Method for thermal crosslinking of previously irradiated polymeric material and medical implant

A method for producing a polymeric material formed from an olefinic compound, the material having significant crosslinking and improved oxidation resistance comprising the steps of:

• (a) heating the polymeric material for a predetermined time at a predetermined temperature sufficiently high to break carbon-carbon links, generate free radicals, and form cross-links in the polymer micro-structure;
• (b) cooling said heated polymeric material in (a) from said temperature in (a) to eliminate free radicals and form crosslinks in the polymer micro-structure.
• (c) irradiating said cooled polymeric material in (b);
• (d) heating said irradiated polymeric material in (c) for a predetermined time at a predetermined temperature sufficiently high to (i) remove oxygen from the material, (ii) break existing crosslinks generated by said radiation in (c), (iii) redistribute free radials generated by said radiation in (c) uniformly in the microstructure, (iv) redistribute free radicals produced by said crosslink breakage in (ii) uniformly in the microstructure, (v) reconnect broken short chains generated by said radiation in (c) with unbroken long molecules, and (vi) create new free radicals by thermal force by breaking carbon-carbon links in the microstructure;
• and
• (e) cooling said irradiated and heated polymeric material in (d) in an oxygen reduced atmosphere from said temperature to eliminate free radicals and form crosslinks in the polymer microstructure.

A method for producing a polymeric material made from a olefinic compound, the material having significant crosslinking and improved oxidation resistance comprising the steps of:

• (a) irradiating the polymeric material;
• (b) aging said irradiated polymeric material in (a) in a heating device for a predetermined time at a predetermined temperature between room temperature and 140 degree C. in the presence of an oxidizing agent to create more free radicals and chemical crosslinks between neighboring molecules;
• (c) heating said irradiated and aged polymeric material in
• (b) for a predetermined time at a predetermined temperature sufficiently high to (i) break carbon-oxygen bonds in the material, (ii) break existing crosslinks generated by said radiation in (a), (iii) redistribute free radials generated by said radiation in (a) uniformly in the microstructure, (iv) redistribute free radicals produced by said crosslink breakage in (ii) uniformly in the microstructure, (v) reconnect broken short chains generated by said radiation in (a) with unbroken long molecules, and (vi) create new free radicals by thermal force by breaking carbon-carbon links in the microstructure;
• and
• (d) cooling said heated polymeric material in (c) in an oxygen reduced atmosphere from said temperature in (c) to eliminate free radicals and form crosslinks in the polymer microstructure.

A method for producing a medical implant made from a solid olefinic material having a molecular weight of between 400,000 and 10,000,000 comprising the steps of:

• (a) irradiating the solid polymeric material;
• (b) placing said irradiated solid polymeric material in (a) in a heating device;
• (c) heating said irradiated solid polymeric material in (a) for a predetermined time at a predetermined temperature sufficiently high to (i) remove oxygen from the material, (ii) break existing crosslinks generated by said radiation in (a), (iii) redistribute free radials generated by said radiation in (a) uniformly in the microstructure, (iv) redistribute free radicals produced by said crosslink breakage in (ii) uniformly in the microstructure, (v) reconnect broken short chains generated by said radiation in (a) with unbroken long molecules, and (vi) create new free radicals by thermal force by breaking carbon-carbon links in the microstructure;
• (d) cooling said irradiated and heated polymeric material in (c) in an oxygen reduced atmosphere in said heating device to eliminate free radicals and form crosslinks in the microstructure;
• and
• (e) fabricating the medical implant from said cooled polymeric material in (d).

A method for producing a medical implant made from a powder olefinic material having a molecular weight of between 400,000 and 10,000,000 comprising the steps of:

• (a) irradiating the powder polymeric material;
• (b) placing said irradiated powder polymeric material in (a) in a forming device;
• (c) heating said irradiated powder polymeric material in (a) for a predetermined time at a predetermined temperature sufficiently high to (i) remove oxygen from the material, (ii) break existing crosslinks generated by said radiation in (a), (iii) redistribute free radials generated by said radiation in (a) uniformly in the microstructure, (iv) redistribute free radicals produced by said crosslink breakage in (ii) uniformly in the microstructure, (v) reconnect broken short chains generated by said radiation in (a) with unbroken long molecules, and (vi) create new free radicals by thermal force by breaking carbon-carbon links in the microstructure;
• (d) forming the solid polymeric material from said irradiated and heated powder polymeric material in (c) in an oxygen reduced atmosphere in said forming device by simultaneously applying sufficient pressure and heat followed by cooling from said temperature into a solid material to eliminate free radicals and form crosslinks in the microstructure;
• and
• (e) fabricating the medical implant from said cooled solid olefinic material in (d).

A method for producing a perform or nearly finished shape of a medical implant made from a powder olefinic material having a molecular weight of between 400,000 and 10,000,000 comprising the steps of:

• (a) irradiating the powder polymeric material;
• (b) placing said irradiated powder polymeric material in (a) in the cavity of a compression mold;
• (c) heating said irradiated powder polymeric material in said mold cavity in (b) for a predetermined time at a predetermined temperature sufficiently high to (i) remove oxygen from the material, (ii) break existing crosslinks generated by said radiation in (a), (iii) redistribute free radials generated by said radiation in (a) uniformly in the microstructure, (iv) redistribute free radicals produced by said crosslink breakage in (ii) uniformly in the microstructure, (v) reconnect broken short chains generated by said radiation in (a) with unbroken long molecules, and (vi) create new free radicals by thermal force by breaking carbon-carbon links in the microstructure;
• (d) forming the perform or near-finished shape of a medical implant from said irradiated and heated powder olefinic material in (c) in an oxygen reduced atmosphere in said mold cavity by simultaneously applying sufficient pressure and heat followed by cooling from said temperature into a solid material to eliminate free radicals and form crosslinks in the microstructure;
• and
• (e) fabricating the medical implant from said cooled solid olefinic material in (d).

A method for removing oxygen from a oxidized polymeric material formed from an olefinic compound, the material having improved oxidation resistance and restored material property comprising the steps of:

• (a) placing the oxidized polymeric material in a heating device;
• (b) heating said oxidized polymeric material in (a) for a predetermined time at a predetermined temperature sufficiently high to break carbon-oxygen bonds in the microstructure;
• and
• (c) cooling said heated polymeric material in (b) in an oxygen reduced atmosphere from said temperature to eliminate free radicals and form crosslinks in the polymer microstructure.

A method for producing a polymeric material formed from an olefinic compound, the material having significant chemical crosslinking and improved material property without radiation comprising the steps of:

• (a) placing the polymeric material in a heating device;
• (b) heating said polymeric material in the presence of an oxidizing agent for a predetermined time at a predetermined temperature sufficiently high to break carbon-carbon links in said polymeric material to create free radicals and chemical crosslinking between neighboring molecules;
• (c) aging said heated polymeric material in (b) for a predetermined time at a predetermined temperature lower than said predetermined temperature in (b) in the presence of an oxidizing agent to create more free radicals and chemical crosslinking between neighboring molecules;
• (d) replacing said oxidizing atmosphere in the heating device with a non-oxidizing atmosphere;
• (e) heating said heated and aged polymeric material in (c) for a predetermined time at a predetermined temperature sufficiently high to break carbon-oxygen bonds in the microstructure;
• and
• (f) cooling said heated polymeric material in (e) in an oxygen reduced atmosphere from said temperature in (e) to eliminate free radicals and form crosslinks in the polymer microstructure.