Additive Manufacturing Lisbon Design Challenge 2015 Final Report

Summary Every year, 41 thousand people suffer from arm fractures, only in Portugal. Our project presents an alternative to traditional cast for the immobilization of arm fractures during its healing period. Lightness, comfort, ability to wash and using during bath and aesthetics are the main advantages of our solution compared with the currently available ones. Additive manufacturing was used as a manufacturing process due to its advantages on personalization and geometry flexibility features. This report intents to describe the several phases of the project, since the identification of the problem until the printing of the first working prototype and explain the reasons behind each decision taken during the development of the product.

Group João Pinho - 1st year Master student in Mechanical Engineering, IST Vasco Mergulhão - 1st year Master student in Mechanical Engineering, IST João Pires - PhD Candidate in Engineering Design and Advanced Manufacturing, IST

1. Context This work was a result of the work performed for the Additive Manufacturing Lisbon Design Challenge 2015, organized by Instituto Superior Técnico. After accepting this challenge our team decided to talk and interview all types of professionals and ordinary people in order to identify real problems and needs that a new product, combined with the full potential of additive manufacturing, could solve. One of these interviews led us to the Firefighter’s Formation School. After a guided visit throughout some of the major procedures, the group identified, alongside with the firefighter’s corporation, several needs that a product design and development project could solve. However, due to some of the specifications of those products (mechanical strength, durability, cost) we concluded that the advantages of bringing additive manufacturing to this project were very few. We then focused on other areas, especially in medical department. After some attempts, the group believes to have found a specific solution to replace an old fashion product, not only matching all of its benefits but adding several more. All this, by using additive manufacturing as manufacturing process. Our goal is to replace cast as an immobilization solution for fractures/broken limbs, while adding new capabilities and, if possible, improve the rehabilitation of the injury.

2. Current status 2.1.

Introduction

A cast is a solid supportive bandage that holds a broken bone in place, for healing purposes. It also helps to prevent or decrease muscle contractions, and are effective at providing immobilization, especially after surgery. Casts immobilize the joint above and the joint below the area that is to be kept straight and without motion. They come in many shapes and sizes, but the two most common types of cast material used are plaster and fiberglass.

2.2.

Types of Fractures

All bone fractures, regardless of cause, are sorted into two major classes: simple and compound fractures. Simple fractures, also called closed fractures, are broken bones that remain within the body and do not penetrate the skin. On the other hand, compound fractures, also called open fractures, are broken bones that penetrate through the skin and expose the bone and deep tissues to the exterior environment. Compound fractures are considered much more serious than simple fractures because they may be complicated by deep infections if pathogens enter the body through the wound. Within this two types there are different specific types of fractures. In this first attempt, the project focused in looking at one of the less severe of forearm fractures: partial radius fracture. Nevertheless, the goal is to extend to more severe fractures and ultimately cover the full range of arm fractures.

2.3.

Rehabilitation Process

The period immediately after a bone fracture is critical for the proper repair of the bone and healing of the affected tissues. Bones begin to heal very quickly after a fracture and the bone tissue will knit together with any nearby bone fragments to form a callus of cartilage and eventually new bone tissue. The ultimate goal of bone healing is to reach a proper union of the fractured bone pieces that restores the original bone anatomy and restores full function to the muscles and joints that move the bone. Figure 1 pictures a typical example of the rehabilitation process of an arm fracture from the moment the bone breaks until its complete healing. When a bone is broken, the first step in repair is to take an X-ray to confirm the diagnosis and to provide a clear picture of the type of fracture and the degree of displacement and misalignment. The first step of the treatment is guarantee that the bone ends are align with each other, so that when the fracture heals correctly. Bone ends that have been displaced are manually placed back in the correct position. Once the fracture has been placed in proper position, the bone is immobilized to allow the broken pieces to reunite firmly. In most cases, a rigid cast is used to immobilize the bones for several weeks and achieve the proper union. After this, the patient can usually go home to begin the recovering process.

Figure 1 - Typical patient path since the fracture to the removal of the cast.

This healing period can go from 6 to 8 weeks, after which the patient must return to a medical facility to remove the cast. In some cases, mostly in private healthcare, an intermediate check-up can be performed after 1 or 2 weeks to see if the bones are aligned and if cast is still fulfilling its function properly. The cast is usually removed by a qualified medical professional with the help of an electric cutter. After this, the patient should be submitted to physiotherapy to complete the rehabilitation process and reacquire its bone and muscular strength. The older a person is, the longer it takes for a bone to heal: a child may recover within a few weeks and an elderly person may take several months. At all ages, some bones will heal faster than others: an arm may heal in a month, but a leg may take up to six months. The elderly and those in poor health who may suffer from delayed union may also be susceptible to nonunion fractures where the bones fail to fuse together. These fractures may also occur in otherwise healthy people that have not had their bones medically treated or have suffered an infection or severe trauma to the soft tissues surrounding the fracture site.

2.4.

Current Solutions

As previously mentioned, after a bone is broken it needs rest and support to heal properly. According to the need of each case, it’s possible to produce a cast that fits the limb of each and every client. This allows a great flexibility in adapting the size and shape to different types of fracture. Table 1 identifies the different types of cast configurations and specifies the cases where they are applied. Figure 2 pictures the different classes of casts described on Table 1.

Type of cast

Location

Uses

Short arm cast

Applied below the elbow to the hand.

Forearm or wrist fractures. Also used to hold the forearm or wrist muscles and tendons in place after surgery.

Long arm cast

Applied from the upper arm to the hand.

Upper arm, elbow, or forearm fractures. Also used to hold the arm or elbow muscles and tendons in place after surgery.

Arm cylinder cast

Applied from the upper arm to the wrist.

To hold the elbow muscles and tendons in place after a dislocation or surgery.

Table 1 - Different cast configurations for each type of fracture in the arm.

Respecting the material, the cast can be made of plaster or fiberglass. While fiberglass material is newer, many casts used today are still made from plaster. Plaster casts are most often used when a fracture reduction (repositioning of the bone) is performed. The reason plaster is used after repositioning the bone is that plaster can be well molded to the patient, and therefore it can support the bone more precisely. When a bone was out of position, and is manipulated back into position, plaster may be used to help hold the bone in the proper position. The problem with plaster is that it is heavy and must remain dry. Plaster casts are a burden for the patient because of their bulky and heavy material. Furthermore, water will distort the cast shape and can cause problems for healing should the cast get wet. Fiberglass casts are usually fitted when the bone is not out of position, or if the healing process has already started. Fiberglass casts are lighter weight, longer wearing, and more breathable than plaster. The fiberglass casts are sturdier than the plaster and require less maintenance. Of course, they are also a more expensive solution for immobilization. Both plaster and fiberglass casts are wrapped over a few layers of cotton that serve to protect the skin. Keeping this cotton clean and dry will be of outmost importance for your comfort.

Figure 2 - Different cast configuration for arm fractures.

2.5.

Limitations of Current Solutions

For a long time, traditional casts made from plaster, and most recently from fiberglass, have been an effective immobilization solution. However, it still faces several limitations that not only interfere with the users’ routine but also with the healing process itself. Some of these problems are listed below: 

Weight: the cast has a significant weight affecting the mobility of the user. This affects the rehabilitation of the bone and becomes uncomfortable for the patient. Usually, children and elderly are the most affected. Fiberglass casts don’t usually have these disadvantage.



Hygiene: if the cast gets wet, it loses its stiffness, increasing difficulty for users to shower without a proper isolation for the casted area. Besides that, the protected area underneath the cast is never washed, which lead to accumulation of sweat and the appearance of unpleasant odors.



Comfort: one of the biggest complains found among users is the hitching problem. If the user gets a hitch in the protected area, it will most likely very hard to scratch that area, which can be very unpleasant.



Unreachable: there is no way of analyzing the fracture without removing the cast. This is a big drawback for healing. If the user removes the cast too soon, the fracture can still not be cured and a new cast needs to be made. If the user removes it too late, time was lost, and the physiotherapy process could have started earlier.



Existence of wounds or injuries: if an open wounds exists around the area of the fracture, it may be necessary to leave space for accessing the wound. This can be complicated using cast material.



Design and Personalization: the cast is not only ugly but also quite large. This can interfere with the allowable clothes for the user and to the general look of the person.

3. The product: Cast Off

3.1.

The Challenge

The major function of traditional cast is to immobilize the arm in order that the bone can be as align as possible so that the rehabilitation occurs as smooth and quick as possible. So to design an alternative to the current solutions, we first had to guarantee that the immobilization feature is assured. We then wanted to create a lighter solution that the ones currently available to provide a more comfortable recovery and also facilitate movement which will benefit the reconstruction of the broken bone. This solution must also be waterproof and allow the skin in the arm to bread so that the arm can be washed and prevent the itchiness in the area. Other feature that can be interesting for this solution for medical reasons, will be the ability to removing the cast. This would enable orthopedists to perform regular check-ups and physiotherapist to start working in rehabilitation.

3.2.

Additive Manufacturing

All these specifications should be considered while creating the design and architecture of the product and choosing the manufacturing processes and assembly procedures. All the mentioned areas influence each other and should all be reevaluated every time that is a change in one of them. However, in this particular case, the manufacturing process was settled at the beginning, since that was the topic of the challenge. Fortunately, the characteristics of additive manufacturing are coincident with most of the requirements needed to tackle most of the previously mentioned challenges. First, additive manufacturing is a good best solution when we are faced with very low production volumes, personalized products and geometry flexibility needs. This not only allows the adaptation of the cast for the arm of each patient but also adjustable thickness and density of the different parts, according with the type and position of the fracture. The easiness of personalization for comfort and aesthetic reasons are also a great advantage of this manufacturing technique. Nevertheless, there is also some disadvantages that need to be contemplated. Additive manufacturing is usually a more expensive solution than other manufacturing techniques, mostly due to the cost of the materials. It is also still a very time consuming operation, which is a huge drawback for this specific application since the immobilization must be done as quick as possible.

3.3.

3D Scanning

The design of the immobilizer should be built around the geometry of the arm, so that the contact area between the product and the arm is as big as possible, allowing a better distribution of its weight. The process must then include a 3D scan of the injured arm to allow a personalized design

for each patient. Figure 3 shows an example of the scanning process and the final digital model. After scanning the arm the image must be processed before it is possible to start building the design of the “cast”. Ideally, after this, a computational routine would create an optimum structure for the product, according to the geometry of the arm and the position of the fracture. For this challenge the design was “manually” developed although our ultimate goal is to develop a computational tool that produces the optimum design for each case.

Figure 3 - An example of the 3D scanning process. In the left, the arm is scanned with the help of a laser that detects the tridimensional shape of the forearm. The upper right figure, the readings of the laser in the software. The final 3D model of the forearm, after post-processing in a CAD software (SolidWorks).

3.4.

Concept Generation

3.4.1. Basic Concept As previously mentioned, the design should be developed around the shape of the arm which constrains placing the “cast” in the arm. By observing Figure 4, it is possible to conclude that the product cannot be put as a glove, since the material is rigid and the geometry has different lengths throughout the arm. To avoid this situation, the product was split in two main parts: top and bottom. With this configuration, the arm should be first carefully placed over the bottom part. The top part should then be placed over the arm and fit it with the other half. A locking mechanism is then necessary to keep the both parts together and preventing the any movement from the injured bone.

3.4.2. Main parts These are the most important parts of the product and the ones that needed careful attention in terms of design. Their main goal is to protect the bone from moving, guaranteeing proper healing process to the fracture. However, they also need to include several other specifications to improve the comfort of the user such as low weight and openings for hygiene. A compromise between these several variables much be achieve and improved throughout the development process according to the different types of fracture, the feedback of the customers and other constrains of the project such as the type of materials, equipment and processes available for the product. To assure the immobilization of the broken bone, the main body of the cast must be fix in the two edges of the forearm. It must also prevent the rest of the limb from significant impacts by covering, at least partially, the surface of the forearm. This specifications would lead to a design similar to the one shown in Figure 4. However this configuration would not solve most of the problems of the traditional solution. To comply with the goals stablished for the product, it was necessary to create openness on the two main parts so that the skin of the forearm can breathe and be washed without removing the cast. This will improve the hygiene of the user, prevent the hitching problem in the forearm without putting at risk the rehabilitation of the fracture. These openness will require less material in the main parts, diminishing the weight of the product. The manufacturing cost of the product can also be lower, although in must be considered that the filler material will probably be replaced by support material. The position, dimension and shape of these openness should be optimized to assure as much exposed area as possible without compromising the security of the fracture and the structural proprieties of the material. The thickness of the main parts can also vary throughout the forearm with the addiction of more material in more sensible areas (usually around the fracture) and minimized the thickness in less structural demanding areas of the cast.

Figure 4 - Sketch of a concept similar to cast that are currently used in the immobilization of arm fractures.

In this first prototype, the several mentioned variables were not optimized, although we consider this an essential process to achieve a functional and appealing product. The openness were then randomly placed throughout the cast, with a hexagonal shape and the thickness was kept constant.

3.4.3. Locking system To allow the immobilization of the forearm at all times, a locking mechanism must be conceived to unite both ends of the top and bottom element. This can have a variety of configurations, although some specifications should be kept in mind. To avoid the displacement of any of the two parts of the main body and jeopardize the immobilization of the fracture, the locking mechanism should prevent displacements in the different directions. For preventing displacement in the horizontal direction, pins were added on the interface surfaces of the top and bottom parts. When jointed, the parts relative movement is constrained in two directions. However, vertically, the elements are still able to move and can easily be separated. After testing several concept, the group arrived at the locking system shown in Figure 7.

Figure 5 - Sketches of different locking concepts for fixing the upper and bottom parts.

3.5.

Prototyping

To test and demonstrate the chosen concept, a prototype was built. This model was also produced by an additive manufacturing process. All the parts were printed in a Dimension SST 768 (Figure 6) with ABS as filler material.

Figure 6 - Dimension SST 768 printer.

Table 2 shows some of the main data from the printing of all the pieces. The main body and the locking pieces were printed in a different session due to dimensional constrains of the printer. The first was fully printed in sparse mode, to reduce the volume of material spent. However, the locking pieces were printed with full density, since they are submitted to the highest mechanical stresses and benefit from the filled configuration. The prototype of the two main parts are shown in Figure 7. Two different designs were tested for this element for testing. It was concluded that the configuration on the left, in Figure 8, was the best, allowing an easier locking procedure. Elements Upper and bottom parts Locking pieces

Filler Material Volume (cm3)

Support Material Volume (cm3)

Printing Time

175.68

164.06

30h33m

6.28

2.25

1h06m

Table 2 - Characteristics of the printing process of the different elements.

Figure 7 - Prototype of the main body of the cast: top and bottom parts.

Figure 8- Different configurations of the locking elements.

After printing, the support material was first removed manually and then soaked in a bath of caustic soda (Figure 9). In the first operation, the majority of the support material is removed while in the latter only the residues, usually located in hard to access locations, are chemically removed.

Figure 9 - Caustic soda bath used in post processing.

As a precaution, no geometrical tolerance was introduced in the interfaces to prevent the locking mechanism from being loose. As a consequence, the excess of material had to me manually removed through a sanding process.

3.6.

Cost Estimate

To evaluate the cost of producing this product and to try to understand how this product can be introduced in the market, some calculation were performed from the few available data. Table 3 presents a brief summary of the estimated cost for the production of the product.

Elements Upper and bottom parts Locking Pieces

Material

Quantity

Material Cost (€)

Energy Cost (€)

ABS

1

97.92

9.76

ABS

4

2.46

0.32

Human Labor Cost (€)

Total Cost (€)

20,0

130.46

Table 3 – Estimated cost of the producing Cast Off. It was assumed a density of 1.04g/cm3, 300€/kg, 0.20€/kWh, 2 hours of human labor at 10€/hour.

The price for the patient was also estimated and two scenarios were considered, as shown in Table 4. First, the case were the same entity or company performs is responsible for the manufacturing and distribution of the product. This can happen is a case where the medical facility has a printer and does everything in-house. Other example could be the case of additive manufacturing centers where you can bring your prescription form the health professional and order your own cast. The second example represents a scenario where the production and distribution is performed by separate stakeholders. An example of this can be a hybrid scenario between the two previously mentioned models, where the medical facility orders the product from a printer center and then sells the cast to the patient. For the two situation, we used margins typical from health and service business.

Healthcare Products Margin Manufacturers + Distribution Manufacturers Distribution

3D Printing Margin

Total Cost (€)

50% 50% 25%

FINAL PRICE (€) 195.69

130.46 228.31

Table 4 – Estimated price for the patient based in typical margin values.

The prices obtained are too high for a generalized acceptance form the patients. There can be some niches where this price could not be an obstacle, especially by adding value to product through aesthetics and personalization. Nevertheless, the costs can and should be reduced in furthers iterations of the design: 

By time constrains, the printing configuration was not optimized in terms of support material consumption. A one by one printing process would result on a lower material consumption and consequently in a cheaper process.



The thickness of the cast can also be optimized after a structural analysis performed alongside with medical professionals and physiotherapists. This can also save of both filler and support material, and reduce the printing time.



Locking pieces can be standardized, independently of the main body configuration. This can allow to look at the mass production of this element, reducing significantly the overall cost of the product.



Other locking systems can also be considered, especially with off-the-shelf elements such as screws and brackets, which can also reduce the production costs.



The investment in a new machine that allow the use of bulk filler and support material can drastically decrease the production cost of the product. After a quick market search, it can be concluded the material cost can be reduced up to 80%. By reviewing the calculation performed in Tables 3 and 4, the final price can reach approximately 70€ (assuming the same energy and labor costs).

4. Limitations and future work

Although several advances were made during this project, several aspects still need to be tackled in order to provide the customer a trustworthy solution for the immobilization of fractures. Listed below are some of the areas were special focus is needed to achieve a good product that can be commercialized:

 After achieving the complete geometry of the product, an optimization of the overall structure should be performed. Varying the thickness and the density of the main parts throughout the arm to reach minimum weigh, while assuring the necessary mechanical features, will not only result on a lighter product but also a cheaper one.  After finding the optimal geometry, it is also essential to print it and test the product to some of its mechanical features. Pressure and impact tests are the most important ones to assure the safeness of the fracture. This can lead to adjust the analysis performed in the previous point.  Other important goal that must be pursued is the maximum comfort for the patient. Improving the contact between the skin and the surface of the product, especially at both ends, while allowing the skin to breathe will add value to this product.  One of the main advantages of this product is the possibility for the patient to take a bath with the cast on. However, without any post processing treatment, the structure is highly porous and can take a significant amount of time to dry completely. A solution to this issue is applying an appropriate coating to the surface of the cast making it waterproof, which will be tested in the next phase.  After achieving a good structural and comfortable design, the focus can be then changed to aesthetical issues. One of the main advantages of additive manufacturing is allowing personalized products, according to each user’s tastes and needs. Making the cast a better looking object can be important to make this product more appealing to the customer. An example, of this personalization option is represented in Figure 10. However, this aesthetical operation should not interfere with the main purpose of the cast: immobilization.  The next improvement is to add to the part that immobilizes the hand. This is crucial for a correct rehabilitation of different fractures that the current configuration cannot tackle, since the movements of the wrist can damage the alignment of most of the forearm bones.

 A very brief and simplified cost model was presented in this report. Although it allows an approximate forecast of the costs involved, a more extensive analysis should be performed to determine the real cost of producing the product.  The business model must also be defined. One of the biggest challenges around additive manufacturing currently is to find solid ways of generating income. There are several alternatives in these case, going from selling a software to work as a printing center, although some with higher potential than others.

Figure 10 - Example of a personalized upper part for younger patients.