BIOE 2010 Week 5 Notes
BIOE 2010 Week 5 Notes BIOE 2010
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This 3 page Class Notes was uploaded by Sara Littlejohn on Friday September 23, 2016. The Class Notes belongs to BIOE 2010 at Clemson University taught by Dr. Alexis and Dr. Webb in Fall 2016. Since its upload, it has received 5 views. For similar materials see Intro to Biomedical Engineering in Bioengineering at Clemson University.
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Date Created: 09/23/16
Biocompatibility Host Response Definitions Host response: changes in cellular and systematic physiology resulting from the implantation of a medical device Biocompatibility: the ability of a material to perform with an appropriate host response in a specific application All devices are approved for a specific application and that application only. Types of Biocompatibility Bioinert: the material has no interaction with physiological tissue o We have never been able to achieve a material that the body just ignores (that is totally bioinert) Bioactive: the material incorporates mechanisms capable of eliciting specific cellular responses and tissue integration Hemocompatability: the ability of a material to perform appropriately in the presence of blood Biocompatibility Dynamic and continual process governed by effects of that material on the surrounding tissue as well as effects of the physiological environment on the material Biocompatibility changes over time. Factors governing Biocompatibility Chemical/ Physical properties of the material Wear Corrosion Mechanical integration/ micro-motion Leachables Implant geometry Surface properties o Chemistry o Topography/roughness Implant Response Extrusion: pocket formed around an implant adjacent to epithelial tissue o Uncommon but can happen o Example: splinter Resorption (degradation): implant site resolves into a collapsed scar (soft tissue) or may completely disappear (bone) (Desired-degradable) Integration: close, possibly adhesive, approximation of nearly normal host tissue to implant without intervening fibrous capsule (Desired-permanent) o Most desired Encapsulation: implant blocked off from surrounding tissue by fibrous capsule Wound Response vs. Implant response The response of host tissue to an implant is similar to normal wound response at first o Inflammation, cellular invasion and proliferation Process then enters chronic phase in response to continued presence of implant Chronic phase is characterized by chronic inflammation and classic foreign body response o Macrophages o Macrophage fusion (foreign body giant cells) o Fibrous encapsulation Capsule Formation Maintained by continuous presence of implant The thickness of the capsule is related to several factors: o Chemical activity of material o Motion between tissue and implant o Shape of implant o Presence of electrical current Surface Modification Prevent protein adsorption (make bioinert) o Chemical modification with polyethylene oxide (PEO) PEO is one of the more inert materials in nature PEO repels blood proteins Immobilize anti-coagulation molecules (heparin) o Activates anti-thrombin III, blocks thrombin cleavage of fibrinogen Surface modification allows us to select our material for its mechanical properties and we can change the surface to target the biological response Biocompatibility of Biological Materials Sources of biological materials (grafts) o Autologous: the patient’s own tissue No immunological response Example: ACL repair Skin graphs o Allogenic: another humans tissue Example: Organ transplant o Xenogeneic: animal tissue Synthetic vs. Natural Materials Synthetic materials: non-specific response involving primarily macrophages o Synthetic materials are non-specific because there is no protein Naturally derived materials: specific immune response mediated by lymphocytes and antibodies which recognize foreign proteins (rejection) The proteins that mediate rejection are very specific cell surface proteins that are bound to the plasma membrane and exposed to the extracellular environment and hence the immune system In general, out immune systems recognize proteins Autologous Materials No immune rejection complications All proteins in autologous graft material are derived from the patient’s own body The immune system does not recognize “self” proteins Allogenic Grafts Generally rejected over 1-2 weeks Exceptions: some minimally vascularized tissues such as tendons/cartilage are tolerated Mechanism: immune recognition of blood group proteins (A, B, O) and major histocompatibility (MHC) cell surface proteins o MHC is special because it is composed of 6 genes. For each gene there are approximately 100 copies within the human population Can be controlled for organ transplantation through chronic administration of immune suppressive drugs Xenogeneic Grafts Always rejected within 1-2 days Mechanism: differences in blood group protein and MHC How to use Allogenic/Xenogeneic Materials Immunosuppression: allogenic transplantation De-cellularization: a variety of techniques that are used for extracting all cells and cell associated proteins from tissue, it leaves intact extracellular matrix which is often a useful biomaterial itself Removal of cellular proteins results in removal of basis for immune rejection
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