Surface Patterning & Biotextiles

What is surface patterning and why is it important?

What: Creating chemically or physically distinct regions on a surface to control biological interactions (cells, proteins).

Why: Because cell behavior is strongly influenced by surface chemistry and structure.

What is resolution in surface patterning?

The smallest feature size that can be created.

High resolution is not always applicable (cell patterning)

What is throughput?

The area patterned per unit time (important for manufacturing).

Drives cost

What is contrast?

How well patterned regions are distinguished from background
→ often depends on biomolecule density and non-fouling background.

What is bioactivity (in patterning)?

Ability of patterned biomolecules to retain function after processing.

What is direct-write patterning?

Using a tool to “write” patterns directly onto a surface.

High res, Low throughput (limitation)

What is DPN?

AFM (atomic force microscope) based technique that deposits molecules with very high resolution (<100 nm).

(nano-imprinting and nano-engraving)

How does inkjet patterning work?

Deposits droplets (10–20 pL) of bio-inks (proteins, DNA, cells) onto surfaces in defined patterns.

• high throughput

• contact-free

• works in ambient conditions

What is the focused fields direct-write technique?

Scanning electric and magnetic fields, has lower spatial resolution and use to elicit local electrochemical reactions.

What is electron beam lithography and its limitations?

Uses electrons to create patterns with ~10 nm resolution.

• requires vacuum

• low throughput

• not ideal for direct biological patterning

• expensive

What is focused ion beam lithography?

uses high mass ions as energetic particles that bombard and ablate surface molecules

• engraves sub-mircon features

What is lithography and therefore photolithography?

Use of etched stones coated with ink to create pictures in the stone age

Uses light and a mask to pattern surfaces via photoresist reactions.

200nm resolution (i.e. diffraction limit of visible light)

Difference between positive and negative photoresist.

• Positive → exposed regions dissolve

• Negative → exposed regions harden

What is soft lithography and advantages?

Uses PDMS (elastomeric molds) to transfer patterns onto surfaces.

Cured as a relief pattern from silicone master.

“stamp”

• inexpensive

• scalable (over large areas)

• works for biological materials

What is self-assembly patterning?

Pattern formation driven by thermodynamics (minimizing free energy).

self-assembly patterning example: block copolymer self-assembly.

Phase separation of polymer blocks → nanoscale patterns.

High throughput

self-assembly patterning example: nanosphere lithography

Nanoparticles self-organize into ordered arrays for patterning.

High throughput

self-assembly patterning example: magnetic self-assembly

Particles align using magnetic fields → can guide cell positioning.

Why are textured implants better than smooth ones?

• promote tissue integration

• reduce fibrous capsule formation

• improve implant stability

How does surface texturing reduce inflammation?

Reduces micromotion and alters collagen organization → less fibrosis

Examples of surface texturing methods.

• acid etching

• sandblasting or grit

• anodization

• micro-machining

Ideal pore size for tissue ingrowth.

• >100 um —> allow cell filtrations

• <1000 µm → avoid fibrous tissue ingrowth

Goals of manufacturing porous materials

• stimulate tissue ingrowth

• disrupt fibrosis

• promote angiogenesis

Optimal pore size for bone ingrowth.

100–400 µm

Minimum pore size for vascularization

50–100 µm

(100 min. for continuous growth)

Tradeoff of porous materials

Increased porosity → decreased mechanical strength

What is osteointegration?

Direct bone bonding to implant surface.

How do porous implants improve osteointegration?

Allow bone ingrowth → reduces stress shielding and implant loosening.

What are biotextiles?

Fibrous materials used in medical applications (e.g., grafts, sutures, implants).

• vascular grafts

• hernia repair

• heart valves

• wound dressings

Key properties of biotextiles.

• flexible

• strong

• porous

• high surface area

What polymer properties are needed for fibers (to facilitate crystallization)?

• high molecular weight

• linear chains (no bulk)

• ability to crystallize

• strong intermolecular interactions for chain alignment

What does a decitex metrify?

yarn linear density (mass per 10 or 9000 meters of fiber)

Textile processing: What is melt spinning?

Polymer resin is melted and extruded into fibers (used for thermoplastics).

Textile processing: What is wet/gel spinning and when is it used?

Polymer solution dissolved and extruded into a bath → precipitates into solid fibers.

For polymers that degrade at high temperatures (natural materials).

• 10um for multifilament yarns (weak but ductile)

• 500um for monofilament yarns (strong but large)

Textile processing: What is electrospinning?

Uses electric field to overcome surface tension and accelerate jets to a target form nano-scale fibers (100 nm–µm). very small

Creates structures that mimic ECM architecture.***

What factors affect electrospinning?

• polymer type

• solution concentration

• voltage

• system geometry

Why align fibers?

Improves:

• mechanical properties

• cell alignment and phenotype