DYNAMIC MECHANICAL ANALYSISsixties when commercial instruments became more user-friendly. About 1966, Gillham developed the TBA (10) and started the modern period of DMA. In 1971, Starita and Macosko (11) built a DMA that measured normal forces and from this came the Rheometrics Corporation. In 1976, Bohlin also developed a commercial DMA and started Bohlin Rheologia. Both instruments used torsional geometry. The early instruments were, regardless of manufacturer, difficult to use, slow, and limited in their ability to process data. In the late seventies, Murayani (12) and Read and Brown (13) wrote books on the uses of DMA for material characterization. Several thermal and rheological instrument companies introduced DMA's in the same time period, and currently most thermal and rheological vendors offer some type of DMA. Polymer Labs offered a dynamic mechanical thermal analyzer (DMTA using an axial geometry in the early 1980s. This was soon followed by an instrument from Du Pont. Perkin-Elmer developed a controlled stress analyzer based on their thermomechanical analyzer (TMA) technology, which was designed for increased low-end sensitivity. Triton Technologies, acquired by Mettler Toledo in 2010, developed a very easy to use design that formalized both immersion and humidity methods. On the high force end of applications, Mettler Toledo also makes an instrument capable of 40 N loads and both Gabo and MetaVib work exclusively in high load instruments. Small vendors include Hitachi, Bosch, and others. The competition between vendors has led to easier to use, faster, and less expensive instruments. The revolution in computer technology, which has so affected the laboratory, changed the latter, and DMA of all types became more user-friendly as computers and software evolved. This movement to easier to use instruments has led to more use in quality control and the development of ASTM standards (14).

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Fundamental aspects of biomineralization may be important in order to understand and improve calcification onto the surface of biomaterials. The biomineralization process is mainly followed in vitro by assessing the evolution of the apatite layer that is formed upon immersion of the material in Simulated Body Fluid (SBF). In this work we propose an innovative methodology to monitor apatite deposition by looking at the evolution of the mechanical/viscoelastic properties of the sample while immersed in SBF, using non-conventional dynamic mechanical analysis (DMA) performed under distinct displacement amplitudes (d). The biomimetic biomineralization process in composite membranes of chitosan (CTS) with Bioglass® (BG) was followed by measuring the change of the storage modulus, E′, and the loss factor, tan δ, at 37°C and in SBF, both online (d = 10 μm and d = 30 μm) and offline (d = 0 μm). The online experiments revealed that the E′ decreased continuously up in the first hours of immersion in SBF that should be related to the dissolution of BG particles. After that, an increase of the stiffness was verified due to the apatite deposition. SEM/EDS observations upon 24 h of immersion in SBF showed higher development of apatite deposition with increasing displacement amplitude.