Vascular anastomosis using controlled phase transitions in poloxamer gels

Journal name:
Nature Medicine
Volume:
17,
Pages:
1147–1152
Year published:
DOI:
doi:10.1038/nm.2424
Received
Accepted
Published online

Abstract

Vascular anastomosis is the cornerstone of vascular, cardiovascular and transplant surgery. Most anastomoses are performed with sutures, which are technically challenging and can lead to failure from intimal hyperplasia and foreign body reaction. Numerous alternatives to sutures have been proposed, but none has proven superior, particularly in small or atherosclerotic vessels. We have developed a new method of sutureless and atraumatic vascular anastomosis that uses US Food and Drug Administration (FDA)-approved thermoreversible tri-block polymers to temporarily maintain an open lumen for precise approximation with commercially available glues. We performed end-to-end anastomoses five times more rapidly than we performed hand-sewn controls, and vessels that were too small (<1.0 mm) to sew were successfully reconstructed with this sutureless approach. Imaging of reconstructed rat aorta confirmed equivalent patency, flow and burst strength, and histological analysis demonstrated decreased inflammation and fibrosis at up to 2 years after the procedure. This new technology has potential for improving efficiency and outcomes in the surgical treatment of cardiovascular disease.

At a glance

Figures

  1. Thermoreversible properties of poloxamer nanogel.
    Figure 1: Thermoreversible properties of poloxamer nanogel.

    (a) Diagram of the traditional vascular anastomosis procedure. Sutures are placed in collapsed vessel from adventitia through intima on one end, followed by suture placement from intima to adventitia on the other vessel end (left). Sutures are laid down flat and tightened, which approximates the intima, while the lumen is opened to allow placement of sutures (middle). Sutures are then applied circumferentially for the anastomosis, making a complete seal to prevent leakage (right). (b) Elastic modulus of P407 dissolved in PBS in varying concentrations from 15.0% (wt/vol) to 18.0% (wt/vol) with heating from 10 °C to 40 °C. Increasing poloxamer concentration had a correlative increase in the elastic modulus and a corresponding decrease in the transition temperature. (c) Graph shows the rapid transition of 16.5% (wt/vol) P407 to a stabilized elastic modulus when heated from 10 °C to 40 °C, with rapid melting to baseline after cooling. (d) Elastic modulus of P407 with BSA added in 0.25% (wt/vol) increments to 1.5%. A formulation of 16.5% (wt/vol) P407 containing 0.25% (wt/vol) BSA was able to initiate phase transition at 30 °C and achieve a maximal elastic modulus of approximately 10,000 Pa at a temperature of 40 °C. (e) The heated poloxamer easily stabilized an open lumen and allowed precise approximation of the intima (above). Poloxamer extrusion from the tube demonstrated maintenance of luminal shape (middle). Cooling to room temperature resulted in melted poloxamer and subsequent luminal collapse (below).

  2. Thermoreversible poloxamer nanogel and cyanoacrylate glue sutureless anastomoses in vivo.
    Figure 2: Thermoreversible poloxamer nanogel and cyanoacrylate glue sutureless anastomoses in vivo.

    (a) Schematic representation of anastomosis procedure using the poloxamer nanogel formulation as a temporary intraluminal stent to facilitate a stable, sutureless end-to-end microvascular anastomosis in a rat aorta model. (b) Intraoperative photographs showing the steps of the procedure. (c) Graphical representation of temperature measurements taken in the rat abdominal cavity at specific time points during the end-to-end anastomosis procedure.

  3. Poloxamer nanogel anastomoses show long-term patency, flow and equivalent burst strength in vivo.
    Figure 3: Poloxamer nanogel anastomoses show long-term patency, flow and equivalent burst strength in vivo.

    (a) Comparison of end-to-end anastomosis performed using standard hand-sewn technique versus the sutureless approach. *P < 0.01. (b) Postoperative CT angiograms performed at 6 weeks confirmed equivalent patent anastomoses using the poloxamer (left) and hand-sewn (right) techniques (arrows point to sites of anastomoses; P > 0.05). (c) MR angiograms performed at 1 year showing equivalent patency of poloxamer (left) and hand-sewn (right) anastomoses (arrows point to sites of anastomoses; P > 0.05). (d) Patency in end-to-end anastomoses were assessed between sutureless and hand-sewn anastomoses (*P < 0.001). (e,f) Ultrasound Doppler studies performed at 6 months after operation (n = 5 per group) showing no significant differences in vessel lumen diameter (P > 0.05) and confirming the patency of all end-to-end anastomoses with similar volumetric flow rates (P > 0.05) when comparing the poloxamer versus the hand-sewn technique. (g) Burst strength of native aortas, poloxamer-anastomosed aortas and hand-sewn aortas. Data are presented as mean ± s.d.

  4. Poloxamer nanogel anastomoses show less vascular intimal damage.
    Figure 4: Poloxamer nanogel anastomoses show less vascular intimal damage.

    (a) Schematic and photographic representation of end-to-side microvascular anastomosis performed using the poloxamer formulation to form a stable, sutureless anastomosis in a rat iliac model. (b) H&E staining of poloxamer (above) and hand-sewn (below) anastomoses tissue sections at 6 weeks after operation showing that the hand-sewn technique caused a greater inflammatory response than did the poloxamer technique (scale bars, 200 μm). (c) Immunostaining of a vessel wall showing CD68 expression (brown staining with DAB secondary antibody; scale bars, 200 μm). (d) Quantification of CD68-positive cells showing percentage of CD68-positive cells in the hand-sewn and poloxamer anastomoses. (e) CD31 immunostaining (with DAPI counterstain) of poloxamer anastomoses showing intact endothelium (scale bars, 200 μm). (f) H&E histology of poloxamer (above) and hand-sewn (below) anastomoses 1 year after operation showing that the hand-sewn technique also resulted in a greater inflammatory response compared to the poloxamer technique (scale bars, 200 μm). (g) Quantification of the inflammatory response at 1 week and 6 weeks after operation. (h) Modified elastic van Gieson stain at 2 years after operation (200-μm scale bar) demonstrating patent lumen of anastomosis. (i) Scanning electron microscopy at 1 year after operation showing qualitatively less intimal damage in anastomoses performed with poloxamer (top, with digitally magnified anastomosis site in box) than in anastomoses performed with sutures (bottom, with digitally magnified anastomosis site in box). Scale bars, 200 μm. HPF, high-powered field. Data are presented as mean ± s.d. *P < 0.05.

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Author information

  1. These authors contributed equally to this work.

    • Edward I Chang &
    • Michael G Galvez

Affiliations

  1. Stanford University School of Medicine, Department of Surgery, Division of Plastic and Reconstructive Surgery, Stanford, California, USA.

    • Edward I Chang,
    • Michael G Galvez,
    • Jason P Glotzbach,
    • Cynthia D Hamou,
    • Samyra El-ftesi,
    • C Travis Rappleye,
    • Oscar J Abilez,
    • Michael T Longaker &
    • Geoffrey C Gurtner
  2. Stanford University School of Engineering, Department of Chemical Engineering, Stanford, California, USA.

    • Kristin-Maria Sommer,
    • Jayakumar Rajadas &
    • Gerald G Fuller
  3. Stanford University School of Medicine, Department of Bioengineering, Stanford, California, USA.

    • Oscar J Abilez &
    • Michael T Longaker

Contributions

E.I.C. was responsible for experimental design and data analysis, and wrote the manuscript. M.G.G. designed experiments, analyzed data and wrote the manuscript. J.P.G. analyzed data and wrote the manuscript. C.D.H. designed experiments and analyzed data. S.E. performed imaging studies and analyzed data. C.T.R. and J.R. designed poloxamer experiments and analyzed data. K.-M.S. designed poloxamer experiments. O.J.A. was responsible for burst strength experimental design and data analysis. G.G.F. supervised poloxamer experiments and data analysis. M.T.L. provided ideas and wrote the manuscript. G.C.G. supervised all aspects of this work and wrote the manuscript.

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The authors declare no competing financial interests.

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