IIH researchers have built the Solarclave™, a novel solar-thermal autoclave for rural clinics in resource-limited settings using locally-sourced supplies and local manufacturing.
Prototypes of the Solarclave™ under test in Ocotal, Nicaragua
Rural clinics in developing countries provide primary care for 3 billion people worldwide, but more than half of these do not have access to electricity. This means that electrical autoclaves, which represent the gold standard for medical instrument sterilization, cannot be operated in these clinics. Even in clinics that do have access to electricity, supply can be intermittent and unstable, leading to blown fuses and burnt circuitry.
Broken steam autoclave Broken dry heat autoclave
The Centers for Disease Control specify the wet-steam sterilization requirement as maintaining a temperature of 121°C (250°F) for 30 minutes. This requires an enormous amount of energy. In the many rural communities where fuels are scarce and electricity is intermittent, this means proper instrument sterilization is not possible. On our many research trips, we spoke to nurses that worked in rural clinics so remote that the only way to sterilize instruments was via a day-trip to the nearest regional health center.
Rural health clinic, Jicarito, Nicaragua
The Solarclave is a solar-powered surgical instrument sterilizer that uses the energy of the sun’s rays to directly heat surgical instruments to sterilization requirements. It uses locally-available materials and manufacturing techniques that are already available in thousands of rural workshops across the world. Its thermodynamic efficiency allows for a small size that is easily transportable to remote clinics and is simple for one healthcare worker to set up.
Prototype Solarclave integrated on stand, locally-built in Nicaragua
The Solarclave has two main parts: a Reflector that concentrates the sun’s rays and a Pressure Vessel that holds the surgical instruments and receives the focused solar energy.
The Reflector is made from 140 mirrors held in a precise orientation and provides the heat energy needed to sterilize medical instruments. Though the geometry of the mirrors is complicated, the reflector itself is easy to manufacture. The mirrors are supported by a lattice of plywood made from only two basic patterns. In combination, these two patterns hold each mirror at just the required geometry. Further, we have created a way to manufacture these precise patterns using only simple tools. This prototype is capable of heating to over 300°F.
Solarclave Reflector panel prototypes set up for test Closeup of mirror squares in reflector panel
The Pressure Vessel sits in the focus of the reflector and holds the surgical instruments that need to be sterilized. Our Pressure Vessel works similarly to a Thermos bottle: we insulate our container to keep the heat inside. A modified pressure cooker is wrapped in layers of fiberglass insulation and shielded by a plastic bucket. At the bottom of the Pressure Vessel, a short duct lets in sunlight while trapping hot air. Since it tries to rise but can’t go anywhere, the hot air acts as an invisible insulating blanket that further increases the efficiency.
The Solarclave pressure vessel seen from the side and bottom
The Reflector and Pressure Vessel are held in the proper orientation by a mobile stand that moves like a wheelbarrow, with one front wheel and two rear legs. This allows easy transportation around a rural clinic site, which may have many steep slopes and high ledges.
We estimate the total cost of materials to be US$150 when purchased in Nicaragua, with 95% of materials locally-available. Our local manufacturing partners have built prototypes of all major assemblies.
The Solarclave being built by Las Mujeres Solares in Sabana Grande, Nicaragua
Our design focus at IIH goes beyond creating new appropriate medical devices. We believe that users can be inventors and we seek to cultivate local innovation.
Working in collaboration with MIT D-Lab, University of Dayton ETHOS, Las Mujeres Solares of Sabana Grande, Nicaragua.
Funding from MIT IDEAS 2011 Global Challenge and Salud del Sol, Inc.
— V. Ted Liao (IIH Researcher, Solarclave Project Technical Lead)
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