Failure of a constrained acetabular liner without reinforcement ring disruption.

Several risk factors for dislocation after total hip arthroplasty (THA) have been identified including operative-, patient-, and implant-related factors. The following case report describes the dislocation of a revision THA without disruption of the constrained liner or containment ring. The possible mechanisms leading to this type of failure include lever-out impingement and poor abductor function, or tension secondary to prior surgery. Dislocation without disruption of containment ring has not been described for the Pinnacle Acetabular Cup with the Enhanced Stability Constrained Liner (DePuy Orthopaedics, Warsaw, Indiana).

Stop-flow lithography for the production of shape-evolving degradable microgel particles.

Microgel particles capable of bulk degradation have been synthesized from a solution of diacrylated triblock copolymer composed of poly(ethylene glycol) and poly(lactic acid) in a microfluidic device using stop-flow lithography (SFL). It has been previously demonstrated that SFL can be used to fabricate particles with precise control over particle size and shape. Here, we have fabricated hydrogel particles of varying size and shape and examined their mass-loss and swelling behavior histologically and mechanically. We report that these features, as well as degradation behavior of the hydrogel particles may be tailored with SFL. By reducing the applied UV dose during fabrication, hydrogel particles can be made to exhibit a distinct deviation from the classical erosion profiles of bulk-degrading hydrogels. At higher UV doses, a saturation in cross-linking density occurs and bulk-degrading behavior is observed. Finally, we synthesized multifunctional composite particles, providing unique features not found in homogeneous hydrogels.

Cell-based therapies and tissue engineering.

Tissue engineering is a rapidly evolving discipline that may some-day afford surgeons a limitless supply of autologous tissue for transplantation or allow in situ tissue regeneration. A number of biologic, engineering, and clinical challenges continue to face tissue engineers and surgeons alike. One important example is the choice of an appropriate cell scaffold that promotes growth and is eventually resorbed by the body. Although the application of bioengineered tissue is specific to the anatomic areas of interest,continued advances bring tissue engineering closer to reality in all areas of otolaryngology.

Incorporation of tissue-specific molecules alters chondrocyte metabolism and gene expression in photocrosslinked hydrogels.

Hydrogels are highly swollen, insoluble networks which can entrap chondrocytes and provide a 3-D environment necessary for the re-growth of cartilaginous tissue. In this study, hydrogels were formulated with a synthetic poly(ethylene glycol) (PEG) component to provide control over the macroscopic gel properties and from a cartilage specific compound, chondroitin sulfate (ChSA), to capture features of the chondrocytes' native environment. PEG was chosen as the base hydrogel chemistry, because it forms a 3-D environment that maintains chondrocyte function. ChSA, a highly negatively charged main component of proteoglycans, was then selectively incorporated into the PEG gel. Macroscopic gel properties were manipulated to obtain high compressive moduli coupled with a high degree of swelling by formulating copolymer gels with these chemistries. The gel compressive modulus of cell-free PEG gels increased from 34 to 140 kPa with the incorporation of ChSA for similar degrees of swelling. When chondrocytes were encapsulated in pure ChSA gels, synthesis of collagen and glycosaminoglycans was inhibited. However, when PEG was introduced into the copolymer gels, both extracellular matrix components were stimulated. Total collagen content increased from non-detectable in the pure ChSA gels to 0.48+/-0.05 mg/g wet weight in the copolymer gels (40/60 ChSA/PEG). Gene expression for collagen type II was also enhanced by the incorporation of PEG into the gel, illustrating an important influence of gel chemistry on chondrocyte function; however, aggrecan gene expression was unaffected. This study demonstrates that the macroscopic properties of chondrocyte gel carriers can be controlled through the incorporation of charge into networks by ChSA, but the neutral, non-interactive base PEG chemistry facilitates extracellular matrix deposition.