Macromolecular crowding (MMC) is a biophysical phenomenon that accelerates thermodynamic activities and biological processes by several orders of magnitude. Herein, we ventured to identify the optimal crowder and to assess the influence of MMC in umbilical cord mesenchymal stem cell. 7 types of carrageenan (κ&λ, κ-LV1, κ-LV2, λ-MV, λ-HV, ι-MV, ι-HV) acted as crowder and biophysical properties were assessed respectively. Human umbilical cord mesenchymal stem cells were seeded at 15,000 cells/cm² in 24 well plates and allowed to attach for 24 h. Subsequently, the medium was changed to medium with 7 types of carrageenan (10, 50, 100, 500 μg/ml) and 100 μM L-ascorbic acid phosphate (Sigma Aldrich). Medium without carrageenan was used as control. Cell morphology and SDS-PAGE analysis were conducted after 3, 5 and 7 days. Biophysical assessment showed 7 types of carrageenan have increased particle size with concentration, good polydispersity and negative charges. SDS-PAGE and densitometric analyses revealed significant increase (p < 0.001) in collagen deposition in the presence of 10 μg/ml carrageenan λ and ι at all the time points. SDS-PAGE and densitometric analysis also showed that the highest collagen deposition was observed in culture at 50 μg/ml carrageenan λ. No significant difference was observed in cell morphology between the groups. Collectively, these data primarily illustrate the beneficial effect of carrageenan λ in human umbilical cord mesenchymal stem cell culture.

The goal of total knee arthroplasty (TKA) is to relieve pain and restore the function of the knee joint. Recently the number of TKA cases in Korea has increased considerably with increase in elderly population and change in life style. Accordingly, demand for TKA design that is capable of better accommodating anatomical dimensions and life styles of Koreans is also on the rise. During the prototype design process for the Korean-TKA, different stem and keel designs of the tibial base plate have been attempted to improve fixation and longevity of the implant. In this study, we conducted a biomechanical analysis of the tibial base plate using finite element analysis (FEA). Specifically, biomechanical effects of insert positioning in the tibia were assessed to investigate the likelihood of tibial fracture and implant loosening due to mal-positioning of the implant.

A 3-D finite element(FE) models of the left femur, patella, and tibia were developed from computed tomography (CT) scan data (a normal Korean male, 27 years of age, 70 kg). 2-D truss elements were chosen to represent ligamentous structures such as lateral & medial collateral ligament, posterior cruciate ligament, patella tendon and patella ligament. Nonlinear elastic materal properties for the soft-tissue structures were also adopted from literatures. The surgical model was then constructed after inserting Korean-TKA prototype in the intact model. Here, the implant was the posterior cruciate ligament retaining type (CR) with the fixed bearing system. To simulate loading on the knee joint in heel strike and toe off positions, 15° and 45° flexions of the femur orientation were simulated under the compressive load of 3.8 and 5.7 times of body weight (BW= 700N), respectively, in a uniform pressure at the horizontal section of the femur. The tibia was assumed to be completely constrained. The surgical position of the tibial insert was varied from the center either to the medial or to the lateral direction by 3-mm. The peak von mises stresses (PVMS) at the stem and the keel regions of the tibial insert were assessed.

With respect to the central positioning the lateral shift of the tibial plate resulted in higher PVMS than the medial. Particularly, increases of 24.5 %, 29.8%, and 28.4% were observed at the stem, the lateral keel, and the medial keel, respectively, due to lateral mal-positioning of the implant. With the medial shift, on the other hand, PVMS increase remained at around 6% level at the stem and the lateral keel. A decrease of 4.5 % was noted at the medial keel region.

In this study, a computational approach was used to evaluate biomechanical effect of tibial plate positioning on the stress distribution within the implant. The lateral mal-positioning showed more stress concentration than the medial. This may be due to the fact that body weight is transmitted more to the lateral portion of the tibia (5.5:4.5) that is smaller and thinner than its counterpart. These results suggest that the lateral deviation of the implant can be more likely cause TKR loosening and tibial fracture.