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We studied the tissue growth dynamics for tissue-engineered cartilage at the early growth stage after cell seeding for four weeks using sodium triple-quantum coherence NMR spectroscopy. The following tissue-engineering constructs were studied: 1. Bovine chondrocytes cultured in alginate beads, 2. Bovine chondrocytes cultured as pellets (scaffold-free chondrocyte pellets), 3. Human Marrow Stromal Cells (HMSC) seeded in Collagen/Chitosan based scaffolds of chondrogenic extracellular matrix environment expecting chondrogenic differentiation, named as biomimetic scaffolds. We found that the sodium triple quantum coherence spectroscopy can differentiate between different tissue-engineering constructs and the native tissues based on the fast and the slow relaxation rates as well as based on the average quadrupolar coupling. Both the fast (Tf) and the slow (Ts) relaxation times were found to be longer in the chondrocyte pellets and the biomimetic scaffolds as compared to the chondrocytes suspended in alginate beads and the human articular cartilage tissues. In all cases, it was found that the relaxation rates and the motion of sodium ions, as measured from correlation time, were dependent on the amount of macromolecules, high cell density and the anisotropy of the cartilage tissue engineering constructs. Average quadrupolar couplings were found to be lower in the engineered tissue as compared to the native tissues, presumably due to the lack of order in collagen accumulated in the engineered tissue. These results indicate the use of sodium triple quantum coherence spectroscopy as a tool to investigate anisotropy and growth dynamics of cartilage tissue engineered constructs in a simple and reliable way.

The spin lattice relaxation of I=3/2 quadrupolar spin system due to domain walls in order-disorder ferroelectrics has been studied and a general method is proposed for the measurement of domain width in nano ferroelectrics. Based on the fact that electric polarization undergoes spiral orientation as one moves from one domain to the other, it is assumed that at low temperatures the spins at and near domain walls undergo relaxation due to possible easy reorientation of electric polarization in domain walls even though such a relaxation in the main body of the domain has almost ceased. The spins present inside the domain undergo relaxation through transfer of magnetization to the domain walls through a spin diffusion process by nearest neighbour interaction. Rate equations for spin populations are formed by representing the ferroelectric domain by a one-dimensional chain of equidistant spins having dipolar coupling. Spin populations are calculated as a function of time for different ratios of quadrupolar to dipolar transition probabilities for a sample subjected to selective rf pulse. Expression for spin- lattice relaxation time T1 is derived in terms of domain width and ratio of quadrupolar to dipolar transition probabilities. It is found that the domain width can be estimated provided the value of spin lattice relaxation time T1 is known for the corresponding crystal with normal sized grains. The results are quite general and can be applied to any order disorder ferroelectric with nano sized domains and having spin I=3/2 nuclei., 31 pages, 5 figures, 1 table