Anchoring knots

Figure 10 Diagram showing three methods of wound closure after insertion of a ganciclovir sustained-release device. (A) Wound closure with an X suture on either side of the anchoring suture. Note that the X suture is started within the wound so that the knot remains buried when the suture ends are trimmed. The long ends of the anchoring suture are placed under the two X sutures. (B, C) Wound closures with a running suture. Note that the suture is started within the wound so that the knot remains buried when the suture ends are trimmed. The long ends of the anchoring suture are placed under the running suture.

The amino acid sequence of decorin includes six cysteine residues paired to form three disulphides (23). The crystal structure of decorin (21) revealed that the four cysteines on the A -terminal side of the LRR domain contained within a CxjCxCx C motif form a cystine knot, with the first cysteine connected to the third and the second to the fourth. The third disulphide located toward the C-terminal end of the LRR domain connects LRRs 11 and 12, providing a stable scaffold anchoring the ends of the flexible ear loop. Collectively, these three disulphides, and the tertiary structure they maintain, are critical for function because chemical reduction (23) leads to irreversible loss of the ability of decorin to bind to collagen (see below). 

Fig. 3 Elements of molecular templates (a) a crossover reacts with a linker to give (i) a catenane and (ii) a rotaxane (b) a fused turn closed with a fused linker gives a macrobicycle (c) two anchors and two pairs of inverted ditopic turns template a trefoil knot (d) composite knots require two two-anchor templates and (e) oligocatenanes can be formed with multicrossover templates on a single anchor.

The folding of a protein explained in the Introduction to this chapter creates an intertwined chemical structure. Ponnuswamy et al. (2012) fabricated knotted molecules, similar to protein structure, which took advantage of hydrophobic interactions. The molecular structure was comprised of three hydrophobic naphthalene diimides held together with alanine linkers and anchored at both ends with cysteine amino acid. 

It is also important that the suture material is stable to radiation. This can occur when, following gynecologic cancer, a patient is prescribed abdominal radiation for palliative or curative therapy. The ionizing effect of the radiation may adversely affect suture strength, and may lead to wound dehiscence (Orr et al, 2004). The use of a knotted monofilament suture presents a high risk in such cases, since, if the suture breaks at one point, the entire length of the suture stitch is rendered ineffective in keeping the wound closed. Several small suture stitches may be used but this increases the time of operation and can lead to complications due to the presence of multiple knots. A barbed suture, however, can effectively eliminate both these risks. Since it anchors at multiple points, should the suture break it will still hold the wound tissue in closed apposition at the next barb. Secondly, since the suture stays inside the tissue there is less scar formation. 

Distributed mechanical stress In order to perform, monofilaments have to be anchored in their environment. The knot is accepted by surgeons as the only irrefutable means to anchor smooth suture material. Unfortunately, knots created unequal tension burdens placed on the knots rather than on the length of the suture line. Then, an uneven distribution of tension occurred within/across the biological tissue with potential impact on healing process, distortion of the tissue, and marked inflammatory responses to foreign body material. 

A barbed suture, which is self-anchoring with no knots required for wound closure, is manufactured from polydioxanone. This suture consists of axially barbed segments on each side of a mid-point at which the barbs change direction. This wound closure device appears to offer gastrointestinal closure comparable to the poly(GA-co-TMC) suture. 

Figure 3.7 Polyurethane fibers realized by soft molding lithography, (a) Disordered bundle, (b) Knot made by flexible fibers with circular cross-section, (c) Single fiber, diameter 300 run. (d) Anchoring of an elastomeric fragment by polyurethane fibers. Reproduced with permission from Ref 115, Appl. Phys. Lett., 2005, 87, 123109. Doi 10.1063/1.2046731. Copyright 2005, Ameriean Institute of Physics.

Figure 12.17 shows the formation process of such a pill. In the beginning, single fibers are more or less dragged out of the textile (a, b). Then after further friction is applied, the fiber ends form loops (c). Cloud-like fiber agglomerations are formed (d), and finally, the fibers can form knot-like structures (e). This knot is connected to the textile surface by a single fiber, the so-called anchor fiber. 

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