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The experiment described in the article demonstrated how to optically track a drug delivery patch made of porous and polymer microneedles. The method entailed modeling silicon crystalline electrochemically. Until anodization, silicon substrates were dipped in an HF solution for around two minutes. The aim was to strip the layers of native oxide. During the design process, a five-minute time break was required to restore the HF concentration at dissolution. This move was also used to aid in the formulation of the zero current density such that it was consistent over all layers. In an optical point of view, the membrane of porous silicon has the same character as those of Bragg mirror.
For this experiment, a Bragg mirror was created by 30 periods. The method also involved using 72.6% porosity layers by employing a current density of 200Am/Cm2 also; low porosity layers were acquired through the current density of 100Am/cm2.
The thickness and porosities were measured using spectroscopic ellipsometry measurements on each of the samples after which the values of refractive indexes were obtained by applying Bruggeman approximation. To turn the reaction into an electrochemical polishing position and also to separate the porous silicon membrane from the silicon substrate, anodization current density was increased from its initial value to 600mA/cm2 and then further to 800mA/cm2 . The membrane of floating porous silicon was oxidized into ethanol solution.
Microneedles Array Fabrication
Microneedle arrays were fabricated using photolithography which involved applying photoresist solution of PEDGA as well as Darcour at a level of 2% volume concentration. This solution acted as a negative photoresist so that when it is exposed to UV lights, it crosses links and it becomes less soluble.
The final part of the device was fabricated through the assembling of microneedles array and the porous silicon membrane. The method also applied ethanol with floating oxidized membrane of Psi that was then cast on hardened PEGDA then dried at a room temperature (Henry et al.15). Then the drop casting technique that uses 50 µl of a saturated aqueous solution of fluorescein was applied to load the dried membrane. The drug reservoir of Psi was then blocked and sealed using microneedles array. The drops of 50 µl liquid photoresists were poured around the membrane of porous silicon so as to create a sandwich-like device.
Figure of Patch Assembling Process
The release of molecules at hermetic was evaluated by immersing the microneedles patch device in a solution containing PBS1X at pH.of 7.2 for interval hours of 2, 4, 8 and 24.
In the figure above shows the flow process of microneedles array. Steps 1 to step 6 are the fabrication processes.
The result of process of photolithographic can be summarized in the photo below
Figure a shows the MNs arrays, b, shows micro-images of single needles and c is the macroscopic view of the MNs arrays. D is the tip measurement.
The result shows that the PEDGA got a better flexibility that is useful in patch applications.
There was an overlap of PSiMB by fluorescent; this was discovered through a comparison between these devices views. Bright filed mode could be seen in one of the devices while the other device was spotted with the fluorescent mode. According to the result of the experiment, only fluorescent mode affects PSiMB by extending beyond it.
There were about 210 counts of fluorescent as revealed by accounting estimation of the fluorescent (Henry et al.14). PSiMB was just below the arrays of MNs and only four counts in which MNs were photographed. This was confirmation that proves polymeric MNS never showed an inherent signal of fluorescent. The cross section of the device, as well as the picture of single microneedles arrays that was detached from PEGDA support, was acquired in fluorescent mode. Also, the images showed that the fluorescein was equally distributed from the base of Microneedles arrays to its tips. This was evidence that the fluorescein molecules were not bonded chemically and not even mechanically fixed to the polymeric matrix and therefore can easily be detached from the layers of PSiMBmesoporous to that of the polymeric matrix. Also noted was the fact that diffusion stopped naturally at the time when the equilibrium between the device and the fluorescein concentration in PSiMB was reached. The time constant of the rate of diffusion was estimated to be two minutes by microgravimetry.
PSiMB did not act only as naked eye optical monitor of what was going on in the molecule store but also physical tank for drug load. Also, there was a change in the color of PSiMB that was recognized was due to photonic stop band in the region that was visible. The stack of alternating films that has a proper thickness as well as reflective indexes that satisfy the relationship of the Bragg was an interferometric mirror that was able to exhibit maximum reflection for a given interval of the wavelength. The stop bands also shifted when thickness or the refractive indexes were modified. The porous silicon based Bragg mirror in which the top band position depended on the porosity of the stack. The optical spectrum red also shifted towards the regions with higher wavelength. This was realized could be as a result of the dense of material. When the water contract angle that was measured to be 37, five µg of fluorescein was loaded in the device, the position of resonant wavelength changed to a stable position. This was also after bonding and sealing. Also, the diffusion of fluorescein in PEGA matrix did not modify optical spectrum strongly. There was no observation of depletion of Psi reservoir. The red-shift was also proportional to the flourescein concentration in the solution. Different concentration of fluorescein was also registered without using any optical filter. The calibration curve revealed the relationship that exists between the optical response of the Bragg mirror and the fluorescein concentration that was loaded. Also, these results showed that the higher the fluorescein stored in porous silicon, the higher the red shifts of spectrum reflectivity of the structure of the optical. However, there was a strong blue shift of spectrum that was observed after it was immersed in water.
Henry S., McAllister D. V., Allen M. G., Prausnitz M. R., “Microfabricated Microneedles: A Novel Approach to Transdermal Drug Delivery,” J. Pharm. Sci. 87(8), 922–925 (1998).10.1021/js980042
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