A petrographic investigation into the durability of common replacement sandstones to the crystallisation of de-icing salts

Scottish sandstone buildings are now suffering the long-term effects of salt-crystallisation damage, owing in part to the repeated deposition of de-icing salts during winter months. The use of de-icing salts is necessary in order to maintain safe road and pavement conditions during cold weather, but their use comes at a price. Sodium chloride (NaCl), which is used as the primary de-icing salt throughout the country, is a salt known to be damaging to sandstone masonry. However, there remains a range of alternative, commercially available de-icing salts. It is unknown however, what effect these salts have on porous building materials, such as sandstone. In order to protect our built heritage against salt-induced decay, it is vital to understand the effects of these different salts on the range of sandstone types that we see within the historic buildings of Scotland. Eleven common types of sandstone were characterised using a suite of methods in order to understand their mineralogy, pore structure and their response to moisture movement, which are vital properties that govern a stone’s response to weathering and decay. Sandstones were then placed through a range of durability tests designed to measure their resistance to various weathering processes. Three salt crystallisation tests were undertaken on the sandstones over a range of 16 to 50 cycles, which tested their durability to NaCl, CaCl2, MgCl2 and a chloride blend salt. Samples were primarily analysed by measuring their dry weight loss after each cycle, visually after each cycle and by other complimentary methods in order to understand their changing response to moisture uptake after salt treatment. Salt crystallisation was identified as the primary mechanism of decay across each salt, with the extent of damage in each sandstone influenced by environmental conditions and pore-grain properties of the stone. Damage recorded in salt crystallisation tests was ultimately caused by the generation of high crystallisation pressures within the confined pore networks of each stone. Stone and test-specific parameters controlled the location and magnitude of damage, with the amount of micro-pores, their spatial distribution, the water absorption coefficient and the drying efficiency of each stone being identified as the most important stone-specific properties influencing salt-induced decay. Strong correlations were found between the dry weight loss of NaCl treated samples and the proportion of pores <1µm in diameter. Crystallisation pressures are known to scale inversely with pore size, while the spatial distribution of these micro-pores is thought to influence the rate, overall extent and type of decay within the stone by concentrating crystallisation pressures in specific regions of the stone. The water absorption determines the total amount of moisture entering into the stone, which represents the total amount of void space for salt crystallisation. The drying parameters on the other hand, ultimately control the distribution of salt crystallisation. Those stones that were characterised by a combination of a high proportion of micro-pores, high water absorption values and slow drying kinetics were shown to be most vulnerable to NaCl-induced decay. CaCl2 and MgCl2 are shown to have similar crystallisation behaviour, forming thin crystalline sheets under low relative humidity and/or high temperature conditions. Distinct differences in their behaviour that are influenced by test specific criteria were identified. The location of MgCl2 crystallisation close to the stone surface, as influenced by prolonged drying under moderate temperature drying conditions, was identified as the main factor that caused substantial dry weight loss in specific stone types. CaCl2 solutions remained unaffected under these conditions and only crystallised under high temperatures. Homogeneous crystallisation of CaCl2 throughout the stone produced greater internal change, with little dry weight loss recorded. NaCl formed distinctive isometric hopper crystals that caused damage through the non-equilibrium growth of salts in trapped regions of the stone. Damage was sustained as granular decay and contour scaling across most stone types. The pore network and hydric properties of the stones continually evolve in response to salt crystallisation, creating a dynamic system whereby the initial, known properties of clean quarried stone will not continually govern the processes of salt crystallisation, nor indeed can they continually predict the behaviour of stone to salt-induced decay.

Using induced pluripotent stem cells (IPSCS) as a replacement for in vivo models to screen novel therapies in chronic myeloid leukaemia (CML)

Tyrpsine kinase inhibitors (TKIs) effectively target progenitors and mature leukaemic cells but prove less effective at eliminating leukaemic stem cells (LSCs) in patients with chronic myeloid leukaemia (CML). Several reports indicate that the TGFβ superfamily pathway is important for LSC survival and quiescence. We conducted extensive microarray analyses to compare expression patterns in normal haemopoietic stem cells (HSC) and progenitors with CML LSC and progenitor populations in chronic phase (CP), accelerated phase (AP) and blast crisis (BC) CML. The BMP/SMAD pathway and downstream signalling molecules were identified as significantly deregulated in all three phases of CML. The changes observed could potentiate altered autocrine signalling, as BMP2, BMP4 (p<0.05), and ACTIVIN A (p<0.001) were all down regulated, whereas BMP7, BMP10 and TGFβ (p<0.05) were up regulated in CP. This was accompanied by up regulation of BMPRI (p<0.05) and downstream SMADs (p<0.005). Interestingly, as CML progressed, the profile altered, with BC patients showing significant over-expression of ACTIVIN A and its receptor ACVR1C. To further characterise the BMP pathway and identify potential candidate biomarkers within a larger cohort, expression analysis of 42 genes in 60 newly diagnosed CP CML patient samples, enrolled on a phase III clinical trial (www.spirit-cml.org) with greater than 12 months follow-up data on their response to TKI was performed. Analysis revealed that the pathway was highly deregulated, with no clear distinction when patients were stratified into good, intermediate and poor response to treatment. One of the major issues in developing new treatments to target LSCs is the ability to test small molecule inhibitors effectively as it is difficult to obtain sufficient LSCs from primary patient material. Using reprogramming technologies, we generated induced pluripotent stem cells (iPSCs) from CP CML patients and normal donors. CML- and normal-derived iPSCs were differentiated along the mesodermal axis to generate haemopoietic and endothelial precursors (haemangioblasts). IPSC-derived haemangioblasts exhibited sensitivity to TKI treatment with increased apoptosis and reduction in the phosphorylation of downstream target proteins. 4 Dual inhibition studies were performed using BMP pathway inhibitors in combination with TKI on CML cell lines, primary cells and patient derived iPSCs. Results indicate that they act synergistically to target CML cells both in the presence and absence of BMP4 ligand. Inhibition resulted in decreased proliferation, irreversible cell cycle arrest, increased apoptosis, reduced haemopoietic colony formation, altered gene expression pattern, reduction in self-renewal and a significant reduction in the phosphorylation of downstream target proteins. These changes offer a therapeutic window in CML, with intervention using BMP inhibitors in combination with TKI having the potential to prevent LSC self-renewal and improve outcome for patients. By successfully developing and validating iPSCs for CML drug screening we hope to substantially reduce the reliance on animal models for early preclinical drug screening in leukaemia.