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PMMA

Radical polymerization

Property	Typical Value / Description
Appearance	Transparent, colorless, glass-like
Density	~1.18 g/cm³
Refractive Index	~1.49 (high optical clarity, close to glass)
Glass Transition Temperature (Tg)	~105 °C
Melting Point (Tm)	~160 °C (amorphous, softens rather than sharp melting)
Water Absorption	~0.3% (low, but higher than PTFE or PE)
Moisture Permeability	Relatively low

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Polymer	Transparency / Light Transmission	Refractive Index (n)	UV/Visible Behavior	Optical Applications
PMMA (Polymethyl methacrylate)	~92% transmission (higher than glass), excellent clarity	~1.49	Good UV stability (but can yellow over long exposure without stabilizers)	Intraocular lenses, contact lenses (historical), dental prosthetics, light guides
PU (Polyurethane)	Can be transparent, but typically lower clarity and more yellowing than PMMA	~1.50–1.60 (depends on formulation, soft segments increase scattering)	Susceptible to UV degradation (needs stabilizers), can discolor	Transparent wound dressings, elastomeric films (not high-precision optics)
PEEK (Polyether ether ketone)	Naturally beige/opaque → poor transparency	~1.65	Not suitable for optical clarity, absorbs in visible range	Rare in optics; used structurally in implants where optics not required
PET (Polyethylene terephthalate)	Transparent films, ~85–90% transmission	~1.57–1.58	Good visible transparency, but poor UV resistance (yellows, degrades under UV)	Packaging films, biomedical membranes, sometimes optical films (not implants)

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UV Absorbers (UVA)

Molecules that absorb harmful UV light (280–400 nm) and re-emit it as harmless heat.
Common examples:

Benzotriazoles (e.g., Tinuvin 328, 327)
Benzophenones
Triazines

Benzotriazoles

Benzophenones

Triazines

Hindered Amine Light Stabilizers (HALS)

Do not absorb UV directly, but neutralize free radicals formed when UV hits the polymer.
Work like antioxidants, trapping radicals and stopping chain reactions.
Very effective for long-term outdoor exposure (used in PU, PP, PE, coatings).

HALS

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Polymer	Young’s Modulus (E)	Flexural Modulus	Key Notes
PMMA (Polymethyl methacrylate)	2.0–3.3 GPa	~3.0 GPa	Stiff, glassy, brittle. High rigidity but low toughness.
PU (Polyurethane)	1–100 MPa (soft, elastomeric) to ~0.2–0.8 GPa (hard PU)	Depends on formulation	Extremely tunable: can be soft rubber-like or semi-rigid. Much lower modulus than PMMA, PEEK, PET.
PEEK (Polyether ether ketone)	3.6–4.0 GPa	~4.0 GPa	Strongest among these. Excellent for load-bearing implants (spine cages, dental implants). High toughness + strength.
PET (Polyethylene terephthalate)	2.0–2.8 GPa	~2.5–3.0 GPa	Similar to PMMA in stiffness. Used in films, fibers, and membranes. Slightly tougher than PMMA.

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Polymer	Crystalline / Amorphous	Typical Degree of Crystallinity	Notes & Biomedical Implications
PMMA (Polymethyl methacrylate)	Amorphous	0% (no crystallinity)	Fully amorphous → high transparency (optical clarity), but brittle. No crystalline reinforcement, so modulus is moderate.
PU (Polyurethane)	Semi-crystalline (phase-separated)	Highly variable (soft segment: amorphous, hard segment: crystalline domains)	Microphase separation gives PU elasticity. Hard segment crystallinity acts like physical crosslinks → mechanical tunability. Not optically transparent at high crystallinity.
PEEK (Polyether ether ketone)	Semi-crystalline	~30–40% crystalline	High crystallinity → high stiffness, strength, chemical/thermal stability. Makes PEEK opaque, but excellent for load-bearing implants.
PET (Polyethylene terephthalate)	Semi-crystalline	~30–40% (depending on processing, can range 20–55%)	Crystallinity gives PET good strength, barrier properties, and toughness. Amorphous PET (APET) is transparent; crystalline PET (CPET) is opaque and heat-resistant.

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Property	PMMA (Polymethyl methacrylate)	PE (Polyethylene)
Structure / Nature	Amorphous, glassy polymer	Semi-crystalline polyolefin
Transparency	Highly transparent (~92% light transmission) → optical clarity	Opaque to translucent (depends on crystallinity, but not optically clear)
Mechanical	Rigid, stiff (E ≈ 2–3 GPa), brittle	Tough, ductile, flexible (HDPE E ≈ 0.8 GPa; UHMWPE softer but very wear-resistant)
Biocompatibility	Biocompatible in polymerized form, used for long-term implants	Excellent biocompatibility, especially UHMWPE in load-bearing joints
Degradability	Not biodegradable	Not biodegradable
Surface Properties	Hydrophobic, smooth, good polishability	Hydrophobic, very low friction (self-lubricating), chemical inertness
Sterilization	Stable under gamma radiation, ethylene oxide	Stable under ethylene oxide, but radiation can degrade PE (oxidation)

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1. Orthopedics

Bone cement: PMMA is one of the most common materials for bone cements in orthopedic surgery, especially in hip and knee replacements. It anchors implants (like artificial joints) to the bone.
Vertebroplasty & kyphoplasty: PMMA bone cement is injected into fractured vertebrae to stabilize them and reduce pain.

2. Dental Applications

Dentures & prosthetics: Used as a base material for dentures because of its strength, ease of molding, and aesthetic similarity to natural gums.
Temporary crowns, bridges, and orthodontic devices.
Dental fillings: PMMA is sometimes used in provisional restorative materials.

3. Ophthalmology

Intraocular lenses (IOLs): Earlier generations of artificial lenses after cataract surgery were made of PMMA. While flexible polymers like silicone and acrylics are now more common, PMMA IOLs are still used in certain cases.
Contact lenses: PMMA was the first material used for rigid contact lenses (though now largely replaced by gas-permeable materials since PMMA is not oxygen-permeable).

4. Craniofacial & Neurosurgery

Cranial implants: PMMA is molded to replace parts of the skull after trauma or surgery.
Cosmetic and reconstructive surgery: PMMA microspheres suspended in collagen can be used as permanent dermal fillers.
Customized implants: 3D printing with PMMA has been explored for patient-specific implants.

5. Drug Delivery & Bioengineering

Drug carriers: PMMA nanoparticles and microspheres can encapsulate and release drugs in a controlled manner.
Tissue engineering scaffolds: PMMA structures can serve as biocompatible scaffolds for cell growth (though PMMA is not biodegradable, so applications are selective).

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Polymer	Key Biomedical Applications	Advantages	Limitations
PMMA (Polymethyl methacrylate)	Bone cement (orthopedic, vertebroplasty), dentures, intraocular lenses, cranial implants, dermal fillers, drug carriers, hearing aids	High transparency, strong and rigid, good biocompatibility, easy processing, stable in vivo	Not biodegradable, brittle (can crack), poor oxygen permeability (limits contact lens use)
PLA (Polylactic acid)	Resorbable sutures, drug delivery, tissue engineering scaffolds, implants	Biodegradable, good mechanical strength, derived from renewable resources	Hydrolysis produces acidic byproducts (may cause inflammation), slower degradation in some tissues, brittle
PEEK (Polyether ether ketone)	Spinal cages, orthopedic implants, dental prosthetics	Excellent mechanical strength, radiolucent (X-rays pass through), chemically inert, biocompatible	Very expensive, not biodegradable, requires advanced processing
PTFE (Polytetrafluoroethylene, Teflon®)	Vascular grafts, heart patches, catheters, surgical meshes	Excellent chemical resistance, hydrophobic, low friction (anti-adhesive), stable in vivo	Not biodegradable, difficult to process, limited tissue integration (inert surface)
PU (Polyurethane)	Catheters, pacemaker leads, heart assist devices, wound dressings, flexible implants	Highly elastic, tunable mechanical properties, relatively biocompatible, can be made degradable	Can degrade in vivo under oxidative stress, some formulations may cause immune responses

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Polymer	Water Absorption (24 h, % by weight)	Notes & Biomedical Implications
PMMA (Polymethyl methacrylate)	0.3–0.5%	Low, but higher than PE/PTFE. Maintains transparency in aqueous environments (good for intraocular lenses, dentures).
PU (Polyurethane)	0.5–2.0% (varies)	Depends on soft/hard segment ratio. Hydrophilic urethane groups (–NH–CO–O–) attract water. Leads to swelling, especially in biomedical PU foams or hydrogels.
PEEK (Polyether ether ketone)	~0.1%	Very low absorption → excellent dimensional stability. Good for long-term load-bearing implants (spinal cages, dental).
PET (Polyethylene terephthalate)	~0.2–0.5%	Slightly lower than PMMA. Stable in water, but hydrolyzes slowly under high temp/humidity (limiting long-term implant use).
PTFE (Polytetrafluoroethylene)	~0.01% (nearly zero)	Extremely hydrophobic and chemically inert. No swelling in water. Great for vascular grafts, catheters.
PE (Polyethylene, HDPE/UHMWPE)	<0.01% (nearly zero)	Hydrophobic, does not absorb water. Critical for joint prostheses (UHMWPE articulating surfaces).

PMMA is moderately hydrophobic (contact angle ~70–80°).

Hydrophobicity comes from its hydrocarbon backbone and methyl groups, partially balanced by polar ester groups.

It absorbs very little water, keeping it dimensionally stable and optically clear.