Biostable Polyurethane with Polysiloxane Soft Segment
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Solution Overview
Problem
Biostable polyurethanes with high silicone content in the soft segment face challenges in maintaining mechanical properties and are prone to degradation due to oxidizable groups, which affects their stability and performance in medical devices.
Innovation Solution
A biostable polyurethane composition with a soft segment comprising greater than 98 wt % of a polysiloxane and a hard segment reaction product of a diisocyanate and a linear difunctional chain extender, processed through high shear mixing to enhance phase separation and stability, reducing the need for polyether components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyether polyol is added to act as a compatibiliser between isocyanate rich hard segment and silicone rich soft segment, then mechanical properties are improved, but biological stability deteriorates due to presence of oxidisable groups
Solution Approach 1:
The invention extracts and removes the polyether polyol component from the soft segment formulation, replacing it entirely with hydroxyl-terminated polysiloxane. This elimination of oxidisable groups resolves the contradiction by sacrificing the compatibiliser function (which is no longer needed due to direct reaction between isocyanate and polysiloxane hydroxyl groups) while gaining biological stability.
Solution Approach 2:
The invention changes the chemical composition parameter of the soft segment from a polyether-polymer mixture to pure polysiloxane with greater than 98 wt% content. This parameter change eliminates oxidisable ether groups while maintaining the necessary hydroxyl functionality for reaction with diisocyanate, thereby improving biological stability without compromising mechanical properties.
2Reliability
If silicone content in soft segment is increased beyond 80 wt%, then biological stability is improved, but mechanical properties deteriorate
Solution Approach 1:
The invention extracts the polyether polyol component that previously limited silicone content to 80 wt%. By removing this component, the formulation can accommodate greater than 98 wt% polysiloxane while maintaining mechanical integrity through direct chemical reaction between the polysiloxane hydroxyl groups and diisocyanate, forming stable urethane linkages.
Solution Approach 2:
The invention creates a composite structure where hydroxyl-terminated polysiloxane (greater than 98 wt%) forms the soft segment matrix, and the reaction product of diisocyanate with the polysiloxane hydroxyl groups forms the hard segment. This composite approach allows high silicone content while maintaining mechanical properties through the interpenetrating network of soft and hard segments.
3Ease of manufacture
If polyether polyol is used as soft segment component, then ease of manufacture is improved through compatibilisation, but loss of substance occurs due to oxidation of polyether groups
Solution Approach 1:
The invention extracts and eliminates the polyether polyol component that is prone to oxidation. By formulating the soft segment with greater than 98 wt% hydroxyl-terminated polysiloxane, the patent removes the source of oxidative degradation while maintaining manufacturability through the direct reaction between polysiloxane hydroxyl groups and diisocyanate.
Solution Approach 2:
The invention creates an inherently more chemically inert soft segment by using polysiloxane instead of polyether polyol. The siloxane backbone and methyl side groups provide greater resistance to oxidation compared to the ether linkages in polyether polyol, effectively creating a more stable chemical environment that resists degradation.
Data Source
AI summary
The present invention relates to a biostable polyurethane or polyurea comprising: (a) a soft segment comprising a polysiloxane of the general formula (I); and (b) greater than 0 and less than 40 wt % of a hard segment which is a reaction product of a diisocyanate and a linear difunctional chain extender, processes for their preparation and their use in the manufacture of biomaterials, devices, articles or implants.