Silver Assessment of a Closed Incision Negative Pressure Therapy System In Vitro and in an Acute Miniature Swine Model
Sandra N. Osborne, Ph.D1; Scout L. Stern, B.S.2; K. Mark Weineck, Ph.D3; Kristine M. Kieswetter, Ph.D, M.B.A.1
1
Department of Research & Technology and 2Operations Integration, KCI, an ACELITY Company, San Antonio, TX; 3Microbiology and Antimicrobials, Milliken & Company, Spartanburg, SC
Introduction
Methods (Cont’d)
Results (Cont’d)
Reticulated open cell foam based closed incision negative pressure therapy (ROCF-ciNPT)*
consists of a hermetically sealed system connected to a disposable hand-held therapy unit that
delivers negative pressure at -125mmHg over a closed surgical incision for up to 7 days. Preclinical
and clinical studies have elucidated mechanisms of action for NPT over closed incisions showing
decreased dead space and lateral tensile stresses between and around surgical sutures, reduction
in tissue hematoma and seroma, and improved mechanical and tissue properties.1-4 The ROCFciNPT dressing provided as part of this closed system has a drape that can act as a barrier to
reduce the risk of contamination from the external environment, a foam bolster in the center to
distribute NPT, and a skin interface layer that absorbs fluid from the skin surface and reduces the
potential for bacterial colonization within the fabric via a small amount (0.019%) of ionic silver
(Figure 1).
• The antimicrobial properties of the silver containing interface material was evaluated at 0 and
168 hours post-inoculation with Candida albicans, Pseudomonas aeruginosa, and Staphylococcus
aureus.
Table 1. Diffusion of silver from ROCF-ciNPT and SOC dressings into blood, excretions, and tissue as a function of time
• The in vivo silver diffusion study included 8 castrated male Yucatan miniature swine that were
equally divided into 2 treatment groups. Each animal underwent a sterile surgical procedure
to create a single full thickness 20cm dermal incision on the dorsum. Incisions of Group 1
animals were dressed with SOC (non-silver) dressings and the incisions of Group 2 animals
were dressed with the ROCF-ciNPT dressing along with negative pressure (-125mmHg). Feces,
urine, and whole blood samples were collected on days 0 (pre-dose), 1, 3, 5, and 7 for silver
analysis using inductively coupled plasma optical emission spectrometry (ICP-OES) at Exova
(Santa Fe Springs, CA). Feces, urine, whole blood, kidney, liver, and laboratory blank (matrices)
were spiked with 10mg/g of silver for positive detection. Following 7 days post-surgery, each
animal was euthanized and representative kidney and liver samples were collected for silver
analysis or embedded in paraffin, stained with hematoxylin and eosin (H&E), and evaluated
microscopically at HSRL (Mt. Jackson, VA).
Silver Detection
Limit
(µg/g)
Silver
Control Spike
Concentration
(µg/g)
Average Spike
Recovery
(%)
Feces
0.2
10
94.5
Urine
0.04
1
97
Blood
0.04
1
90
Kidney
0.1
10
103
Liver
0.1
9.9
102
Sample
Silver (µg/g)
Test Dressing
SOC
ROCF-ciNPT
SOC
ROCF-ciNPT
SOC
ROCF-ciNPT
SOC
ROCF-ciNPT
SOC
ROCF-ciNPT
0 Hrs
24 Hrs
72 Hrs
120 Hrs
168 Hrs
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD
BLD= below levels of detection
Additionally, resulting pathology data showed no test-article-related findings in either the liver
or kidney in pigs that received ROCF-ciNPT dressing with silver versus SOC (Figure 5).
Results
The ROCF-ciNPT dressing showed reduced bioburden after 7 days compared to SOC (Figure 3). In
addition, the highest total cumulative amount of silver released in the in vitro study was 0.35mg
at 7 days (Figure 4) with no measurable concentrations of silver detected in any tissue sample
at any time point during the 7-day in vivo study while silver spiked controls were recovered at a
range of 94.5 - 103% (Table 1).
Figure 1. ROCF-ciNPT dressing composition
Purpose
This good laboratory practice study assessed
the in vitro silver antimicrobial properties and
release, and the in vivo diffusion properties
of the skin interface dressing material into
blood, excretions (urine and feces), kidney, and
liver tissue in an acute miniature swine closed
incision model compared to standard-of-care
(SOC; sterile absorbent dressings) without
silver† (Figure 2).
SOC
ROCF-ciNPT Dressing
Figure 5. Representative images of liver and kidney histology cross-sections from SOC and ROCF-ciNPT
treated animals at 168 hours. Top panels show kidney H&E; bottom panels show liver H&E
Conclusions
In summary, while ROCF-ciNPT dressings contain sufficient silver to reduce bioburden in the
dressing, silver is not released in significant quantities into body tissues under actual use
conditions.
Figure 2. SOC (left) and ROCF-ciNPT (right) dressings
Figure 4. Total amount of silver released by ROCF-ciNPT
dressing as a function of time (mean ± sd)
Methods
• The in vitro silver release was evaluated by extracting soaked dressings in saline and 1%
bovine serum albumin in triplicate at 6, 12, 24, 48, and 169 hours, and atomic absorption
spectroscopy (AAS) was performed using an AAnalyst 200 double-beam Atomic Absorption
Spectrometer (PerkinElmer, Waltham,MA).
Presented at the Symposium on Advanced Wound Care/Wound Healing Society, April 5-9, 2017, San Diego, CA
Figure 3. Log reduction of S. aureus (mean ± standard
deviation (sd); *p=0.0114), and P. aeruginosa (mean ± sd);
**p=0.0011) within the ROCF-ciNPT dressing compared to
SOC dressings at inoculation and 168 hours
References
1. Wilkes RP, Kilpadi DV, Zhao Y, et al. Surg Innov. 2012;19:67-75.
2. Glaser DA, Farnsworth CL, Varley ES, et al. Wounds. 2012;24:308-316.
3. Kilpadi DV, Lessing C, Derrick K. Aestetic Plast Surg. 2014;38:767-778.
4. Kilpadi DV, Cunninghman MR. Wound Repair Regen. 2011;19:588-596.
*PREVENA™ Incision Management System (KCI, an ACELITY Company, San Antonio, TX); †Mepore® Film & Pad (Mölnlycke
Health Care, Norcorss, GA)
The authors thanks Julie Robertson for assistance with poster preparation and production.