Abstract
We present a new thermomechanical method and a platform to measure the phase transition temperature at microscale. A thin film metal sensor on a membrane simultaneously measures both temperature and mechanical strain of the sample during heating and cooling cycles. This thermomechanical principle of operation is described in detail. Physical hydrogel samples are prepared as a disc-shaped gels (200 μm thick and 1 mm diameter) and placed between an on-chip heater and sensor devices. The sol-gel transition temperature of gelatin solution at various concentrations, used as a model physical hydrogel, shows less than 3% deviation from in-depth rheological results. The developed thermomechanical methodology is promising for precise characterization of phase transition temperature of thermogels at microscale.
Highlights
In biomedical and pharmaceutical applications, thermosensitive hydrogel systems are widely used to deliver various bioactive agents via a thermally triggered transition as the physical form changes from solution to gel [1,2,3,4]
The operation of the experimental setup and accuracy of the sensor are demonstrated by measuring the phase transition temperature of a purified wax and comparing with the standard differential scanning calorimetry (DSC) measurement result
The result shows the phase transition temperature measured by the micro-thermomechanical method agrees with the DSC method
Summary
In biomedical and pharmaceutical applications, thermosensitive hydrogel systems are widely used to deliver various bioactive agents via a thermally triggered transition as the physical form changes from solution to gel [1,2,3,4]. The thermally triggered transition can be specified as the gelation temperature, which depends on various factors such as the rate of temperature change, the concentration, and the chemical and physical structures of the hydrogel [4, 5]. Because the polymer chains in the physical hydrogel systems have steady association and disassociation with the heating rate, the gelation time is inevitably longer for a bulk sample [7] and dehydration may occur. The temperature across the microscale sample is more uniform due to the minimal thermal loss to the environment.
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