Rituparna Duarah and her colleagues at Tezpur University and the Indian Institute of Technology Guwahati have developed a suture material that can tighten itself, to close wounds with the perfect amount of pressure. In their recent study, the authors describe how they synthesized the suture from a bio-based material and tested its physical and biological properties (Biomed. Mater. 13 045004).
While the suture was not as strong as commercially available sutures, it appeared to be strong enough. In addition, it degrades over time and provides a scaffold for the growth of new cells. When tested for biological reactions, using cells like those in muscles and blood vessels, the material exhibited minimal negative effects.
How it works
At room temperature, the suture is short, but when heated, it can be stretched to up to twice its length. This long shape is then fixed by cooling to -15°C, and the suture can then be brought back to room temperature in the elongated shape. At this point, knots can be introduced. Upon reaching body temperature, the suture returns to its short state and thereby tightens the knot and any stitches that were made.
The advantage of a self-tightening suture is that the surgeon cannot over- or under-tighten the material. Too tight and the suture might rip, leading to wound opening; too loose and the wound is not closed properly. If the surgeon notices the problem and repeats the suture, valuable time is lost; if not, wound healing is delayed. This inspired the researchers to find a suitable self-tightening material.
But inventing a self-tightening suture is not easy. Previously tested materials were not strong enough and not as biologically compatible. Further, the suture needs to degrade in the wound over time, or else the wound will have to be opened up again to remove the suture from lower tissue layers. A matrix made from bio-based hyperbranched polyurethane (HPU) and reduced carbon dots, a form of graphite, yielded a new material that fulfilled these requirements. HPU alone was not stable enough, but the carbon dots improved how much the suture could be stretched before breaking.
Is it biocompatible?
To test bio-compatibility, the researchers performed a number of in vitro tests on three types of blood cells. When in contact with the suture material, significantly more red blood cells stayed intact than in a control condition, implying that the material does not cause blood lysis. Platelet cells did not attach to the material as much as to a control material. This is good because platelet attachment can lead to thrombosis. When macrophages, which are immune cells, were exposed to the material, they did not signal for an inflammatory immune response as strongly as they did when exposed to a control substance. These assays showed that the suture material did not have negative effects on blood cells.
On top of that, Duarah and her team found that the material promoted the attachment of muscle and blood vessel cells, which then grew well. This suggests that the material does not only not cause damage, but also has the positive effect of allowing cells to attach, grow and heal the wound.
In a surgical procedure, cuts are made through several layers of tissue – each of which needs to be sewn back together afterwards. Self-degrading sutures allow stitching of lower-lying layers of tissue together without the need to open up the wound to remove the suture. To investigate whether the new suture material degrades, Duarah and her colleagues placed it in PBS, a salt solution at stable pH. The material lost up to 7% of its weight in 90 days. It is expected that the degradation might be faster in the presence of the body’s enzymes.
