Papers by Author: Ross Crawford

Abstract: Polymer microspheres loaded with bioactive particles, biomolecules, proteins, and/or growth factors play important roles in tissue engineering, drug delivery, and cell therapy. The conventional double emulsion method and a new method of electrospraying into liquid nitrogen were used to prepare bovine serum albumin (BAS)-loaded poly(lactic-co-glycolic acid) (PLGA) porous microspheres. The particle size, the surface morphology and the internal porous structure of the microspheres were observed using scanning electron microscopy (SEM). The loading efficiency, the encapsulation efficiency, and the release profile of the BSA-loaded PLGA microspheres were measured and studied. It was shown that the microspheres from double emulsion had smaller particle sizes (3-50 m), a less porous structure, a poor loading efficiency (5.2 %), and a poor encapsulation efficiency (43.5%). However, the microspheres from the electrospraying into liquid nitrogen had larger particle sizes (400-600 m), a highly porous structure, a high loading efficiency (12.2%), and a high encapsulation efficiency (93.8%). Thus the combination of electrospraying with freezing in liquid nitrogen and subsequent freeze drying represented a suitable way to produce polymer microspheres for effective loading and sustained release of proteins.

Abstract: The limitations of autogenic, allogenic and xenogenic grafting methods have led to the development of synthetic grafts as an alternative. The aim of this study was to manufacture highly porous and well interconnected hydroxyapatite scaffolds and modify them with a poly(lactic-co-glycolic acid) (PLGA)-bioactive glass composite coating to achieve mechanical properties close to those of natural cancellous bones. In this study, hydroxyapatite scaffolds were prepared from a calcium phosphate cement (CPC) powder and cell culture using fibroblast cells was done to examine the cytotoxicity of the materials used for the scaffolds. The average pore size of the scaffolds was found to be 650μm and the total porosity was about 80%. The hydroxyapatite scaffolds without the coating had a mean compressive strength and a mean compressive modulus of 0.74 MPa and 20.46 MPa, respectively, which were in contrast to those of the scaffolds coated with the PLGA-bioacitve glass composite material (1.36 MPa and 24.58 MPa, respectively). The fibroblast cells were observed to proliferate well on the PLGA-bioactive glass coated scaffolds. The cells had also penetrated into the scaffold to a depth of approximately 2mm. Thus the scaffolds fabricated in this study exhibited a favourable porous structure and good cell response which are desirable for bone tissue engineering.

Abstract: It has been recently established that mechanical indentation does not sufficiently discriminate between normal and degraded articular cartilage. Consequently, we have carried out preliminary research to develop and evaluate a number of indices and parameters that can characterise and categorise the tissue into viable and degraded types relative to functional integrity. In this paper, we report the outcome of correlation studies between the instantaneous structural rebound following unloading from a known level of indentation and reflected ultrasound signals, analysed in the frequency domain. We subjected 137 samples from 10 normal and 10 osteoarthritic joints to ultrasound waves and mechanical indentation-rebound tests, and determined the degree of correlation between the instantaneous rebound and the principal components of the ultrasound spectra and further investigated this using canonical discriminate analysis that was fitted with a general linear model. Our results demonstrate a strong correlation between rebound and ultrasound results, leading to the conclusion that it is possible to determine the mechanical and structural viability of articular cartilage using non-contact methods.

Abstract: Cell-based therapy is one of the major potential therapeutic strategies for cardiovascular, neuronal and degenerative diseases in recent years. The aims of this study is to develop a novel biomimic polymeric materials which will facilitate the delivery cells, control cell bioactivities and enhance the focal integration of graft cells with host tissues. We synthesized a novel tri-block copolymer, methoxy-terminated poly (ethylene glycol) (MPEG)-polyL-lactide (PLLA)-polylysine (PLL) via sequential polymerization of PLLA onto MPEG, followed by ring opening polymerization of PLL onto the functionalized chain end. The triblock copolymer (5%) was then mixed with high molecular weight PLLA (95%) to form cell-delivery membranes. The spectra of copolymers were determined by NMR and ATR-FTIR spectroscopy. Human osteoblasts were used for testing biocompatibility and initial cellular reaction. It was noted that no cytotoxicity was detectable in our synthesized copolymers. Compared with pure PLLA and diblock copolymers, the triblock copolymers showed significantly better cell adhesion and proliferation. Interestingly we identified that cellular activity (attachment, proliferation and differentiation) could be regulated by the molecular weight and composition of the triblock copolymers. In conclusion controllable synthetic copolymers can be designed and synthesized to modulate cellular function in facilitating tissue repair and regeneration.