Poly­mer Twin: New Implant Imit­ates Bone Structure

Ultra high molecu­lar weight poly­ethyl­ene (UHM­WPE) and poly­ethereth­er­ketone (PEEK) are among the most fre­quently used mater­i­als in ortho­ped­ics. Each of them has a cer­tain set of prop­er­ties, and the choice of mater­i­al is based mainly on what kind of bone defect should be elim­in­ated. Thus, UHM­WPE is tra­di­tion­ally used in joint replace­ment, and PEEK due to its great­er strength, is mainly used in spin­al sur­gery. Moreover, PEEK is a fairly expens­ive mater­i­al, so it is used less often than UHM­WPE. Sci­ent­ists from the Cen­ter of Com­pos­ite Mater­i­als (NUST MIS­IS) applied the pre­vi­ously developed tech­no­logy for the form­a­tion of por­ous bio­mi­met­ic mater­i­als and con­duc­ted an exper­i­ment­al com­par­at­ive ana­lys­is of the mech­an­ic­al prop­er­ties of mod­i­fied UHM­WPE and PEEK. As a res­ult, they pro­posed a fun­da­ment­ally new hybrid mater­i­al that com­bines the use­ful prop­er­ties of both poly­mers. ​“We have been work­ing with UHM­WPE for quite a long peri­od of time. Appar­ently, PEEK is rel­at­ively new for us. Due to the fact that we were try­ing to imit­ate nat­ur­al por­ous bone struc­ture in implants made of UHM­WPE, we decided to also do this with PEEK. Next, we tested and com­pared the com­pres­sion prop­er­ties of the mater­i­als” — Fedor Sen­atov, PhD, head of the research group. How­ever, the high hard­ness of the PEEK had a neg­at­ive impact on the por­ous modi­fic­a­tion of the mater­i­al: although PEEK demon­strated good prop­er­ties at com­pres­sion test, it was found that when cut­ting (and dur­ing install­a­tion of the implant sur­geon is required to ​“adjust” it under the edge of the defect) it starts to crumble. Crumbs in the area of implant­a­tion are unac­cept­able, so sci­ent­ists decided to try to cre­ate a hybrid that would retain only the bene­fi­cial prop­er­ties of both poly­mers. This is espe­cially inter­est­ing from the point of view of imit­a­tion of the struc­ture of the bone itself, because in the core (tra­bec­u­lar part) it is just softer, and on the shell (cor­tic­al part) is harder. ​“We have cre­ated a hybrid cyl­indric­al implant, which core and shell are made of soft por­ous UHM­WPE and hard non-por­ous PEEK respect­ively. Tests of the mech­an­ic­al strength of the implant showed that its char­ac­ter­ist­ics almost com­pletely cor­res­pond to the nor­mal human bone: the tra­bec­u­lar bone has elast­ic mod­u­lus from 0.001 GPa to 0.002 GPa, and the por­ous UHM­WPE has about 0.002 GPa; cor­tic­al bone has elast­ic mod­u­lus about 11 GPa, and PEEK has about 9 GPa” — Alex­an­der Chubrik, 4^th year stu­dent, co-author of the research. The imit­a­tion of the human bone is not the only advant­age of the implant: moreover, the por­ous part will allow the bone to ​“pen­et­rate” the implant. This means that over time, the fix­ing plates can be removed, and the implant will already behave as a bone. In addi­tion, due to the fact that the con­sump­tion of PEEK will decrease, such implants will be more afford­able. Sci­ent­ists pro­ceed the research in two dir­ec­tions: they test the hybrid mater­i­al in vivo, and work on the attach­ing bio­ceram­ics to the implant sur­face to accel­er­ate regen­er­a­tion in the replaced bone area. Source: Nation­al Uni­ver­sity of Sci­ence and Tech­no­logy MIS­iS, news, 15.02.2019