Preparation and properties of poly-lactic acid, nanohydroxyapatite and graphene nanocomposite blends for load bearing bone implants

Naturally, bones have a remarkable capacity to regenerate in case of minor injury and continuously remodel throughout an adult life. However, major injuries involving the load bearing bones, such as spine, hips and knee, require orthopaedic surgeries. These bone implants are made from biomaterials. As a result, this study investigates the use of biomaterials such as poly-lactic acid (PLA), nanohydroxyapatite (NHA) and graphene nanoplatelets (GNP) for applications related to bone implants. In this study, NHA was synthesised using precipitation method assisted with ultrasonication. The process parameters (reaction temperature, ultrasonic time and amplitude) were optimised using response surface methodology (RSM) based on 3 factors and 5 level central composite design (CCD). Upon characterisation, the synthesised NHA was confirmed to mimic the HA present in the human bone both chemically and morphologically. The synthesised NHA was then compounded with PLA matrix via melt-mixing by varying the NHA loading (1-5wt%). The impact strength of the PLA-NHA nanocomposites increased with NHA loading, attaining 21.6% enhancement in comparison to neat PLA. In contrast, the tensile strength and modulus of the PLA-NHA nanocomposites exhibited an initial increase of 0.7% and 10.6%, respectively, for 1wt% NHA loading, but deteriorated with the increasing NHA loading. The FESEM microstructures of the impact fractured samples also depicted agglomeration of NHA particles and poor interfacial adhesion between NHA and PLA. Hence, to improve the dispersion, NHA was surface modified (mNHA) using three different surface modifiers namely, 3-aminopropyl triethoxysilane (APTES), sodium n-dodecyl sulfate (SDS) and poly-ethylenimine (PEI). The FESEM analysis revealed an improved interfacial adhesion between PLA matrix and mNHA(APTES), which, enhanced the mechanical, thermal and dynamic mechanical properties of the PLA-5wt%mNHA(APTES). Meanwhile, mNHA(SDS) and mNHA (PEI) had no significant effect on interfacial adhesion, ultimately, failing to improve the properties of the PLA-5wt%mNHA(SDS) and PLA-5wt%mNHA (PEI), respectively. GNP was added into the mNHA in order to further improve the properties of the PLA-5wt%mNHA(APTES) nanocomposite. With the addition of only 0.01wt% of GNP, the impact strength of the PLA-mNHA-GNP nanocomposite was increased by 22.1% (neat PLA) and 7.9% (PLA-5wt%mNHA(APTES)). Nonetheless, the tensile strength recorded a drop of 8.7% (neat PLA) and 9.7% (PLA-5wt%mNHA(APTES)). It is important to note the tensile strength obtained for the PLA-mNHA-GNP nanocomposite was within the acceptable limit of bone strength requirements. Biocompatibility of the nanocomposites (PLA, PLA-NHA, PLA-mNHA and PLA-mNHA-GNP) was investigated using in-vitro analysis. The results show the MG63 cells adhere and grow well on the nanocomposites. Moreover, the nanocomposites encouraged the cells to proliferate and differentiate within 7 days and 21 days of incubation period, respectively. Thus, the in-vitro analysis evidenced the prepared nanocomposites were biocompatible with the MG63 cells. Finally, possible extensions and future works for these prepared nanocomposites as bone implants have been highlighted

Preparation and properties of poly-lactic acid, nanohydroxyapatite and graphene nanocomposite blends for load bearing bone implants

Naturally, bones have a remarkable capacity to regenerate in case of minor injury and continuously remodel throughout an adult life. However, major injuries involving the load bearing bones, such as spine, hips and knee, require orthopaedic surgeries. These bone implants are made from biomaterials. As a result, this study investigates the use of biomaterials such as poly-lactic acid (PLA), nanohydroxyapatite (NHA) and graphene nanoplatelets (GNP) for applications related to bone implants. In this study, NHA was synthesised using precipitation method assisted with ultrasonication. The process parameters (reaction temperature, ultrasonic time and amplitude) were optimised using response surface methodology (RSM) based on 3 factors and 5 level central composite design (CCD). Upon characterisation, the synthesised NHA was confirmed to mimic the HA present in the human bone both chemically and morphologically. The synthesised NHA was then compounded with PLA matrix via melt-mixing by varying the NHA loading (1-5wt%). The impact strength of the PLA-NHA nanocomposites increased with NHA loading, attaining 21.6% enhancement in comparison to neat PLA. In contrast, the tensile strength and modulus of the PLA-NHA nanocomposites exhibited an initial increase of 0.7% and 10.6%, respectively, for 1wt% NHA loading, but deteriorated with the increasing NHA loading. The FESEM microstructures of the impact fractured samples also depicted agglomeration of NHA particles and poor interfacial adhesion between NHA and PLA. Hence, to improve the dispersion, NHA was surface modified (mNHA) using three different surface modifiers namely, 3-aminopropyl triethoxysilane (APTES), sodium n-dodecyl sulfate (SDS) and poly-ethylenimine (PEI). The FESEM analysis revealed an improved interfacial adhesion between PLA matrix and mNHA(APTES), which, enhanced the mechanical, thermal and dynamic mechanical properties of the PLA-5wt%mNHA(APTES). Meanwhile, mNHA(SDS) and mNHA (PEI) had no significant effect on interfacial adhesion, ultimately, failing to improve the properties of the PLA-5wt%mNHA(SDS) and PLA-5wt%mNHA (PEI), respectively. GNP was added into the mNHA in order to further improve the properties of the PLA-5wt%mNHA(APTES) nanocomposite. With the addition of only 0.01wt% of GNP, the impact strength of the PLA-mNHA-GNP nanocomposite was increased by 22.1% (neat PLA) and 7.9% (PLA-5wt%mNHA(APTES)). Nonetheless, the tensile strength recorded a drop of 8.7% (neat PLA) and 9.7% (PLA-5wt%mNHA(APTES)). It is important to note the tensile strength obtained for the PLA-mNHA-GNP nanocomposite was within the acceptable limit of bone strength requirements. Biocompatibility of the nanocomposites (PLA, PLA-NHA, PLA-mNHA and PLA-mNHA-GNP) was investigated using in-vitro analysis. The results show the MG63 cells adhere and grow well on the nanocomposites. Moreover, the nanocomposites encouraged the cells to proliferate and differentiate within 7 days and 21 days of incubation period, respectively. Thus, the in-vitro analysis evidenced the prepared nanocomposites were biocompatible with the MG63 cells. Finally, possible extensions and future works for these prepared nanocomposites as bone implants have been highlighted

Viscoelastic Properties and Thermal Stability of Nanohydroxyapatite Reinforced Poly-Lactic Acid for Load Bearing Applications

We studied the reinforcing effects of treated and untreated nanohydroxyapatite (NHA) on poly-lactic acid (PLA). The NHA surface was treated with three different types of chemicals; 3-aminopropyl triethoxysilane (APTES), sodium n-dodecyl sulfate (SDS) and polyethylenimine (PEI). The nanocomposite samples were prepared using melt mixing techniques by blending 5 wt% untreated NHA and 5 wt% surface-treated NHA (mNHA). Based on the FESEM images, the interfacial adhesion between the mNHA filler and PLA matrix was improved upon surface treatment in the order of mNHA (APTES) > mNHA (SDS) > mNHA (PEI). As a result, the PLA-5wt%mNHA (APTES) nanocomposite showed increased viscoelastic properties such as storage modulus, damping parameter, and creep permanent deformation compared to pure PLA. Similarly, PLA-5wt%mNHA (APTES) thermal properties improved, attaining higher Tc and Tm than pure PLA, reflecting the enhanced nucleating effect of the mNHA (APTES) filler