Laser sintering of nano-hydroxyapatite coated polyamide 12 powders

As part of a larger study on the laser sintering (LS) of nano-composite structures for biomedical applications, a wet mixing method was used to coat Polyamide 12 (PA12) particles with nano-hydroxyapatite (nHA). The addition of nHA significantly affected powder processability due to laser absorption and heat transfer effects which led to part warping. This phenomenon has not been reported in other studies investigating LS of polymer/HA and nHA powders. Nano-composites containing 0.5–1.5 wt% nHA were successfully produced and tensile testing showed that 0.5 wt% nHA provided the greatest reinforcement with a 20% and 15% increase in modulus and strength respectively. However, the elongation at break had significantly declined which was likely due to the formation of nHA aggregates at the sintering borders following the processing of the coated powders despite being initially well dispersed on the particle surface

Effect of Q-switched laser surface texturing of titanium on osteoblast cell response

Titanium and its alloys are important biomedical materials. It is known that the surface texture of implanted medical devices affects cell response. Control of cell response has the potential to enhance fixation of implants into bone and, in other applications, to prevent undesired cell adhesion. The potential use of a 100W Q-switched YAG laser miller (DMG Lasertec 60 HSC) for texturing titanium is investigated. A series of regular features with dimensions of the order of tens of micrometers are generated in the surface of titanium samples and the cell response to these features is determined. Characterisation of the laser milled features reveals features with a lengthscale of a few microns superposed on the larger scale structures, this is attributed to resolidification of molten droplets generated and propelled over the surface by individual laser pulses. The laser textured samples are exposed to osteoblast cells and it is seen that cells do respond to the features in the laser textured surfaces

Transient serum exposure regimes to support dual differentiation of human mesenchymal stem cells

Human mesenchymal stem cells (MSCs), which can generate both osteoblasts and chondrocytes, represent an ideal resource for orthopaedic repair using tissue-engineering approaches. One major difficulty for the development of osteochondral constructs using undifferentiated MSCs is that serum is typically used in culture protocols to promote differentiation of the osteogenic component, whereas existing chondrogenic differentiation protocols rely on the use of serum-free conditions. In order to define conditions which could be compatible with both chondrogenic and osteogenic differentiation in a single bioreactor, we have analysed the efficiency of new biphasic differentiation regimes based on transient serum exposure followed by serum-free treatment. MSC differentiation was assessed either in serum-free medium or with a range of transient exposure to serum, and compared to continuous serum-containing treatment. Although osteogenic differentation was not supported in the complete absence of serum, marker expression and extensive mineralization analyses established that 5 days of transient exposure triggered a level of differentiation comparable to that observed when serum was present throughout. This initial phase of serum exposure was further shown to support the successful chondrogenic differentiation of MSCs, comparable to controls maintained in serum-free conditions throughout. This study indicates that a culture based on temporal serum exposure followed by serum-free treatment is compatible with both osteogenic and chondrogenic differentiation of MSCs. These results will allow the development of novel strategies for osteochondral tissue engineering approaches using MSCs for regenerative medicine

Effect of Q-switched laser surface texturing of titanium on osteoblast cell response

Titanium and its alloys are important biomedical materials. It is known that the surface texture of implanted medical devices affects cell response. Control of cell response has the potential to enhance fixation of implants into bone and, in other applications, to prevent undesired cell adhesion. The potential use of a 100W Q-switched YAG laser miller (DMG Lasertec 60 HSC) for texturing titanium is investigated. A series of regular features with dimensions of the order of tens of micrometers are generated in the surface of titanium samples and the cell response to these features is determined. Characterisation of the laser milled features reveals features with a lengthscale of a few microns superposed on the larger scale structures, this is attributed to resolidification of molten droplets generated and propelled over the surface by individual laser pulses. The laser textured samples are exposed to osteoblast cells and it is seen that cells do respond to the features in the laser textured surfaces

Functional performance of a bi-layered chitosan-nano-hydroxyapatite osteochondral scaffold: a pre-clinical <i>in vitro</i> tribological study

Osteochondral grafts are used for repair of focal osteochondral lesions. Autologous grafts are the gold standard treatment; however, limited graft availability and donor site morbidity restrict use. Therefore, there is a clinical need for different graft sources/materials which replicate natural cartilage function. Chitosan has been proposed for this application. The aim of this study was to assess the biomechanics and biotribology of a bioresorbable chitosan/chitosan-nano-hydroxyapatite osteochondral construct (OCC), implanted in an in vitro porcine knee experimental simulation model. The OCC implanted in different surgical positions (flush, proud and inverted) was compared to predicate grafts in current clinical use and a positive control consisting of a stainless steel graft implanted proud of the cartilage surface. After 3 h (10 800 cycles) wear simulation under a walking gait, subsidence occurred in all OCC samples irrespective of surgical positioning, but with no apparent loss of material and low meniscus wear. Half the predicate grafts exhibited delamination and scratching of the cartilage surfaces. No graft subsidence occurred in the positive controls but wear and deformation of the meniscus were apparent. Implanting a new chitosan-based OCC either optimally (flush), inverted or proud of the cartilage surface resulted in minimal wear, damage and deformation of the meniscus

Scanning electron microscopy of biomaterials

A comparison of conventional high vacuum scanning electron microscopy (HVSEM), environmental SEM (ESEM) and confocal laser scanning microscopy (CLSM) in the assessment of cell-material interactions is made. The processing of cells cultured for conventional HVSEM leads to the loss of morphological features that are retained when using ESEM. The use of ESEM in conjunction with CLSM of the labeled cytoskeleton gives an indication of changes to the cell morphology as a consequence of incubation time and substrate surface features

Osteoblast responses to collagen PVA bioartificial polymers in vitro: the effects of crosslinking method and collagen content

A range of 'bioartificial' collagen/poly(vinyl alcohol) blends have been produced, cast as films and cross-linked using either glutaraldehyde or a dehydrothermal treatment (DHT). Films were used as substrates for the culture of osteoblast-like cells. The attachment, adhesion and proliferative responses of these cells to the range of films were examined using proliferation assays, light, electron and confocal microscopy. There was an inverse relationship between collagen content of gluataraldehyde cross-linked films and the extent of cell proliferation on them. A cytotoxicity assay demonstrated no toxic effect related to increasing collagen content. The greatest differences in cell responses observed were associated with the choice of cross-linking method. Films cross-linked with glutaraldehyde showed variation related to collagen content in cell adhesion, proliferation and morphology. Such differences were not apparent with the DHT cross-linked films. Collagen/PVA 'bioartificial' films can be dehydrothermally cross-linked to increase biological stability and reduce water solubility. The method of cross-linking employed is the greater influence in determining osteoblast compatibility with these materials. The DHT cross-linking method is a preferable alternative to the use of glutaraldehyde. Collagen/PVA bioartificial films cross-linked by the DHT method have shown potential for biocompatibility with osteoblasts. A range of `bioartificial' collagen/poly(vinyl alcohol) blends have produced, cast as using been films and cross-linked either glutaraldehyde or a dehydrothermal treatment (DHT). Films were used as substrates for the culture of osteoblast-like cells. The attachment, adhesion and proliferative responses of these cells to the range of films were examined using proliferation assays, light, electron and confocal microscopy. There was an inverse relationship between collagen content of glutaraldehyde cross-linked films and the extent of cell proliferation on them. A cytotoxicity assay demonstrated no toxic effect related to increasing collagen content. The greatest differences in cell responses observed were associated with the choice of cross-linking method. Films cross-linked with glutaraldehyde showed variation related to collagen content in cell adhesion, proliferation and morphology. Such differences were not apparent with the DHT cross-linked films. Collagen/PVA `bioartificial' films can be dehydrothermally cross-linked to increase biological stability and reduce water solubility. The method of cross-linking employed is the greater influence in determining osteoblast compatibility with these materials. The DHT cross-linking method is a preferable alternative to the use of glutaraldehyde. Collagen/PVA bioartificial films cross-linked by the DHT method have shown potential for biocompatibility with osteoblasts