Study On Functionalization Of Poly (Lactic Acid) And Graphene Oxide And Their Biomedical Applications

Advances in biomaterials require the implant material to promote cell functions such as adhesion and proliferation. As a result, the enhanced cell-materail interaction can lead to fast integration of material into host tissues after implantation. Also the repair of damaged tissues or organs in human body can be accelerated, and the complications coursed by implants can be avoided. The functionalization and modification of the traditional biomaterials are essential to obtain biomimetic biomaterials by introducing the biomolecules.Our research in this thesis focuses on the functionalization and modification of the biocompatible polymer(Poly(lactic acid), PLA) and the newly discovered carbon material(Graphene Oxide, GO). To explore their promising biomedical applications, the interactions between modified materials and osteoblast were evaluated by a systematic cell study.Poly(lactic acid), PLA, or polylactide, has been approvaled by the United States Food and Drug Administration(FDA) as drug carrier, absorbable medical surgical suture and internal fracture fixation material and widely used in biomedical field. Despite some encouraging advantages of PLA, it also possesses some significant drawbacks, such as low hydrophilicity, poor cell affinity, difficulty in controlling the degradation, and generation of local acidic condition during degradation. To improve the functions of PLA for biomedical applications, modifications with other molecules covalently or non-covalently, have been investigated. We report here a facile chemistry route to prepare symmetric poly(L-lactide)(PLLA)-based dendritic L-lysine copolymer(PLLA-d), with PLLA block as the core and the lysine dendron in the two ends to provide certain density of positive charges, through a divergent method. The polymers were characterized by 1H NMR, and GPC to confirm the well-defined chemical architecture. The lysine dendron disrupted PLLA crystalline region and lowered the melting point and the tensile modulus of PLLA, but improved the hydrophilicity of PLLA. The PLLA-d was fabricated into honeycomb films(H-PLLA-d) through breath-figure method for water contact angle test and in vitro study. Mouse osteoblastic cell(MC3T3-E1) functions including cell attachment, adhesion, proliferation, and differentiation were investigated on H-PLLA-d films. The results indicated that MC3T3-E1 cell functions were significantly enhanced on H-PLLA-d films.As one of the most important graphene derivatives, GO chemically exfoliated from oxidized graphite is considered as a promising material for biomedical applications and has already shown potential for use as biosensors, bioimaging, drug delivery, and substrates for stem cell differentiation due to its excellent aqueous processability, amphiphilicity, surface functionalizability and low costs. Even though the research regarding biomedical applications of graphene-based nanomaterials is expanding rapidly, relatively little is known about their influence on biological systems or intrinsic toxicity. In general, the effect of GO-based materials on biological systems is still not clear. It is essential to improve the biocompatibility of GO before its application in biomedical field. Here, we prepared RGD tripeptide functionlized GO(GO-RGD) by a one step modification. The synthesized GO-RGD was characterized by FTIR and elemental analysis to confirm the modified chemical structure. The surface morphology of GO-RGD was studied by SEM and TEM, and TEM results confirmed RGD bonding to GO by comparing the morphology changes before and after functionalization. Mouse osteoblastic cell(MC3T3-E1) functions including cell attachment, adhesion, proliferation, and differentiation were investigated on GO-RGD films prepared by filtration. The results indicated that MC3T3-E1 cell functions were significantly enhanced on GO-RGD films compared with GO ones. And this enhancement of cell functions depends on the contents of RGD. Our study here provides a potential biomaterial for bone repair by improving osteoblastic cell functions.Furthermore, in this study, gelatin-functionalized graphene oxide(GOGel) was synthesized by a simple one step modification, GO and GOGel were used to develop surface coatings on Nitinol substrates. Mouse osteoblastic cell(MC3T3-E1) functions, including cell attachment, proliferation, and differentiation, were investigated on GO-based coatings. The results indicated that MC3T3-E1 cell functions were significantly enhanced on both GO coated Nitinol(GO@Ni Ti) and GOGel coated Nitinol(GOGel@Ni Ti), compared with the control Nitinol without coating(Ni Ti). Especially, the GOGel@Ni Ti surface exhibited the best performance for cell adhesion, proliferation, and differentiation. Additionally, the antimicrobial property of GO-based coatings against E.coli was studied with the evaluation of colony forming units(CFU) counting, live/dead fluorescent staining and scanning electron microscope(SEM). We found that the growth of E.coli was inhibited on GOGel@Ni Ti and particularly on GO@Ni Ti. SEM images revealed that the cell membrane of bacteria lost their integrity and live/dead fluorescent images confirmed the low live/dead ratio of E.coli after incubation on GOGel@Ni Ti and GO@Ni Ti. We concluded that GO-based coatings on Ni Ti combine the antimicrobial activity and improved biocompatibility, and therefore present a remarkable potential in biomedical implant applications.In conclusion, the biocompatibility of PLA and GO was significantly improved after functionalization and modification by biomolecules. This study not only lays the foundation for the biomedical application of PLA and GO, but also provides some theories and data support in the design and synthesis of advanced PLA and GO based biomaterials with biofuncions.