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Oliveira M.B.,European Institute of Excellence on Tissue Engineering and Regenerative Medicine | Oliveira M.B.,Bs PT Government Associated Laboratory | Kossover O.,Technion - Israel Institute of Technology | Mano J.F.,European Institute of Excellence on Tissue Engineering and Regenerative Medicine | And 2 more authors.
Acta Biomaterialia | Year: 2015

A new methodology is reported for the continuous, solvent- and oil-free production of photopolymerizable microparticles containing encapsulated human dermal fibroblasts. A precursor solution of cells in photoreactive poly(ethylene glycol) (PEG)-fibrinogen (PF) polymer was transported through a transparent injector exposed to light irradiation before being atomized in a jet-in-air nozzle. Shear rheometry data revealed the crosslinking kinetics of the PF/cell solution, which was then used to determine the amount of irradiation required to partially polymerize the mixture just prior to atomization. The partially polymerized drops of PF/cells fell into a gelation bath for further crosslinking until fully polymerized hydrogel microparticles were formed. As the drops of solution exited the air-in-jet nozzle, their viscosity was designed to be sufficiently high so as to prevent rapid mixing and/or dilution in the gelation bath, but without undergoing complete gelation in the nozzle. Several parameters of this system were varied to control the size and polydispersity of the microparticles, including the cell density, the flow rate and the air pressure in the nozzle. The system was capable of producing cell-laden microparticles with an average diameter of between 88.1 to 347.1 μm, and a dispersity of between 1.1 and 2.4, depending on the parameters chosen. Varying the precursor flow rate and/or cell density was beneficial in controlling the size and polydispersity of the microparticles; all microparticles exhibited very high cell viability, which was not affected by these parameters. In conclusion, this dropwise photopolymerization methodology for preparing cell-laden microparticles is an attractive alternative to existing techniques that use harsh solvents/oils and offer limited control over particle size and polydispersity. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Leite A.J.,European Institute of Excellence on Tissue Engineering and Regenerative Medicine | Leite A.J.,Bs PT Government Associated Laboratory | Sher P.,European Institute of Excellence on Tissue Engineering and Regenerative Medicine | Sher P.,Bs PT Government Associated Laboratory | And 2 more authors.
Materials Letters | Year: 2014

We investigated the interaction of natural derived macromolecular multilayers with calcium and phosphate ions entirely processed using the layer-by-layer (LbL) technique. A nanostructured multilayer component, with 5 or 10 bilayers, was first produced using weak polyelectrolyte biopolymers, chitosan and chondroitin sulfate. This was followed by sequential passing of solutions containing Ca2+ and PO43- over the multilayers. QCM-D, SEM and EDX results conferred the formation of calcium phosphate (CaP) over the polyelectrolyte multilayers. Initiation of precipitation was observed earlier in the 10 bilayers coating than in the 5 bilayers one. These results indicate the potential of multilayers to trap ions, as a biomimetic approach that can be used to induce CaP precipitation. This could enable the preparation of more performant bioactive composite biomaterials for orthopedic applications, including in bone tissue engineering. © 2014 Elsevier B.V.

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