Modulation of apatite crystal growth on Bioglass (R) by recombinant amelogenin

The effects of a recombinant mouse amelogenin (rM179) on the growth of apat ite crystals nucleated on a bioactive glass (45S5 type Bioglass(R)) surface were investigated with a view to gaining a better understanding of the rol e of amelogenin protein in tooth enamel formation and of its potential appl ication in the design of novel enamel-like biomaterials. Bioglass(R) discs were incubated in phosphate-buffered saline (PBS) to preform a calcium phos phate surface layer and subsequently immersed in blank, bovine serum albumi n (BSA)- and rM179-containing supersaturated calcification solutions (SCSB, SCSBSA and SCSrM179), respectively. Calcium phosphate layers formed on all the treated samples and were characterized to be apatite by X-ray diffract ion and Fourier transmission infrared spectrophotometry. Under scanning ele ctron microscopy, plate-shaped crystals (similar to 50 nm thick and 300-600 nm across) were observed on the samples after PBS incubation. The crystals grown from SCSB were of the typical plate shape except for an increased th ickness, while needle-shaped crystals (200-300 nm long and 50-70 nm thick) were precipitated on the SCSBSA-immersed samples. Interestingly, it was fou nd that the crystals deposited on the SCSrM179-immersed samples adopted an elongated, curved shape (similar to 500 nm long and similar to 120 nm thick ). Further TEM observations showed that the crystals generated by the SCSrM 179 immersion appeared to be composed of bundles of lengthwise crystals (15 -20 nm thick) orientated parallel to one another, much alike the long and t hin crystals observed in the very early stage of enamel formation. The sign ificant modulation by the rM179 protein of apatite crystal growth is quite different from the overall inhibition observed by BSA and most likely is re levant to the specific function of the amelogenin matrix in controlling ena mel crystal growth in vivo. (C) 1999 Elsevier Science Ltd. All rights reser ved.