Porous Open-Сell UHMWPE: Experimental Study of Structure and Mechanical Properties

Alexei I. Salimon,Michael Yu. Zadorozhnyy,Alexander A. Safonov,Alexander M. Korsunsky,Dmitry D. Zherebtsov,Eugene S. Statnik,Fedor S. Senatov

doi:10.3390/ma12132195

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) is a bioinert polymer that is widely used as bulk material in reconstructive surgery for structural replacements of bone and cartilage. Porous UHMWPE can be used for trabecular bone tissue replacement, and it can be used in living cell studies as bioinert 3D substrate permeable to physiological fluids. It is important to develop techniques to govern the morphology of open-cell porous UHMWPE structures (pore size, shape, and connectivity), since this allows control over proliferation and differentiation in living cell populations. We report experimental results on the mechanical behavior of porous open-cell UHMWPE obtained through sacrificial removal (desalination) of hot-molded UHMWPE-NaCl powder mixtures with pore sizes in the range 75 µm to 500 µm. The structures were characterized using SEM and mechanically tested under static compression and dynamic mechanical analysis (DMA), bending, and tensile tests. Apparent elastic modulus and complex modulus were in the range of 1.2 to 2.5 MPa showing a weak dependence on cell size. Densification under compression caused the apparent elastic modulus to increase to 130 MPa.

Highlights

Ultra-high molecular weight polyethylene (UHMWPE) is a bioinert polymer that has been used in orthopedics as bearing material in artificial joints and in metal-on-UHMWPE articulation
High viscosity of molten UHMWPE precludes the use of 3D additive techniques to create complex structures similar to trabecular bone tissue, it has been demonstrated that the sacrificial templating technique can introduce some additivity into manipulations with UHMWPE [4], at a precision and spatial resolution of about 500 μm
We report the results of Scanning Electron Microscopy (SEM) structure studies and static and dynamic mechanical testing at compression, bending, and tensile

Summary

Introduction

Ultra-high molecular weight polyethylene (UHMWPE) is a bioinert polymer that has been used in orthopedics as bearing material in artificial joints and in metal-on-UHMWPE articulation. 1990s, owing to its combination of excellent bioinertness and mechanical performance, UHMWPE has attracted permanent interest as a suitable solution in the reconstructive surgery of cartilage in hip and knee joints [1] and in intervertebral discs [2], as well as in oral and maxillofacial surgery [3]. The current practice of implant fabrication involves hot molding and further subtractive mechanical shaping of bulk UHMWPE. Hot molding of UHMWPE-NaCl powder mixtures with subsequent desalination is especially suitable when feature sizes down to tens of μm are sought in complex structures. The flexibility is an attractive aspect of this technique, as the following types of structures can be produced using relatively simple equipment: Materials 2019, 12, 2195; doi:10.3390/ma12132195 www.mdpi.com/journal/materials

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