| The application range of biomaterials and its development level has been one of theimportant sign to measure a nation’s modernization medical level now. As we moveforward in the new millennium, looking for biomaterials similaring to natural humantissue structure and performance, which are designed to be completely integrated andcause the full reproduction of damaged tissue, become a research hotspot of biomedicalmaterials. PDLLA have been approved by the Food and Drug Administration of UnitedStates of America (FDA) as the safety of the biodegradable biomedical materials in thebody. However, some shortcomings of PDLLA have been limited their applications inthe field of biomedical engineering, such as lack of human cell specific recognitionsignal sites and absence of bioactive. Therefore their biomimetic modification designand research has important scientific significance and profound social significance inbiomaterials and biomedical engineering fields in future.In this study, A novel biomimetic poly (D, L-lactic acid)(PDLLA) modification wasdesigned and synthesized based on the24amino acid peptide analog corresponding tothe unique C-terminal E-domain in mechano-growth factor (MGF-Ct24E) grafted intothe maleic anhydride modified PDLLA (MPLA). MGF-Ct24E was grafted into the sidechain of MPLA via a stable covalent amide bond by using1-ethyl-3-(3-dimethyllaminopropyl) carbodiimide hydrochloride (EDC) and N-Hydroxysuccinimide(NHS) as the condensing agent to produce biomimetic MPLA materials (MGF-Ct24E-MPLA). The characterization of the biomimetic biomaterials was by means ofthe Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy(XPS), Differential scanning calorimeter (DSC), Amino acid analyzer (AAA),Elementary analysis (EA) and classical chemical analysis to estimate the structures andthe properties. Thereafter, the basic physical properties and mechanical performance, invitro biodegradation, the influence of degradation products on the inflammatoryresponse and biocompatibility of the synthetic biomimetic biomaterials wereinvestigated. The main works and conclusions are as follows:1. On the condition of maintaining the main chain structure, MGF-Ct24E wasgrafted into the side chain of MPLA via a stable covalent amide bond by using EDC andNHS as the condensing agent to produce novel biomimetic MPLA materials.①FTIR, XPS, DSC AAA and EA analysis revealed that, MGF-Ct24E was successfully modified into MPLA and the average contents of MGF-Ct24E inMGF-Ct24E-MPLA materials was1.05μmol/g and the coupling efficiency was29.91%.②DSC results showed that the glass transition temperature of MPLAwas42.73oC，but the glass transition temperature of MGF-Ct24E-MPLA was raised to55.85oC.2. The basic physical properties and mechanical properties of the PDLLA, MPLAand MGF-Ct24E-MPLA materials were characterized by the molecular weight, staticwater contact Angle, water absorption rate, mechanical tensile tests and compressiontest.①The molecular weight of the three kinds of polymers molecular weight was in thesequence of PDLLA> MPLA> MGF-Ct24E-MPLA. This is because that as themodification of PDLLA with maleic anhydride and MGF-Ct24E, the thermaldegradation and aminolysis phenomenon was occurred in succession in reaction process.Therefore the molecular weight of modified PDLLA continuously reduced.②The hydrophilicity of three kinds of polymers materials was in the sequence ofPDLLA<MPLA<MGF-Ct24E-MPLA. This is because that as the introductions ofmaleic anhydride and MGF-Ct24E into PDLLA in succession, the hydrophilic groups(such as-COOH,-OH,-NH2, and-CONH-) were increased, which made thehydrophilicity of modified PDLLA enhance.③The maleic anhydridet grafted into PDLLAmade MPLAand the tensile andcompression performance of MPLA increased as to PDLLA. Futhermore, the MPLAmodified with MGF-Ct24E then reduced the tensile and compression strength ofMGF-Ct24E-MPLA.3. In vitro biodegradation and the influence of degradation products on theinflammatory response of PDLLA, MPLA and MGF-Ct24E-MPLA were investigated.The evaluation indicators of in vitro biodegradation behavior were weight loss ratio,surface topography, water absorption ratio and pH value changes. Moreover, in vitro theinflammatory response of the degradation products of the three materials were evaluatedby monitoring the expression of cytokines such as the, tumor necrosis factor-α (TNF-α)and interleukin-1β (IL-1β) and the release of NO by macrophages in contact withdegradation products.①Results of hydrolytic degradation of the polymers during12weeks indicated thatthe in vitro degradation stability of MGF-Ct24E-MPLA was better than PDLLA and MPLA. This was because the alkaline polypeptides MGF-Ct24E could eliminate orweaken the acid induced auto-catalysis during the degradation of MGF-Ct24E-MPLA.②The inflammatory response experiments indicated that macrophages culturedwith degradation products of MPLA showed increased secretion levels of TNF-α, IL-1βand NO, whereas macrophages cultured with degradation products ofMGF-Ct24E-MPLA revealed decreased secretion levels of TNF-α, IL-1β and NO,related to macrophages cultured with degradation products of PDLLA as control. Themodification of PDLLA with polypeptides MGF-Ct24E could alleviate inflammatoryresponse during the degradation of polymers.4. In this study, we evaluated the cytocompatibility of MGF-Ct24E chemicallygrafted and physically blended with MPLA, relative to maleic MPLA as the control. Ratcalvarial osteoblasts were seeded on the three polymer films, and cell adhesion,spreading, proliferation, differentiation and mineralization were assessed.①Compared with MPLA, MGF-Ct24E-MPLA and MGF-Ct24E/MPLA blendspromoted osteoblasts adhesion and spreading, and there was no significant difference incell viability between the MGF-Ct24E-MPLA and MGF-Ct24E/MPLA blends (p <0.05).②The proliferation ability of rat calvarial osteoblasts cultured on theMGF-Ct24E-MPLA and MGF-Ct24E/MPLA blends films was significantly strongerthan that on MPLA. There was no significant difference in cell proliferation behavior onthe MGF-Ct24E-MPLA and MGFCt24E/MPLA films at the prophase of osteoblastsgrowth stage. Interestingly, the cell proliferation activity on the MGFCt24E-MPLAfilms was greater than that on the MGF-Ct24E/MPLA blends films at the anaphase ofosteoblasts growth stage. The phenomenon occurred because MGF-Ct24E blending intoMPLA easily decreases. Then the MGF-Ct24E alone was metabolized quickly duringcell metabolism over time. However, when MGF-Ct24E was grafted into MPLA byusing the chemical method, it was sustained and released as MGF-Ct24E-MPLAdegraded. Therefore, MGFCt24E-MPLA has a sustaining effect on promoting cellgrowth, compared to the MGFCt24E/MPLA blends over time③MGF-Ct24E-MPLA and MGF-Ct24E/MPLA materials blends had dual influenceon the differentiation of rat calvarial osteoblasts. In the early period of cell growth, theMGFCt24E-MPLA and MGF-Ct24E/MPLA blends promoted osteoblast proliferationand temporarily restrained differentiation. During the late period of cell growth, theMGF-Ct24E-MPLA and MGF-Ct24E/MPLA blends enhanced osteoblast differentiation. MGF-Ct24E-MPLA has a stronger effect on promoting cells differentiation compared tothe MGF-Ct24E/MPLA blends. Therefore it can be conjectured thatMGF-Ct24E-MPLA did not inhibit differentiation but delayed.④MGF-Ct24E-MPLA significantly enhanced mineralization of the rat calvarialosteoblasts compared with the MGFCt24E/MPLA blends and MPLA, between whichthere was no significant difference. |
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