Abstract:

Objective Minimally invasive intervention with esophageal covered stents is an important means of palliative treatment of esophageal stenosis. However, adverse events of conventional esophageal covered stents have often been reported in publications recently. A new mechanically braided integrated esophageal covered stent is designed and expected to overcome the shortcomings of the existing esophageal covered stent and become the next generation of innovative products, but its basic research is not sufficient.

Method A series of integrated esophageal covered stents were braided using integrated braiding technology by adjusting the point per inch (PPI), the diameter of nickel titanium alloy wire and the number ratio of the wire to PET yarns. Moreover, the mechanical properties and compliance of these covered stents were systematically studied, mainly discussing the structure-property relationship between the above braiding parameters and the radial compression force, elastic recovery rate, stress relaxation rate, diameter reduction rate and elastic straightening force of the covered stents.

Results The diameter of nickel titanium alloy wire is the main parameter affecting the radial compression force of the esophageal covered stent. Within the scope of this study, the larger the diameter of nickel titanium alloy wire, the better the radial support of the covered stent. Compared with 0.24 mm nickel titanium alloy wire, 0.20 mm and 0.22 mm nickel titanium alloy wires can meet the radial support force required for esophageal stent, and a larger nickel titanium alloy wire diameter reduced the flexibility of the covered stent (Fig.7), so the suitable nickel titanium alloy wire diameter should be 0.20-0.22 mm. PPI has less effect on the radial support and compliance of the covered stent (Fig.4), that when the PPI increases, the radial support of the covered stent is better. When the PPI is 40, the diameter reduction rate increases when it is bent (Fig.7), so the optimal PPI should be 35. The number ratio of the wire essentially refers to the content of nickel titanium alloy wire in the covered stent. The ratio is large, the content of nickel titanium alloy wire is high, and the radial support force of the covered stent is high (Fig.4). However, at the same time, that the diameter reduction rate and elastic straightening force of the covered stent increase, that is, the compliance decreases (Fig.7 and Fig.8). Therefore, the more suitable number ratio should be 1:3. It is comprehensively considered from the perspective of the properties of radial support, bending compliance and lumen conformation of mechanically braided integrated esophageal covered stent, that its optimal parameter combination included the diameter of nickel titanium alloy wire were 0.20 mm and 0.22 mm, PPI was 35, and the number ratio of the wire was 1:3.

Conclusion Correlations of braiding parameters and mechanical properties of mechanically braided integrated esophageal covered stents have been established by designing, braiding and characterizing a series of esophageal covered stents. Disclosure of the structure-property relationship may extremely facilitate and push the development of mechanically braided integrated esophageal covered stents, since braiding machines for producing large diameter ones are customized and high-cost. On the other hand, clinical needs for the mechanically braided integrated esophageal covered stents are versatile and personalized. Therefore, it is facilitated to design and produce customized covered stents for varying patients based on the results of the present work. If one needs a strong support covered stent, the first influencing factor considered should be the diameter of nickel titanium alloy wire. Likewise, if the permeability is firstly considered, then PPI should be selected to adjust first. The number ratio mainly affects the flexibility of the covered stents. To sum up, this study may provide an experimental basis for accelerating the commercialization of the mechanically braided integrated esophageal covered stent. It is expected that this study can provide beneficial reference for the further development of integrated esophageal covered stent products, and promote the personalized and precise treatment of esophageal covered stent in clinical practice.

Key words: esophageal stenosis, esophageal covered stent, braiding, mechanical property, integrated