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One of the major challenges in tissue engineering remains the construction of vascularized 3D transplants in vitro.We recently proposed novel technologies, termed "magnetic force-based tissue engineering" (Mag-TE), to establish three-dimensional (3D) tissues without using scaffolds. Magnetite cationic liposomes (MCLs), which contain 10-nm magnetite nanoparticles in order to improve accumulation of magnetite nanoparticles in target cells, were used to magnetically label normal human dermal fibroblasts (NHDFs). Magnetically labeled NHDFs were seeded onto ultralow-attachment plates. When a magnet was placed under the plate, cells accumulate on the bottom of the well. After a 24-h-incubation period, the cells form a sheet-like structure, which contains the major dermal extracellular matrix (ECM) components (fibronectin and type I collagen) within the NHDF sheet. Human umbilical vein endothelial cells (HUVECs) were co-cultured with NHDF sheets by two methods: HUVECs and NHDFs were mixed and then allowed to form cell sheets by Mag-TE; or NHDF sheets were constructed by Mag-TE and HUVECs were subsequently seeded onto NHDF sheets. These methods gave tube-like formation of HAECs, resembling early capillaries, within or on the surface NHDF sheets after short-term 3D co-culture, thus suggesting that Mag-TE may be useful for constructing 3D-tissue involving capillaries.

A new way to administer platelet-rich plasma (PRP) to improve its viability in more complex and chronic wound healing and soft/hard tissue regeneration in alveolar ridge preservation is demanded. In this study, PRP was encapsulated in chitosan to form a nanosphere with size below 100 nm with an idea to prolong PRP's growth factors release. Chitosan nanosphere was prepared by ionic gelation method, while PRP was encapsulated by inclusion method. Morphology analysis by transmission electron microscope (TEM) showed that PRP was encapsulated efficiently in the chitosan matrix, making a spherical shape with size of 30-80 nm. Particle size analysis by dynamic Light Scattering (DLS) method further showed that the average size of chitosan-PRP nanosphere was 51.27±33.75 nm, which is a good indication for biomaterials used in body. The stability of the nanoparticle colloid was confirmed with zeta potential score of 50.42 mV. 200 μl encapsulation of PRP in chitosan nanosphere had the highest encapsulation efficiency, that was further used in total protein release analysis in phosphate buffered saline (PBS) solution. It started with initial burst at 7 h, followed by steady release, then 'quasi-plateau' after 96 h (at around 60%), dominated by Korsmeyer-Peppas kinetics model and Fick's diffusion mechanism. Finally, the nanosphere showed an excellent antibacterial activity against S. mutans as shown from 90.63% bacteria inhibition during assay. The results showed that chitosan-PRP nanosphere could be used as a novel approach for complex/ chronic wound healing and soft/hard tissue regeneration following periodontitis treatment or tooth extraction that needs prolonged growth factor release.

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