Rapid Prototyping Journal

Manak Jain; Sanjay Dhande; Nalinaksh Vyas

2009 Rapid Prototyping Journal

doi: 10.1108/13552540910960253

Purpose – Congenital telipes equinovarus (CTEV) or club foot is a historical foot deformity where the foot is turned in and pointing down causing the subject to walk on the outside edges of foot. The non‐surgical correction of this deformity is an unsolved challenging problem in the medical domain and it becomes interesting due to the increasing number of such patients. The purpose of this paper is to build a biomodel of this historical foot deformity in newborn babies and hence an attempt to develop a corrective procedure using rapid prototyping (RP). Design/methodology/approach – Biomodeling is a new technology that allows medical scan data sets to generate solid plastic replicas of anatomical structures. The medical scan data sets of live club foot baby patients were acquired and after image processing, biomodels of four live unilateral club foot baby patients are developed in a fused deposition modeling RP system. Findings – The paper shows the location and position of abnormal bones and abnormal tarsal joints and is useful for management of club foot deformity in newborn babies. On visual study, it is observed that the talus is underdeveloped, talar neck is shorter and deviated in the medial and planter direction. Research limitations/implications – The major outcome of this paper is the detailed geometrical visualization of talus bone of club foot and normal foot that assists in diagnosis and better treatment of CTEV. In future, the developed biomodels of club foot help to develop a corrective device that assists in bringing the club to normal foot geometrys. Practical implications – These developed biomodels of club foot help in deciding the best corrective procedure for surgeons. The geometrical comparison between normal and club foot helps in developing a non‐surgical corrective procedure of this historical foot deformity. A 3D representation of talus bone provides an opportunity to view talus and analyse the ankle joint geometry that develops a favorable condition for diagnosis and treatment of this deformity. Originality/value – The first time developed biomodels of clubfeet helps orthopaedic surgeons in preoperative surgical planning and consequently in carrying out biomechanical studies of club foot. The presented research plays a major role in planning a non‐surgical corrective procedure of this historical deformity. It also provides a platform for finite element analysis of club foot.

Luca Facchini; Emanuele Magalini; Pierfrancesco Robotti; Alberto Molinari

2009 Rapid Prototyping Journal

doi: 10.1108/13552540910960262

Purpose – The purpose of this paper is the microstructural and mechanical characterization of a biomedical Ti‐6Al‐4V alloy produced by electron beam melting, and the study of the stability of the as‐built microstructure upon heat treatment. Design/methodology/approach – Ti‐6Al‐4V alloy produced by electron beam melting has been mechanically characterized through tensile and fatigue testing. Its microstructure has been investigated by optical observation after etching and by X‐ray diffractometry analysis. The stability of the microstructure of the as‐built material has been deepened carrying out suitable heat treatments, after an analysis by dilatometry test. Findings – The microstructure of a Ti‐6Al‐4V alloy produced by electron beam melting has a very fine and acicular morphology, because of the intrinsically high‐solidification rate of the process. This microstructure is very stable, and the traditional thermal treatments cannot modify it; the microstructure changes significantly only when an amount of strain is introduced in the material. However, the mechanical properties of the alloy produced by electron beam melting are good. Originality/value – The paper provides evidence of the microstructural stability of the material produced by electron beam melting. Even if the microstructure of the as‐built material is not recommended by the specific ISO standard, the related mechanical properties are fully satisfactory. This is a significant indication from the point of view of the production of Ti‐6Al‐4V orthopaedic and dental prostheses by electron beam melting.

Nagahanumaiah; B. Ravi

2009 Rapid Prototyping Journal

doi: 10.1108/13552540910960271

Purpose – The purpose of this paper is to present the results of an investigation into the effect of injection molding process parameters on the performance of direct metal laser sintered (DMLS) mold in producing quality Zytel nylon 66 plastic parts with consistency in part shrinkage and shot/part weight. Design/methodology/approach – The injection mold for an industrial component (hub gear) was fabricated in EOS M‐250 machine using bronze‐based material. The effect of four injection molding parameters (injection pressure, melt temperature, speed, and injection time) on part shrinkage and weight were studied experimentally using L 9 orthogonal array. The weight of the part just after ejecting from the cavity, and the average shrinkage measured after cooling, were used in grey relational analysis technique to assess the effect of each molding parameter. Further, surface properties such as surface finish, wear, scratch and corrosion resistance tests were conducted on DMLS mold material samples, in order to evaluate its use in rapid manufacturing applications. Findings – The study found that injection speed and melt temperature have significant influence on part weight and shrinkage. The optimized molding process variables were slightly more in the case of DMLS molds as compared with the parameters suggested in the plastic datasheet. Scanning electro microscope (SEM) analysis of the mold surface after producing 5,000 glass filled Nylon 66 (Zytel) moldings did not indicate any surface degradation, confirming the use of DMLS mold in rapid manufacturing of few thousands of moldings. Research limitations/implications – The grey relational analysis does not compute the effect of any two or more variables together unlike ANNOVA. Second, this study alone is not enough to estimate life of DMLS mold, although 5,000 glass filled nylon 66 moldings are successfully produced without any damage on mold surface. Practical implications – This investigation demonstrates a generic approach of using grey relational analysis to quantify the effect of different molding process variables on selected quality parameters. This method can be easily extended for new processes and materials. The preliminary tests on surface finish, scratch, wear and corrosion resistance performed on DMLS mold samples have highlighted the need for improving surface properties to enhance their life. The authors are currently working on hard coating of DMLS molds as one of the solutions. Originality/value – Use of grey relational analysis is new to the problem of injection molding process optimization. Moreover, effect of injection molding parameters on part weight and shrinkage in DMLS mold has not been studied previously. This study helps while considering DMLS molds for manufacturing few thousands of parts.

Sadegh Rahmati

2009 Rapid Prototyping Journal

doi: 10.1108/13552540910960280

Purpose – This paper aims to focus on redesigning a 3D printing machine, using piezoelectric demand‐mode technology head in order to improve the factors of accuracy, surface finishing and color quality of fabricated models. Design/methodology/approach – The work first identifies two kinds of ink‐jet printing heads, and then develops a new design of 3D printing machine, based on piezoelectric head technology. Fabricated models by this new 3D printing machine were compared with the same models fabricated by current 3D printing machines (z406). Findings – The comparison between the constructed models by two types of 3D printing machines shows improvement factors of accuracy, surface finishing and color quality using piezoelectric head in the current 3D printing machine. Research limitations/implications – In order to provide a colorful binder, a type of binder such as ZB56 was combined with six different colors of ink namely black, cyan, magenta, yellow, light cyan, and light magenta. Practical implications – The new designed and manufactured 3D printing machine provides the ability to construct more accurate models with improved quality. Originality/value – Apart from the above practical implications, this work provides an accurate tool for injection of the live cells into vital textures in order to create bones, members and dentures without any chemical or physical changes in cells.

Krassimir Dotchev; Wan Yusoff

2009 Rapid Prototyping Journal

doi: 10.1108/13552540910960299

Purpose – The purpose of this paper is to investigate the polyamide 12 (PA12) powder properties deterioration in the laser sintering (LS) process and propose a methodology for more efficient powder recycling. The main goals are: to recommend a level of input PA2200 powder properties which could guarantee acceptable part quality in the LS process; and selection of the refresh rate in order to minimise the consumption of fresh material. Design/methodology/approach – The paper analyses the LS processing conditions and current recycling practices in relation to the deterioration or ageing of the PA12‐based powders. Samples of new and recycled grades of PA2200 powder were artificially aged in a temperature‐controlled oven and then tested using melt flow rate (MFR) indexer. Also, un‐sintered powder samples collected from different locations within various builds, and different LS machines (EOSINT P700 and Sinterstation ® 2500 HiQ) were tested. Findings – The powder exposed at higher temperature and longer time experiences a much higher deterioration rate. The temperature and the time at which the un‐sintered material was exposed are the most influential parameters for the powder aging. It was confirmed that the MFR index is a very sensitive indicator of the changes in the powder properties and provides a relatively fast and inexpensive method of measuring the rate of the powder degradation because of the LS process. The powder located in the periphery and the top of a build has a higher MFR and therefore is less deteriorated. In contrast, powder located in the centre, or in the bottom of a long build has much lower MFR and therefore is less usable. Practical implications – Based on the findings, a methodology for powder recycling is proposed. It allows a better control of the input material properties, a consistent quality of the fabricated parts, and more efficient use of the LS material. Originality/value – The paper provides some useful information for the properties deterioration of PA12‐based powders (PA2200) in relation to the temperature and time at which the material is exposed in the LS.

P.S. Maher; R.P. Keatch; K. Donnelly; R.E. Mackay; J.Z. Paxton

2009 Rapid Prototyping Journal

doi: 10.1108/13552540910960307

Purpose – Hydrogels with low viscosities tend to be difficult to use in constructing tissue engineering (TE) scaffolds used to replace or restore damaged tissue, due to the length of time it takes for final gelation to take place resulting in the scaffolds collapsing due to their mechanical instability. However, recent advances in rapid prototyping have allowed for a new technology called bioplotting to be developed, which aims to circumvent these inherent problems. This paper aims to present details of the process. Design/methodology/approach – The paper demonstrates how by using the bioplotting technique complex 3D geometrical scaffolds with accurate feature sizes and good pore definition can be fabriated for use as biological matrices. PEG gels containing the cell‐adhesive RGD peptide sequence were patterned using this method to produce layers of directional microchannels which have a functionalised bioactive surface. Seeding these gels with C2C12 myoblasts showed that the cells responded to the topographical features and aligned themselves along the direction of the channels. Findings – This process allows plotting of various materials into a media bath containing material of similar rheological properties which can be used to both support the structure as it is dispensed and also to initiate cross‐linking of the hydrogel. By controlling concentrations, viscosity and the temperature of both the plotting material and the plotting media, the speed of the hydrogel gelation can be enhanced whilst it is cross‐linking in the media bath. TE scaffolds have been produced using a variety of materials including poly(ethylene glycol) (PEG), gelatin, alginic acid and agarose at various concentrations and viscosities. Originality/value – This paper describes one of the very few examples of accurate construction of 3D biological microporous matrices using hydrogel material fabricated by the bioplotting technique. This demonstrates that this technique can be used to produce 3D scaffolds which promote tissue regeneration.

António Manuel de A. Monteiro Ramos; José António Simões

2009 Rapid Prototyping Journal

doi: 10.1108/13552540910960316

Purpose – The purpose of this paper is to present the development of a technical procedure for the manufacturing of medical implant prototypes. Design/methodology/approach – The paper was performed on a new hip implant design and manufactured with different metallic alloys F75 (ASTM) commonly used in biomedical applications. Dimensional parameters between the computer‐aided design (CAD) geometry and the prototypes and surface roughness for different casting alloy were compared. A CAD model was used for machining of a prototype. Room temperature vulcanising (RTV) rubber moulds allowed the manufacturing of wax models of the femoral prosthesis. A specific lost‐wax casting (LWC) technology was used to manufacture prototypes for in vitro tests. The final geometry was dimensionally controlled using different type of parameters (performance, average, standard, maximum and minimum deviations), surface roughness ( Ra , Rt and Rp ) were measured for all prototypes. Findings – To obtain a small number of implants, RTV rubber vacuum casting technique can be used to obtain lost wax models with good dimensional stability. No significant dimensional differences were observed relatively to the virtual model. However, the temperature of the wax and the rubber mould were important parameters to obtain good quality wax models. Surface roughness was different for different alloys. Practical implications – The design and development of a new hip femoral prosthesis prototype based on rapid tooling techniques to manufacture LWC prototypes is suitable for clinical trials. Originality/value – This paper describes a biomanufacturing methodology to manufacture biomedical implant prototypes.

Abbas Azari; Sakineh Nikzad

2009 Rapid Prototyping Journal

doi: 10.1108/13552540910961946

Purpose – The goal of rapid mechanical prototyping is to be able to quickly fabricate complex‐shaped, 3D parts directly from computer‐aided design models. The key idea of this novel technology is based upon decomposition of 3D computer models data into thin cross‐sectional layers, followed by physically forming the layers and stacking them up; “layer by layer technique.” This new method of modeling has raised many attentions in dentistry especially in the field of surgery and implantology. The purpose of this review study is to represent the historical development and various methods currently used for building dental appliances. It is also aimed to show the many benefits which can be achieved by using this new technology in various branches of dentistry. Design/methodology/approach – The major existing resources, including unpublished data on the internet, were considered. Findings – Although, creating 3D objects in a layered fashion is an idea almost as old as human civilization but, this technology has only recently been employed to build 3D complex models in dentistry. It seems that in near future many other methods will develop which could change traditional dental practices. It is advisable to include more unit hours in dental curriculums to acquaint dental students with the many benefits of this novel technology. Originality/value – It is hard to believe that the routine dental techniques were affected by revolutionary concepts originally theorized by engineering methods. It is a reality that in future, most of the restorative disciplines will be fully revised and the computer methods be evolved to an extent where dentistry can be performed by computer‐assisted methods with optimum safety, simplicity, and reliability.