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Interaction of Dendrimers (Artificial Proteins) with Biological Hydroxyapatite Crystals

¹ University of Michigan School of Dentistry, 1011 N. University, Ann Arbor, MI 48109-1078;
² University of Michigan Department of Chemistry;
³ University of Michigan Department of Physics;
⁴ University of Michigan, Internal Medicine; and
⁵ Center for Biologic Nanotechnology;

View larger version (74K): [in a new window]   Figure 1. Structure and size comparison of polyamidoamine dendrimer. (a) Polyamidoamine (PAMAM) dendrimers, also known as "artificial proteins", with a well-defined structure, can act as a nanoprobe to probe specific surface domains on the surfaces of enamel crystals. Three types of PAMAM dendrimers, with amine-, carboxylic-acid-, and acetamide-capped surfaces, respectively, were used in this study. Tapping-mode AFM images of enamel crystals (control). (b) Enamel crystals on a mica surface, imaged in air prior to the introduction of dendrimers. (c) Enamel crystals on a mica surface, imaged in air after the sample (b) was rinsed with distilled water (pH 7.4) and dried in a desiccator. AFM images show the topographical image (1 µm x 1 µm) on the left, and phase image (1 µm x 1 µm) on the right.

View larger version (68K): [in a new window]   Figure 2. Tapping-mode AFM images of enamel crystals after interaction with acetamide-capped PAMAM dendrimers. A solution containing G7 PAMAM dendrimers with an acetamide (-NHC(O)CH3)-capped surface was allowed to flow over the crystals and allowed to remain for 2 min before being wicked off. The sample was dried in a desiccator before being imaged in air. (a) After exposure to 1 µL 7-nM dendrimer solution. (b) After exposure to 5 µL 7-nM dendrimer solution. (c) After sample (b) was rinsed with distilled water (pH 7.4). AFM images show the topographical image (1 µm x 1 µm) on the left, and phase image (1 µm x 1 µm) on the right.

View larger version (109K): [in a new window]   Figure 3. Tapping-mode AFM images of enamel crystals after interaction with carboxylic-acid-capped PAMAM dendrimers. A solution containing G7 PAMAM dendrimers with carboxylic-acid (-COOH)-capped surface was allowed to flow over the crystals and allowed to remain for 2 min before being wicked off. The sample was dried in a desiccator before being imaged in air. (a) Crystal surfaces after exposure to 1 µL 570-nM dendrimer solution (arrows denote dendrimers at crystal interface). (b) Crystal surfaces after exposure to 1.5 µL 285-nM dendrimer solution (arrows denote dendrimers on crystal surface). (c) Crystal surfaces after exposure to 2 µL 570-nM dendrimer solution. (d) After sample (c) was rinsed with distilled water (pH 7.4). (e) After sample (d) was rinsed with 100 mM phosphate buffer (pH 7.4). AFM images show the topographical image (1 µm x 1 µm) on the left, and phase image (1 µm x 1 µm) on the right.

View larger version (92K): [in a new window]   Figure 4. Tapping-mode AFM images of enamel crystals after interaction with amine-capped PAMAM dendrimers. A solution of G7 PAMAM dendrimers with an amine (-NH2)-capped surface was allowed to flow over the crystals and allowed to remain for 2 min before being wicked off. The sample was dried in a desiccator before being imaged in air. (a) Crystal surfaces after exposure to 1 µL 78-nM dendrimer solution. (b) Crystal surfaces after exposure to 2 µL 78-nM dendrimer solution. (c) After the distilled-water-washed sample was rinsed with 100 mM phosphate buffer (pH 7.4). (d) After the sample (c) was rinsed with 200 mM phosphate buffer (pH 7.4). AFM images show the topographical image (1 µm x 1 µm) on the left, and phase image (1 µm x 1 µm) on the right.