Biodegradable Polyurethanes

Polyurethanes are increasingly becoming the biomaterial of choice for biomedical applications due to their superior mechanical strength, biocompatibility, abrasion resistance, and manufacturability.

There are two main categories of medical grade polyurethanes: biostable and biodegradable. Biostable polyurethanes are used in medical devices such as catheters, infusion pumps, and cardiac pacemakers. Absorbable polyurethanes are an emerging biomaterial used for implantable medical devices in wound healing, cardiovascular, musculoskeletal, and neural repair applications.

Biodegradable polyurethanes are not all the same.

There are several different ways of developing absorbable polyurethanes, each with its own benefits and drawbacks. The spectrum of biodegradable polyurethanes extends from least degradable to fully degradable options, dating as far back as the early 1980s. The least degradable formulations are blends of biostable polyurethanes that do not degrade with other absorbable polymers such as polylactides. The biostable polyurethane provided the mechanical strength while the polylactide offered a desirable degradation profile. However, many implantable medical device applications require full degradation, so several biodegradable polyurethane approaches emerged.

The typical synthesis of thermoplastic biodegradable polyurethanes includes three components: a diisocyanate, a polymer diol, and a chain extender of diol or diamine (Figure 1). Most often, the diisocyanate and the chain extender are the hard segment, and the polymer diol is the soft segment. The soft segment has a low glass transition temperature, whereas the hard segment defines the melting temperature and has high modulus and strength. The polymer diol contains hydrolysable bonds that render the material biodegradable. Xu and Hong provide an overview of biodegradable thermoplastic polyurethanes for tissue repair.

Figure 1: Absorbable polyurethane chemistry.

Bezwada Biomedical has developed highly reactive isocyanates that are biodegradable and have tunable hydrolytic degradation profiles so that both the hard and the soft segments are fully degradable. By adding a degradable linkage between the aromatic rings instead of the non-degradable methylene group, the monomer linkage added can be selected from a wide variety of biocompatible and biodegradable materials to precisely tune degradation rate and mechanical properties (Figure 2).

Figure 2: Absorption profile of polyurethanes.

Our inventory includes absorbable diisocyanates and multi-isocyanates with examples shown in Figure 3. The degradation rates of these diisocyanates are controlled by varying the glycolic acid moiety with the lactic acid moiety as well as by varying the length of the degradable segment. The hard segments derived from these isocyanates are also hydrolytically unstable.

Figure 3: Examples of Bezwada’s novel absorbable aromatic diisocyanates.

Bezwada’s biodegradable polyurethanes have so far added value in several medical device applications. They have been fabricated as porous scaffolds that facilitate cell attachment and proliferation for bone regeneration applications, custom bioinks for 3D printing, biomaterial scaffolds for tissue engineering and drug delivery, and tissue adhesives, sealants, and mesh fixation devices. Learn more about Bezwada’s proprietary biodegradable polyurethanes and contact us to discuss your application.