Bone ingrowth into porous silicon nitride

Abstract

Achieving solid skeletal attachment is a requirement for the clinical success of orthopedic implants. Porous or roughened surfaces and coatings have been developed and used with mixed success to achieve attachment due to bone ingrowth. Silicon nitride is a high performance ceramic whose strength, imaging properties, and biocompatibility make it a candidate material for orthopedic implants. A porous form of silicon nitride, cancellous-structured ceramic (CSC), has been developed. CSC is a nonresorbable, partially radiolucent porous structure that can be bonded to orthopedic implants made of silicon nitride to facilitate skeletal attachment. The purpose of this study was to quantify the extent and rate of bone ingrowth into CSC in a large animal model. Cylindrical implants were placed bilaterally using staged surgeries in the medial femoral condyle of six sheep. Condyles were retrieved after 3 and 6 months in situ and prepared for examination of bone growth under SEM. Bone grew into CSC to extents and at rates similar to those reported for other titanium porous surfaces in studies involving large animals and postmortem retrievals in humans. Bone ingrowth was observed at depths of penetration greater than 3 mm in some implants after only 12 weeks in situ. Bone ingrowth into CSC is a viable method for achieving skeletal attachment.

Ceramics and ceramic coatings in orthopaedics

“…For Si 3 N 4 , several studies demonstrated its osseointegration capabilities. Anderson et al showed osseous penetration of up to 3 mm in ∼72% porous Si 3 N 4 with excellent vascularization twelve weeks after implantation in an ovine model [105]. Similar studies by Guedes e Silva et al showed good boney apposition for Si 3 N 4 samples in rabbits evaluated eight weeks after implantation [103,104].…”

“…Si 3 N 4 has been shown to be biocompatible, possessing favorable cell interaction characteristics [83,84,[97][98][99][100][101][102]. These and other studies indicate that porous or unpolished Si 3 N 4 osteointegrates with adjacent bone [102][103][104][105][106] and exhibits bacteriostasis [106,107] . In its dense and polished form, it has been shown to produce implants with exceptionally low wear rates [108][109][110][111][112][113][114][115][116][117][118].…”

“…Porosity in thermally sprayed HAp coatings is governed by plasma conditions [191] and can vary from about 2% to greater than 10% [192,193]. A broad range of porosity can also be engineered into most ceramics for use as arthrodesis devices, scaffolds, or bone substitutes [21,105,[194][195][196][197]. In summary, the amount of porosity within an implant is an important design parameter.…”

The Rationale for Silicon Nitride Bearings in Orthopaedic Applications

“…[56][57][58][59] A cancellous-structured porous silicon nitride composite ceramic has been developed and is in commercial use as a spinal fusion implant; cylindrical implants have shown bone ingrowth rates similar to those reported for porous titanium, indicating that porous silicon nitride is an excellent substrate for implants designed for direct, biological skeletal fixation. 60 New bone forms even in the cortical region of the rabbit tibia, and around silicon nitride implants, suggesting that the material is osteoconductive, and promotes stable osseous fixation. 61 …”

A novel pressed porous silicon-polycaprolactone composite as a dual-purpose implant for the delivery of cells and drugs to the eye

“…Porous silicon (pSi) shows potential as a biocompatible scaffold for applications in orthopaedics (Li et al, 1998;Coffer et al, 2005;Whitehead et al, 2008;Anderson et al, 2010), oncology (Zhang et al, 2005;Mann et al, 2011;Park et al, 2011) and ophthalmology (Low et al, 2006;Cheng et al, 2008;Low et al, 2009;Kashanian et al, 2010). For use in ophthalmic implants designed to deliver drugs or cells to the eye, the advantages of pSi include its large surface area for drug-loading and cell attachment, and good ocular biocompatibility (Low et al, 2009;Kashanian et al, 2010).…”