Effects Of Hyaluronic Acid Filler On The Mechanical Properties Of PPDO Thread And Skin Collagen

Background:Many doctors suggested simultaneous use of Hyaluronic Acid?HA?filler and Poly?p-dioxanone??PPDO?thread to meet the effect of lifting and filling at the same time.However,some scholars hold the objection that HA filler will accelerate the degradation of the thread and destroy the mechanical properties of the thread.Due to the obvious difference between the in vitro experiment and in vivo,it is not enough to criticism the existence of HA filler is an unfavorable factor to PPDO thread.In order to answer this further,we designed in vivo experiment to explore the pros and cons of HA filler on PPDO thread.Objective:To study the effects of HA fillers on the mechanical properties of PPDO thread in rat's vivo and on the collagen synthesis of skin stimulated by PPDO thread,so as to provide experimental evidence reference for the positive or negative influence of HA filler on PPDO thread.Methods:The experiment was carried out 15 SPF female Wistar rats.12 rats were randomly selected and embedded with PPDO thread subcutaneously in the back on both sides of the spine.0.5ml HA filler was injected subcutaneously at the midpoint of PPDO thread buried on the left side,while the Normal saline?NS?was injected on the right side as the self-control.The rest three rats were cut subcutaneous tissue of the back as blank control.In the 1^st week,the 4^th week,the 8^th week and the 12^th week after operation,three rats were randomly selected to observe the general situation,and tissue samples and wire samples were collected.And HE staining,Sirius red staining and immunohistochemistry were used to compare the increase of collagen in each group;DNS100 electronic universal testing machine was used to test the PPDO thread samples taken out at each time point;one NS+PPDO thread sample was randomly selected at each time point,and the change in surface morphology of PPDO thread at different degradation time was observed by scanning electron microscope?SEM?.The experimental data were analyzed by GraphPad prism 8 software,and the statistical chart was drawn.The measured data were all expressed as?±s.The comparison between the two samples was tested by t and P<0.05 indicated that there was statistical difference.Results:1.General observation:the rats were generally in good condition during the experiment,and there was no infection on the skin of PPDO thread puncture point and buried area.In the NS+PPDO group,there was no visible local uplift on the skin of back of rats and the intact wires could be touched in the first 8 weeks,but it was found that the wires were broken into small segments in the 12^th week.In the HA+PPDO group,it is thus clear that there was local uplift in the injection site of the filler in the whole process of the experiment,and as in the NS+PPDO group,the HA+PPDO group only found that the wire broke into segments at the 12^th week.2.Histological observation:HE staining shows that the collagen fibers of the two group were gradually increased with time,and in the 1^st and 4^th week,there were a few inflammatory cells in the tissues of both groups,but in the 8^th and 12^thh week,the number of inflammatory cells decreased significantly.Immunohistochemistry staining shows that the expression of type I collagen fibers of the two group were gradually increased with time and were significantly higher than that in blank control group?p<0.05?.Besides,the expression of type I collagen in HA+PPDO group was significantly higher than that in NS+PPDO group at the same time?p<0.05?.Sirius red staining shows that with time gose by,type I collagen fibers gradually increased while type III collagen fibers gradually decreased in both groups.3.Tensile test:The initial maximum stress of PPDO thread was?34.60±1.04?N and the stress percentage was?25.60±0.73?%.The maximum stress of each time point in the HA+PPDO group were?25.53±1.56?N in the 1^st week,?17.60±1.08?N in the4^th week and?11.63±1.34?N in the 8^th week respectively and the stress percentages in the HA+PPDO group were?14.37±0.70?%,?8.50±0.67?%,and?5.67±0.76?%respectively;the maximum stress in the NS+PPDO group were?26.70±1.40?N in the 1^st week,?18.10±0.85?N in the 4^th week and?12.03±1.27?N in the 8^th week and the stress percentages in the NS+PPDO group were?15.49±0.85?%,?9.44±0.88?%,and?5.65±1.41?%respectively.There was no significant difference between the HA+PPDO group and the NS+PPDO group for the maximum stress and the strain percentage?p>0.05?.With the extension of the implantation time,the maximum stress and the stress percentages of each group in the HA+PPDO group and NS+PPDO group decreased significantly?p<0.05?.4.SEM observation:The physical morphology changes of PPDO thread in the degradation process are as follows,the barb of PPDO thread which was not put into the tissue fitted the thread itself,and the thread is smooth without cracks.With the prolongation of tissue insertion time of PPDO thread,the barb of the thread gradually deviated to the main body and its shape curved outwards,the internal cracking degree of barb to the thread body deepened and and the surface of PPDO thread appeared scattered small cracks.The diameter of PPDO thread increased with time in the degradation process.Conclusion:PPDO thread has good mechanical properties,and can stimulate skin to synthesize collagen.HA filler has no obvious effect on the mechanical properties of PPDO thread in rat's vivo,but it can enhance the collagen synthesis of skin stimulated by PPDO thread.