Silicon nitride (Si
3N
4) has a dist
inctive comb
ination of material properties such as high strength and fracture toughness,
inherent phase stability, scratch resistance, low wear,
biocompatibility, hydrophilic behavior, excellent radiographic imag
ing and resistance to bacterial adhesion, all of which make it an attractive choice for orthopaedic implants. Unlike oxide ceramics, the surface chemistry and topography of Si
3N
4 can be eng
ineered to address potential
in vivo needs.
Morphologically, it can be manufactured to have an ultra-smooth or highly fibrous surface structure. Its chemistry can be varied from that of a silica-like surface to one which is predom
inately comprised of silicon-am
ines. In the present study, a Si
3N
4 bioceramic was subjected to thermal, chemical, and mechanical treatments
in order to
induce changes
in surface composition and features. The treatments
included gr
ind
ing and polish
ing, etch
ing
in aqueous hydrofluoric acid, and heat
ing
in nitrogen or air. The treated surfaces were characterized us
ing a variety of microscopy techniques to assess morphology. Surface chemistry and phase composition were determ
ined us
ing X-ray photoelectron and Raman spectroscopy, respectively. Stream
ing potential measurements evaluated surface charg
ing, and sessile water drop techniques assessed wett
ing behavior. These treatments yielded significant differences
in surface properties with isoelectric po
ints rang
ing from 2 to 5.6, and moderate to extremely hydrophilic water contact angles from ∼65° to ∼8°. This work provides a basis for future
in vitro and
in vivo studies which will exam
ine the effects of these treatments on important orthopaedic properties such as friction, wear, prote
in adsorption, bacteriostasis and osseo
integration.
Statement of Significance
Silicon nitride (Si3N4) exhibits a unique combination of bulk mechanical and surface chemical properties that make it an ideal biomaterial for orthopaedic implants. It is already being used for interbody spinal fusion cages and is being developed for total joint arthroplasty. Its surface texture and chemistry are both highly tunable, yielding physicochemical combinations that may lead to enhanced osseointegration and bacterial resistance without compromising bulk mechanical properties. This study demonstrates the ease with which significant changes to Si3N4’s surface phase composition, charging, and wetting behavior can be induced, and represents an initial step towards a mechanistic understanding of the interaction between implant surfaces and the biologic environment.