Cervical Augmentation with an Injectable Silk-Based Gel: Biocompatibility in a Rat Model of Pregnancy

Abstract

The aim of this study was to study the biocompatibility of an injectable silk gel in the cervix in a rat model of pregnancy. The rationale is to study an injectable gel as an alternate treatment for cervical insufficiency. We further aimed to perform cervical injections via a vaginal route to mimic the clinical procedure of a cervical cerclage. We performed an in vivo study in pregnant female Sprague Dawley rats. Cervical procedures were performed using a customized speculum under general anesthesia. Injections were performed on gestational day 16. The responses to silk gel injections were compared to polyethylene terephthalate suture and saline controls on gestational day 19 and postpartum. The inflammatory response was evaluated by histology, PCR for inflammatory gene expression, and ELISA for protein levels of proinflammatory mediators. Silk gel injections were performed on 13 animals. All animals tolerated the procedure. Silk gel occupied 5% of the stroma after injection. Injected silk gel caused neither preterm birth nor prolonged pregnancy and had no effect on the kits. When comparing inflammatory responses, expression of inflammatory genes and proinflammatory proteins in the silk gel group was intermediate between saline (lowest) and cerclage suture (highest). Injectable silk gel was more inflammatory compared to saline injections but less inflammatory compared to the suture material used for cervical cerclage. This study is an important step toward development of an alternative treatment for cervical insufficiency.

Keywords: Cerclage; Cervical insufficiency; Injectable gel; Preterm birth.

Fig. 1

Visualization of the cervix using a customized speculum. (a) The cervix prior to cervical injection. (b) The cervix after silk gel injection. (c) Polyethylene terephthalate (PET) 5–0 cerclage suture placed in the cervix. Of note the suture was not placed around the cervix like as in clinical practice due to size constraints. (d) Silk gel in the cervical stroma

Fig. 2

Schematic overview of the experiment protocol. Sacrificed animals on gestational day 16 (time point 1) to quantify the amount of silk gel in the tissue; gestational day 19 (time point 2) for histology and for RNA and protein assays; postpartum day 3 (time point 3) for effect on parturition and histology

Fig. 3

Left: Silk gel was quantified in the stroma by visualizing the gel as a homogeneous, pale area separate from the tissue. Silk gel is indicated by the arrows. Silk gel occupied approximately 5% of the tissue area. Right: Three days after injection, a mild inflammatory reaction was seen around the silk gel and cerclage suture. A mild, postpartum inflammatory reaction was also seen around the silk gel. The arrows indicate the silk gel. The scale bar is 200 μm

Fig. 4

(a) Expression of inflammatory genes in the silk gel, cerclage, and saline groups. Expression of inflammatory genes in the silk gel group was intermediate between saline (lowest) and cerclage (highest). (b) Protein assay for IL-6 and IL-8. Levels of IL-6 were highest in the cerclage group. For IL-8, levels in the silk gel group were intermediate between saline (lowest) and cerclage highest (* p < 0.05 vs. saline; # p < 0.05 vs. cerclage)