Fabrication and Characterization
In  the chitin fibers were linked with PLLA, by dissolving chitin, PLLA dicy- clohexylcarbodimide into dichloromethane. The collagen nano hydroxyapatite solution was prepared by mixing an appropriate concentration, lyophilizing and then grinding into a fine powder according to the method described in . Then the PLLA was dissolved in dioxane, which allowed for pore formation, and the nHAC was added to the solution. The treated chitin fibers were added to the solution and after appropriate processing the liquid was lyophilized for 12 h.
The SEM images Fig. 4.6 illustrate that when the chitin fibers were not linked with PLLA, free-standing fibers could be clearly distinguished within the composite as they did not bind well with the matrix . In the case, however, that the chitin was linked with PLLA, the fibers were distributed very well within the matrix such that it was difficult to distinguish them. Furthermore in the chitin treated case the pore size was larger and more uniform than in the untreated case. A large size is preferred for scaffold engineering since the tissue can grow within the pores, while a uniform microstructure allows for uniform degradation. Furthermore, the porosity of the samples decreased by increasing the fiber content as would be expected, however, the decrease was small, since the 10% chitin samples had a porosity of ~90% while the 50% samples had a porosity of ~80% . The porosity between the treated and untreated scaffolds was similar for the 10% and 50% fiber content composites but it was slightly lower for the treated case for the 30% and 40% chitin composites.
The compression strength of the nHCA/PLLA scaffolds was 2 MPa, while mechanical mixing with the chitin fibers increased it to ~3 MPa. Treating the chitin fibers resulted in this strength to double as it was measured to be ~6.2 MPa . This significant increase was due to the strong interface bonding between the fiber and matrix, which allowed for the stresses to be transferred to the fiber and therefore support the nHCA/PLLA matrix mechanical stability.