Ambiphilicity of ring-expanded N-heterocyclic carbenes.

N-heterocyclic carbenes, such as imidazole-2-ylidenes and imidazolin-2-ylidenes, the popular class of singlet carbenes introduced by Arduengo in 1991 have not been shown to be ambiphilic owing to the two σ-withdrawing, π-donating amino groups flanking the carbene centre. However, our experimental data suggest that ring-expanded N-heterocyclic carbenes (RE-NHCs), especially the seven and eight membered rings, are significantly ambiphilic. Our results also show that the steric environment in RE-NHCs can become a determining factor for controlling the E-H bond activation.

The Synergistic Effects of Matrix Stiffness and Composition on the Response of Chondroprogenitor Cells in a 3D Precondensation Microenvironment.

Improve functional quality of cartilage tissue engineered from stem cells requires a better understanding of the functional evolution of native cartilage tissue. Therefore, a biosynthetic hydrogel was developed containing RGD, hyaluronic acid and/or type-I collagen conjugated to poly(ethylene glycol) acrylate to recapitulate the precondensation microenvironment of the developing limb. Conjugation of any combination of the three ligands did not alter the shear moduli or diffusion properties of the PEG hydrogels; thus, the influence of ligand composition on chondrogenesis could be investigated in the context of varying matrix stiffness. Gene expression of ligand receptors (CD44 and the b1-integrin) as well as markers of condensation (cell clustering and N-cadherin gene expression) and chondrogenesis (Col2a1 gene expression and sGAG production) by chondroprogenitor cells in this system were modulated by both matrix stiffness and ligand composition, with the highest gene expression occurring in softer hydrogels containing all three ligands. Cell proliferation in these 3D matrices for 7 d prior to chondrogenic induction increased the rate of sGAG production in a stiffness-dependent manner. This biosynthetic hydrogel supports the features of early limb-bud condensation and chondrogenesis and is a novel platform in which the influence of the matrix physicochemical properties on these processes can be elucidated.

A novel, minimally-invasive technique of cartilage repair in the human knee using arthroscopic microfracture and injections of mesenchymal stem cells and hyaluronic acid--a prospective comparative study on safety and short-term efficacy.

INTRODUCTION: Most current cell-based cartilage repair techniques require some form of scaffolds and 2 separate surgical procedures. We propose a novel, scaffold-less technique of cartilage repair in the human knee that combines arthroscopic microfracture and outpatient intra-articular injections of autologous bone marrow-derived mesenchymal stem cells (MSCs) and hyaluronic acid (HA). MATERIALS AND METHODS: Seventy matched (age, sex, lesion size) knees with symptomatic cartilage defects underwent cartilage repair with the proposed technique (n = 35) or an open technique (n = 35) in which the MSCs were implanted beneath a sutured periosteal patch over the defect. Prospective evaluation of both groups were performed using the International Cartilage Repair Society (ICRS) Cartilage Injury Evaluation Package, which included questions from the Short-Form (SF-36) Health Survey, International Knee Documentation Committee (IKDC) subjective knee evaluation form, Lysholm knee scale, and Tegner activity level scale. Postoperative magnetic resonance imaging (MRI) evaluation was also performed at 1 year for most patients. RESULTS: There were no clinically significant adverse events reported through the course of our study. At the fi nal follow-up (mean = 24.5 months), there was significant improvement in mean IKDC, Lysholm, SF-36 physical component score and visual analogue pain scores in both treatment groups. CONCLUSION: In the short term, the results of this novel technique are comparable to the open procedure with the added advantages of being minimally invasive and requiring only a single operation under general anaesthesia. Its safety has been validated and its efficacy is currently being evaluated in an ongoing randomised controlled trial.

Medium-term outcome of total hip replacement for dysplastic hips in Singapore.

PURPOSE: To review medium-term outcomes of 46 patients who underwent total hip replacement (THR) for osteoarthritis secondary to dysplastic hips. METHODS: Records of 58 hips in 6 men and 40 women aged 32 to 76 (mean, 62) years who underwent THR for osteoarthritis secondary to dysplastic hips and had been followed up for a mean of 4 (range, 2-8) years were retrospectively reviewed. The hips were classified according to the Crowe's grading, Sharp's acetabular angle, and centre-edge angle. The radiological uncoverage of acetabular cup (RUAC) index was calculated. The outcomes of THR were evaluated in terms of cup inclination, RUAC index, cup migration, lysis or loosening (radiolucency), heterotopic ossification, component incorporation and positioning, thigh pain, and subsidence. RESULTS: 51 of the hips were Crowe's type I, 6 were type II, and one was type IV. The mean acetabular angle was 46.3 degrees and the mean centre-edge angle was 15.4 degrees. The mean cup, head, and stem sizes were 50.4 mm, 28.7 mm, and 10.9 mm, respectively. The mean RUAC index was 16.9% and the mean cup inclination was 40.7 degrees. Radiolucency of 1 mm in the acetabular zone I was observed in 16 cases, but only one failed. For cemented and uncemented stems, the most common positioning was neutral and valgus, respectively. Five patients had complications of greater trochanter fracture, aseptic loosening, split calcar, stem loosening, and/or heterotopic ossification. CONCLUSION: Conventional THR can achieve good medium-term results in low-grade dysplastic hips.