*5.1.3.3. Nucleating effect*

*5.1.3. Inorganic reinforcements*

140 Composites from Renewable and Sustainable Materials

are too of great interest.

widely reported [90, 91, 92, 93].

composites for fracture fixation plates [97].

results in a bioactive composite [107].

*5.1.3.2. Radiopacity*

*5.1.3.1. Bone repair*

Bioresorbable polymers play great relevance in biomedical field. Due to its excellent mechan‐ ical properties related to stiffness and tensile strength, polylactides are proposed for using in implants with safety‐critical applications [87]. Hence, fixation and bone reconstruction are compulsory for a good health and reconstruction of the damaged zone. Most of implants based on polylactide polymer are focused on bone repair; however, radiopacity and other properties

In this context, inorganic reinforcements play the most important role, because the natural bone is formed up to 70 wt. % by calcium phosphate very similar to hydroxyapatite (HA) [88]. HA is an inorganic compound, which helps the differentiation of osteoblasts in regeneration of the bone structure [89]. For this reason, incorporation of HA into PLA matrices has been

Tricalcium phosphate (β‐TCP) has been also widely used due its bioactivity and biodegrada‐ bility. Its degradation rate is incremented 3–12 times compared with HA [94] and this favors bonding of bone to the bioceremic [95]. However, combination of β‐TCP and HA in denomi‐ nated biphasic calcium phosphates (BCP) shows the advantages of both components: reactivity of β‐TCP and stability of HA. BCP with 60–40% of HA‐TCP incubed in simulated body fluid produces the precipitation of needle‐shaped apatite crystals [96], allowing polylactide/BCP

Furthermore, discovery of bioactive glasses by L. L. Hench in 1969 catapults the use of these inorganic particles in tissue engineering due to their excellent biocompatibility and the ability of bone bonding [98]. A common characteristic of bioactive glasses and ceramics is a time‐ dependent kinetic modification of the surface that occurs upon implantation [99]. Bioactive glasses originate a superficial layer of calcium deficient carbonate, which permits a chemical adhesion to bone. This adhesion is appealed as bioactivity and is associated with the formation of carbonated hydrocyapatite (HCA) when glass is implanted or in contact with simulated body fluids [100, 101]. The HCA layers formed on a scaffold made of 45S5Bioglass® immersed in SBF takes a "cauliflower" typical morphology [99] and allows osteogenic formation [102].

Some researches of PLA/bioactive glass composites have been reported [103, 104]. However, melt processing of bioglass with polylactides affects the thermal stability of the composite [105], and to overcome this handicap, protection of bioactive ceramic with and acrylic plasma treatment has been proposed [106]. An easier treatment than plasma has been proposed by A. Larrañaga by covering these particles with a mussel inspired polydopamine coating, which

Although alternative radiopacifiers have been proposed in bibliography [108, 109], barium sulfate (BaSO4) is still the gold standard for medical applications [110]. Incorporation of BaSO4 The influence of the nature of the filler on the mechanical properties of PLA has been reported for two silicated clays, both having a platelet‐like shape [112]. Talc is a more efficient filler regarding mechanical reinforcement of PLA as compared to kaolin. This better reinforcing effect in the case of talc is ascribed to its higher affinity with the PLA. It was also evidenced that talc has a nucleating effect on the PLA crystallization [113], while kaolin has no or very limited effect on the crystallization behavior of PLA. In conclusion, the existence of crystallo‐ graphic relationships between the structures of the filler and the polymer crystals is also a key parameter for the observation of a nucleating effect.
