Self-bonding of PEEK for active medical implants applications

Abstract

In an effort to select the best possible medical grade of polyether ether ketone (PEEK) for active medical implants application, it was necessary to inspect surface thermodynamic properties of different grades and correlate with self-bonding (autohesion) strength. Autohesion is the process of choice for encapsulating active medical implants made of PEEK. Temperature modulated DSC was used to investigate crystallinity and thermal events of range of medical grade PEEK (semicrystalline, amorphous, semi-crystalline with amorphous surface, minerals and black masterbatch filled). Lab shear test was used to measure autohesive forces between PEEK samples pressed at moderate temperature (200°C) and pressure. Samples with higher mobile amorphous region (MAF) and lower degree of crystallinity (W c ) resulted in higher autohesivce bonding strength. However, semi crystalline PEEK with surfaces that showed high MAF and low W c resulted in higher autohesive bonding strength when compared with crystalline samples. The presence of fillers (minerals and black masterbatch) in the crystalline structure doubled the autohesive bonding strength values of the semi-crystalline sample. The presence of large crystalline region and a larger portion of the rigid amorphous region acted negatively on autohesion strength. Semi-crystalline PEEK with a special manufacturing procedure to produce amorphous surface produced the best choice among the PEEK grades. This grade have the desired thermodynamical properties in the bulk while exhibiting best surface adhesion strength.

Effect of nitrogen plasma treatment on the crystallinity and self‐bonding of polyetheretherketone (PEEK) for biomedical applications

“…The crystallinity index is an important parameter for polymers, as it affects many physical properties, including polymer density, melting point, hardness, elastic modulus, tensile strength, stiffness and permeability. Polymer crystallinity is also supposed to influence autohesion phenomena, although self‐bonding highly depends on processing parameters, including bonding method, working temperature, pressure and time.…”

“…The final bonding configuration is reported in Figure b. Polymer specimens were maintained in the press at 200°C and 3 MPa operating pressure for 2 h or 7.5 h. …”

“…In the case of PEEK polymers, self‐bonding and consolidation can be achieved through hot press under controlled working conditions . However, due to the presence of non‐polar groups, PEEK is characterized by low surface energy, with unfavourable consequences for auto‐adhesion processes.…”

Effect of interfacial crystalline growth on autohesion of PEEK

“…For semi-crystalline polymers, it is commonly admitted that the effective bonding starts from melting temperature, the presence of crystalline zone prevents the macromolecules of the amorphous phase from moving to the neighborhood. However, some studies show that a physical bond is formed between two surfaces of amorphous PEEK at temperature below its melting temperature [9][10][11][12][13]. Rationally, Boiko noticed in 2001 that the crystallization hinders auto-adhesion phenomenon applied to PEEK [14].…”

Analysis of the Thermoplastic Composite Overmolding Process: Interface Strength

“…After performing isothermal bonding experiments in the vicinity of the glass transition temperature for amorphous and semi-crystalline PET, it was found that the strength values of bonded semi-crystalline specimens were one order of magnitude smaller than the strength of bonded amorphous specimens. This was explained not only by the immobility of the crystalline fraction, but also since a part of the amorphous polymer chains is firmly fixed by the surrounding crystalline regions, which severely limits the penetration depth of the polymer chains into the adjacent substrate (Boiko et al, 2001;Awaja and Zhang, 2015). As a result, the crystallinity of the polymer directly influences the concentration of mobile chain ends at the interface.…”