Issuu on Google+

Natural fiber bone plates as substitutes for orthopaedic alloy plates Chandramohan Devarajan1, Marimuthu Krishnaswamy2 1

Department of Mechanical Engineering, Adhiyamaan College of Engineering, Hosur, Tamil Nadu 635109, India; Email: mail_2_cm@yahoo.com 2 Department of Mechanical Engineering, Coimbatore Institute of Technology, Coimbatore, Tamil Nadu 641014, India

ABSTRACT Bones are living tissues, consists of minerals like calcium and phosphorus. They grow rapidly during one's early years and renew themselves. The bone is considered as a linear-elastic, isotropic and homogeneous material. Bones are the essential part of the human skeleton. It helps to support the softer parts of the body. Trauma is a major cause of death and disability in both developed and developing countries. The World Health Organization (WHO) predicts that by the year 2020, trauma will be the leading cause of years of life lost for both developed and developing nations. The aim of this review is to compare the orthopaedic alloy plates (stainless steel, titanium, cobalt chrome and zirconium) and natural fiber (Agave sisalana fiber, Musa sapientum fiber and Hibiscus sabdariffa fiber) reinforced polymer composite bone plates used in humerus fractures. Also this review focuses a new method of using data obtained from CT images combined with digital CAD and rapid prototyping model for surgical planning and this new application enables the surgeon to choose the proper configuration and location of internal fixation of plate on humerus bone during orthopaedic surgery. Keywords: Orthopaedic alloys, NFRPC, mechanical properties, finite element analysis, CT, CAD, RPT

INTRODUCTION Orthopaedic surgeons have been using metallic bone plates for the fixation of humerus bone fractures. Apparently, metallic prostheses, which are generally made of stainless steel and titanium alloys, cause problems like metal incompatibility, corrosion, magnetism effect, anode-cathode reactions, including a decrease in bone mass (osteopenia), increase in bone porosity (osteoporosis), and delay in fracture healing [1-3]. Due to insufficient bone growth, refractures after the removal of the prostheses are also widely reported [1,3]. It was also found that the difference in the elasticity of a metallic implant and bone may cause loosening of the implant [4]. Also, in composite plates, the screw at the area of maximum bending moment was found to back out of the bone while it is rare in metal plates [1,3]. Thus, research on alternative implant materials have been undertaken in the past decade. Natural fiber reinforced polymer composite materials which are less rigid than metals may be good alternatives because of properties closer to bone mechanical properties. It was found that they help to avoid stress shielding and increase bone remodeling [1,5]. We compare the efficacy of metallic bone plates and composites on the bone and fracture site. The finite element analysis tool ANSYS was used for the solution. As it is well known, the term ‘rapid prototyping’ refers to a number of different but related technologies that can be used for building very complex physical models and prototype parts directly from 3D CAD model. Among these technologies are stereolithography (SLA), selective laser sintering (SLS), fused deposition modeling (FDM), laminated object manufacturing (LOM), inkjet-based systems and three dimensional printing (3DP). Rapid Tooling (RP) technologies can use wide range of materials (from paper, plastic to metal and nowadays biomaterials) which gives Invited Review, Biotechnol. Bioinf. Bioeng. 2011, 1(4):405-413 Š 2011 Society for Applied Biotechnology. Printed in India; ISSN 2249-9075


406

possibility for their application in different fields. RP has primary been developed for manufacturing industry in order to speed up the development of new products. They have showed a great impact in this area (prototypes, concept models, form, fit, and function testing, tooling patterns, final products-direct parts). Preliminary research results show significant potential in application of RP technologies in many different fields including medicine. This review covers possibilities of using RP technologies as a multi-discipline area in the field of orthopaedics. Using RP in medicine is a quite complex task which implies a multidisciplinary approach and very good knowledge of engineering as well as medicine; it also demands many human resources and tight collaboration between doctors and engineers.

RAPID PROTOTYPING Rapid prototyping plays a key role in the development of products. This serves as a design visualization tool as well as for fit and function application to speed up the product development. Rapid prototyping works on the basis of adding layers of material to form the desired shape. The majority of commercial rapid prototyping system build object by adding one layer after another. For simplicity, it can be visualized as stacking slices of bread until complete three-dimensional bread loaf is achieved. Rapid prototyping is a highly automated layer manufacturing process. The object is designed in any solid modeling software (CAD) and the data is converted into a standard format widely known as standard triangularisation language (STL) which is understandable by the rapid prototyping machine. Rapid prototyping software receives data in this format and creates a complete set of instructions for fabrication on rapid prototyping machine such as tool path, layer thickness, processing speed, etc. Rapid Prototyping machine then manufactures the object using layer manufacturing method. Upon completion of a three-dimensional model, it is subjected to postprocessing treatment for removing support material that was used to support overhang features during fabrication. Figure 1 show steps involved in rapid prototyping process.

ACRYLONITRILE BUTADIENE STYRENE (ABS) Acrylonitrile Butadiene Styrene [chemical formula (C8H8)x路(C4H6)y路(C3H3N)z)] is a common thermoplastic used to make light, rigid, molded products. ABS plastic ground down to an average diameter of less than 1 micrometer is used as the colorant in some tattoo inks. It is a copolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The proportions can vary from 15 to 35% acrylonitrile, 5 to 30% butadiene and 40 to 60% styrene. The result is a long chain of polybutadiene criss-crossed with shorter chains of poly (styrene-co-acrylonitrile). The nitrile groups from neighboring chains, being polar, attract each other and bind the chains together, making ABS stronger than pure polystyrene. The most important mechanical properties of ABS are resistance and toughness.

APPLICATIONS OF RAPID PROTOTYPING IN ORTHOPAEDICS Production of prototypes for medical modeling (orthopaedics) in general can be classified into two broad categories based on manufacturing process route and type of data available, i.e., designed data and scanned/digitized data. Designed data is data that is created according to a person's idea on computer aided design (CAD) system. For this type of data, the designer has total control to modify, adjust and manipulate design ideas to serve the functional purpose of design. Producing models with this type of data is very straight forward and no further data treatment is required. CAD solid model can be directly converted to STL format for use in subsequent rapid prototyping process.


407

Figure 1. Steps involved in rapid prototyping [6].

Scanner or digitizer is normally used to capture structures that exist in physical form, either dead or living things, and using surface modeler software, three-dimensional CAD representation is created. For this type of data, the user has limited capability to modify and manipulate the geometry and further processing is required before they can be readily used by rapid prototyping system. For example, further data treatment is needed for scanned data from computed tomography (CT) and magnetic resonance imaging (MRI) scanners which capture soft and hard tissue information based on density threshold value. The undesired soft tissue data is removed before it is sent to rapid prototyping machine for fabrication. Segregating soft tissue data and leaving only hard tissue (humerus bone) structure can be carried out by applying certain range of density threshold value. This procedure can be a daunting task for complex structure and one has to repeat the procedure many times until satisfactory result is achieved. There are a number of commercial software’s such as MIMICS and Go-build which translate this data to the format required by RP systems. In reverse engineering method, point cloud data for an existing object is captured using coordinate measuring machine or laser digital surface scanner and using surface modeler, this raw data is processed to form three-dimensional model of the object in CAD system. The morphological data of the humerus bone was collected using the above mentioned CT scanner. A 3D data set was acquired producing 119 slices with a slice thickness of 1 mm. The reconstructed CT data was transferred to a CD and loaded into the MIMICS software. The humerus scanning data and model STL manipulation were processed using MIMICS RP Software (Figure 2). The modeling software is a general purpose segmentation programme for grey value images. This software can generate both the frontal and lateral view from the CT scans (Figure 3). From CT data 3D model of humerus bone has been created. RP made a real copy of the bone (Figure 4) and was


408

used for planning of orthopedic surgery (Figure 5) especially choice of implant type, implant position and application procedure.

Figure 2. Humerus bone in MAGICS software [10].

Figure 3. CT scans of Humerus bone [6].

Figure 4. RPT model of Humerus bone using ABS material [6].


409

Figure 5. Model of Humerus bone with plate [10].

PLANNING AND EXPLAINING COMPLEX SURGICAL OPERATIONS This is a very important role of RP technologies in medicine which enable pre-surgery planning. The use of 3D model of humerus bone helps the surgeon to plan and perform complex surgical procedures and simulations and gives an opportunity to study the bone structures of the patient before the surgery, to increase surgical precision, to reduce time of procedures and risk during surgery as well as costs (thus making surgery more efficient). The possibility to mark different structures in different colors (due to segmentation technique) in a 3D physical model can be very useful for surgery planning and better understanding of the problem as well as for teaching purpose. RP models can be used as teaching aids for students in the classroom as well as for researchers. These models can be made in many colors and provide a better illustration of anatomy, allow viewing of internal structures and much better understanding of some problems or procedures which should be taken in concrete case. They are also used as teaching simulators. RP models can be used as teaching aids for students in the classroom as well as for researchers. These models can be made in many colors and provide a better illustration of anatomy, allow viewing of internal structures and much better understanding of some problems or procedures which should be taken in concrete case. They are also used as teaching simulators. Natural fibers present important advantages such as low density, appropriate stiffness and mechanical properties and high disposability and renewability. Moreover, they are recyclable and biodegradable. Over the last decade, composites of polymers reinforced by natural fibers have received increased attention. Natural fibers such as sisal and roselle possess good reinforcing capability when properly compounded with polymers. The fibers are powdered, cleaned normally in running water and then dried. After adequate drying of the fibers in normal shading for 2 to 3 hours, the fibers are taken and soaked in the NaOH solution. Soaking is carried out for different time intervals depending upon the strength of fiber required. In this work, the fibers are soaked in the solution for three hours. After the fibers are taken out and washed in running water, these are dried for another 2 hours. The fibers are then taken for the next fabrication process namely the procasting process. Chemical treatment with NaOH removes moisture content from the fibers thereby increasing its strength. Also, chemical treatment enhances the flexural rigidity of the fibers. Moreover, this treatment clears all the impurities that are adjoining the fiber material and also stabilizes the molecular orientation. Tensile, flexural and impact specimens as per ASTM standards were cut from the fabricated plate. Edges of the samples were sealed with polyester resin and subjected to moisture absorption. The composite specimens to be used for moisture absorption test were first dried in an air oven at 50ยบC. Then these conditioned composite specimens were immersed in distilled water at 30ยบC for


410

about 5 days. At regular intervals, the specimens were removed from water and wiped with filter paper to remove surface water and weighed using a digital balance of 0.01 mg resolution. The samples were immersed in water to permit the continuation of sorption until saturation limit was reached. The weighing was done within 30 s, in order to avoid any errors due to evaporation. The test was carried out according to ASTM D570 to find out the swelling of specimen. After 5 days, the test specimens were again taken out of the water bath and weighed. After moisture absorption tests, the tensile strength of the composites was measured with a universal testing machine in accordance with the ASTM D638 procedure at a crosshead speed of 2 mm/min. Flexural tests were performed on the same machine, using the 3-point bending fixture according to ASTM D790 with the cross-head speed of 2 mm/min. In the impact test, the strength of the samples was measured using an Izod impact test machine. All test samples were notched and the procedure used for impact testing was ISO 180. The test specimen was supported as a vertical cantilever beam and broken by a single swing of a pendulum. Table 1 shows the salient properties of some of these biomaterials. Table 1. Properties of biomaterials. Biomaterials +

Humerus bone Titanium + Stainless steel + Cobalt chrome + Zirconium ++ Roselle and sisal (hybrid) ++ Roselle and banana (hybrid) ++ Sisal and banana (hybrid) +

Young’s Modulus N/mm² 17.2×103 120×103 200×103 230×103 200×103 18857.075 22061.9593

Density Kg/mm3 1.9×10-6 4.51×10-6 8×10-6 8.5×10-6 6.1×10-6 1.450×10-6 1.5×10-6

Poisson ratio

References

0.30 0.34 0.20 0.30 0.30 0.33 0.32

[1,8] [1,8] [1,8] [1,8] [1,8] [1,6,7] [1,6,7]

25779.2532

1.350×10-6

0.30

[1,6,7]

FINITE ELEMENT ANALYSIS Analysis package used for Stress Analysis on Humeral Shaft along with plate is ANSYS 11.0. Element types used in the finite element model were SOLID92 and SHELL99.SOLID92 was used in case of metallic bone plates while SHELL99 was chosen in case of composites. Metallic plate materials were taken as isotropic, NFRP composites and the fractured bone as orthotropic materials. Computerized tomography scanning image [CT scan] of humerus bone in .stl file was converted in to .iges file then imported to ANSYS for the stress analysis on humeral shaft with plate and without plate. The dimensions of plate are length of the plate (l): 150mm; thickness of the plate (t): 4.5mm; and width of the plate (w) : 10mm. The project case is mainly for youngsters during the bike riding. The weight of the person was assumed to be around 60 kg. Assumption made as initial velocity of vehicle V1 is 60kmph, final velocity of vehicle V2 is zero, mass of human body=60kg, external diameter of bone [D] = 22 mm, internal diameter [d] = 11 mm, bending stress on solid shaft: σьmax = (32×Mmax) / (3.14×d³); σьmax - Maximum bending stress in N/mm2; and Mmax - Maximum bending moment in N mm (Table 2 and 3).


411

Table 2. Comparison of results of bending stress on hollow shaft. Material

Manual (N/mm²)

ANSYS (N/mm²)

Bone

64.320

64.543

Stainless steel

65.370

65.327

Cobalt chrome

65.460

65.482

Titanium

65.560

65.604

Zirconium

65.480

65.543

Roselle and sisal (hybrid)

65.032

65.095

Sisal and banana (hybrid)

65.010

65.050

Roselle and banana (hybrid)

65.014

65.041

CONCLUSION AND FUTURE PERSPECTIVES The stress analysis of humerus bone and fixation of plate for the fractured bone has been carried out with stainless steel, cobalt chrome, titanium, zirconium, roselle + sisal (hybrid), sisal + banana (hybrid) and roselle + banana (hybrid). After plate fixation, the stress induced on the bone with plate and without plate is calculated both manually and using ANSYS software. Although titanium alloy has high strength, when compared to other materials (Table 2 and 3), the problems associated with its use include metal incompatibility, corrosion, magnetism effect, anode-cathode reactions, decrease in bone mass (osteopenia), increase in bone porosity (osteoporosis) and delay in fracture healing (callus formation, ossification) [6-10]. Thus, with the development of biocomposite materials, an increase in bone density is promoted due to a more suitable environment for bone growth due to the high resistance to corrosion of biopolymers and natural fibers. Fracture healing can be faster with the natural fiber reinforced polymer composite bone plates. Hence this work


412

muscularly gives confidence to utilize the advantages offered by renewable resources and its application in the field of orthopaedics for bone graft substitutes. Table 3. Comparison of results of bending stress on solid shaft. Materials

Manual (N/mm²)

ANSYS (N/mm²)

Bone

64.320

74.709

Stainless steel

65.370

74.953

Cobalt chrome

65.460

75.124

Titanium

65.560

75.221

Zirconium

65.480

74.973

Roselle and sisal (hybrid)

65.032

73.111

Sisal and banana (hybrid)

65.010

73.233

Roselle and banana (hybrid)

65.014

73.523


413

When a bone is severely crushed, physicians usually cannot set it and bone grafts or amputation - until now - has remained a primary option. The same is true for bones damaged by disease such as cancer. If, for instance, the humerus bone in the arm is injured and damaged, CT scan or MRI image can be made of the good arm bone and converted to a ‘growth code’ - a 3-D virtual image - of the replacement bone segment needed. As a replacement for orthopaedics alloys such as titanium, cobalt chrome, stainless steel and zirconium, this work aimed to fabricate natural fiber reinforced polymer composite plate material with bio epoxy resin. The material sisal and roselle (hybrid) was coated with calcium phosphate and hydroxy apatite (hybrid) composite and it can be used for both internal and external fixation on human body for fractured bone. Coated polymer 'bone' which is then surgically implanted into the arm where the damaged bone has been removed. The coating is very thin and allows the bone cells to attach themselves to the implant. Acknowledgements: This work was supported by the Institution of Engineers (India), Kolkata.

REFERENCES [1] Chandramohan D, Marimuthu K. European Journal of Scientific Research 2011, 54:384-406. [2] Chandramohan D, Marimuthu K. Acta of Bioengineering and Biomechanics 2011, 13:77-84. [3] Chandramohan D, Marimuthu K. International Journal of Advanced Medical Sciences and Applied Research 2011, 1:9-12. [4] Chandramohan D, Marimuthu K. International Journal of Advanced Engineering Technology 2011, 2:435-448. [5] Chandramohan D, Marimuthu K. International Journal of Current Research 2011, 3:331-337. [6] Chandramohan D, Marimuthu K. International Journal of Engineering Research and Applications 2011, 1:1256-1261. [7] Chandramohan D, Marimuthu K. International Journal of Advanced Engineering Sciences and Technologies 2011, 6:97-104. [8] Chandramohan D, Marimuthu K. International Journal of Materials Science 2010, 3:445-463. [9] Chandramohan D, Marimuthu K, Rajesh S, Ravikumar MM. International Journal of Applied Engineering Research 2010, 5:1653-1666. [10] Chandramohan D, Marimuthu K, Rajesh S, Ravikumar MM. Malaysian Journal of Educational Technology 2010, 10:73-81.


Natural fiber bone plates as substitutes for orthopaedic alloy plates