Solar-Powered Sterilizer for Surgical Instruments
Christian T. Firsching ’15 & Benjamin C. Williams ’15
J. Harry Blaise, Faculty Advisor
Abstract
Electronics & User Interface
Sterilization of surgical instruments is required to prevent infection and the spread of disease.
The electronic components revolve around an Arduino Trinket Pro micro-controller and a type-K
Common sterilization methods require electricity, however rural clinics in developing nations
thermocouple.
often do not have access to dependable electricity. These clinics are responsible for providing
contents have been sterilized.
healthcare to three billion people worldwide, nearly half the world population [1].
A user interface consisting of an LCD, two pushbuttons, an On/Off switch, and an LED indicator is
This project consisted of the design and fabrication of a compact, user-friendly, and high quality
mounted in the lid of the housing. Found inside the housing are the micro-controller, a buzzer, a
solar sterilization system. The system consists of an evacuated tube solar collector set at the focal
lithium polymer battery, an AC to DC adapter, a relay, a “break-out board” to interface the
point of a parabolic reflector. A micro-controller tracks temperature and displays sterilization
thermocouple, and a power board to keep the battery charged.
status. Also accommodated in the design is a regular AC power option for when access to
Outside of the housing, mounted on the reflector, is a photovoltaic array. This panel charges the
electricity is made available.
battery, powering the electronics when grid power is not available.
The system effectively sterilizes surgical instruments under dry heat in accordance with the
Design Overview
guidelines of the Centers for Disease Control (CDC).
The final project consists of two components: the insert and the solar collector
This system using the thermocouple and a timer to determine when the
Solar Collector
• Evacuated tube solar collector absorbs solar radiation and utilizes a vacuum layer to keep
heat in
• Solar panels power the control panel
• Parabolic reflector reflects suns rays to the evacuated tube
Insert
• Surgical instruments are placed in the insert, then insert goes into solar collector
• Control panel allows user to initiate sterilization and LCD displays temperature and time until
sterilization is complete
• Interface between electronic housing and instrument tray is made of stainless steel and filled
with fiberglass insulation to prevent conduction of heat out of the sterilizer
AC Heating Design
A project goal was to ensure that the solar-powered sterilizer remains useful even after its
owners gain access to reliable electricity. AC heating is far more powerful and efficient than
Solar Heating Design
weather-dependent solar heating. With this in mind, an electric heating system was included.
Project Goals
The solar heating design revolves around two key components: an evacuated tube solar
The goal of this project was to create a functioning, complete, and production-ready prototype
collector and a parabolic reflector. These are paired together to transfer the sun’s energy with
of a solar-powered sterilizer.
maximum efficiency.
The minimum requirement of the design was the ability to sterilize surgical instruments in line
An evacuated tube solar collector is very similar to a thermos: it has a double glass wall with an
inside the tube is lower than necessary for sterilization, and turn off when above the required
with the guidelines set by the Centers for Disease Control (See “Requirements for Sterilization”).
insulating vacuum between the layers. The outer layer is clear, to allow the sun’s radiation
temperature. This simple temperature control system maintains the internal heat at the required
through, while the inner layer is coated with a black absorbing layer. The solar radiation is
sterilization temperature until complete.
Beyond this minimum requirement, there were a number of other desirable goals:
• Portability - The system should be able to be carried and deployed by one person
• Ease of Use - A maximum of one hour of training is required for a person to learn and
understand the operation of the system
This system allows the sterilizer to be used indoors with AC power.
The AC heating system consists of a resistance heating element and an optically isolated solidstate relay. The relay is interfaced with the micro-controller to turn on when the temperature
absorbed by the black layer and trapped by the vacuum, which results in the interior of the tube
heating up and holding the heat in.
The parabolic reflector focuses the sun’s rays on a single point, the focal point. The evacuated
Acknowledgments
tube is placed at the focal point, amplifying solar radiation on the tube.
We would like to thank Professor Harry Blaise, Professor John Mertens, and Professor Prabhakar
• Dual Energy - The system should be able to operate with energy from the sun, or energy
Venkateswaran for their guidance and advice, Andrew Musulin for technical help, and Thomas
from the power grid
Firsching for manufacturing support and materials.
Requirements for Sterilization
References
High temperatures over a particular period of time kills microbes and pathogens, sterilizing
[1] Liao, V. “IIH Solarclave: Solar-Powered Medical Instrument Sterilization.” 2011. Innovations in
International Health at MIT. Cambridge, MA.
whatever object is held under those conditions. The Centers for Disease Control (CDC) maintain
guidelines for sterilization of surgical instruments with specific lengths of time for a few different
[2] Rutala, W., Weber, D., and Healthcare Infection Control Practices Advisory Committee. 2008.
temperatures. For dry-heat sterilization, instruments must be subjected to temperatures of
“Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008.” Centers for
170℃ for 60 minutes, 160℃ for 120 minutes, or 150℃ for 150 minutes [2].
Prototype Parabolic Reflector and Temperature Data
Disease Control and Prevention.