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Cover Story

Development Of Critical Use Medical Devices

D. S. Nagesh
Scientist/Engineer-G, Biomedical Technology Wing,
Sree Chitra Tirunal Institute for Medical Sciences and Technology

Introduction :

Behind the development of critical use medical device, there exist numerous processes and procedures consuming lot of resources, time and in addition demanding high level of dedication and perseverance. Medical devices have different classifications for depend on the regulatory bodies. Other than the potential harm the device can contribute, time and nature of contact with the body/body fluids is the other most important factor determining the criticality of the device. And the time of contact varies from few seconds for the needle of a syringe to many decades for products like artificial heart valve. Inputs required in the design, development and evaluation activity of these devices are essentially based on these factors.

Specification :

 

The first and the foremost consideration in the medical device development is of having the right specification, which has to evolved from the inputs of both clinicians, who are end users as well as from a though market survey. The need of the potential market and the user segments is the key in this decision making.

 

With the clarity in specification, to aid the development, the next step is to fragment the device into various subsystems based on functions/properties.

 

Subsystems design & evaluation :

 

Most of the medical devices consist of different subsystems, based either on function or on properties. For design and analysis, these subsystems can be simulated independently using various computational methods like Finite element analysis (FEM), Computational fluid dynamics (CFD) etc. Other ways of simulation is prototyping, full size or scaled versions, which can be machined or may be made using techniques like rapid prototyping. As far as rapid prototyping is concerned, with the current technology available, getting transparent components made of biocompatible materials, with adequate surface finish, is not very easy.

 

Along with these studies, for many devices, ergonomics also needs to be looked into.

 

Sub systems so made, need to undergo bench top evaluation. Depends on the characteristics, it may have to undergo testing using test systems with analog fluids, mechanisms, accelerated testing etc.

 

Material & characterisation :

 

Characterisation of materials for its biocompatibility as per ISO10993 is a primary requirement in medical device development. Biocompatibility evaluations consist of both tissue compatibility as well as blood compatibility. Ideally the material needs to be non-toxic, but practically the choice is to get minimal reaction, minimal damage to the body and the durability for entire life cycle.
 

Blood compatibility depends on the property of blood, flow of blood and the surface properties. In addition, leachables, effect due to movements, heat generation etc., where applicable, need to be assessed.

 

Various types of materials are used in medical devices. These materials also undergo different processes and processing conditions. Hence it is appropriate to test the materials which have undergone all processes.

 

Other than biocompatibility, physicochemical characterisation is essential for establishing the mechanical, thermal, electrical, magnetic properties and so forth as required.

 

In-vitro evaluation :

 

Based on the bench top subsystem qualification, the subassemblies or combination of subassemblies or the device prototype as such has to undergo in-vitro evaluation. Here the evaluation is more close to actual use. Specialised test systems as per the standard protocols are essential for that. International standards are also available for most of these devices. In the absence of absolute acceptable criteria for test results, appropriate controls are also required. In-vitro evaluations provided data for detailed analysis on the design. Based on these values design improvements can be carried out.

 

Packing and sterilisation :

 

To avoid last minute surprises, method of terminal sterilisation also need to be decided along with the development. There are different methods of sterilisation are available like steam, Ethylene oxide, gamma ray or ion beam etc. Since all materials cannot undergo all the different methods of sterilisation, early decision of sterilisation method is very important. Along with standardisation of sterilisation, package also needs to be validated. It is always advisable to carryout the biocompatibility testing on the material which has undergone the same sterilisation process as planned for the final product.

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