Process, challenges modifications

In essence, the basic steps of making cell blocks consist of fixation, centrifugation to make cell pellet, transfer the pellet to a labeled tissue cassette which then is processed and embedded in paraffin. The most challenging component of this technique is the methods to harden the cell pellet so it can be easily picked up from the tube without losing precious material. With only a simple sedimentation technique, the cell pellet is usually small and friable. In order to harden the cell pellet, several technical modifications have been reported. The most popular methodology includes plasma-thrombin clot technique, agar technique, and fixation with Bouin s solution. 

The synthesis of catalytic photocathodes for H2 evolution provides evidence that deliberate surface modification can significantly improve the overall efficiency. However, the synthesis of rugged, very active catalytic surfaces remains a challenge. The results so far establish that it is possible, by rational means, to synthesize a desired photosensitive interface and to prove the gross structure. Continued improvements in photoelectrochemical H2 evolution efficiently can be expected, while new surface catalysts are needed for N2 and CO2 reduction processes. 

The control of kinetic vs thermodynamic product formation can often be achieved by suitable modification of reaction conditions. A far more difficult task is to switch from the formation of a favoured major product to a disfavoured minor product, especially when the transition states for the two processes share most features in common. This challenge has been met by antibodies with considerable success, both for reaction pathways differing in regioselectivity and also for ones differing in stereoselectivity. In both situations, control of entropy in the transition state must hold the key. 

---