Biological Samples

In the dental field enamel and dentin are materials under investigation. Effects of demineralization, for example, by soft drinks on the natural tooth structure, and improvements of resin adhesion important in dental therapy were studied.

Topographical changes of human teeth in various liquids were characterized in [223]. The initially smooth and finely grained surfaces were changed to a rougher and more coarsely grained surface. Dissolution rates for soda pops with pH values between 4 and 5 were calculated to be 3 mm/year in contrast to water with a rate of 0.4 mm/year. The change in mechanical properties of tooth enamel induced by demineralization via soft drinks was investigated in [224]. The changes in hardness are the first step in the dissolution process. The influence of different drinks (orange juice, a black currant drink, and water) could be determined in hardness and topography, where orange juice showed the strongest demineralization. A small critical discussion about the applicability of the model of enamel erosion characterized via SFM topography measurements is given in [225].

The influence of sodium hypochloride on dentin and dentin collagen was characterized by checking on the topography and the hardness respectively the reduced elastic modulus via an SFM in contact mode respectively a nanoindenter [226]. Dentin was removed, leaving a remnant collagen matrix and resulting in a hardness of 75% of its original value. The enhanced roughness could provide a better bonding substrate because of the enhanced surface area. The mechanism of the bonding via the adhesive Gluma consisting of glutardialdehyde and hydroxyethylmethacrylate (HEMA) could be elucidated with SFM imaging of the interaction taking place upon introduction of the adhesive to the tooth hard tissue. It forms a solid layer covering the dentin tubules. The mechanism of the amide-induced polymerization of aqueous HEMA glutardialdehyde mixtures could be confirmed by SFM [227]. Other similar SFM investigations on dentin are published in [107] and a detailed review of characterization of dentin, enamel, and collagen covering as well macroscopical features is given in [120]. The ultrastructure and nanoleakage of dentin bonding by the use of a two-step, polyalkenoic acid-containing, self-priming dentin adhesive in human molars was observed by TEM [228] to also check the effect of a 5% sodium hypochlorite solution (NaOCl) treatment. The NaOCl should remove the collagen fibrils at demineralized dentin and so may facilitate the infiltration of adhesive resins into a dentin substrate. To get a comparison, dentin was also acid-etched by 35% H3PO4; the leakage manifestations were similar for both treatments. So no additional advantage in using NaOCl with the used adhesives was found.

Some final features of surface investigations by nanoana-lytical tools discussed in the remainder of this section show in which broad range of biologically modified surfaces scanning probe techniques can be used. These studies include molecular layers like lipids or proteins and extend to cellular arrangements. They are only a small selection showing the principal ability of the technique.

The activity of a liposome layer with ganglioside G(M1) was tested with SFM [229]. Supported phospholipid bilayers (SPBs) as model substrates for cell membranes are imaged with SFM in [230]. The height, adhesion, and friction of mixed phospholipid layers is monitored in [231].

Microelastic mapping of living cells was done by SFM [28, 232].

A recent overview of the characterization of bacterial biofilms is given in [163].

Still a lot of experiments were done in ambient conditions and biological materials such as hexagonal packed intermediate (HPI) layers, DNA, tobacco mosaic virus, and collagen deposited on various substrates were imaged with noncon-tact dynamic force modes with little destruction but not in native states [233].

STM as well is usually used for investigations of biological films in air, leaving a change in structure. Pictures could be taken from C-phycocyanin (C-PC) which was isolated from the blue-green alga Spirulina platensis [234], and tobacco mosaic virus [235].

Nonhuman hard tissue like abalone nacre [236] was imaged and mineralization pathways revealed to form single crystals [237], and the elasticity of cow cartilage was tested [28].

The magnetic force from a magnetotactic bacterium [238] could be imaged with the magnetic force mode with SFM. Membrane deformation of living glial cells [239] or fibrob-lasts [240] were done via SFM. Other measurements are mentioned in [241] where local elastic properties respectively Young's modulus were mapped via force mapping.

The viscous properties of cells have been investigated on kidney epithelial cells with laser tracking microrheol-ogy. Comparisons with other authors are given, revealing cytoplasmic viscosities that range for different experiments within five orders of magnitude around 2-103 Pas [110]. Also viscous properties of fibroblasts were measured with magnetic bead microrheometry [109].

An overview of renal cell characterization with the SFM is given in [242]. Immobilized antibodies have been characterized by SECM to monitor the active binding sites [243].

Microelastic properties of bone marrow (cow tibia) were measured via SFM in [244].

This demonstrates that nanoanalytical tools not only are useful for characterizing the pure biomaterial surface alone but are also helpful for investigating surfaces in contact with biological materials of all kinds.

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