Magnesium and Calcium-Containing Scaffolds for Bone Tissue Regeneration

Bone is a living tissue that constantly remodels and adapts to the stresses imposed upon it. Bone disorders are of growing concern as the median age of our population rises. Healing and recovery from fractures requires bone cells to have a 3-dimensional (3D) structural base, or scaffold, to grow out from. In addition to providing mechanical support, the scaffold, an extracellular matrix (ECM) assembly, enables the transport of nutrients and oxygen in and removal of waste materials from cells that are growing into new tissue. In this research, a 3D scaffold was synthesized with chitosan (CS), carboxymethyl chitosan (CMC), calcium phosphate monobasic and magnesium oxide (MgO). CS is a positiviely-charged natural bioactive polymer. It is combined with its negatively-charged derivative, CMC, to form a complex scaffold. Magnesium phosphate biocement (MgP), formed by reacting calcium phosphate monobasic and MgO, was incorporated into CMC solution before adding CS solution. Scaffolds were prepared by casting, freezing and lyophilization. The scaffolds were characterized in terms of pore microstructures, surface topography, water uptake and retention abilities, and crystal structure. The results show that the developed scaffolds exhibit highly interconnected pores and present the ideal pore size range (100–300 μm) to be morphometrically suitable for the proposed bone tissue engineering applications. These scaffolds not only mimic the nanostructured architecture and the chemical composition of natural bone tissue matrices but also serve as a source for soluble ions of magnesium (Mg++) and calcium (Ca++) that are favorable to osteoblast cells. The scaffolds thus provide a desirable microenvironment to facilitate biomineralization. These observations provide a new effective approach for preparing scaffold materials suitable for bone tissue engineering.

Salt-Resistant Alpha-Helical Cationic Antimicrobial Peptides

ABSTRACT Analogues based on the insect cecropin–bee melittin hybrid peptide (CEME) were studied and analyzed for activity and salt resistance. The new variants were designed to have an increase in amphipathic α-helical content (CP29 and CP26) and in overall positive charge (CP26). The α-helicity of these peptides was demonstrated by circular dichroism spectroscopy in the presence of liposomes. CP29 was shown to have activity against gram-negative bacteria that was similar to or better than those of the parent peptides, and CP26 had similar activity. CP29 had cytoplasmic membrane permeabilization activity, as assessed by the unmasking of cytoplasmic β-galactosidase, similar to that of CEME and its more positively charged derivative named CEMA, whereas CP26 was substantially less effective. The activity of the peptides was not greatly attenuated by an uncoupler of membrane potential, carbonyl cyanide-m-chlorophenylhydrazone. The tryptophan residue in position 2 was shown to be necessary for interaction with cell membranes, as demonstrated by a complete lack of activity in the peptide CP208. Peptides CP29, CEME, and CEMA were resistant to antagonism by 0.1 to 0.3 M NaCl; however, CP26 was resistant to antagonism only by up to 160 mM NaCl. The peptides were generally more antagonized by 3 and 5 mM Mg2+ and by the polyanion alginate. It appeared that the positively charged C terminus in CP26 altered its ability to permeabilize the cytoplasmic membrane of Escherichia coli, although CP26 maintained its ability to kill gram-negative bacteria. These peptides are potential candidates for future therapeutic drugs.

Excess tachycardia: heart rate after antimuscarinic agents in conscious dogs

In conscious dogs the heart rate after atropine is higher than after bilateral vagotomy; we have termed the additional heart rate with atropine "excess tachycardia" (ET). In six dogs the cervical vagosympathetic trunks were exteriorized in skin tubes, and arterial and venous catheters were chronically implanted. Atropine sulfate (0.1 mg/kg iv) injected during cold blockade of the vagi increased the heart rate by only 6 +/- 4 (SE) beats/min (NS) but rewarming the vagi in five of the six dogs after atropine resulted in an additional heart rate increase (ET) of 26 +/- 6 beats/min (P less than 0.005). The ET (41 +/- 11 beats/min) tended to be larger when the animals were pretreated with 1 mg/kg propranolol (P = 0.09). Similar results were obtained when atropine methylbromide, a charged derivative of atropine sulfate, or glycopyrrolate, a synthetic antimuscarinic agent, was substituted for atropine sulfate (ET: 51 +/- 6 and 51 +/- 16 beats/min, respectively). Raising the arterial blood pressure with phenylephrine increased the heart rate further; lowering the blood pressure with sodium nitroprusside attenuated or abolished the ET. Our results show that ET is produced by antimuscarinic agents in general and is not mediated by the beta-adrenergic system. Furthermore, ET is present only when the cervical vagi are intact, probably because ET is mediated by cholinergic vagal efferent fibers via a mechanism that has not yet been recognized in cardiac rate control.

Paper 3: Turbo-Charged Diesel Engines in Production

This paper describes some of the practical problems encountered and the resolutions applied during the design and development of a turbo-charged derivative of a production engine. Some further problems are described which were met when the prototype designs were manufactured in the production area. A very brief summary of the reasons for turbo-charging, and the performance results, are also included. The base engine was a 6-litre direct injection dry-linered diesel engine with a rated speed of 2800 rev/min in its naturally aspirated form, used for commercial vehicle propulsion plus industrial and marine purposes.