Nanotechnologies offer a wide range of treatment possibilities when used in medical devices. According to Global Market Insights, the global market for nanotechnology in medical devices was valued at over $3 billion in 2021 and is projected to grow at a compound annual growth rate (CAGR) of more than 8% from 2022 to 2030, reaching $7 billion by 2030.
Before using nanotechnologies on patients, it is essential to evaluate the biocompatibility of the materials constituting them. ISO/Technical Report (TR) 10993 Part 22, also referred to as ISO/TR 10993-22, clarifies the process and highlights commons pitfalls which need to be considered when assessing the safety of medical devices composed of, containing, and/or generating nano-objects.
As the ISO/TC 194 group prepares to update ISO/TR 10993-22, originally published in 2017, let us refresh our memory of the most important biocompatibility considerations regarding the use of nanomaterials in medical devices.
Why Use Nanomaterials in Medical Devices?
Nanomaterials are defined per ISO/TR 10993-22 as materials with any external dimension in the nanoscale (~1 to 100 nm) or having internal or surface structure in the nanoscale. Nano-objects are discrete pieces of material with one (= nanoplate), two (= nanorod), or three (= nanoparticles) external dimensions in the nanoscale.
Nanomaterials are manufactured and used because of their unique properties and numerous advantages compared to bulk materials that can be associated with the decrease in size accompanied by an increase of surface area. Medical devices containing nanomaterials can be used nearly everywhere in or on the body (see Figure 1).
Figure 1: Examples of medical devices containing nanomaterials (Copied from ACS Appl. Bio Mater. 2019, 2, 1, 1–13)
Nanomaterials used in medical devices can be categorized as follows:
- Surface nanostructures
- Nano-objects bound to or incorporated within a medical device without intention of being released
- Nano-objects/nanostructures on the surface of or within a medical device with intentional/expected release from the device
- Nano-object medical device
- Nano-objects released from a medical device as a product of degradation, wear, or from mechanical treatment processes (e.g. in situ grinding or polishing)
What are the Concerns with Nanomaterials?
The use of free nano-objects or their release from medical devices are considered to pose the highest potential for risk in view of potential internal exposure. Due to their comparable sizes (see Figure 2), nanomaterials can interact with microorganisms and cell walls or membranes by electrostatic attraction, such as Van der Walls forces, or transpose the cell wall or membrane.
Figure 2: Length scales for natural and synthetic structures (copied from Casarett & Doull’s Toxicology: The Basic Science of Poisons, 9th edition, Curtis D. Klaassen)
How to Assess Biocompatibility
Biocompatibility evaluation of medical devices composed of, containing, and/or generating nano-objects can be divided into two steps: characterization and testing.
Characterization Step
ISO/TR 10993-22 provides a list of parameters considered relevant for physical and chemical characterization of nanomaterials derived from ISO/TR 13014.
- Chemical composition and purity
- Particle size/Particle size distribution
- Aggregation and agglomeration state
- Shape
- Surface area
- Surface nanostructures
- Surface chemistry
- Surface charge
- Solubility/Dispersibility
For each parameter, adequate methods and ISO guidance are also indicated. These properties serve as a starting point. Others can be included on a case-by-case basis.
Testing Step
Biocompatibility evaluations according to ISO 10993-1 often require chemical and/or biological testing as risk control measures.
When the medical device cannot be tested directly, extractions should be carried out to evaluate the extractables/leachables instead. Some specific considerations are needed when extracting nanomaterials-containing medical devices:
- When medical devices and/or test samples in the form of nanomaterials are to be evaluated, sample filtrations shall not be performed.
- For medical devices with nanostructured surfaces, ISO 10993-12 surface-based extraction ratios are applicable. If measured at the external dimensions, the total surface area can be underestimated, since surface irregularities are not considered. This approximation would lead to less volume of extraction vehicle and a higher concentration of extractables/leachables, which represents an acceptable conservative approach.
- Soluble nanomaterials exert an effect similar to non-nanoscaled materials, since they would be in molecular form in the extraction vehicle. On the contrary, insoluble nanomaterials would correspond to dispersed nano-objects in the extraction vehicle. A direct assessment of their biological hazards would therefore be possible, as long as limitations of testing particle-containing extracts (e.g., intravenous injections, compatibility with analytical instruments) are considered.
In addition, ISO/TR 10993:22 provides several considerations accompanied by justifications for testing according to various ISO 10993 standards. Some important ones are listed below in Table 1.
- Nanomaterials generally taken up by mammalian cells
- Interferences possible with assay
- Various kinetics of nanomaterials depending on size (e.g., diffusion, sedimentation, agglomeration)
Table 1: Important biological testing considerations for nanomaterial-containing medical devices (where applicable)
| Endpoint | Testing considerations | Justification |
| Cytotoxicity | – Several test methods may be needed (ex: phagocytic and non-phagocytic cell lines). | – Nanomaterials generally taken up by mammalian cells – Interferences possible with assay – Various kinetics of nanomaterials depending on size (e.g., diffusion, sedimentation, agglomeration) |
| Sensitization | – In vivo assays (Guinea Pig Maximization Test (GPMT), Local Lymph Node Assay (LLNA)…): might not be effective – In vitro assays: unclear if they can assess sensitization potential | – Due to the barrier function of the skin, target cells and organs for sensitization (dendritic cells in the skin and the draining lymph node) might not be reached by the nano-objects |
| Irritation | – Intracutaneous reactivity test to consider first | – Intracutaneous introduction of the nano-objects bypasses the stratum corneum |
| Hemocompatibility | – Complement system activation needed. – Other methods from ISO 10993-4 can be used to evaluate devices with nanostructured surfaces; evaluation can be much more challenging for free nano-objects | – Abnormal increases in complement system activation due to the presence of nanoscale materials in blood can induce significant inflammatory reactions – Since surface/volume ratio higher than bulk materials, more serum protein may readily adsorb onto free nano-objects, distorting the subsequent cascade of reactions occurring in the blood as soon as foreign bodies enter systemic circulation – Interactions with platelets, coagulation factors and endothelial cells might be altered due to potential aggregation/agglomeration of free nano-objects once in contact with blood |
| Systemic toxicity | – Selection of tissues/organ should be considered on a case-by-case basis with special emphasis on mononuclear phagocyte system (MPS, e.g. notably liver, spleen), kidneys, brain, bone marrow – Complementary analyses could be needed for free nano-objects (e.g., Transmission Electron Microscopy (TEM) on specific organs) – Special attention should be paid to the administered dose | – Nano-objects can potentially be distributed throughout the body – Concern of accumulation and biopersistence of insoluble nanomaterials – The dose metric of mass or concentration usually applicable to bulk materials may not be suitable for nanomaterials whose systemic toxicity will mainly depend on the particle itself interacting with a biological system. The particle number administered and/or the resulting surface area to which a patient was exposed might be better parameters to describe a dose response relationship. |
| Implantation | – Free nano-objects: direct injection in appropriate tissues to consider & focus on migration into local draining lymph nodes | – For most exposure routes other than intravenous, the majority of nano-objects remain at the entry point in nearby tissues, or the local draining lymph nodes |
| Genotoxicity | – The bacterial reverse mutation test is not appropriate for free nano-objects, while it may be for devices with nanostructured surfaces – Mammalian cell systems recommended (examples: Mouse Lymphoma Assay (MLA), Hypoxanthine-guanine Phosphoribosyltransferase (HPRT)) | – Uncertainty of nano-object uptake by bacteria strains, and thus, of DNA exposure |
Conclusion
Biocompatibility evaluation of nanomaterials per ISO 10993-1 should be adapted on a case-by-case basis, depending on the nanomaterial category and physical/chemical characterization outcomes.
As stated in ISO 10993-1, physical and chemical characterization per ISO/TS 10993-19 and ISO 10993-18 should be considered as a crucial first step, prior to biological testing.
A Biological Evaluation Plan is imperative to identify unique hazards, characterize the risks, and determine specific parameters that go beyond those applicable to medical devices manufactured with conventional raw materials. An efficient and effective biocompatibility evaluation requires the collaboration of a team of experts in various areas, including medical device manufacturing, analytical chemistry, biological assays, materials science, biomedical engineering, and toxicology. All these areas can be covered by NAMSA experts.
Guidelines
This document is based on the requirements and recommendations provided in the guidelines listed in Table 2.
Table 2: Applicable Guidelines
| Reference | Title |
| ISO 10993-1:2018 | Biological evaluation of medical devices – Part 1: Evaluation and testing within a risk management process and applicable ISO 10993 standards |
| ISO 10993-12:2021 | Biological Evaluation of Medical devices – Part 12: Sample preparation and reference materials |
| ISO 10993-18:2020/AMD 1:2022 | Biological evaluation of medical devices – Part 18: Chemical characterization of medical device materials within a risk management process |
| ISO/TS 10993-19:2020 | Biological evaluation of medical devices – Part 19: Physico-chemical, morphological and topographical characterization of materials |
| ISO/TR 10993-22 :2017 | Biological evaluation of medical devices – Guidance on nanomaterials |
| ISO/TR 13014 :2012 | Nanotechnologies – Guidance on physico-chemical characterization of engineered nanoscale materials for toxicologic assessment |
| SCENIHR Guidance on Nanomaterials in Medical Devices (2015) | SCENIHR (Scientific Committee on Emerging and Newly Identified Health Risks), Final Opinion on the Guidance on the Determination of Potential Health Effects of Nanomaterials Used in Medical Devices, January 2015. |
