Công nghệ vật liệu trong y sinh học biom aterials chapter 2 phần 2 2

Sillicone5 Advanced Program Biomedical Engineering – HUST, Vietnam 2.2.Silicone elastomer •Cross-linking with radicals - For high consistency silicone rubber extrusion or injection - Ini

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Chap.2 – 2.2 Silicone

1 Advanced Program Biomedical Engineering – HUST, Vietnam

1 Introduction to silicone

-1824: tetrachlorosilane (SiCl4); 1863: tetraethylsilane; 1871:diethyldiethoxysilane

1901- 1931:foundation of organosilicon chemistry

1940s: became commercial

- Basic repeating units: siloxane; PDMS (polydimethylsiloxane): most common silicone

R can be different

-Have unique properties, possible use as fluids, emulsions, compounds, resins, elastomer

- Widely used in a lot of application

In aerospace industry (low- and high temperature performance)

In electronic field: Electrical insulator, semi conductor

In construction: Sealants, adhesives, water proof coatings (due to long-term durability)

Widely used in personal care, pharmaceutical, medical device application (excellent biocompatibility)

Silicone Chemistry and nomenclature

Example: Trimethylsiloxy: most common

M: Si connected with 1 oxygen atom D: Si connected with 2 oxygen atoms T: Si connected with 3 oxygen atoms Q: Si connected with 3 oxygen atoms

MDnM

cuu duong than cong com

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Chap.2 – 2.2 Sillicone

2 Synthesis

2.1 Silicone polymer

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2.2.Silicone elastomer

•Cross-linking with radicals

- For high consistency silicone rubber (extrusion or injection)

- Initiator: peroxide (radicals forming)

•Cross-linking by condensation

- Mostly for silicone caulks, sealants, silicone adhesives for medical devices

- Catalyst needed

- By products

•Cross-linking by addition

- Catalyst: Pt or Rh metal complexes

- No by products

- For molded parts

•Elastomer filler

- To enhance the strength and modify several properties of silicone elastomer

- Fillers: titanium oxide, barium sulphate, pigments, fumed silica (most favorable) but needs surface modification (with silane)

- Processing:: two roll mill, twin-screw extruder, Z-blade mixer

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with low surface tension of organic side groups:

Biocompatible elastomer (surface tension 20-30 mN/m)

Capable to wetting themselves

Silicone organic copolymers can be prepared with surfactant properties (e.g

in silicone glycol copolymer

- Have week intermolecular interactions:

Very low glass temperature

Have high permeability to oxygen, nitrogen, water vapor…

Viscosity id less dependent on temperature than hydrocarbon

3 Some properties

Medical textiles: medical products and devices for

-Wound dressing, bandages…

-Biotextiles, tissue engineering scaffolds, vascular implants…

* Medical fibercan be fabricated from monofilament, multifilament, staple…

* Materials for medical textiles: synthetic polymers, natural polymers, or genetically engineered polymers and the way to choose suitable fiber configuration and materials: based on the requirements of device design and the manner in which fiber is to be used

- Non-absorbable synthetic polymers:

PET (polyethylene terephthalate)- (Dacron): for most large-caliber textiles vacular grafts

PVC copolymer (Vinyon), acrylic polymers, nylon, PTFE-polytetraflourethylene (Teflon)…: for vascular grafts since 1950s

.Today only PTFE & PET are still used for vascular grafts (inert, flexible, resilent, durable and resistant to biological degradation

- Absorbable polymers: PVA- poly(vinyl alcohol), PLA- poly(lactic acid), PGA-polyglycolide…: for absorbable sutures…

- Biopolymers and modified biopolymers (natural polymers:

Collagen, polysacharides (alginates, biomimetic polymer synthesized by generic engineering of peptide sequences from elastin, collagen and spider silk…): for absorbent wound dressing, wound

management, scaffolds for cell cultures, surgical hemostats…

Cotton has been commonly used for bandages, surgical sponges, drapes, and surgical apparel, and in surgical gowns

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Chap.2 – 2.3 Medical Fibers and Biotextiles

Important Note! for most synthetic

polymers:additive (dyes, stabilizer,

antioxidants, delustrants) problems

from commercial polymers

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Chap.2 –

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Chap.2 –

Preparation

•Melt Spinning

•Wet spinning

•Electrospinning

Melt spinning:

-Typically used with thermoplastics -Yarn can be further processed

Size of spun fiber: 10 µm (multifilaments)

-500 µm or more (for monofilament)

Electrospinning:

- For very fine fiber

- Use electrostatic field and high voltage (5-30 kV)

- Fiber diameter: 1 µm-100 nm

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Wet spinning

Low-temperature process (related to degradation proplems)

Construction

•Nonwovens

-Is a textile structure produced directly from fibers without the intermediate step of yarn production -Fibers: bond or interlocked together by chemical, or thermal action or by using adhesive or solvent; oriented random or in one or more directions

•Woven fabrics:

-Textile configuration where the primary structural yarns are oriented at 90o to each other

- Plain, twill, satin weaves

-Water permeability should be controlled (50-350 ml cm-2.min-1)

•Knits

-Made by interloping yarn in horizontal row and vertical columns of stitches

•Braids

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Finishing

Testing

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Chap.2 – 2.4 Hydrogels

Hydrogel:Polymer that can adsorb water 30% or more of its weight

- Are water-swollen, cross-linked structure

- Containing ether covalent bonds produced by simple reaction of one or more comonomers

- Containing physical cross-linked from entanglements, association bond such as hydrogen bonds or strong Van der Waal interaction between chains

- Have received significant attention for biomedical applications

- Classification:

Based on preparation: homopolymer hydrogels, copolymer hydrogels, multipolymer hydrogels, interpenetrating polymeric hydrogels

Based on ionic charge: neutral, anionic, cationic or ampholytic hydrogels

Based on physical structural feature: amorphous (chain are arranged randomly), semicrystalline (charcterized by dense regions of crystallites) hydrogels, hydrogen- bonded or cpmplexation structure (may be responsible for the three-dimetional structure formed) hydrogels

-Structure:

Connection points of several chains: junction (tetrafunctional cross-linked), multifunctional junction, physical molecular entanglements

Possible a junction is an association of polymer chains caused by van der Waal forces

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Chap.2 – 2.4 Hydrogels

Preparation:swelling cross-linked structure in water or in biological fluids

Chemical cross-linking: direct reaction of linear or branched polymer with at least one crss-linking agents (difunctional, small molecular weight) or copolymerization cross-linking reaction, or cross-linking a combination of monomer and linear polymeric chains by interlinking agents

Photopolymerization or irradiation cross-linking

Important biomedical hydrogels

- PHEMA (poly(2-hydroxylethyl methacrylate): most widely used, inert to normal biological processes, resistant to degradation, not absorb by the body, biocompatible, withstand heat sterilization wothour damage, can easily prepared in several shapes and forms, used for blood-compatible applications, artifical tendon materials

-Polyacryamide

-MAA (methacrylic acid), MMA, MAH (maleic anhydride): useful monomer for preparation of hydrogels -PVA:hydrophilic, nontoxic, good mucoadhesive properties

-PEO and PEG

Applications:

-Used for blood-compatible applications, artificial tendon materials, wound healing bioadhesive, artificial kidney membranes, artificial skin, articular cartilage (PHEMA, PVA, Polyacryamide)

-Very popular in pharmaceutical application: swelling-controlled release system (for bioactive agents), such as drug release system (PHEMA, PVA

Smart polymers (Stimulus-responsive, interlligent polymers)

-Are polymers that respond with sharp, large property change to small change in physical or chemical conditions

-Other names: environmentally sensitive polymer

-Can take many forms

-May be dissolved in aqueous solution (convert from solution to a gel): polymers with alcohol groups: poly(hydropropyl acrylate), PVA derivates…

- May be absorbed or grafted on aqueous-solid interfaces (converting interface fron hydrophilic to hydrophobic):PNIPAAm

- May be cross-linked in the form of hydrogels: PNIPAAm

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Chap.2 – 2.5 Smart polymers

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Chap.2 – 2.6 Biodegradable polymers

Examples of

Biodegradable Polymers

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Chap.2 – 2.6 Biodegradable polymers

Mechanism of

chemical degradation

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Chap.2 – 2.7 Natural polymers

Examples of natural polymers

Structure of protein

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Chap.2 – 2.7 Natural materials

Collagen

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Elastin

Glucosaminoglycans

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