The Apollo Patient Isolation Hood (PIH) is a localized negative-pressure ventilation system for hospital beds to help contain the droplet spread of COVID-19, including during aerosol-generating medical procedures such as intubation and extubation. The PIH encloses a patient’s upper torso and head in a negative-pressure environment. It provides barrier protection between a healthcare provider (HCP) and patient, and aerosol control via the negative pressure environment. The hood may also contain the spread of the virus from less critically- ill patients, reducing the need for invasive procedures.
The versatility of the Apollo PIH means that it can be used in any care setting (OR, PACU, ICU, ED, EMS) and can be rapidly secured to a variety of beds. The lightweight (<5 lbs) design allows for ease of assembly, use, and disposal. The primary structure is composed of a single flat sheet of PETG plastic that is assembled into a 3-dimensional form, minimizing the number of seams for optimal viewing clarity. Flexible sealed arm ports provide HCP access to patients. A minimal amount of folds and seams in the primary enclosure provide optimal viewing clarity.
The main intention was to use simple techniques of creating stable 3d forms from readily available flat sheets and minimal joinery, which can be rapidly deployed to help frontline medical workers. The design of the ‘Apollo’ is based on the principles of ‘Active Bending,’ which describes surfaces that base their geometry on the elastic deformation of initially straight elements((Gengnagel, Alpermann, and Hernández 2014)).
All initial small-scale prototypes were made of 130 gsm (80lb) Bristol paper with a Cricut Maker, which proved to be a quick and straightforward method for a rapid iterative process.
PETG, well known as a material for scaling up origami concepts (Baerlecken et al. 2014), was used to make prototypes at full scale. Both 30mil (1/32”) and 60mil (1/16”) PETG sheets work well based on the required size and stability that is needed for the PIH. Most of the prototyping was done with 60 mils and the final design is a combination of stability, flexibility, and lightness.
The initial guidelines of the design were flat foldability, optical clarity, and simple assembly. The origami approach catered to most of this requirement, but the designs still had seams at the folds.
Hence the next step in the design process was to achieve bending without folding, and thus we looked at the principle of ‘Active Bending’.
Applying spherical linkages enabled us to get rid of the folds and have a seamless 3d form from flat sheets. Small single vertex spherical prototypes were made to test the stability of the structure. This concept was then applied to a simple unfolded cuboid based on the clinical dimensions with partial overlap between the sides. Modifications were made to improve the interface of the base perimeter with the bed and to taper the viewing angle.
The design went through numerous iterations based on the anthropometric, functional, and clinical requirements associated with the process of intubation and provided by the clinicians at MGB & BCH. The design needed to cater to a lot of different parameters and be adaptable so that it could be used in various hospital settings, attached to different sized hospital beds and be used on patients of varying age groups and body type. A variety of alternative designs were prototyped, which differed in size, attachment details (rivets, slots/tabs), and ability to nest on commonly available sheet stock as well as available fabrication infrastructure.
Some of the prominent iterations are briefly explained below.
The novelty of the ‘Apollo3’ design is that it can be made up of thin sheets of flat materials, and based on the calculated overlap of the side-arms, a double thickness structure is provided at the base for stability while making the rest, pliable and light.
Several key features of the prototype are outlined below:
The fabrication of the ‘Apollo3’ hood can be subdivided into two parts:
For the Bill of Materials. See ‘here.’(Link)
The primary design element of the Apollo PIH is the enclosure – a thin sheet of clear PET-G plastic in 60mil (approximately 1/16”) thickness. It can be CNC cut from a flat sheet of PET-G measuring a minimum of 48” x 72”. The Apollo PIH enclosure measures approximately 22” in width, 23” in height and 22” in depth and is about 0.15 m3 in volume.
The Apollo PIH requires a minimum stock size of 72” x 48”. The stock can be cut using several CNC processes, including a knife cutter, laser cutter, or router. In the case of a CNC router, a ⅛” diameter endmill is required to cut small interior features successfully. A list of suggested cut settings is provided below. Please keep in mind that these settings are specific to the machines listed and will likely need to be modified for other scenarios.
Knife Cutter (Zund G3M2500)
Bed Size: 98” x 52”.
Tool: Universal Cutting Tool (UCT) with glide shoe)
Blade: Type6 blade
Depth: 0.02” per pass
Speed: 6” per second
Total Time: ~ 18 minutes.
Laser Cutter (450 Watt Multicam Magnus 48×96 CNC Laser, 4” Focal Lens)
Speed: 480 IPM
Frequency: 10,000 PPI
The base plate (2 offshoots located at the base of the design) is responsible for imparting stability to the hood, and also the method of connection makes it adapt to different bed sizes as it makes the hood behave as a compliant mechanism.
The base plate portion of the Apollo PIH enclosure must be cold-formed to a 90-degree angle relative to the rest before assembly. To date, this has been successfully accomplished on a sheet metal finger brake, such as the Baileigh SBR-4020 shear brake roll (Link). Additional forming processes, such as the use of a line brake or heat gun or design modifications to the enclosure, such as eliminating the base plate or incorporating a secondary hinge mechanism, exist as potential alternatives. However, they have not been tested by the design team.
A variety of different snaps/connection options were explored, ranging from pop-rivets, push-in rivets, tabs/slots, and button snaps to keep the actively bent shape stable.
The fabric snaps added an extra step in the assembly by creating an offset in thickness between the overlapping sheets. They compromised the airtightness of the hood and increased the risk of contamination. The tabs/slots proved advantageous by not needing extra hardware, hence making the hood recyclable due to the presence of a single material but were susceptible to plastic deformation and breaking after multiple cycles.
Push-in Plastic rivets were selected as the preferred fastener, as they were simple to use and had no sharp edges that could catch on to clothing, medical instruments, etc. 3/16” holes in the main enclosure facilitated the riveting and were done by hand. Sixteen rivets are needed (8 per side of symmetry) for maintaining the shape of the Apollo while two rivets (or one rivet & a button snap)are necessary for the baseplate ( 1 to pivot (red) and 1 to lock (blue)).
The width of the Apollo can be adjusted by adjusting the location of the pivot and the lock. A simple grasshopper script was used to determine the position of the snaps so that it gives a required width (in case of the ‘Apollo 3’, it was 23inches). Multiple perforations can be added to have it adapt to a range of widths.
Each arm and auxiliary port on the Apollo PIH is composed of three primary components – a laser-cut five mil TPU portal, a transparent, double-sided adhesive film, and a port cover.
Multiple iterations of the arm port design were undertaken with various materials and can be found in the diagram above.
Perforations are located on the base perimeter (dark blue in Reference drawing) of the backplate to enable the use of cords/straps to attach the Apollo to different sized beds.
The drape is a rectangular piece of LDPE with dimensions 85” x 40”. Refer to the reference drawing and assembly instructions for details. A 12” offset has been left on both ends to facilitate tucking under the patient to get a good seal.
A full attribution list is as follows Aaron Ross, Adam Smith, Aditya Kumar, Alex Kobald, Alex Yang, Alexander Kuo, Angela Dai, Brianna Slatnick, Celeste Day, Chris Hansen, Chris White, Daniel Castelo, Daniel Tish, David Concha, David Hamm, David Wallace, Eric Howeler, Euan Mowat, Farokh Demehri, Fernanda Sakamoto, Heung Bae Kim, James Weaver, Jonathan Grinham, Jonathan Langer, Koushik Garapti, Kristian Olson, Kyle Wu, Lara Tomholt, Martin Bechthold, Mehra Golshan, Michael Sherman, Michele Szabo, Norman Wen, Robert Crum, Ryan Pierce, Sam Smith, Saurabh Mhatre, Ted Ngai, Ted Sirota, Zach Seibold.
Baerlecken, Daniel, Russell Gentry, Matthew Swarts, and Nixon Wonoto. 2014. “Structural, Deployable Folds-Design and Simulation of Biological Inspired Folded Structures.” International Journal of Architectural Computing 12 (3): 243–62. https://doi.org/10.1260/1478-07188.8.131.52.
Gengnagel, Christoph, Holger Alpermann, and Elisa Hernández. 2014. Active Bending in Hybrid Structures.