| Background:Maxillary canines play an important role in facial beauty,dental aesthetics,dental arch development and functional occlusion.Impacted canines are often accompanied by cysts.In view of the normal physical and psychological development of patients,timely treatment of cysts is of great significance.At present,the methods for impacted teeth include:(1)Combined orthodontic and surgical treatment,so called Surgically guided eruption treatment;(2)Auto-transplantation of impacted teeth;(3)Early interceptive treatment and etc.However,for the canine teeth with deep impacted position,the use of conventional surgically guided eruption treatment will cause greater trauma to patients.We can first release the pressure inside the cyst through cyst fenestration decompression,and promote the centripetal growth of the surrounding bone wall into the cyst cavity,so that the impacted tooth can erupt by itself for a period of time along the predetermined eruption channel.It is a great method to maximize the preservation of soft and hard tissues.However,due to the open wound caused by this method,drainage devices such as iodoform gauze need to be placed at the wound and channel of eruption to avoid secondary infection,which means the compliance of patients and their families has a great impact on the prognosis.Therefore,it is nessary to study a kind of antibacterial biodegradable polymer material,which does not need frequent flushing and dressing change after filling the wound,and has a continuous and stable bacteriostatic effect.Polylactic acid((Poly(l-lacticacid),PLLA))is a kind of high molecular polymer with good biocompatibility and easy to obtain,so it is often used as a drug loading device for bone repair.The PLLA fiber prepared by melt spinning technology has good mechanical properties and can be made into a fiber material with three-dimensional structure similar to cotton,which can be used for wound filling.However,because of the lack of enough antibacterial properties,the PLLA fiber can not meet the clinical needs of filling materials after windowing decompression.We plan to modify its surface in order to obtain good antibacterial properties.Antimicrobial peptide(Antimicrobial Peptides,AMPs)is a powerful broad-spectrum antibacterial amino-peptide,which has a rapid role,a low minimum inhibitory concentration and it is hard to produce drug resistance.It can be used as an effective substitute for antibiotics in clinical treatment,but there are few studies on its application in fiber modification.Therefore,in this study,PLLA fibers were prepared by melt spinning,then through the chemical reaction between the surface group of Polydopamine(PDA)and the special group on the surface of the antimicrobial peptide and the physical adsorption produced by the three-dimensional structure of the PLLA fiber,the antimicrobial peptides were modified onto the fiber surface to complete the modification.On the basis of not changing the original good properties of PLLA fiber,the modified material has better antibacterial and biocompatibility,which provides a theoretical basis for PLLA fiber biomimetic cotton as a filling material is used in clinical practice.Methods:1.Preparation of original PLLA fiber(PLLA group)The melt spinning technology is used to prepare PLLA particles into PLLA fibers.2.Preparation of polydopamine-assisted grafted antimicrobial peptide PLLA fiber(PLLA/DH-36 group)and only polydopamine grafted PLLA fiber(PLLA/PDA group)Polydopamine assisted deposition technology and antimicrobial peptides are used to modify the surface of PLLA fibers to complete the modification.3.Characterization of Physico-Chemical Properties of materialsThrough XPS elemental analysis,contact angle,scanning electron microscope,Fourier transform infrared spectroscopy(FT-IR)analysis to verify the success of the modification.4.Evaluation of antibacterial properties of materialsS.aureus and E.coli were selected as the experimental strains for the evaluation of the antibacterial properties of the materials,and the experiments were divided into three groups: group of original PLLA fiber(PLLA group),group of only polydopamine grafted PLLA fiber(PLLA/PDA group),and group of polydopamine-assisted grafted antimicrobial peptide PLLA fiber(PLLA/DH-36 group).The materials was co-cultured with the bacterial solution,and the bacterial concentration of each group was detected by multi-detection microplate reader.The material was placed on Agar plate for bacteriostatic rings test;Live/dead staining was used to observe the bacterial morphology on the surface of the material;At the same time,the release rate of antimicrobial peptides in vitro was characterized by the release experiment of antimicrobial peptides.5.Material cytocompatibility evaluationTo evaluate the cytocompatibility of materials,MC3T3-E1(mouse preosteoblast line)cells were cultured in 96-well plates,and different groups of materials were placed in them.At the same time,a blank control group was set up.After 24 hours of culture,the cytotoxicity of the above materials was detected by CCK-8 method,and the number and morphology of cells on the surface of the materials were observed by DAPI-FITC staining.6.Animal experimentA skin infection model was established on the back of the mouse.Seven days after each group of materials was implanted,the skin tissue containing the material was collected to prepare soft tissue sections for HE staining analysis,to observe the type and number of cells in the tissue,and to evaluate the antibacterial activity of the material in vivo.Results:1.Characterization of Physico-Chemical Properties of materialsThe results of scanning electron microscope showed that the PLLA fiber with a diameter of about 8 ? m-16 ? m was successfully synthesized,and the fiber was uniform,there was no unmelted polymer on the surface.The surface N content of the PLLA/DH-36 group was about 17.08%,which was higher than 14.61% of the PLLA/PDA group and 3.68% of the PLLA group.The results of contact angle test were 0 °in PLLA/DH-36 group,109.13 °in PLLA/PDA group and 123.63 °in PLLA group.The results of Fourier transform infrared spectroscopy showed that there were obvious amino functional groups in the PLLA/DH-36 group,which indicated that the antimicrobial peptides were successfully grafted onto the surface of PLLA fibers,and the wettability and hydrophilicity of the fibers were improved.2.In vitro release experiment showed that the release efficiency of antimicrobial peptides in 150 min increased gradually,reached the highest in 150 min,and then decreased slowly;after 7 days of observation,the release rate tends to flatten out.3.The antimicrobial activity experiment shows that the PLLA/DH-36 group has good antibacterial activity,but the antibacterial process can only be carried out in situ.4.CCK-8 test showed that due to the explosive release of AMPs,the cytotoxicity of PLLA/DH-36 group was slightly higher than that of blank group within 3 days,but there was no significant difference between PLLA/DH-36 group and PLLA group,and its good biocompatibility could be restored after 3 days.The result of DAPI-FITC staining was consistent with that of CCK-8.5.Tissue section staining showed that 7 days after the material was implanted into the body,there were more fibroblasts in the PLLA/DH-36 group than in the PLLA group,which proved that it could stimulate the formation of granulation tissue and promote wound healing.Conclusion:1.PLLA fibers with uniform diameter distribution can be successfully prepared by melt spinning technology.The modified materials(PLLA/DH-36 group)with antibacterial properties and good biocompatibility can be obtained by surface modification of raw fibers with PDA and antimicrobial peptides.2.The PLLA/DH-36 group of materials combined with the antimicrobial peptide HHC-36 has a good antibacterial effect on both gram-positive and gram-negative bacteria,but its proliferation-promoting effect has not been observed.This may be due to the three-dimensional structure of the fiber is not conducive to cell adhesion.3.PLLA/DH-36 group did not produce bacteriostatic loop,indicating that its in-situ antibacterial effect is better,and the local reaction only occurred after implantation,which would not lead to serious systemic reaction. |
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