Abstract:

A promising route to the fabrication of biomimetic coatings for artificial implants is the deposition of org./inorg. composite materials consisting of polyelectrolyte multilayers alternating with layers of "in situ" grown calcium phosphate crystals. To facilitate understanding of the underlying mechanisms, in this paper we discuss the influence of polyelectrolytes (PEs), polystyrene sulfonate (PSS), poly-L-lysine (PLL), and poly-L-glutamic acid (PGA) on the formation and properties of amorphous calcium phosphate (ACP) and on the nucleation and growth morphol. of the cryst. phase. PH vs. time curves revealed three distinct pptn. events, i.e., (I) pptn. of ACP, (II) secondary pptn. of a cryst. phase upon the amorphous precursor, and (III) soln.-mediated phase transformation and crystal growth. Finally, cryst. mixts. with low Ca/P molar ratios (1.39), consisting of octacalcium phosphate crystals and small amts. of apatite, were obtained. From the pH vs. time curves, the induction time, ti, preceding crystal nucleation was detd. All PEs at low concns. induced and at high concns. inhibited nucleation. The efficiency of induction increased in the order: LMw PGA equiv. HMw PGA \textless LMw PLL \textless HMw PLL \textless PSS, while the inhibition efficiency increased as LMw PLL equiv. HMw PLL \textless PSS \textless LMw PGA \textless HMw PGA. ACP particles formed in the presence of PE were smaller and less aggregated and had a higher surface charge than in the controls. All investigated PEs also inhibited growth of the cryst. phase in a nonspecific way. [on SciFinder(R)]