Optical tweezers were used to study the interaction and attachment of human bone cells to various types of medical implant materials. Ideally, the implant should facilitate cell attachment and promote migration of the progenitor cells in order to decrease the healing time. It is therefore of interest, in a controlled manner, to be able to monitor the cell adhesion process. Results from such studies would help foresee the clinical outcome of integrating medical implants. The interactions between two primary cell culture models, human gingival fibroblasts and bone forming human osteoblast cells, and three different implant materials, glass, titanium, and hydroxyapatite, were studied. A novel type of optical tweezers, which has a newly designed quadrant detector and a powerful 3 W laser was constructed and force calibrated using two different methods: one method in which the stiffness of the optical trap was obtained by monitoring the phase lag between the trap and the moved object when imposing a forced oscillation on the trapped object and another method in which the maximum trapping force was derived from the critical velocity at which the object escapes the trap. Polystyrene beads as well as cells were utilized for the calibrations. This is the first time that cells have been used directly for these types of force calibrations and, hence, direct measurements of forces exerted on cells can be performed, thus avoiding the difficulties often encountered when translating the results obtained from cell measurements to the calibrations obtained with reference materials. This more straightforward approach represents an advantage in comparison to established methods.

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The observed junction between α-CuInSe2 and the In-rich compositions in the β-phase domain (e.g. CuIn3Se5) appears to play an important role in the photovoltaic process [1]. There remain, however, inconsistencies and uncertainties about the boundary and structure of this phase. In general the structure of this phase belongs to defect tetrahedral family of structures [2], which can be described as normal tetrahedral structures with a certain fixed number of unoccupied structure sites. In this work, the local structures of various (Cu2Se)x(In2Se3)1−x semiconductor alloys in the β-phase domain were studied by Extended X-ray Absorption Fine Structure (EXAFS) and the results were compared to those for the α-CuInSe2 phase. The long- range order of these compositions was studied by X-Ray powder Diffraction (XRD) and electron diffraction. It was found the local structures of these compounds are well defined. These compounds, however, could not be well described by any long-range order structure model, especially the selenium position. First-principles band structure calculations were performed to assist in assigning crystal structures to CuInSe2, CuIn3Se5 and CuIn5Se8. The calculations indicated that the local environments of these compounds are well defined. Their long-range order might depend sensitively on growth history and the configurational entropies as suggested by the similar formation energies of several possible crystal structures for CuIn3Se5 and CuIn5Se8.