Poly (Lactide-co-Ethylene Oxide Fumarate) gel Reinforced with a Poly-L-Lactic Acid Fibers
A more recent study  tried to mimic the structure of bone to a greater extent by fabricating laminates of electrospun PLLA fibers coated with hydrogel solution that contained hydroxyapatite nanoparticles, and then stacking the laminates together. The reasons this microstructure is more representative of bone are: (i) the fibers within the extracellular matrix of bone form a random network as opposed to the aligned one produced in Sect. 4.6, (ii) bone contains apatite crystals in the extracellular matrix that allow for an increased mechanical stability.
The hydrogel chosen in  was based on a poly(lactide-co-ethylene oxide fumarate) (PLEOF) precursor, which was crosslinked in an aqueous environment with redox or ultraviolet initiators. Its biodegradability was tuned by adjusting the molecular weight of the lactide chains and also the ratio between the lactide and ethylene glycol [55, 56]. It should be noted that in order to increase the elastic modulus of the PLEOF/HA precursor the HA crystals were treated with an acrylate- functionalized glutamic acid sequence, while conjugating bioactive peptides to the PLEOF can increase its biocompatibility. Hence, an acrylamide-terminated integrin- binding Arg-Gly-Asp (RGD) peptide (Ac-RGD) was used in the PLEOF/HA precursor.
It should be noted that other research groups have used electrospun fibers to reinforce hydrogels, such as polyethylene glycol (PEG)  and chitosan-hyal- uronic acid  hydrogels reinforced with PCL fiber mats. However, those constructs did not have a multilayer structure to the extent of the system that will be described in the sequel and they also did not consider the addition of HA in order to further increase the biocompatibility and mechanical properties of the possible scaffolds. Below the work of  is summarized.