BNG 331 Cell-Tissue Material Interactions. Biomaterial Surfaces

Transcription

1 BNG 331 Cell-Tissue Material Interactions Biomaterial Surfaces

2 Course update Updated syllabus Homework 4 due today LBL 5 Friday Schedule for today: Chapter 8 Biomaterial surface characterization Surface responses to healing Engineering biomaterial surfaces

3 Biomaterial surfaces are heterogeneous!

4 Surface characterization methods In order to study the effects of a surface on wound healing events, we need to know details about the surface Surface analytical techniques generate information about the outermost layer to ten atomic layers Chemical, topographical, mechanical & eletrical properties may affect how proteins & cells interact with the material Outline of techniques: Contact angle analysis X-ray photoelectron spectroscopy (XPS) Fourier-transform infrared spectroscopy (FTIR) Secondary ion mass spectroscopy (SIMS) Scanning electron microscopy (SEM) Atomic force microscopy (AFM)

5 Contact angle analysis Measure of angle of contact between a liquid and a surface Contact angle is an inverse measure of the ability of a liquid to wet a surface Larger θ hydrophobic Smaller θ hydrophilic

6 Contact angle analysis Wettability of a surface has some use, but surface properties are better understood using a material s surface energy γsv Surface energy is directly proportional to the tendency of molecules to adsorb Provides information on how the surface interacts with gases, liquids, and possibly biomolecules Help chemists determine the properties of detergents, surfuctants, coatings, adhesives, etc.

7 X-ray photoelectron spectroscopy

8 X-ray photoelectron spectroscopy XPS is conducted without special preparation of samples However, it is carried out in an ultrahigh vacuum environment Biomaterials must be in a dry state Precludes analysis of biological samples, i.e., absorbed proteins State of the art equipment can analyze frozen hydrated samples

9 X-ray photoelectron spectroscopy X-rays can penetrate 1 µm or more, but XPS can only provide information on the outermost 5 75 angstroms (note 1 angstrom is 1/10 nm) Chemicals information as a function of depth can be obtained by: Sputtering away surface layers Change detection angle of photoelectrons

10 FTIR spectroscopy Fourier transform infrared (FTIR) spectroscopy Analyzes molecular bond vibrations induced by infrared radiation Background: molecules with >2 atoms have numerous ways they can vibrate ( vibrational modes ): TIR

11 FTIR spectroscopy When exposed to IR light, radiation at the frequency matching a mode of vibration of the molecule is absorbed: asymetric stretching higher energy

12 Detecting chemical makeup with FTIR

13 Secondary ion mass spectroscopy

14 Scanning electron microscopy (SEM) Beam of high energy electrons is scanned across the samples Primary electrons penetrate energy and transfer energy to the material Incident electrons transfer sufficient energy for secondary electrons to be emitted from samples The intensity of the 2º depends on the topography of the surface

15 Scanning electron microscopy (SEM) tissue-culture polystyrene molded PCL PLGA mesh collagen matrix fibrin

16 Environmental SEM Allows for collection of micrographs of wet samples by allowing for a gaseous environment in the specimen chamber fibroblasts atop pillers macrophages endocystosing particles

17 Atomic force microscopy 2 modes of operation Vary the tip-surface distance to maintain constant interatomic force Maintain constant tipsurface distance with variable interatomic force Height adjustments or changes in interatomic force are recorded generate images of the surface topography

18 Atomic force microscopy

19 Atomic force microscopy AFM can also be used to measure the local mechanics of an elastic substrate before surface contact (in free space) Cantilever acts as a spring Signal provides spring displacement F = ks in contact with the surface

20 Atomic force microscopy Technique to determine elastic modulus of materials with a different local versus bulk elastic modulus: ~5 kpa ~15 kpa 2 μm Fibrous hydrogel Local (single fiber) mechanics in GPa range Bulk modulus in kpa range Photopatterned hydrogel Dark region single crosslinking Red region dual crosslinking

21 Surface responses to healing Biochemical & cellular mediators of the wound healing process can affect the material surface properties The changes caused by these mediators can in turn lead to altered biological responses

22 Protein fouling Within milliseconds, an implanted biomaterial is covered by adsorbed proteins Where are these proteins coming from? Take home point: implant s surface is almost immediately converted from a bare surface to one coated with biomolecules This, in turn, can mediate the biological response

23 Degradation and dissolution The warm, neutral saline environment with dissolved O 2, cells, enzymes, etc., harms metals, polymers, and ceramics Metals ~ corrosion, the deterioration and removal of a metal by a chemical attack Polymeric biomaterials ~ subjected to degradation Ceramics ~ calcium phosphate ceramics are disposted to dissolution

24 Calcification Deposition of calcium-containing minerals on a surface of a biomaterial can occur after implantation Absorption of calcium-binding proteins on a biomaterial surface may nucleate mineral leading to calcification Remnants of cells ruptured during wound healing Growth of mineral crystals not only cause significant chemical changes, but also mechanical changes

25 Heart valve calcification Beyond limiting implant lifetime, calcification also increases risk of heart attack 1 1 Afsar CU et al. Clin Invest Med 2012

26 Morphologic modifications Alterations in surface morphology and roughness have been used influence cell and tissue responses to implants Coatings with pores objective is to encourage tissue ingrowth Grooved surface to induce contact guidance Bryant SJ et al. Biomaterials 2007 Porous poly(2-hydroxyethyl methacrylate) hydrogels Fibroblasts on microgrooved PMMA surfaces Alaerts JA et al. Biomaterials 2001

27 Physiochemical modifications Surface energy, surface charge, and surface composition have been altered to change material and biological responses Glow discharge surfaces are exposed to ionized inert gas Ion implantation process like that described by SIMS Surfaces with a negative charge tend to delay thrombogenesis and positive charge can accelerate

28 Li X et al Prog Polymer Sci 2012 Biological modifications Goal is to control cell and tissue responses to an implant by immobilizing biomolecules on biomaterials RGD peptides deposited on surface promote cell attachment Heparin/heparin-sulfate binding peptides enhance cell adhesion Attachment of growth factors Dorsal root ganglion (DRG) outgrowth into 3-dimensional RGD-modified channels