UTILIZATION OF SILK AS A NOVEL BIOMATERIAL IN BLADDER AUGMENTATION
Glenn M. Cannon, Jr., M.D., Edward M. Gong, M.D., Joshua R. Mauney, Ph.D., Madavi Oliver, Ph.D., Patricia S. Dunning, R.T., Richard N. Yu, M.D., Ph.D., Roslyn M. Adam, Ph.D., Carlos R. Estrada, M.D..
Children's Hospital, Boston, Boston, MA, USA.
The ideal biomaterial for bladder tissue engineering remains elusive. Silk has been successfully utilized as a biomaterial in vascular and orthopaedic applications. It possesses the strength, elasticity, and biological properties to make it potentially useful for urologic applications. We examined the utility of silk as a biomaterial scaffold for bladder augmentation.
Silk fibroin protein derived from Bombyx mori silkworm cocoons was woven into tubes that were cut into patches. Force-length and dynamic stiffness testing was performed to compare silk, PGA and SIS to normal mouse bladder tissue. Bladder augmentations were performed in 25 CD-1 female mice by creating an anterior wall cystotomy and suturing 5x4mm non-cell seeded silk, PGA, or SIS patches with 8-0 polyglactin sutures under an operative microscope. Sham operations consisting only of cystotomy were performed. Postoperative assessment occurred at 1, 3, 6, and/or 9 weeks and included: (1) voiding stain on paper (VSOP) testing for qualitative and quantitative assessment of voiding function, (2) ultrasound to assess bladder and renal appearance, and (3) histological analysis.
Force-length testing and dynamic stiffness analysis revealed that silk is similar to SIS and significantly less stiff than PGA . Mice whose bladders were augmented with silk and PGA suffered no untoward effects up to 9 weeks of follow-up, whereas augmentation with SIS was associated with an increased incidence of postoperative leak and animal loss. Ultrasound revealed new bladder tissue formation around the silk scaffolds resulting in a bladder appearance similar to sham-operated controls. Hydronephrosis was not present in any of the silk-augmented mice. Postoperative voiding function returned to a normal pattern 1 week after bladder augmentation with silk. Voiding patterns remained normal up to 9 weeks of follow-up. Compared to PGA and SIS, postoperative voided volumes after augmentation with silk scaffolds most closely resembled unoperated controls. Histological analysis 9 weeks after silk scaffold augmentation revealed new bladder tissue formation around the scaffold.
Silk is a novel biomaterial that can be successfully utilized to perform bladder augmentation in mice. This represents a new option in urologic tissue engineering applications.