Design And Characterization Of Warp Knitted Pelvic Floor Mesh

Pelvic muscles may be damaged with the female age increase and harm brought by birth,which causes gynecological diseases including pelvic organ prolapse(POP)and stress urinary inconvenience(SUI).Adoption of medical mesh to reinforce and support pelvic muscles is a common treating method.Polypropylene(PP)is a main material used in pelvic floor mesh.Lightweight PP mesh type consisted of less amount of material is considered to have good effect.The paper adopted three-bar warp knitting technology to repair lightweight PP meshes with three structure,including rhombus pore-shape structure A,rectangle pore-shape structure B,hexagon pore-shape structure C.Ten specimens were prepared by heat setting technology with different pore-size,porosity and surface density.The effect of porosity,knitted structure and materials on mesh structural parameters and mechanical property was discussed,in order to achieve both light weight and stable mechanical property.Four optimal lightweight PP meshes and one PLA meshes were chosen for biocompatibility characterization.Cytotoxicity was measured by CCK8 method.Blood safety was analyzed by hemolytic test and blood clotting test.Reproductive and developmental toxicity was measured by hypodermic implantation in 24 rats with two generations-one nest testing method.Implantation property was measured by 150 meshes and 90 rabbits.Animal health condition was recorded and mesh-tissue thickness,breaking strength,adhesion,shrinkage,pathologies were tested after 1 month,3 months,6 months of implantation respectively.PP-A-4 mesh and commercial Avaulta~? mesh were used for clinical research by132 meshes in pelvic floor reconstructive surgery.Patients were followed up 6 weeks,3 months and 6 months;POP-Q and gynecologic ultrasonography were examined;the recurrence of complications were recorded.The paper used two-bar warp knitting technology to fabricate warp sateen PP/Polylactic acid(PLA)composite mesh with hexagon pore shape.Membrane-coated composite meshes with macroporous PP mesh support were prepared using electrospinning method and dipping method.The PP/PLA composite mesh’s structural parameters,mechanical property and degradation property were discussed.The membrane-coated meshes’ structural parameters,mechanical property,hydrophilic performance,hot water shrinkage performance and degradation property were discussed.Three composite meshes were used for biocompatibility characterization.Cytotoxicity was measured by CCK8 method.Blood safety was analyzed by hemolytic test and blood clotting test.Implantation property was measured by 48 meshes and 24 rats;thickness,breaking strength,adhesion,shrinkage,pathologies were tested after 2 weeks,4 weeks of implantation respectively.For lightweight mesh type,the design requirement was raised basing on a good repair ability and moderate inflammatory response.Mesh should have surface density less than 50 g/m~2,pore size larger than 75 μm,porosity larger than 60%.Three commercial meshes(Surgimesh~? Prolapse,Surgimesh~? Sling,Gynemesh~? PS)were chosen as reference model for mesh design.Three kinds of lightweight meshes were fabricated by three-bar warp knitting technology,IV including pillar/inlay structure A with rhombus pore shape,pillar/inlay structure B with rectangle pore shape,modified locknit structure C with hexagon pore shape.Nine PP mesh specimens were fabricated using 0.1 mm PP monofilaments as raw material and warping,knitting,heat setting technology.One PLA mesh specimen was fabricated by 0.12 mm PLA monofilaments.Different loop density was designed in the heat setting technology and changed mesh pore size,porosity and surface density.The paper discussed effect of porosity,knitted structure and composed material on lightweight mesh’s structural parameters and mechanical property.The results revealed that: mesh pore size,surface density and thickness decreased with the increase of porosity.Mesh breaking strength,bursting strength,bending stiffness decreased with the increase of porosity,but suture pulling-our force almost had no change.Porosity of 68.53% and 64.46% was considered to be better for mesh being light and soft,with supplementary strength.Mesh with pillar/inlay structure had larger porosity,significant difference between mesh longitudinal direction and transverse direction.Modified locknit structure mesh had smaller surface density and thickness;the difference between properties in two directions was little.Under the condition of a same composed material,similar loop density and thickness,knitting structure almost had no effect on mesh bursting strength.Because of the 0.12 mm diameter of PLA monofilaments,the PLA-A-1 mesh was obvious thicker and heavier(92 g/m~2).Because of the PLA monofilaments’ lower strength(30.55 c N/tex)to PP monofilaments(57 c N/tex and 58.31 c N/tex),the mesh’s breaking strength,bursting strength and suture pulling-out force was weaker than that of two lightweight PP meshes(SP Model and PP-A-2),but the bending stiffness was larger.The paper conducted research on the biocompatibility of lightweight PP mesh.Based on different monofilament type,meshes’ cytotoxicity,blood compatibility,reproductive and developmental toxicity were tested and analyzed.Based on different monofilament type and knitting structure,150 meshes were implanted on 90 animals and evaluated after 1 month,3 months,6 months respectively.The results revealed that: the cell relative growth rate of each mesh group was larger than 82%,scaled as grade I,the materials used were proved to be safe.All mesh groups’ hemolysis ratio were smaller than 1%,satisfied the standard requirement(≤5%).The difference value of blood clotting time before and after mesh implantation was smaller than 2 s.Female rate could give birth to offspring normally;the litter size and weight between two generations had no difference.Lightweight PP mesh was demonstrated to have good safety,no harm in cell growing,blood and reproductive development.More than 90 percent of animals(82/90)had good surgical wound healing.Four cases of abscess occurred in PLA-A-1 mesh group,in which animals’ weight increased slowly in the first 3 months but recovered later.The modified locknit structure of PP-C-4 mesh led to a larger folding rate(46.67%).Meh-tissue thickness,breaking strength,morphologies and pathologies presented a normal tissue growing condition in the 6 months period;no significant different was observed among each group.Shrinkage of PP-C-4 and PLA-A-1 was the smallest(<3%).PP-A-4 and SP model were deformed along transverse direction with better stretching performance,causing larger shrinkage(about 30%).Adhesion between mesh and tissue was mainly suitable moderate adhesion.Only PLA-A-1 was tested of a severe adhesion and caused damage during separation in surgery.The clinical research was conducted by 132 meshes in 6 months postoperatively.The recovery rate of PP-A-4 was 98.39% and that of control group was 100%.No significant difference was found in POP-Q follow-up survey between two groups.The postoperative PFIQ-7 was obvious lower;patients’ life quality was improved by operative treatment.Two kinds of composite meshes were designed in this work,which are PP/PLA composite mesh and membrane-coated mesh.Two-bar warp knitting technology was used for mesh fabrication consisted of 0.1 mm PP monofilaments and PLA monofilaments by RSEL compound needle machine.PP/PLA composite mesh was knitted to a warp sateen structure and hexagon pore shape named Inter-PP/PLA.Membrane-coated meshes with macroporous PP support were prepared by electrospinning and dipping method.An optimal processing parameter was decided by discussing the effect on membrane structure,which was PLA/PCL of 7/3,DCM:DMF of 80:20,solution concentration of 8%,voltage of 14 KV,receiving distance of 15 cm,solution flow rate of 0.6 ml/h.The aluminum foil with PP mesh adhesion was receiver for electrospinning microfiber;fluororubber-acetone solution(w/v 8%)was binder between PP support layer and membrane layer.Two electrospinning membrane-coated mesh were named Coa-Ele-PP(A)and Coa-Ele-PP(C).The dip-coating process was: immersing PP macroporous support in PLA/PCL solution for a certain time and taking out for dry.The dipping membrane-coated meshes were named Coa-Dip-PP(A)and Coa-Dip-PP(C).Mechanical property and degradation property were discussed in this work.Inter-PP/PLA mesh was superior to a similar commercial mesh with a smaller surface density(19.9 g/m~2)and higher porosity(84.1%).The breaking strength,bursting strength of Inter-PP/PLA mesh was similar to that of lightweight PP mesh-SP Model,but suture pulling-out force and bending stiffness were larger.The larger stiffness of mesh would improve surgical convenience.Inter-PP/PLA mesh was completely degraded in 74 weeks in PBS solution,with mass weight loss reaching to 62.4±0.3%.The strength loss reached to a peak value after 64 weeks degradation,with value of 63.2±0.8% in longitudinal direction and 69.2±0.9% in transverse direction.Electrospinning membrane-coated mesh and dipping membrane-coated mesh both had small thickness value(<0.5 mm),but the latter one also had large surface density(79.96±8.07 g/m~2 and 65.34±4.12 g/m~2).The mechanical property of membrane-coated mesh mainly depends on the PP macroporous support.Membrane crushing phenomenon only occurred on dipping mesh and caused weaker flexibility,unexpected for pelvic floor repair.Electrospinning membrane was degraded in 20 weeks,shorter than that of dipping membrane,basically degraded in 32 weeks.The paper discussed biocompatibility of composite mesh.Three meshes’ [Inter-PP/PLA,Coa-Ele-PP(A),Coa-Dip-PP(C)] cytotoxicity,blood compatibility were tested and analyzed.Forty-eight meshes were implanted in 24 rats and evaluated after 2 weeks,4 weeks respectively.The results revealed that: cell relative growth rate of each mesh group was larger than 89%,scaled as grade I,the materials used proved to be safe.All mesh groups’ hemolysis ratio were smaller than 2%,satisfied the standard requirement(≤5%).The difference value of blood clotting time before and after mesh implantation was smaller than 2 s.Composite mesh was demonstrated to have good safety,with no harm in cell growing and blood.After 4 weeks of implantation,continuous tissue growth was observed on Inter-PP/PLA and Coa-Ele-PP(A)mesh,but no tissue growing on Coa-Dip-PP(C)during 0 to 2 week.The fresh tissue increased mesh-tissue complex’s thickness and strength.Coa-Dip-PP(C)had the most stable area with shrinkage smaller than 3%,while the shrinkage of Inter-PP/PLA and Coa-Ele-PP(A)was larger than 10%.The adhesion condition between meshes and their surrounding tissues was: Inter-PP/PLA(severe adhesion)> Coa-Ele-PP(A)(moderate adhesion)> Coa-Dip-PP(C)(mild adhesion).The tight adhesion for Coa-Ele-PP(A)was considered to be most suitable for composite mesh use in repairing pelvic floor.In conclusion,the paper conducted systematized research on lightweight mesh and composite mesh.Mesh design,fabrication an characterization were discussed in order to satisfy the requirement for light weight,stable mechanical property and good biocompatibility.The work provides research foundation for pelvic floor mesh with knitted structure.