APPLIED 
RADIATION 
CASE HISTORY 
NO. 1 
Electron-Beam Sterilization 
of Surgical Sutures 
Substituting radiation for heat results in a stronger product, 
a better package, simpler manufacture and continuous processing. 
Savings in these areas help pay for more expensive sterilization 
By CHARLES ARTANDI and WALTON VAN WINKLE, Jr. 
Ethicon, Incorporated, Somerville, New Jersey 
ELECTRONS FROM A microwave linear 
accelerator are routinely sterilizing 
surgical sutures in Ethicon’s Somer- 
ville, N. J. plant, the world’s largest 
producer of surgical sutures (NU, Feb. 
58, p. 27). Catgut sterilization using 
heat has always presented difficult prob- 
lems. Our commercial electron steril- 
ization has grown out of a five-year re- 
search program to find a better way. 
For our purposes the best radiation 
source is the linear accelerator, or linac. 
Ours has been installed in a special 
split-level building with appropriate 
conveyor facilities and monitoring 
equipment. We monitor the acceler- 
ator, the process and the product, in 
some instances with methods that we 
have invented for our own needs. It 
is hard to estimate our costs, but it is 
plain that electron sterilization is ex- 
pensive. Nevertheless it has brought 
us many benefits including better pack- 
aging, simpler manufacture and even 
customer appeal. Figure 1 shows a 
tray of sutures on its way to sterilization. 
Catgut Sterilization 
Surgical sutures are of two main 
types: absorbable and nonabsorbable. 
The absorbable variety, known as “‘ cat- 
gut,’ is derived from connective-tissue 
layers of the intestines of beef and 
sheep. It is with this type of material 
144 
that the suture industry has always had 
sterilization problems. 
Classically sterilization has always 
used heat—high enough temperature 
for a long enough time kills all bacteria 
and other forms of microbial life. Un- 
fortunately catgut sutures are com- 
posed of an animal protein, collagen, 
and like all proteins it is ‘‘cooked” by 
heat. This cooking reduces tensile 
strength, pliability and other important 
properties of the suture. To avoid 
damage as much as possible, the prac- 
tice has been to dehydrate the sutures 
for 8-12 hr at 100—-110° C, then immerse 
them in an anhydrous hydrocarbon 
bath and sterilize at 156° C for an hour. 
This must be done before sealing the 
container. After sterilization, an asep- 
tic process is used to fill the container 
with sterile tubing fluid, rehydrate the 
suture and seal the container. This 
process requires manufacturing with 
operating-room precautions. 
Heat-sterilized sutures are always 
packaged in glass tubes—the only 
economical material suitable for the 
high sterilizing temperatures. Getting 
the suture in the operating room re- 
quires breaking the glass container with 
attendant hazards of broken glass near 
the operative field. 
Another objection to heat steriliza- 
tion is that it isa batch process. Thus 
it is a bar to continuous flow of mate- 
rials and automation. A method that 
permits conveyor-belt operation makes 
possible automation and leads to manu- 
facturing economies in several areas. 
It is obviously desirable to find some 
sterilization method that will: 
© Minimize damage to the suture 
© Permit sterilization in the final, sealed 
container 
© Allow use of new and more conven- 
ient packaging 
® Lend itself to continuous operation. 
Exploration 
As early as 1949 it was well estab- 
lished that electron-beam irradiation 
is capable of killing microorganisms at 
doses that do not adversely affect many 
materials. Subsequent work estab- 
lished the dose parameters necessary to 
sterilize sutures and similar objects (1). 
However, the large capital investment 
required and the lack of definitive ex- 
perience with the commercial use of 
electron accelerators, beta, and gamma 
radiation deterred most industries from 
extensive development work. 
Early in 1953 the problems peculiar 
to the suture industry prompted us to 
undertake a detailed feasibility study 
of radiation sterilization of sutures. 
We rented a 2-Mev 0.5-kw Van de 
Graaff accelerator from High Voltage 
