Development of Functional Continua Made of Bio-absorbable Material and Its Application for Medical Technology

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In this study, functional continua made of bio-absorbable material were applied to drug delivery system (DDS). It is necessary to control of absorption time of drug capsule made of bio-absorbable material in drug delivery system, in order to release the drug concentrated at an affected part. It is difficult to control absorption of the drug capsule only by changing size of the capsule. Shape of DDS capsule was designed by considering as a functional continuum made of bio-absorbable material. Drug capsule with non-uniform thickness is useful to control the absorption time because capsule break and drug release occur at a thinnest part of the capsule. Mechanical stress occurred in bio-absorbable material also affect to its absorption ratio, so it is possible to control the absorption time by varying residual stress value if residual stress is given for the drug capsule of DDS. We investigated effect of the non-uniform shape and residual stress to the absorption time in two-dimensional ring made of bio-absorbable material. A Two-dimensional ring with non-uniform thickness was made of PLLA. A part of the ring was cut off and adhere the cutting face again to generate residual stress along the ring. Residual stress depends on cut off length of the ring, and it was determined by curved beam theory. Absorption examination of the ring was carried out in HCOOH solution for the case with and without residual stress. From the results, absorption time of the ring with residual stress was shorter than the case with no residual stress. It was established absorption time of drug capsule in DDS was controllable by capsule shape with non-uniform thickness and residual stress. The method proposed in this study is applicable to design the drug capsule of DDS in case of necessity of precise absorption time control.