom) suggesting that any nucleant can only be effective in certain supersaturation window, which is decided by the degree of supersaturation as well as rate of achieving supersaturation. 58. Shah UV, 3D Nanotemplates for Protein Crystallisation, PhD Thesis, 2012, Imperial College London: London. p. 184-194. 17 59. Smejkal B, Agrawal NJ, Helk B, Schulz H, Giffard M, Mechelke M, Ortner F, Heckmeier P, Trout BL, and Hekmat D: Fast and scalable purification of a therapeutic full-length antibody based on process crystallization. Biotechnol. Bioeng. 2013, 110: 2452-2461. 60. Cramer SM and Holstein MA: Downstream bioprocessing: recent advances and future promise. Curr. Opin. Chem. Eng. 2011, 1: 27-37. 61. Drioli E, Di Profio G, and Curcio E: Progress in membrane crystallization. Curr. Opin. Chem. Eng. 2012, 1: 178-182. 62. Saridakis E, Khurshid S, Govada L, Phan Q, Hawkins D, Crichlow GV, Lolis E, Reddy SM, and Chayen NE: Protein crystallization facilitated by molecularly imprinted polymers. Proc. Natl. Acad. Sci. U.S.A. 2011, 108: 11081-11086. 63. Diao Y, Helgeson ME, Myerson AS, Hatton TA, Doyle PS, and Trout BL: Controlled Nucleation from Solution Using Polymer Microgels. J. Am. Chem. Soc. 2011, 133: 3756-3759. 64. Eral HB, López-Mejías V, O’Mahony M, Trout BL, Myerson AS, and Doyle PS: Biocompatible Alginate Microgel Particles as Heteronucleants and Encapsulating Vehicles for Hydrophilic and Hydrophobic Drugs. Cryst. Growth Des. 2014, 14: 2073-2082. 65. Profio GD, Polino M, Nicoletta FP, Belviso BD, Caliandro R, Fontananova E, Filpo GD, Curcio E, and Drioli E: Tailored Hydrogel Membranes for Efficient Protein Crystallization. Adv. Funct. Mater. 2014, 24: 1582-1590. 66. Eral HB, O’Mahony M, Shaw R, Trout BL, Myerson AS, and Doyle PS: Composite Hydrogels Laden with Crystalline Active Pharmaceutical Ingredients of Controlled Size and Loading. Chem. Mater. 2014, 26: 6213-6220.** Recent report proposing biocompatible nucleants, which can control not only nucleation kinetics, polymorphic form, but also has potential of controlling particle size in nanoscale. This manuscript reports on the potential of crystallisation and formulation development within composite hydrogels. 18