https://www.oarsijournal.com/article/S1063-4584(02)90801-0/pdf

Articular cartilage repair: basic science and clinical progress. A review of the current status and prospects.

This paper reviews biodegradable synthetic polymers focusing on their potential in tissue engineering applications. The major classes of polymers are briefly discussed with regard to synthesis, properties and biodegradability, and known degradation modes and products are indicated based on studies reported in the literature. A vast majority of biodegradable polymers studied belongs to the polyester family, which includes polyglycolides and polylactides. Some disadvantages of these polymers in tissue engineering applications are their poor biocompatibility, release of acidic degradation products, poor processability and loss of mechanical properties very early during degradation. Other degradable polymers such as polyorthoesters, polyanhydrides, polyphosphazenes, and polyurethanes are also discussed and their advantages and disadvantages summarised. With advancements in tissue engineering it has become necessary to develop polymers that meet more demanding requirements. Recent work has focused on developing injectable polymer compositions based on poly (propylene fumarate) and poly (anhydrides) to meet these requirements in orthopaedic tissue engineering. Polyurethanes have received recent attention for development of degradable polymers because of their great potential in tailoring polymer structure to achieve mechanical properties and biodegradability to suit a variety of applications.

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Biodegradable synthetic polymers for tissue engineering

Properties of lactic acid based polymers and their correlation with composition

At present, strong requirements in orthopaedics are still to be met, both in bone and joint substitution and in the repair and regeneration of bone defects. In this framework, tremendous advances in the biomaterials field have been made in the last 50 years where materials intended for biomedical purposes have evolved through three different generations, namely first generation (bioinert materials), second generation (bioactive and biodegradable materials) and third generation (materials designed to stimulate specific responses at the molecular level). In this review, the evolution of different metals, ceramics and polymers most commonly used in orthopaedic applications is discussed, as well as the different approaches used to fulfil the challenges faced by this medical field.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2008.0151

Biomaterials in orthopaedics.

Elastomeric biomaterials for tissue engineering

Solvent-free fabrication of micro-porous polyurethane amide and polyurethane-urea scaffolds for repair and replacement of the knee-joint meniscus.

New biomedical polyurethanes and a polyurethane urea based on epsilon-caprolactone and 1,4-butanediisocyanate have been developed. On degradation, only non-toxic products are produced. The polyurethane urea with poly(epsilon-caprolactone) soft segments and butanediisocyanate/butanediamine hard segments shows a high tensile strength, a high modulus and a high resistance to tearing but as a result of the strong interactions between the solvent and the polymer processing is difficult. When butanediamine is replaced by butanediol in the chain extension step, a processible polyurethane is obtained but the polymer lacks the desired mechanical properties for biomedical applications. By chain extending with a longer urethane diol block, a processible polymer was obtained with mechanical properties comparable to the polyurethane urea. This polyurethane has been made porous and can be used as a meniscal prosthesis.

High molecular weight polyurethanes and a polyurethane urea based on 1,4-butanediisocyanate

A new approach to the synthesis of biomedical polyurethanes based on e-caprolactone and 1,4-butanediisocyanate with a high modulus, has been developed. By chain extending an e-caprolactone prepolymer with a long uniform-size diisocyanate block, a segmented polyurethane with uniform-size hard segments was obtained. It shows excellent mechanical properties; an extremely high modulus of 105 MPa and a tensile strength of 35 MPa. The polymer is soluble at high concentrations in various volatile solvents such as chloroform and 1,4-dioxane. By a combination of salt-leaching and freeze-drying, porous materials have been obtained in which macropores ranging in size from 150–300 μm are highly interconnected by micropores. The material shows a sufficiently high compression modulus of 200 kPa and appears to be suitable for biomedical applications such as meniscal prostheses. © 1998 Kluwer Academic Publishers

A new biomedical polyurethane with a high modulus based on 1,4-butanediisocyanate and epsilon-caprolactone.

Polyurethanes based on a 50/50 copoly(L-lactide/epsilon-caprolactone) prepolymer and butanediisocyanate were made. Chain extending a diisocyanate terminated prepolymer with butanediamine was not possible due to the susceptibility of the lactide bond to aminolysis. Chain extension with butanediol resulted in a polymer with poor mechanical properties due to transesterification. When the copolymer prepolymer was chain-extended with an isocyanate terminated block, transesterification with the chain-extender was avoided and the mechanical properties were increased. When the length of the hard segments was increased the mechanical properties increased further. A L-lactide/epsilon-caprolactone based polyurethane with a tensile strength and modulus of respectively 45 MPa and 60 MPa was made. The polymer contained no poly(L-lactide) crystals and was easy to process. Compared to the high molecular weight 50/50 copoly(L-lactide/epsilon-caprolactone) the polyurethane showed better mechanical properties, is expected to have the same adhesive properties and is expected to have a slower degradation rate. These factors makes this polymer excessively useful for in-vivo tissue engineering in for instance meniscal reconstruction material, nerve guide and artificial skin.

On the role of aminolysis and transesterification in the synthesis of epsilon-caprolactone and L-lactide based polyurethanes

The present invention relates to new hydrogels with improved mechanical properties and methods of their preparation. The hydrogels are formed from hydrophilic polymers having function hydroxyl groups and have low elasticity modulus typically less than about 10 kPa, a tensile strength above 1 Mpa, an elongation above 50% which makes suitable as medical implants, in particular intraocular lenses. The hydrogels are prepared by a crosslinking method with a comparatively low concentration of hydrophilic polymer of a sufficiently high molecular weight dissolved in a good solvent.

Coenraad Jan Spaans

Papers

Solvent-free fabrication of micro-porous polyurethane amide and polyurethane-urea scaffolds for repair and replacement of the knee-joint meniscus.

High molecular weight polyurethanes and a polyurethane urea based on 1,4-butanediisocyanate

A new biomedical polyurethane with a high modulus based on 1,4-butanediisocyanate and epsilon-caprolactone.

On the role of aminolysis and transesterification in the synthesis of epsilon-caprolactone and L-lactide based polyurethanes

Hydrogels and methods for their production