| Background and objective:Tracheal stenosis is a kind of emergency condition that is relatively common in clinical practice.It is a narrowing of the trachea and bronchus due to the airway itself or the compression of external lesions.Mild tracheal stenosis can cause symptoms such as cough,sputum,chest tightness,etc.Severe tracheal stenosis can cause severe dyspnea,sitting breathing,and obvious"three concave sign".Simultaneously,the discharge of sputum is difficult and suffocation occurs at any time which condition must be dealt with urgently.At present,the treatment of tracheal stenosis is mainly based on interventional therapy,in which airway stenosis can be immediately relieved.Now it has been widely used in the treatment of various benign and malignant tracheal and bronchial stenosis.However,there are many postoperative complications in this treatment method,such as stent dislocation,granulation tissue hyperplasia,stent fracture,and airway restenosis.Once the stent is found to be displaced or broken,it needs immediate treatment and removal of the stent if necessary.The removal of the stent has a higher risk and increases the patient's pain and expense,which greatly hinders the application of airway stents.In order to avoid and handle related complications,various new types of stents are under continuous development.The biodegradable stent is a new type of stent that can support the airway in a certain period of time.Once the stent is no longer needed,the stent can gradually degrade until it disappears.Biodegradable stent can meet the requirements of immediate relief of stenosis and ensure airway patency.At the same time,it has good biocompatibility and is easily tolerated by patients.It can also reduce the risk of stent restenosis caused by granulation tissue hyperplasia;especially for patients with benign airway stenosis.After the cause of stenosis is removed,the stent can be degraded by the body,which avoids the risk and pain of secondary removal and reduces the patient's treatment cost.It has been a major hot spot for clinical research.Our study mainly focused on the application of degradable magnesium alloy stents,providing relevant experience for the development and application of novel stents,and applying them to animal models of airway stenosis to understand its safety and feasibility with the aim to provide new methods to dealt with clinical complications.Materials and methods:1.Establishment of animal models of airway stenosisThirty two healthy New Zealand white rabbits were used,then were under operation of the trachea between tracheal cartilage rings,and an airway stenosis animal model was prepared by brushing and injuring the tracheal mucosa.Four weeks later,rabbits were taken thoracic MSCT in order to determine the tracheal stenosis and to calculate the stenosis rate.2.Preparation of biodegradable magnesium alloy stentTwo kinds of biodegradable alloy wires were made by hot extrusion and cold drawing technique using the materials of magnesium-zinc-bismuth alloy,the diameter of which were 0.24mm and 0.28mm respectively.Two kinds of alloy wires were applied to a single-wire integrated weaving technique to make 15 bare supports with8mm*20mm,and their physical properties such as supporting force were measured.3.Application of biodegradable magnesium alloy stent in animal model of airway stenosisThirty rabbits with airway stenosis were established.Fifteen stents made of two alloy wires each with different diameters were placed under the DSA into the trachea of experimental rabbits,and then the general condition of rabbits and stent expansion were observed.Three experimental rabbits were sacrificed at 3 days,7 days,15 days,one month and two months after stent placement,and the stents were taken out after dissection to observe the fracture of stent wire and stents compression and degradation.Tracheas of these rabbits were used to observe the proliferation of granulation tissue and the retention of sputum in the rabbit airway mucosa,and the gross specimen were taken for histopathological examination.Results:1.Establishment of animal models of airway stenosis.Thirty experimental rabbits were generally in good condition after applying hair brush to damage airway mucosa.Two rabbits died of airway bleeding the second day.Four weeks later,rabbits were taken MSCT,the stenosis rate of tracheal was43.07-83.72%.The Myer-Cotton method was used to evaluate the stenosis rate of trachea.13.33%(4/30)of rabbits suffered grade I degree stenosis,56.67%(17/30)suffered grade II degree stenosis,30%(9/30)was in grade III of stenosis.2.The performance test of biodegradable magnesium alloy stents.The supporting force of biodegradable magnesium alloy stents made of alloy wire with diameters of 0.24mm and 0.28mm in diameter both stronger than that of the nickel-titanium(Ni-Ti)alloy stents.And the supporting force of stents with wire diameter of 0.28mm is greater than that of 0.24mm.The average expansion rate of the biodegradable magnesium alloy stents made of the wire diameter of 0.24mm and0.28mm was respectively 74.86%and 83.99%.Compared with the self-expanding nickel-titanium alloy stents,the expansion performance of magnesium alloy stents was poor.3.The general condition of the experimental rabbits after stent implantation.All magnesium alloy stents were successfully placed in the trachea of experimental rabbits.The second day,some experimental rabbits appeared anorexia,audible and wheezing breathing,but all experimental rabbits were in good condition both mentally and physically.All experimental rabbits survived until the end of the experiment.4.The situation of granulation tissue hyperplasia and the degradation of magnesium alloy stent.The experimental animals were dissected 3 days,7 days,15 days,1 month and 2months after the insertion of the inner stent.At day 3,the stents were taken out and it was found that the scaffold structure was intact without collapse,no alloy wire was broken,the inner wall of the trachea was smooth,no fluid retention was observed,and no granulation tissue proliferation was observed.At day 7,the stent structure was basically complete,some of the alloy wire was seen to be broken,and a small amount of sputum was retained on the inner wall of the trachea and the stent.But no granulation tissue proliferation was observed.At day 15,the stent structure basically collapsed,and most of the alloy wires were seen to be broken.There were more phlegm retention on the inner wall of the trachea and the remaining alloy wire,and no granulation tissue proliferation was observed.One month later,stents and fractured alloy wires were not seen.Considering that the magnesium alloy stent was completely degraded and absorbed,the inner wall of the airway was smooth,no obvious phlegm retention was observed,and no granulation tissue proliferation was observed.In the 2~ndd month,no stents or fractured alloy wires were found.The wall of the airway was smooth,no fluid retention was observed,and no granulation tissue proliferation was observed.Conclusions:The biodegradable magnesium alloy airway stent has good radial support force but poor expansion performance.After being inserted into the airway,the wire stent is prone to breakage than metal wire stent,but has good biocompatibility and less proliferation of granulation tissue. |
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