BACKGROUND

Hamilton syringes are manufactured to be accurate within ±1% of nominal volume and with precision within 1%, measured at 80% of total scale volume. The design of the barrel and plunger dimensions assure high levels of accuracy and precision. Since Hamilton syringes are very precise, researchers often use them to deliver extremely small volumes in microliters.  Hamilton syringes are frequently utilized for administration of biological hazards (e.g., viral vectors, siRNA) via stereotactic injection into mouse and rat models.  Administration of these biological hazards means that disinfection of the Hamilton syringe, both initially and between animals is important.

IACUC Policy

This document outlines the recommendations of the WSU Institutional Animal Care and Use Committee (IACUC) for the initial disinfection of the Hamilton syringe following use, and the subsequent steps that must be performed to prepare the unit for re-use.  Please note that the procedure below for disinfection must be completed between each animal being injected.  Exceptions to this policy require IACUC approval.

Initial disinfection

The Hamilton syringe must be thoroughly disinfected following injection of biological hazards.  This initial step allows for either storage of the Hamilton unit until needed, or transition directly into the remainder of the procedure required for re-use of the Hamilton syringe in animal research activities.  

1. Following removal of the Hamilton syringe from the stereotactic frame, the unit must be disinfected.  This must be accomplished by soaking in 10% fresh bleach for 30 minutes or via Microcide SQ for 10 minutes (Warning - Do not mix disinfectants).  Subsequently, lab personnel can either:
   1. Store the unit:  The unit should be rinsed thoroughly with water prior to storage, or
   2. Complete the process below for immediate re-use:  Continue from step 2.b. below.  

Preparation for use

Following consultation with Hamilton, the following has been determined to be acceptable as an alternate to chemical sterilization.  Please note:  The DLAR veterinarians have agreed to this procedure with the caveat that it will be revisited should there be clinical signs of infection and/or meningitis. Any such clinical symptoms must be reported to the veterinarians immediately.

2. Prior to use:  
   1. Hamilton units that have been in storage must be soaked in freshly prepared 10% bleach solution for 30 minutes to 1 hour or Microcide SQ for 10 minutes.
      1. If possible, the Hamilton must be disassembled when soaking. 

1. 2. Units must then be thoroughly rinsed with sterile deionized water or sterile PBS to remove disinfectant residue.
   3. Units must then be rinsed with Acetone to remove water/PBS residue (Hamilton recommendation)
      1. Excess Acetone must be collected as a chemical waste.

2. 4. Air dry unit for at least 30 minutes in a sterile metal tray within the BSC
   5. Unit can subsequently be used for injections.
3. Between use:
   1. It is permissible to replace the needle only, when performing repeat injections in animals.  This must be performed in a sterile manner, and with respect to appropriate hazard considerations.  The whole apparatus, including all used needles, must be disinfected after completion of the injections.  OEHS recommends the use of needle nose pliers for the safe manipulation of needles during the replacement process, and when performing disinfection steps.

Additional notes

• While many units listed on the Hamilton website are described as autoclavable, the maximum temperature that they can be exposed to is 115ºC.  This temperature is lower than the required temperature to achieve sterility (121ºC).  As such, this is not an option.
• Please check the Hamilton Company website for tolerance of specific Hamilton Syringe models to 10% bleach and additional information related to your specific model number of syringe.
• If a Hamilton syringe is used with an extension tubing in a manner such as no liquid enters the Hamilton syringe, disinfection, as described above may not be necessary.  Any tubing would need to either be sanitized or discarded with appropriate consideration to hazard containment.

Approved: July 2023