Designed 3D scanner to achieve the spatial uniformity of the optimal pressure of pressure therapy

Summary

My classmate and aunt have hypertrophic scars after burns, which causes great psychological stress. And the story of Ms. PITT in Australia bravely facing scars inspired me to study on scar rehabilitation.

According to WHO report, every year burns cause about 11 million injuries and up to 70% of patients develop hypertrophic scars after burns. Pressure therapy is recommended by the International Society for Burn Injuries for first-line non-invasive physical therapy for the prevention and control of hypertrophic scars.

According to the pressure formula P=γ1/R1+γ2/R2 derived by myself, the radius of curvature of the pressure surface has a great influence on the pressure generated by the fabric. Due to the lack of 3D surface scanner in hospitals, the inability to measure curvature in pressure therapy of hypertrophic scars is common worldwide, not only in developing countries such as China, but also in developed countries US and EU. So I developed 3D surface scanner and verify its practicality. I conducted the pressure tests on cylinders and verified the pressure formula. The pressure test on my leg also verified the pressure formula also, so both formula and test show how important the radius of curvature is for pressure therapy.

Finally, based on the body curvature obtained from human body 3D modeling, I provided 2 solutions to achieve the spatial uniformity of the optimal pressure: adjusting the curvature of the pressure surface with a flexible pressure pad or changing the pressure transmission mode by replacing the elastic fabric with a rigid pressure pad.

 

Question / Proposal

In October 2016, Dr. Celeste Finnerty published a paper "Hypertrophic scarring: the greatest unmet challenge after burn injury" in THE LANCET, stating that although modern medicine can save the lives of many severely burned patients, but up to 70% of patients develop hypertrophic scars after burns is challenge, and although pressure therapy has been used for scar treatment for decades, but further research is still needed on how to apply pressure accurately.

  

Pressure therapy is recommended by International Society for Burn Injuries and the optimal range of pressure values (20-32 mmHg) is given, but there is no detail introduction on how to apply.

 

But current pressure therapy garments can NOT meet the optimal range of pressure (20-32 mmHg), because the radius of curvature is NOT calculated, and limb can only be simplified as a cylinder, using the average curvature.

 

To obtain the radius of curvature of human body, 3D human body modeling is necessary which we can get through the scanning by 3D surface scanner, but unfortunately there is no 3D surface scanner in hospital, not only in developing countries such as China, but also in developed countries like US and EU. In hospital, only departments that have already used MRI or CT can use existing MRI or CT image data combined with professional software (e.g. Materialise's Mimics) to obtain internal 3D models.

 

So I need to develop a set of surface 3D scanning system and verify its practicality in order to carry out further research.

Research

The objective of this research is to understand how to achieve the spatial uniformity of the optimal pressure value in hypertrophic scar pressure therapy.

 

 

Derivation surface pressure formula of high elastic fabric

 In 1984, Laplace Law was first mentioned in the paper on the hypertrophic scar pressure therapy (7) (8), but there is no derivation of the pressure formula, just the formula based on observation: Pressure = Tension / Radius of Curvature (8). Searching the Burns magazine with "Laplace Law" or "Law of Laplace", we can get 6 articles, all using the formula "Pressure = Tension / Radius of Curvature" without formula derivation (5) (9) (10) (11) (12) (13).

 

 In fact, there is no “Laplace Law” or “Law of Laplace” in physics. This is just a name of the formula Pressure = Tension / Radius of Curvature in medicine. The source of this name and formula should be the famous "Young-Laplace Equation":                                                                                                                                                                                             

The Young-Laplace equation is used to explain the formation and calculation of the additional pressure on the curved surface. It describes the additional pressure difference between the two static fluid interfaces (such as water and air) due to the surface tension phenomenon. ΔP is the pressure difference across the fluid interface, γ is the surface tension, H is the average curvature, and R1 and R2 are the principal radius of curvature. Since the Young-Laplace equation is to study the additional pressure difference created by the two static fluid interfaces, which is completely different from the mechanism of the high elastic fabric generating pressure on the curved surface, so using Laplace's law "Pressure = Tension / Radius of Curvature" to study the pressure of high elastic fabrics in pressure therapy is not accurate.

The pressure formula can be deduced by using the force decomposition and pressure formula in classical mechanics. The derivation process is as follows:

             

 

Development of 3D surface scanner

 In 2009, Microsoft introduced the depth sensor KINECT 1 for XBOX, and later introduced the second generation with higher precision. Intel also introduced the RealSense series depth sensor for machine vision, VR, etc. Companies such as Occipital and PMD subsequently followed up with various depth sensors and the price dropped to hundreds of US dollar. This study uses these consumer-grade depth sensors, combined with the Software Development Kit (SDK) and third-party open source software, to design and build a 3D scanning system for body surface and verify the practicality of the device.

 

According to the comparison of Table 3-2, the Occipital Structure + IPad scheme has the best scanning continuity and resolution. This scheme is selected for further research.

  

 

 

 

 

 

 

Method / Testing and Redesign

Verifying the practicality of 3D surface scanner developed by myself

Scanning the following objects with the Occipital Structure depth sensor: 1) Rectangular box; 2) Cylindrical box; 3) Square, round, rectangular stickers on the human arm. After scanning, the area of each sample was measured using 3D Systems’ Geomagic Studio software, and the results were compared with the results of the ruler measurement.

Scanning the cylinder and measuring the diameter by 3D Systems’ Geomagic Studio software, compare the result measured by ruler. 

 

Tensile stress properties of high elastic fabrics

The high elastic fabric is Infinity Plus (80% nylon, 20% Lycra) from CARVICO, Italy, and the stretching equipment is INSTRON universal system, the test was conducted in Dong Hua University in Shanghai China by fabric supplier CARVICO.

 

Pressure test on cylinder

Pressure test equipment: TT Medi's KIKUHIME pressure tester;

Rigid cylinders: PVC pipes, diameters are: 111, 76, 51, 40 mm;

Elastic garments: 20%, 30%, 40%, 50%, 60% elongation

 

Pressure test on leg

Taking elastic garments of 291, 268, 249, 232, 218 mm circumference on my leg, measuring pressures of three different curvature points, and measuring these points curvature by 3D scanning method.

 

3D modeling and pressure distribution of foot

3D scan my right foot and get 3D digital model, based on this digital model get the curvatures of 3 pressure points by Geomagic Studio software. Test the pressure with pressure sock on these 3 pressure points.  

 

3D modeling and pressure distribution of hand

3D scan my right hand and get 3D digital model, based on this digital model get the curvatures of 2 pressure points by Geomagic Studio software. Test the pressure with pressure glove on these 2 pressure points.  

 

Solutions for spatial uniformity of the optimal pressure

Solution 1 : Adjusting the curvature of the pressure surface with pressure pad

3D scanning my right leg to get the shape of the leg, and designing a cylinder which outside is round and the inside is the shape of my leg. Slicing this object and building a 3D shape with cardboard. Taking this part as pressure pad of my right leg to measure pressure.

Solution 2: Changing the pressure transmission mode by replacing the elastic fabric with a rigid pressure pad

3D scanning my face to get the shape my face, and designing a mask which shape is my face, 3D printing it then get the mask.

Results

Verifying the practicality of 3D surface scanner developed by myself

The accuracy of 3D scanning measurement is comparable to the ruler measurement. The independent designed 3D scanning system is workable.

 

Tensile stress properties of high elastic fabrics

The radial tensile stress γ1 and the latitudinal tensile stress γ2 of this fabric are different, there is few fabric has the same tensile stress at different directions. If it is not uniaxial stretching, the pressure formula P = γ1/R1 + γ2 / R2 should be used.

High elastic fabrics have an elongation of up to 300%, but in practice, it will be generally no more than 60%. Under such condition, the tensile force is linearly related to the elongation, which is the main basis for designing the pressure garments.

 

Pressure test on cylinder

Since the tensile force is linearly related to the elongation (<60%), the result of pressure test on cylinder proved the pressure formula: P=γ1/R1+γ2/R2, when R2=∞ like this case P=γ1/R1.

 

Pressure test on leg

The result of pressure test on leg is similar as the test on cylinder, and  proved the pressure formula: P=γ1/R1+γ2/R2 (in this case R2=∞ ) also. Pressure is proportional to curvature, the greater the curvature, the greater the pressure.

 

3D modeling and pressure distribution of foot

The pressure distribution on the hand also conforms to the pressure formula: the pressure is proportional to the curvature. From the other point of view, because the curvature of the hand varies greatly, it is impossible to achieve the space uniformity of the optimal pressure value (20-32mmHg) by directly wearing the pressure garment. Some area have high pressure, and some area have low pressure because the curvature of each area is different.

 

3D modeling and pressure distribution of hand

This result proves again that it is impossible to achieve the spatial uniformity of the optimal pressure value by directly wearing the pressure garment, because the curvature of each part of the human body is different.

 

Solution 1: Adjusting the curvature of the pressure surface with pressure pad

Compared with wearing a pressure garment directly, changing the curvature through the pressure pad can greatly improve the spatial uniformity of the optimal pressure value.

 

Solution 2: Changing the pressure transmission mode by replacing the elastic fabric with a rigid pressure pad

Compared with wearing an elastic headgear directly, the results show that changing the pressure transfer mode by replacing the elastic fabric with a rigid pressure pad can greatly improve the spatial uniformity of the optimal pressure value.

 

Conclusion

The Young-Laplace equationΔP = γ (1/R1+1/R2) is to study the pressure difference between two static fluid interfaces due to the tension of the curved surface. Simplifying the Young-Laplace equation to Pressure = Tension / Radius of Curvature and calling it “Laplace Law” to calculate human body pressure created by high elastic fabrics is not accurate. The connotations are completely different. In the Yang-Laplace equation, γ is the surface tension, and for isotropic fluids, γ is consistent in all directions, but for high elastic fabrics, γ is different. If the fabric is stressed in both directions, it must be calculated separately. In addition, the high elastic fabric can stretch up to 300%, and its characteristics are completely different from those in the Yang-Laplace equation. 

According to the formula derivation of high elastic fabric pressure: P=γ1/R1+γ2/R2, we know that the pressure generated by the high elastic fabric on the body surface is linear with curvature of the body surface. Since the human body is an irregular body, the curvature of different parts is different, and the curvature difference of some parts is even very large, which causes the pressure difference between these parts to be huge. For example, the curvature of the hand side is more than twice the curvature of the back of the hand, which determines that if there was no pressure pad to adjust curvature, the pressure difference between both sides is more than 2 times. Another example is the leg part, which looks like a cylinder. It seems that the curvature difference is not very large, but after the actual measurement, it is found that the curvature difference is about 3 times. The measured pressure also confirms this result according the formula P=γ1/R1+γ2/R2.

The recommended optimal pressure from International Society for Burn Injuries is 20-32 mmHg, according to the formula P=γ1/R1+γ2/R2, it means that if the maximum curvature of the hypertrophic scar is the highest value of 30 mmHg, the curvature of the same elastic cover should not be less than 2/3 of the maximum curvature, otherwise it will be lower than 20 mmHg. In order to achieve the spatial uniformity of the optimal pressure value of pressure therapy, some parts, such as legs, arms, upper body, etc., which are similar to cylinders, we can adjust the curvature by padding. 3D printing rigid pressure pad can be used in these area where soft padding will affect human function, such as face, foot, hand, etc., the principle is to change the mode in which the elastic fabric tension generates pressure on the curved surface to the solid pressure transfer mode, and the pressure mask is an example. It is impossible to cushion the face into a cylindrical shape by adjusting the curvature. The principle of the pressure mask is to solidify the curved surface of the face into a rigid body and then apply pressure.

About me

I am from High School Affiliated to Shanghai Jiao Tong University, 11th grade, female student, Shanghai Jiaotong University is very famous for science and engineering in China. I took the IB course and chose Math, Physics and English as High Level. 

The sense of pleasure after solving the problem is the main reason why I am very interested in engineering. It is my specialty to find and solve problems from the interdisciplinary field, such as this topic. 3D scanning makes it easy to measure the area of complex shapes. This feature can be used to measure the body surface area of a chemotherapy patient (to calculate the drug dosage of chemotherapy) to replace the existing formula method. In June 2016, “Body surface area formulae: an alarming ambiguity” was published on “Scientific Reports”, reported the details of these problem of formula method. I am very happy that 3D scanner developed by myself can also solve this problem.

My mentor, Professor Xia Zhaofan, is an idol I admire. She uses her knowledge to save many burn patients. My dream school is MIT, and one of my high school alumni who is studying in MIT introduced me a lot about MIT, which makes me very yearning. 

The award means that my research is recognized, and I hope that the results can be widely reported which will help more burn children and women in low- and middle-income countries; The award also means that my chances of entering MIT have increased.

Health & Safety

3D printing of mask was carried out at DSM Shanghai Branch, and the elastic fabric was tested by the fabric manufacturer in Shanghai Donghua University. The rest of the research work was done by myself at home.

The following is the 3D printing operation rules of DSM Shanghai Branch:

3D consumer-grade depth sensors:  Microsoft Kinect 1st generation, Intel RealSense R200, Microsoft Kinect 2nd generation, Occipital Structure and PMD Flexx, are commercial products in the market with safety certification. 

At home, I conduct research on this project according to the safety standards of daily life.

 

Bibliography, references, and acknowledgements

References

1.     Dattesh R. Davé, Neeraja Nagarjan, Joseph K. Canner, Adam L. Kushner, Rethinking burns for low & middle-income countries: Differing patterns of burn epidemiology, care seeking behavior, and outcomes across four countries,Burns 44 (2018) 1228-1234

2.     Celeste C Finnerty, Marc G Jeschke, Ludwik K Branski, Juan P Barret, Peter Dziewulski, David N Herndon, Hypertrophic scarring: the greatest unmet challenge after burn injury, The Lancet, Volume 388, Issue 10052, 1–7 October 2016, Pages 1427-1436

3.     ISBI Practice Guidelines Committee, Steering Subcommittee, Advisory Subcommittee, ISBI Practice Guidelines for Burn Care, Burns 42 (2016) 953-1021

4.     Lisa Macintyre, Margot Baird, Phil Weedall, The Study of Pressure Delivery for Hypertrophic Scar Treatment,《Medical Textiles and Biomaterials for Healthcare 》Woodhead Publishing Series in Textiles,1 edition December 2005,P224-231

5.     Lisa Macintyre, Margot Baird ,Pressure garments for use in the treatment of hypertrophic scars – an evaluation of current construction techniques in NHS hospitals,Burns, Volume 31, Issue 1, February 2005, Pages 11-14

6.     Atiyeh BS, El Khatib AM, Dibo SA. Pressure garment therapy (PGT) of burn scars: evidence-based efficacy. Annals of Burns and Fire Disasters. 2013; 26(4):205-212.

7.     Jeffrey R. Basford, The Law of Laplace and Its Relevance to Contemporary Medicine and Rehabilitation, Archives of Physical Medicine and Rehabilitation, Volume 83, Issue 8, August 2002, Pages 1165-1170

8.     J. C. Y. Cheng, J. H. Evans, K. S. Leung, J. A. Clark, P. C. Leung, Pressure therapy in the treatment of post-burn hypertrophic scar—A critical look into its usefulness and fallacies by pressure monitoring, Burns, Volume 10, Issue 3, February 1984, Pages 154-163

9.     Lisa Macintyre, Rhona Ferguson,Pressure garment design tool to monitor exerted pressures,Burns, Volume 39, Issue 6, September 2013, Pages 1073-1082

10.  Lisa Macintyre, New calibration method for I-scan sensors to enable the precise measurement of pressures delivered by ‘pressure garments’, Burns, Volume 37, Issue 7, November 2011, Pages 1174-1181

11.  Candy H. Y. Lai, Cecilia W. P. Li-Tsang,Validation of the Pliance X System in measuring interface pressure generated by pressure garment, Burns, Volume 35, Issue 6, September 2009, Pages 845-851

12.  Karen Rappoport, Reni Müller, Carlos Flores-Mir,Dental and skeletal changes during pressure garment use in facial burns: A systematic review,Burns, Volume 34, Issue 1, February 2008, Pages 18-23

13.  Lisa Macintyre,Designing pressure garments capable of exerting specific pressures on limbs, Burns, Volume 33, Issue 5, August 2007, Pages 579-58

 

Acknowledgement

At present, there are no 3D body surface scanning equipment in hospitals in China, including Shanghai Chang Hai Hospital and Shanghai Rui Jin Hospital, which are the best burn treatment hospitals in Shanghai. Because my last research was about measuring burn area with 3D scanning, I already have the basis of 3D technology, so Academician Zhao Fan XIA who is the director of Shanghai Chang Hai Hospital Burns Department, and Dr. Peng Fei LUO pointed out that it’s better to further study how to apply pressure, this topic is also blank in the international arena, but it is very useful for the rehabilitation of patients. Although this project is not directly related to the current research of Academician Xia and Dr. Luo, they gave me a lot of guidance about pressure therapy and others knowledge about burn treatment. I would like to thank Academician Xia and Dr. Luo for their support of the research to me who is middle school student, without their guidance, it is impossible for me to do research on burns

3D printing of mask was carried out at DSM Shanghai Branch, and the elastic fabric was tested by the fabric manufacturer in Shanghai Donghua University. The rest of the research work was done by myself at home. 3D depth sensors, pressure testers, IPad and computer with softwares purchased from the market.