20-Bio-A1 Biomaterials and Biocompatibility · December 2019
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams, December 2019 — 04-Bio-A1, Biomaterials and Biocompatibility (3 h, open book). Per the cover-page instructions, FIVE questions constitute a complete paper and the first five as they appear in the answer book are marked, each of equal value (20 marks); all SEVEN questions on this paper are solved below as a complete study resource. Question 2 permits any FOUR of the five sub-parts; all five are answered below for completeness.
Reference texts: Ratner, Hoffman, Schoen & Lemons, Biomaterials Science: An Introduction to Materials in Medicine (4th ed.); Saltzman, Drug Delivery: Engineering Principles for Drug Therapy; Enderle, Blanchard & Bronzino, Introduction to Biomedical Engineering (4th ed.).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
(a) Characterization methods.
| Dataset | Method | What it measures |
|---|---|---|
| (i) | X-ray photoelectron spectroscopy (XPS) | Elemental/chemical composition of the outermost (~1–10 nm) surface layer, from characteristic core-level binding energies. |
| (ii) | Static (sessile-drop) water contact angle goniometry, repeated over time | Surface wettability/hydrophilicity and its stability (aging) after modification. |
| (iii) | Quantitative protein adsorption assay (e.g., radiolabelled or ELISA-based protein quantification) | Mass of protein adsorbed per unit surface area under standardized exposure conditions. |
| (iv) | In vitro cell attachment assay with light/fluorescence micrography and cell counting | Cell density and spreading morphology on the surface after a defined culture period. |
(b) Likely identities. (i) Original: the XPS spectrum showing only F 1s, O 1s, C 1s and F 2s peaks, together with a very high (~100°) and stable contact angle, is the classic signature of PTFE (polytetrafluoroethylene, –(CF₂)₄– repeat unit) — the fluorine-dominated composition and strongly hydrophobic, low-surface-energy character are diagnostic, and PTFE (and expanded PTFE) is a standard vascular-graft and catheter biomaterial, consistent with the "24 h, PTFE" micrograph label given directly in the data. (ii) Modified: the appearance of a new N 1s peak with no change in the base fluoropolymer chemistry, combined with a markedly reduced contact angle (more hydrophilic) and the explicit "NH3"/"plasma" labels in the data, identifies this as ammonia (NH₃) plasma-treated PTFE — a low-temperature plasma discharge in ammonia gas that grafts amine (–NH₂) and other nitrogen-containing functional groups onto the PTFE surface without altering the bulk material.
(c) Two additional validating techniques. ATR-FTIR spectroscopy — measures characteristic vibrational absorption bands (e.g., N–H stretch near 3300–3400 cm⁻¹, C–N stretch) that would independently confirm amine/amide functional groups at the near-surface region, corroborating the XPS N 1s assignment with a different physical principle. Streaming-potential (zeta-potential) measurement — measures the surface's electrokinetic charge as a function of pH; primary amine groups introduced by NH₃ plasma treatment are protonatable near physiological pH, so a shift toward a more positive zeta potential relative to the unmodified PTFE would provide chemical (charge-based) confirmation of successful amination.
(d) Application. NH₃-plasma amination of PTFE is used to improve the biological performance of small-diameter ePTFE vascular grafts: the added amine groups increase surface wettability and protein adsorption (dataset iii) and can serve as reactive anchor points for subsequently grafting cell-adhesive peptides (e.g., RGD) or heparin, promoting endothelial cell attachment and spreading (dataset iv) on a graft lumen that would otherwise remain the poorly cell-adhesive, low-protein-fouling surface described for unmodified PTFE in Question 1(a) — i.e., this modification is a direct engineering response to the small-diameter vascular graft endothelialization problem discussed there.
(e) Predicted host response. The amine-functionalized, more hydrophilic surface will adsorb more protein and support markedly better initial cell attachment and spreading than untreated PTFE (dataset iii/iv), which should translate into a more favourable acute response — a greater capacity to support a confluent cell/endothelial lining and reduced platelet-surface interaction relative to bare PTFE. However, the bulk of the device is still non-degradable, relatively bioinert PTFE, so the underlying foreign-body-response cascade (protein adsorption → acute then chronic inflammation → macrophage/FBGC activity at any exposed or unmodified regions → fibrous encapsulation) is not eliminated, only shifted toward a more favourable balance at the treated interface; long-term, a thin fibrous capsule around the bulk implant, with (ideally) a functional cellularized lining at the amine-modified blood-contacting surface, is the most likely outcome.
