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"Available online 11 May 2016" ; Biodegradable poly(L-lactic acid) (PLLA) and PLLA/CoFe2O4 magnetic microspheres with average sizes ranging between 0.16 -3.9 m and 0.8-2.2 m, respectively, were obtained by an oil-in-water emulsion method using poly(vinyl alcohol) (PVA) solution as the emulsifier agent. The separation of the microspheres in different size ranges was then performed by centrifugation and the colloidal stability assessed at different pH values. Neat PLLA spheres are more stable in alkaline environments when compared to magnetic microspheres, both types being stable for pHs higher than 4, resulting in a colloidal suspension. On the other hand, in acidic environments the microspheres tend to form aggregates. The neat PLLA microspheres show a degree of crystallinity of 40% whereas the composite ones are nearly amorphous (17%). Finally, the biocompatibility was assessed by cell viability studies with MC3T3-E1 pre-osteoblast cells. ; This work is funded by FCT – Fundação para a Ciência e a Tecnologia, grants SFRH/BD/82411/2011 (DMC), SFRH/ BPD/90870/2012 (CR), SFRH/BD/98616/2013 (PMM) and SFRH/ BPD/97739/2013 (PM), respectively. The authors thank support from the COST Action MP1206 ''Electrospun Nano-fibres for bio inspired composite materials and innovative industrial applications" and from the Basque Government Industry Department under the ELKARTEK Program. SLM thanks the Diputación Foral de Bizkaia for financial support under the Bizkaia Talent Programme; European Union's Seventh Framework Programme; Marie Curie Actions–People; Grant agreement no. ...