| Hernia is a disease that part of the body's tissue or organ leaves its normal anatomical position and enters into another part of the body through a congenital or acquired defect or gap in tissue.Nowadays,hernia repair is one of the most common general surgeries performed in the world and affects millions of people each year in America.Many surgical meshes have appeared ever since Usher et al firstly used a mesh material to reinforce the hernia defect in 1950s.The previous reports have shown that the use of meshes indeed improved surgical outcomes.However,complications like chronic pain,infections,fistula,mechanical failures or hernia recurrence are still common after surgeries.One of the major reasons that causes these complications is the mechanical mismatch between repair materials and host tissues.Thus,the development of new material that can mimic the mechanical properties of host tissues is greatly needed.On the other hand,for the complication,infections(about 5%),it is necessary to develop new meshes with antibacterial functions,because most infections are accompanied by the discovery of bacteria.This work designed several warp-knitted large pore polypropylene(PP)meshes based on the requirements of hernia repair and studied the relationship between textile parameters and the physico-mechanical properties of meshes.The structure-performance mechanism was pointed out.To improve the biocompatibility of polypropylene meshes,poly-caprolactone(PCL)was electrospun onto newly designed PP meshes and formed a thin layer of patterned nanofiber mat.The patterns,fiber diameter distribution,cell-material interactions of nanofiber film were also assessed.On the other hand,to fabricate antimicrobial repair meshes,according to the mechanisms of antimicrobial peptides presented in current research literatures,four cationic peptides rich in arginine residues were designed and synthesized in this study.Their antimicrobial activity to four microorganisms(Candida albicans(C.albicans,fungal),Staphylococcus aureus(S.aureus,Gram-positive),Pseudomonas aeruginosa(P.aeruginosa,Gram-negative)and Escherichia coli(E.coli,Gram-negative))and cytotoxicity to human dermal fibroblasts(HDFs)were evaluated.The structure-activity of antimicrobial peptides was also discussed.Two types of antimicrobial meshes were prepared based on antimicrobial peptides and the surface morphology,fourier transform infrared(FTIR)spectroscopy spectra,in vitro release property,mechanical performances,in vitro antibacterial characteristic and cytotoxicity to human dermal fibroblasts of composite scaffolds were evaluated.The results were shown as follows:(1)In order to optimize the performance of hernia repair patches,two types of large-aperture warp knitted meshes were prepared:uniform structure meshes with different pore shapes and ununiform structure meshes with irregular pore shapes.The relationship between the textile structure parameters(such as loop type,guide bar numbers,etc.)and the properties of meshes is comprehensively discussed.Results showed that the pore size of all the prepared meshes were from large pore(1?2mm)to extra-large pore(>2mm).The mechanical properties of the meshes could meet the primary requirements of hernia repair,except for some meshes which showed lower tear resistance strength.The more uniform one textile structure is,the less its anisotropy will be.The addition of the third guide bar increased the ball strength and suture retention strength of meshes.Mesh thickness,mesh density and porosity showed strong or moderate correlation with the ball burst strength,tensile strength in the warp direction and the suture retention strength.The ratio of open loops to closed loops in a repetition of weave of fabric showed influence on the mechanical properties.For example,meshes consisted of all closed loops were more stable and exhibited better mechanical properties than meshes with all open loops.Meshes also showed different properties in the technical face or back and the warp or weft direction.The bending rigidity of the technical back was higher than that of the technical face.The anisotropy of prepared meshes was at a range of 1.25?2.29,which is close to the anisotropy ratio of the composite layer of human abdominal wall reported in literature.In view of these conclusions,the newly prepared macroporous meshes have the potential to be used in hernia repair.Overall,the mechanical properties of meshes designed here are equal or even slightly superior to that of some commercially available meshes reported in previous studies.Therefore,we can meet the demands of specific patients and particular repair sites by designing various meshes with appropriate textile structures.(2)In order to better predict the interactions between mesh and cells in human body,the interaction between cells and materials was studied.By using warp knitted meshes with irregular pore shape as electrospinning receptor,two patterns of nanofiber mats were prepared and their properties were studied.The pattern of nanofiber mats was affected by the structure of meshes.Diverse nanofiber morphology(straight aligned,straight random or spiral random pattern)and fiber diameters(50?70 nm ultra-thin nanofibers or from 330 nm to 700 nm nanofibers)were observed in different regions of a single patterned nanofiber scaffold.The addition of electrospinning nanofibers enhanced cell adherence and proliferation as compared with naked PP meshes.Cell actin filaments spread along the nanofibers and formed a morphology exactly similar with the patterned mats on day 7.Furthermore,cells on thin and aligned patterned nanofibers showed much more elongation and better orientation than that of the spiral random fibers,suggesting that cell morphology can be altered by changing the patterns of scaffolds.This study helps us in further understanding the properties of hernia repair meshes with their textile structures and the biological interactions of cells with different substrates in order to develop new biomedical scaffolds with desired properties.(3)Due to the broad spectrum of antimicrobial peptides and their significant effect on drug-resistant bacteria,four peptides were designed and prepared by solid phase peptide synthesis method according to the antimicrobial mechanism of antimicrobial peptides.Among the four newly designed peptides,PEP-1,PEP-2 and PEP-4 could inhibit and kill these microorganisms at certain concentrations.While PEP-3 only exhibited low inhibition activity against E.coli.PEP-1 rich in arginine residues was more effective against Gram-negative bacteria.PEP-4 with tryptophan and lysine residues in the sequence exhibited enhancement in the antimicrobial activity compared with PEP-3 and presented lowest minimal bactericidal concentration(MBC)to S.aureus and C.albicans in these four peptides.These results indicate that the amount and position of cationic residues in the sequence affects the bactericidal activity and the complement of proline with arginine,tryptophan with arginine and lysine residues would enhance the antimicrobial activity.Moreover,PEP-1,PEP-2 and PEP-4 showed low toxicity at their 1×MBC with no considerable difference with the negative control group in the HDFs cytotoxicity test.This study provides us with a better understanding on the structure-activity relationship,which will be useful for new antimicrobial peptide designs and optimizations.(4)In the AMP-PCL study,namely antimicrobial peptides were mixed with PCL and electrospun onto PP mesh,results showed that PEP-1 was loaded in fibers successfully and could diffuse from nanofibers to inhibit bacteria(E.coli)growth.However,the modified mesh didn't show inhibition to S.aureus.The mechanical properties of fabricated mesh(AMP-PCL)showed no difference with two commercial surgical meshes.What's more,modified mesh was proved to be nontoxic to human dermal fibroblasts,indicating that this method to fabricate meshes with antibacterial activity is feasible and provides a new strategy to the development of surgical meshes.(5)In the study of the other antimicrobial composite meshes,we fabricated four composite patches loaded with different amount of PEP-1(CM-1,CM-3,CM-5 and CM-10).They were consisted of gellan gum,PEP-1,PCL nano fibers and PP mesh.The FTIR spectra indicated that peptides were loaded in patches successfully.The in vitro release of peptides in PBS was prolonged and less than 60%peptides PEP-1 was released for 10 days.The mechanical properties of composite patches were also within the scope of several commercial surgical meshes.In particular,there was no significant difference in the maximum tensile stress and elastic modulus between PROLENE Soft and composite meshes in the warp and weft directions.Composite patches with peptides loading amount of over 3 mg/cm2 showed inhibition against both Gram-negative and Gram-positive bacteria effectively.Four composite patches all presented no toxicity to mammalian cells even at a loading amount of 10 mg/cm2(CM-10).These results demonstrate a new simple and practicable method to make antibacterial materials and the potential application of the antibacterial composite patches for hernia repair.In conclusion,this thesis mainly focuses on the preparation and evaluation of antimicrobial peptides functionalized composite hernia repair patches.First of all,for the mechanical dismatch between hernia repair meshes and the host tissue,the structure-activity relationship between the textile structure parameters and mechanical properties of polypropylene patches was discussed.Then patterned nanofiber membranes were prepared by electrospinning method,and the nanofiber film increased the biocompatibility of patches.Furthermore,broad-spectrum cationic antimicrobial peptides with low toxicity were designed and synthesized;two types of new composite hernia repair patches with antimicrobial function were innovate fabricated by directly mixing or crosslinking method.The results reached the expected goals,and provided development directions and practical guidance for the research and application of antimicrobial composite materials for hernia repair. |
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