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    Diatom silica frustules-doped fibers for controlled release of melatonin for bone regeneration
    (Pergamon-Elsevier Science Ltd, 2023) Dalgic, Ali Deniz; Atila, Deniz; Tezcaner, Aysen; Gurses, Senih; Keskin, Dilek
    Sustained release of a bioactive agent from a tissue engineering scaffold is one of the most common strategies to improve regenerative potential of the construct. However, depending on the chemistry of the agent, achieving high enough loading and controlled release can be challenging depending on the scaffold materials. These shortcomings can be solved by novel scaffold design fabricated by appropriate techniques and materials for the target tissue. In this study, an electrospun scaffold was designed to improve osteogenic activity of cells and diatom silica frustules were used to sustain loading and controlled release of a hydrophilic molecule, melatonin. Fibrous scaffolds were produced via wet electrospinning of the polymer blend solution poly(hydroxybutyrate-co- hydroxyvalerate (PHBV)/poly(epsilon-caprolactone) (PCL) which contains melatonin loaded diatom frustules. In the 3D fiber matrix diatom frustules were covered with a polymer coat which successfully lowered melatonin release more than half through 7 days achieving a controlled release. Melatonin had a concentration dependent effect on ALP activity of cells, while scaffolds bearing melatonin loaded frustules have significantly improved ALP activity of Saos-2 cells. Developed scaffold system has successfully induced osteogenic activity by controlled melatonin delivery and silica nature of diatom frustules which hold potential use for bone tissue engineering.
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    Natural origin bilayer pullulan-PHBV scaffold for wound healing applications
    (Elsevier, 2022) Dalgic, Ali Deniz; Koman, Ezgi; Karatas, Ayten; Tezcaner, Aysen; Keskin, Dilek
    Skin tissue loss that occurs by injury and diseases can turn into chronic wounds as a result of complications alongside infection. Chronic wounds fail to heal by themselves and need advanced treatments like engineered wound dressings and regenerative scaffolds. In this study, a novel, natural origin, bilayer electrospun scaffold was produced from pullulan (PUL) and poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) biopolymers. PHBV production by Cupriavidus necator bacterial strain was optimized and produced polymer was characterized. Characteristic peaks and bands of PHBV were observed by H-NMR and FTIR analyses. Valerate mol percent of produced PHBV copolymer was determined by H-NMR. Average molecular weight of the polymer was determined by SLS technique and crystallinity of PHBV was calculated from DSC curve. Bilayer scaffold was produced by electrospinning of hydrophilic PUL fibrous membrane onto wet-electrospun hydrophobic PHBV 3D fibrous mat. Bilayer scaffold was designed to involve regenerative and barrier fibrous layers. Nano fibrous PUL membrane with smaller pore size was efficient as a barrier against bacterial transmission while enabling optimum oxygen and water vapor transmission. Water retention and degradation properties were found to be optimum for a skin tissue scaffold. In vitro studies showed that PUL membrane sustained L929 cell proliferation while preventing cells from migrating inside the barrier phase while PHBV layer supported cell viability, proliferation, and migration, creating a regenerative 3D structure. Results showed that, novel natural origin PUL/PHBV bilayer scaffold is a promising candidate for wound healing applications.