BIOCOMPATIBILITY TESTING – BENCHTOP EVALUATION OF A MATERIAL’S INTERACTION WITH THE
To gain FDA approval for any medical device that will come in contact with the human body, it must be shown to be biocompatible. The term “biocompatible” means that a material interaction with living tissue or a living system is not toxic, injurious, or physiologically reactive and is not causing rejected by the person’s immune system. As described in the FDA Guidance document “Use of International Standard ISO 10993-1, ‘Biological evaluation of medical devices - Part 1: Evaluation and testing within a risk management process’“ (1), biocompatibility pertains to devices that will have either direct contact (such as artificial hip joints, heart assist devices and prosthetic vascular grafts) or indirect contact (such as tubing that will help deliver fluid or gas into the body)with the body’s tissues.
There are several factors that can affect biocompatibility such as the chemical composition of the materials comprising the device, physical aspects (i.e. shape, surface properties) and potential side products such as leachables or degradation products, all of which may potentially contribute to deleterious tissue effects. Depending on the device configuration, how and where it will contact the body and for how long, biocompatibility testing may be conducted to evaluate the risks of cytotoxicity, sensitization, hemocompatibility, pyrogenicity, genotoxic, reproductive, and developmental toxicities or carcinogenicity (1). For implanted devices, preclinical evaluations could also be undertaken to address how the target material heals within the body. Two questions that these tests can answer are does the material encourage or support normal tissue ingrowth and vascularization or will it promote inflammatory responses and buildup of fibrotic scar tissue?
Biocompatibility and Bio-Spun™ Materials
BioSurfaces has developed and tested several medical devices to date using its proprietary Bio-Spun™ material
technology (Table 1). The company has also used its Bio-Spun™ materials to develop benchtop tissue models. Ensuring biocompatibility of these devices begins early in our development process. Bio-Spun™ devices are produced using our proprietary electrospinning process using polymers that have been a FDA Master File (FDA knows and approves of how the polymer is being made) or are synthesized under Good Manufacturing Practices that ensure reproducibility. The resulting 3-dimensional (3D), nanofibrous nature of these materials closely mimics the structure and scale of the body’s native extracellular matrix (ECM) within which cells normally grow and function, thereby allowing cellular ingrowth into implanted materials. Even so, each material type and device design must be individually evaluated for biocompatibility in the context of its intended use and function. On the “macro” scale, will the device provide the correct shape, size, strength, stiffness or flexibility to perform its function (i.e. a tubular vascular access graft or a multitailed fistula plug)? On the “micro” scale, will the material promote normal ingrowth of the cell types most likely to encounter it? Can capillaries form around or within the material to support healing and growth of new healthy tissue?
Current Biocompatibility Testing Procedures
Several in vitro methods are employed to address various aspects of a device material’s biocompatibility before moving on to an in vivo (animal) pre-clinical model. These include:
· Measurements of material strength and stiffness (how strong and flexible are the materials and is this strength and flexibility a pre-requisite for device implantation?)
· Measurements of fiber sizes and orientation (random vs aligned), sizes of resulting pores throughout the matrix
· Suturability (can materials withstand suturing without tearing?)
Cellular interactions and functional responses (in vitro culture):
· Monitoring of cell viability and proliferation on materials over time (Alamar Blue assay; IVIS luminescence measurements on cells genetically modified to express the firefly luciferase protein) (Figure 1)
· Transepithelial/transendothelial electrical resistance (TEER) measurements in for barrier-forming cell types
· Enzyme-Linked Immunosorbant Assays (ELISA) to measure production of a cell-derived protein in the culture medium.
· Histology/Immunohistochemistry- following culture, fixation and staining of cells and tissues to confirm expression of cell-type and cell-function- specific proteins.
· Keyence imaging to assess cellular interactions with the materials (i.e. morphology and physical positioning of
cells on or within the materials) (Figure 2).
Following in vitro assessment, but prior to human contact, a medical device is typically tested in a living, non-human animal model to assess its overall performance and biocompatibility in an effort to predict how the human body might respond to it both at the local site of interaction and systemically. While animal testing has historically been required by the FDA and international regulatory agencies to asses safety, biocompatibility and efficacy of medical devices, pharmaceuticals and cosmetic ingredients prior to human contact, mounting evidence suggests that animal studies do not necessarily predict biological outcomes in humans, which can contribute to high failure rates when a device or drug progresses into human clinical trials. Questionable clinical translatability, large cost and time commitments, and an increasing societal consciousness about the use of animals or animal-derived products have resulted in a push towards more biologically appropriate, predictive and humane ways to conduct pre-clinical testing.
Next Generation in Biocompatibility Testing: Bio-SpunTM In Vitro Research Tools (IVRT)
New approach methodologies (NAMS) are in development for use in the biomedical and cosmetics arenas to drive the "3Rs" initiatives of Refinement, Reduction and Replacement of animals for pre-clinical, pre-approval studies, using our technology to create a 3D and animal-free testing process (3, 4). The use of human cells to create more complex in vitro tissue models (i.e. full thickness skin or lung), human stem cell-derived organoids comprising multiple cell types, animal-free media and reagents, microphysiological systems (MPS), also known as lab-on-a-chip or organ-on-a chip, and combinations thereof, are all being investigated as potential replacements for the animal-based tests that are currently accepted and approved for use by regulators.
BioSurfaces believes that bringing human cells grown on more native-like scaffolds to the “upstream” in vitro stages of medical device, drug or cosmetics development will better inform early decision making on human biocompatibility and function of product candidates. Improvements in NAMS technologies that can reduce or eliminate dependence on unreliable animal testing models should lead to better candidate devices and drugs moving forward to clinical trials, ultimately improving “downstream” success rates by avoiding surprising side effects or poor efficacy upon translation to humans.
To advance these aims, BioSurfaces offers a full line of in vitro research tools, incorporating a variety of biocompatible Bio-Spun™ scaffold membranes into high- and medium-throughput culture formats (i.e. 96-well and 24-well Transwell™ plates and individual well inserts). As described earlier, these scaffolds resemble native ECM, providing a porous, 3D nanofibrous matrix which encourages cellular ingrowth resembling that of normal tissue. Using these Bio-SpunTM products, our scientists have to date successfully developed a full-thickness in vitro human skin model without the need to first pre-coat the scaffold with animal-derived collagen. We have also demonstrated attachment and outgrowth of human neurospheres on Bio-Spun™ materials (Figure 2). We are currently collaborating with several outside companies developing their own in vitro human models using these products and look forward to bringing Bio-Spun™ scaffolds to MPS technologies in the near future.
Lisa M. Fitzgerald, Ph.D.
Vice President of Research
1. Use of International Standard ISO 10993-1, "Biological evaluation of medical devices - Part 1: Evaluation and testing within a risk management process." (https://www.fda.gov/media/85865/download)
2. Next-Gen Cell Therapy Device (Monthly Spin-Off #5): Bio-Spun™ Cell Chamber - Using the Body’s Normal Functions to Deliver a Targeted Therapy. (https://www.biosurfaces.us/single-post/next-gen-cell-therapy-device-monthly-spin-off-5)
3. Punt A, et al. New approach methodologies (NAMs) for human-relevant biokinetics predictions. Meeting the paradigm shift in toxicology towards an animal-free chemical risk assessment. ALTEX. 2020;37(4):607-622. doi: 10.14573/altex.2003242.
4. The North American 3Rs Collaborative (https://www.na3rsc.org)