Calcium Phosphate Mineralization beneath a Polycationic Monolayer at the Air-Water Interface

• Published in: Macromolecular bioscience Vol. 10; no. 9; pp. 1084 - 1092
• Main Authors: Junginger, Mathias, Kita-Tokarczyk, Katarzyna, Schuster, Thomas, Reiche, Jürgen, Schacher, Felix, Müller, Axel H. E., Cölfen, Helmut, Taubert, Andreas
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 09.09.2010; WILEY‐VCH Verlag
• Subjects: Air; biomimetic; Biomimetics; biomineralization; calcium phosphate; Calcium Phosphates - chemistry; Hydrogen-Ion Concentration; Microscopy, Electron, Transmission; Nanoparticles - chemistry; Polyamines - chemistry; polymer monolayer; Water
• ISSN: 1616-5187; 1616-5195; 1616-5195
• DOI: 10.1002/mabi.201000093

The self‐assembly of the amphiphilic block copolymer poly(n‐butyl methacrylate)‐block‐poly[2‐(dimethylamino)ethyl methacrylate] at the air–water interface has been investigated at different pH values. Similar to Rehfeldt et al. (J. Phys. Chem. B 2006, 110, 9171), the subphase pH strongly affects the monolayer properties. The formation of calcium phosphate beneath the monolayer can be tuned by the subphase pH and hence the monolayer charge. After 12 h of mineralization at pH 5, the polymer monolayers are still transparent, but transmission electron microscopy (TEM) shows that very thin calcium phosphate fibers form, which aggregate into cotton ball‐like features with diameters of 20 to 50 nm. In contrast, after 12 h of mineralization at pH 8, the polymer film is very slightly turbid and TEM shows dense aggregates with sizes between 200 and 700 nm. The formation of calcium phosphate is further confirmed by Raman and energy dispersive X‐ray spectroscopy. The calcium phosphate architectures can be assigned to the monolayer charge, which is high at low pH and low at high pH. The study demonstrates that the effects of polycations should not be ignored if attempting to understand the colloid chemistry of biomimetic mineralization. It also shows that basic block copolymers are useful complementary systems to the much more commonly studied acidic block copolymer templates. Polycationic interfaces are useful model systems to better understand calcium phosphate mineralization under biomimetic conditions. Calcium phosphate is an important but complex biomineral. Here, the potential of amphiphilic block copolymer monolayers with a cationic block to mineralize calcium phosphate at the air–water interface is evaluated at different pH values, including non‐physiological conditions. The results suggest that the degree of charge in the polycations has a major influence on calcium phosphate mineralization.