The nanoindentation technique, known also as instrumented indentation, has been widely accepted as a tool for the mechanical characterization of dental cement composites, and micro-devices as polymeric microspheres. The common thread through these two field is the characteristic magnitude of forces and displacements. The only method to characterize the mechanical behavior of microspheres is the nanoindentaiton, due to their reduced size. On the other side the cements used in dentistry are applied in thin films between a metallic support and the prosthetic crown. However, static protocols that have been developed for metals or alloys, neglecting the viscous nature of these composites, are currently adopted in a very large body of literature. In this study we (1) investigate how the viscous nature of dental composites could corrupt nanoindentation tests, and (2) identify an appropriate protocol that reduces the influence of the viscous, time dependent phenomenon during nanoindentation. Here three different commercial dental cements were tested: Harvard, Telio C.S and, Temp Bond. Static and quasi-static tests were performed. The creep data recorded during the hold phase of the static tests were fit with the Burgers model, by adding a slider. Static tests highlighted the viscoelastoplastic nature of cement composites, indicating a strong correlation between the strain rate imposed during the loading phase and the creep rate recorded in the hold phase. The experiments revealed that the viscous effect can be markedly minimized by applying the quasi-static approach. In this study we proposed a nanoindentation-based, quasi-static approach to minimize viscous effects of dental cement composites. In particular, it was demonstrated that the proposed approach is effective in minimizing the time-dependent phenomena during the unloading phase of the test. Moreover, a viscoelatoplastic model(accounting for nanoindentation test size-dependent output) wassuccessfully adopted to fit the experimental data. This model in now suitable for computer aided simulations of the indentation process making it possible to evaluate at which level viscous phenomena could affect the estimation of the contact area. Polymeric microspheres are largely studied for biomedical applications as, e.g., embolic agents to treat hyper-vascular tumors, or in tissue engineering. The rationale of the study is understand how the used polymers and the presence of the cross-linker influence the mechanical properties of the microspheres and therefore the effectiveness in properly release drugs. The composition of the polymeric microspheres, influences only their mechanical properties. Drug release experiments, performed by using methylene blue clearly indicate that the time course of the release of the therapeutic agent strongly depends on the used polymer(s). blending natural polymers and adding genipin as natural cross-linker could lead the production of natural microspheres with adjustable mechanical properties, suitable for drug transport and delivery. Technically, nanoindentation was applied on microspheres of size in the range 20-70 μm. The mechanical characterization highlighted a viscous-elastic behavior of microspheres, with an increasing area of the characteristics hysteresis loops when the genipin concentration increases. Moreover, on measured load-displacement data, the Hertz model was applied to estimate the Young’s modulus. A protocol for the mechanical characterization of polymeric microspheres used for drug delivery will allow: (1) to support their design phase and (2) to improve their effectiveness in targeting the release of drugs.
MECHANICAL CHARACTERIZATION OF MATERIALS AND NANO-DEVICESO F BIOMEDICAL INTEREST THROUGH NANOINDENTATION TEST / Serino, Gianpaolo. - (2018 May 03).
|Titolo:||MECHANICAL CHARACTERIZATION OF MATERIALS AND NANO-DEVICESO F BIOMEDICAL INTEREST THROUGH NANOINDENTATION TEST|
|Data di pubblicazione:||3-mag-2018|
|Appare nelle tipologie:||8.1 Doctoral thesis Polito|
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