A biodegradable and biocompatible gecko-inspired tissue adhesive

Mahdavi et al. 10.1073/pnas.0712117105.

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SI Figure 5
SI Figure 6
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SI Figure 5

Fig. 5. Representative shear adhesion test (force vs. displacement) result of the PGSA adhesive interfacing with tissue. The maximum shear force is used to quantify adhesion of the materials. For each formulation, we tested four samples to obtain the statistical results.

SI Figure 6

Fig. 6. Modified Anthrone technique for quantification of carbohydrates was used to determine the amount of DXTA on the surface of PGSA nanopattern after rinsing. (A) The quantity of DXTA can be estimated through a linear fit of UV absorbance observed after a reaction time of 19 min. (B) Quantification of DXTA amount on surface of rinsed nanopatterned PGSA polymers.

SI Text

Nanomold fabrication. Four-inch-diameter silicon wafers were oxidized for 10 h at 1,100°C in atmospheric pressure oxygen at 50 standard cubic centimeters per minute flow rate (sccm), and hydrogen (30 sccm) to grow an oxide layer of two microns. Silicon wafers with 10-mm-thick oxide layer were purchased from Silicon Quest International. The oxide layer thickness was measured with Filmetrics F20 and F50 spectral reflectometers. Silicon wafers with oxide layer were baked at 110°C to dehydrate their surface and spin-coated with hexamethyldisilazane (HMDS) at 5,000 rpm for 10 seconds to promote resist adhesion. Photoresist (Shipley 1805) was then spin-coated (EVG101) on the wafers at 3,500 rpm for 20 seconds. The wafer was then softbaked on a hotplate at 115°C for 1 min to yield a resist film thickness of »500 nm. Resist exposure was done with a Karl Suss MA-6 contact aligner with an exposure dose of 96 mJ/cm², and the resist was developed for 45 seconds in Shipley MF-319 developer followed by a 3-minute rinse in deionized (DI) water and spin drying.

Synthesis and characterization of dextran-aldehyde. An aqueous solution of dextran (from Leuconostoc mesenteroides; molecular mass between 64,000 and 76,000 Da, Sigma) (10 g in 100 ml of distilled water) was oxidized with 3.3 g of sodium periodate (Sigma), at room temperature in the absence of light. The resulting solution was dialyzed for 3 days (molecular mass cutoff of 3,500 Da) and lyophilized thereafter. The isolated yield was 90%. The degree of oxidation (DO) of DXTA, defined as the number of oxidized residues per 100 glucose residues, was quantified by using tert-butylcarbazate (tBC) as reported previously by us (1) and ¹H NMR. DXTA solution was spin coated on the surface of the PGSA gecko pattern using a speed of 4,000 rpm, which was determined to be optimal for a uniform surface coating.

X-ray photo-electron spectroscopy (XPS) and FTIR analysis. XPS measurements were carried out on an Axis Ultra spectrometer (Kratos Analytical) by using Al Ka (1486.6 eV) radiation source (150 W). The operating pressure during analysis was in the low 10^-9 Torr range. Survey spectra were collected over a range of 0-1,100 eV with analyzer pass energy of 100 eV. High-resolution C(1s) and O(1s) spectra were collected with an analyzer pass energy of 20 eV. In both cases, 0.3 mm² of the sample was examined and the atomic compositions were quantified using tabulated sensitivity factors. Angle-resolved analysis was performed at a takeoff angle of 70°. Amine coated microarray glass slides (Superamine2 from ArrayIt) with amine concentration of 2 ´ 10¹³ units per mm² (as characterized by the supplier) were used for surface characterization to mimic amine moieties on the tissue surface. Fourier transform infrared spectroscopy was performed using a Nicolet Magna 860 FTIR instrument. One hundred scans were performed with a resolution of 4 cm^-1. The spectra resulting from the three different samples were normalized based on the absorbance at 2930 cm^-1 corresponding to the stretching of the C-H groups in the samples.

Surgical procedures. Animal care, anesthesia, and sacrifice protocols were similar for both the dorsal s.c. and subfascial implantation studies. Male Wistar rats weighing »350 grams (Charles River Laboratories) were acclimatized before surgery. Animals were anesthetized with Ketamine (75 mg/kg) and Dormitor (0.5 mg/kg) and recovered with Antisedan. After surgery, animals were housed in a temperature/humidity controlled environment with 12 h light/dark cycles and had unrestricted access to water and standard rat food. Before sample harvest, the rats were killed with an overdose of Pentobarbital.

1. Maia J, Ferreira C, Corvalho R, Ramos MA, Gil MH (2005) Synthesis and characterization of new injectable and degradable dextran-based hydrogels. Polymer 46:9604-9614.