Surgical sutures: coincidence or experience?

The strength of surgical knots involves a critical interplay between friction and elastoplasticity

Knots are the weakest link in surgical sutures, serving as mechanical ligatures between filaments. Exceeding their safe operational limits can cause fatal complications. The empirical nature of present guidelines calls for a predictive understanding of the mechanisms underlying knot strength. We identify the primary ingredients dictating the mechanics of surgical sliding knots, highlighting the previously overlooked but critical effect of plasticity and its interplay with friction. The characterization of surgeon-tied knots reveals the relevant ranges of tightness and geometric features. Using model experiments coupled with finite element simulations, we uncover a robust master curve for the target knot strength versus the tying pre-tension, number of throws, and frictional properties. These findings could find applications in the training of surgeons and robotic-assisted surgical devices.

Novel Elastic Threads for Intestinal Anastomoses: Feasibility and Mechanical Evaluation in a Porcine and Rabbit Model

Gastrointestinal anastomoses are an important source of postoperative complications. In particular, the ideal suturing material is still the subject of investigation. Therefore, this study aimed to evaluate a newly developed suturing material with elastic properties made from thermoplastic polyurethane (TPU); Polyvinylidene fluoride (PVDF) and TPU were tested in two different textures (round and a modified, “snowflake” structure) in 32 minipigs, with two anastomoses of the small intestine sutured 2 m apart. After 90 days, the anastomoses were evaluated for inflammation, the healing process, and foreign body reactions. A computer-assisted immunohistological analysis of staining for Ki67, CD68, smooth muscle actin (SMA), and Sirius red was performed using TissueFAXS. Additionally, the in vivo elastic properties of the material were assessed by measuring the suture tension in a rabbit model. Each suture was tested twice in three rabbits; No major surgical complications were observed and all anastomoses showed adequate wound healing. The Ki67+ count and SMA area differed between the groups (F (3, 66) = 5.884, p = 0.0013 and F (3, 56) = 6.880, p = 0.0005, respectively). In the TPU-snowflake material, the Ki67+ count was the lowest, while the SMA area provided the highest values. The CD68+ count and collagen I/III ratio did not differ between the groups (F (3, 69) = 2.646, p = 0.0558 and F (3, 54) = 0.496, p = 0.686, respectively). The suture tension measurements showed a significant reduction in suture tension loss for both the TPU threads; Suturing material made from TPU with elastic properties proved applicable for intestinal anastomoses in a porcine model. In addition, our results suggest a successful reduction in tissue incision and an overall suture tension homogenization.

PLGA Nanoparticle Rapamycin- or Necrostatin-1-Coated Sutures Inhibit Inflammatory Reactions after Arterial Closure in Rats

Background: The inflammatory reaction of sutures and oozing after arterial closure depends on the suture material and the amount of oozing surrounding the sutures. Anti-inflammation coatings have been proven to be an effective strategy to decrease this reaction. The aim of this study was to establish an arterial closure oozing model in rats and to test the effect of poly (lactic-co-glycolic acid) (PLGA) nanoparticle (NP) rapamycin- or necrostatin-1(NEC-1)-coated sutures on the inflammatory reaction after arterial closure. Methods and Materials: A 10 mm arteriotomy was carried out on the carotid artery of Sprague-Dawley rats and closed using 11-0 sutures. PLGA NP-rapamycin and NEC-1 were made. The 11/0 nylon sutures were coated with PLGA NP-rapamycin and NEC-1. Sutures were examined by scanning electron microscopy, hemolysis test, and cumulative release. The carotid arteriotomy was closed using uncoated PLGA NP-rapamycin- and NP-NEC-1-coated sutures. The carotid artery was harvested on day 7. Tissues were examined by histology and immunohistochemistry. Results: There were severe inflammatory reactions in the oozing arteries compared to the normal healing arteries (P = 0.0192). PLGA NP-rapamycin- and NEC -1-coated sutures reduced foreign body reaction compared to the uncoated sutures. There were significantly smaller number of CD3 (P = 0.0068), CD45 (P = 0.0300), and CD68 (P = 0.0011) cells in the PLGA NP-rapamycin- and NP-NEC-1-coated groups compared to the uncoated group. There was a smaller number of p-mTOR (P = 0.0198)-positive cells in the PLGA NP-rapamycin-coated group compared to the uncoated group. There was a smaller number of TNFα (P = 0.0198)-positive cells in the PLGA NP-NEC-1-coated group compared to the uncoated group. Conclusions: In this rat carotid artery oozing model, PLGA NP-rapamycin- or NP-NEC-1-coated sutures can inhibit inflammatory reaction and foreign body reaction. Although this was a small rodent animal experiment, this coated suture may have a potential clinical application in the future.

Cross-section modified and highly elastic sutures reduce tissue incision and show comparable biocompatibility: in-vitro and in-vivo evaluation of novel thermoplastic urethane surgical threads

Surgical sutures are indispensable for a vast majority of operative procedures. An ideal suture is characterized by high tissue compliance without cutting into the mended tissue and optimal biocompatibility. Therefore, we assessed these mechanical and biological properties for novel elastic thermoplastic polyurethane (TPU) and cross-sectional modified "snowflake" sutures. Circular and "snowflake"-shaped TPU threads were manufactured and compared to similar surface modified polyvinylidene fluoride (PVDF) sutures. Regular PVDF sutures were used as the control group. Single-axis tensile test with and without gelatinous tissue surrogates were performed to evaluate the suture incision into the specimens. Biocompatibility was evaluated by subcutaneous implantation (n = 18) in rats for 7 and 21 days. Histology and immunohistology was conducted for assessment of the foreign body reaction. Regular and modified TPU threads showed a significant reduction of incision into the tissue surrogates compared to the control. Both TPU sutures and the modified PVDF sutures achieved comparable biocompatibility versus regular PVDF threads. Detailed histology revealed novel tissue integration into the notches of the surface modified sutures, we termed this newly shaped granuloma "intrafilamentous" granuloma. Elastic TPU threads showed a significant reduction of tissue surrogate incision and suture tension loss. Biocompatibility did not significantly differ from standard PVDF. Histology demonstrated tissue ingrowth following the surface modification of the suture referred to as "intrafilamentous" granuloma. Further in vivo studies are required to illuminate the exact potential of the new sutures to optimize intestinal anastomosis.

Miniaturized Sensors Registering the Long-Term Course of Suture Tension In Vivo under Varying Intra-Abdominal Pressure

BACKGROUND

Failure of laparotomy closure develops after up to 20% of abdominal operations. Suture tension has an influence on the quality of tissue regeneration. No sensors are available to register suture tension dynamics in vivo.

METHODS

In a series of animal experiments, the effect of suture tension on the ultrastructure of the healing incision was examined. Surgeons' ability to suture with target tension was tested. An implantable sensor and data logger were developed and tested experimentally in sutures closing midline laparotomies in pigs both under normal and elevated intra-abdominal pressure.

RESULTS

High suture tension has a negative influence on the regeneration of laparotomy incisions. Running sutures for laparotomy closure lose 45% of their initial tension over periods of 23 h. Intermittent elevation of intra-abdominal pressure to 30 mm Hg leads to a near total loss of suture tension after 23 h.

CONCLUSION

Surgeons are not able to control and reproduce suture tension. Suture tension dynamics can be measured in vivo by the sensor developed. Further research is needed to define a tissue-specific suture tension optimum to reduce the incidence of complications after laparotomy. Techniques for laparotomy closure need to be modified.

Positioning of the cross-stitch on the modified Kessler core tendon suture

Cryopreserved human tendons were sutured with different variations of a modified Kessler-type grasping suture in a series of different designs in order to assess the influence of the distance between the cross-stitch on the core suture (5 and 10 mm from the cut tendon edge) on the peripheral suture. An original mathematical model was employed to explain the mechanical behavior (strength, deformation, and distribution of load) of the different suture designs. The effect of the peripheral epitendinous suture, combined with the distance of the core suture, was evaluated. The variation of core suture distance had no relevant consequences on the overall resilience of the design. However, increasing the distance between the cross-stitches of the core suture reduces the deformation that is absorbed not only by the core suture itself but also by the peripheral suture. Adding a peripheral epitendinous suture to a 10-mm design almost doubles the breaking load in absolute values. The mathematical model predicts that the peripheral suture will support a greater load when the distance of the core suture cross-stitches is increased. The evidence level is II.