Thiolene- and Polycaprolactone Methacrylate-Based Polymerized High Internal Phase Emulsion (PolyHIPE) Scaffolds for Tissue Engineering

Highly porous emulsion templated polymers (PolyHIPEs) provide a number of potential advantages in the fabrication of scaffolds for tissue engineering and regenerative medicine. Porosity enables cell ingrowth and nutrient diffusion within, as well as waste removal from, the scaffold. The properties offered by emulsion templating alone include the provision of high interconnected porosity, and, in combination with additive manufacturing, the opportunity to introduce controlled multiscale porosity to complex or custom structures. However, the majority of monomer systems reported for PolyHIPE preparation are unsuitable for clinical applications as they are nondegradable. Thiol-ene chemistry is a promising route to produce biodegradable photocurable PolyHIPEs for the fabrication of scaffolds using conventional or additive manufacturing methods; however, relatively little research has been reported on this approach. This study reports the groundwork to fabricate thiol- and polycaprolactone (PCL)-based PolyHIPE materials via a photoinitiated thiolene click reaction. Two different formulations, either three-arm PCL methacrylate (3PCLMA) or four-arm PCL methacrylate (4PCLMA) moieties, were used in the PolyHIPE formulation. Biocompatibility of the PolyHIPEs was investigated using human dermal fibroblasts (HDFs) and human osteosarcoma cell line (MG-63) by DNA quantification assay, and developed PolyHIPEs were shown to be capable of supporting cell attachment and viability.

Osteogenic Peptides and Attachment Methods Determine Tissue Regeneration in Modified Bone Graft Substitutes

The inclusion of biofunctional molecules with synthetic bone graft substitutes has the potential to enhance tissue regeneration during treatment of traumatic bone injuries. The clinical use of growth factors has though been associated with complications, some serious. The use of smaller, active peptides has the potential to overcome these problems and provide a cost-effective, safe route for the manufacture of enhanced bone graft substitutes. This review considers the design of peptide-enhanced bone graft substitutes, and how peptide selection and attachment method determine clinical efficacy. It was determined that covalent attachment may reduce the known risks associated with growth factor-loaded bone graft substitutes, providing a predictable tissue response and greater clinical efficacy. Peptide choice was found to be critical, but even within recognised families of biologically active peptides, the configurations that appeared to most closely mimic the biological molecules involved in natural bone healing processes were most potent. It was concluded that rational, evidence-based design of peptide-enhanced bone graft substitutes offers a pathway to clinical maturity in this highly promising field.

Reinforcement of poly-l-lactic acid electrospun membranes with strontium borosilicate bioactive glasses for bone tissue engineering

Herein, for the first time, we combined poly-l-lactic acid (PLLA) with a strontium borosilicate bioactive glass (BBG-Sr) using electrospinning to fabricate a composite bioactive PLLA membrane loaded with 10% (w/w) of BBG-Sr glass particles (PLLA-BBG-Sr). The composites were characterised by scanning electron microscopy (SEM) and microcomputer tomography (μ-CT), and the results showed that we successfully fabricated smooth and uniform fibres (1-3μm in width) with a homogeneous distribution of BBG-Sr microparticles (<45μm). Degradation studies (in phosphate buffered saline) demonstrated that the incorporation of BBG-Sr glass particles into the PLLA membranes increased their degradability and water uptake with a continuous release of cations. The addition of BBG-Sr glass particles enhanced the membrane's mechanical properties (69% higher Young modulus and 36% higher tensile strength). Furthermore, cellular in vitro evaluation using bone marrow-derived mesenchymal stem cells (BM-MSCs) demonstrated that PLLA-BBG-Sr membranes promoted the osteogenic differentiation of the cells as demonstrated by increased alkaline phosphatase activity and up-regulated osteogenic gene expression (Alpl, Sp7 and Bglap) in relation to PLLA alone. These results strongly suggest that the composite PLLA membranes reinforced with the BBG-Sr glass particles have potential as an effective biomaterial capable of promoting bone regeneration.

STATEMENT OF SIGNIFICANCE

PLLA membranes were reinforced with 10% (w/w) of strontium-bioactive borosilicate glass microparticles, and their capacity to induce the osteogenic differentiation of bone marrow mesenchymal stem cells (BM-MSCs) was evaluated. These membranes presented an increased: degradability, water uptake, Young modulus and tensile strength. We also demonstrated that these membranes are non-cytotoxic and promote the attachment of BM-MSCs. The addition of the glass microparticles into the PLLA membranes promoted the increase of ALP activity (under osteogenic conditions), as well as the BM-MSCs osteogenic differentiation as shown by the upregulation of Alpl, Sp7 and Bglap gene expression. Overall, we demonstrated that the reinforcement of PLLA with glass microparticles results in a biomaterial with the appropriate properties for the regeneration of bone tissue.

Repair of bone defects in vivo using tissue engineered hypertrophic cartilage grafts produced from nasal chondrocytes

The regeneration of large bone defects remains clinically challenging. The aim of our study was to use a rat model to use nasal chondrocytes to engineer a hypertrophic cartilage tissue which could be remodelled into bone in vivo by endochondral ossification. Primary adult rat nasal chondrocytes were isolated from the nasal septum, the cell numbers expanded in monolayer culture and the cells cultured in vitro on polyglycolic acid scaffolds in chondrogenic medium for culture periods of 5-10 weeks. Hypertrophic differentiation was assessed by determining the temporal expression of key marker genes and proteins involved in hypertrophic cartilage formation. The temporal changes in the genes measured reflected the temporal changes observed in the growth plate. Collagen II gene expression increased 6 fold by day 7 and was then significantly downregulated from day 14 onwards. Conversely, collagen X gene expression was detectable by day 14 and increased 100-fold by day 35. The temporal increase in collagen X expression was mirrored by increases in alkaline phosphatase gene expression which also was detectable by day 14 with a 30-fold increase in gene expression by day 35. Histological and immunohistochemical analysis of the engineered constructs showed increased chondrocyte cell volume (31-45 μm), deposition of collagen X in the extracellular matrix and expression of alkaline phosphatase activity. However, no cartilage mineralisation was observed in in vitro culture of up to 10 weeks. On subcutaneous implantation of the hypertrophic engineered constructs, the grafts became vascularised, cartilage mineralisation occurred and loss of the proteoglycan in the matrix was observed. Implantation of the hypertrophic engineered constructs into a rat cranial defect resulted in angiogenesis, mineralisation and remodelling of the cartilage tissue into bone. Micro-CT analysis indicated that defects which received the engineered hypertrophic constructs showed 38.48% in bone volume compared to 7.01% in the control defects. Development of tissue engineered hypertrophic cartilage to use as a bone graft substitute is an exciting development in regenerative medicine. This is a proof of principal study demonstrating the potential of nasal chondrocytes to engineer hypertrophic cartilage which will remodel into bone on in vivo transplantation. This approach to making engineered hypertrophic cartilage grafts could form the basis of a new potential future clinical treatment for maxillofacial reconstruction.

Genetic modification of chondrocytes using viral vectors

The use of isolated cells to construct engineered tissues provides the opportunity to genetically modify those cells prior to the formation of tissue. This should make it possible to create transgenic human model tissues that can be used to determine gene function as well as to identify or validate potential therapeutic targets. As proof of principle, we have used RNA interference to selectively suppress the expression of aggrecanase genes in human chondrocytes, in an attempt to determine which of these key enzymes have roles in arthritic cartilage destruction. This combination of gene targeting and tissue engineering we are using should be equally applicable to the identification of gene function in other biological systems.

Synovial fluid mesenchymal stem cells in health and early osteoarthritis: detection and functional evaluation at the single-cell level

OBJECTIVE

Arthritic synovial fluid (SF) contains mesenchymal stem cells (MSCs), which could simply reflect their shedding from diseased joint structures. This study used the bovine model to explore SF MSCs in health and enumerated them at the earliest stages of human osteoarthritis (OA) in radiographically normal joints.

METHODS

Clonogenicity and multipotentiality of normal bovine SF MSCs were compared with donor-matched bone marrow (BM) MSCs at the single-cell level. The colony-forming unit-fibroblastic assay was used for MSC enumeration. The XTT assay was employed to assess cell proliferation, and flow cytometry was used to investigate the marker phenotype of bovine and human SF MSCs.

RESULTS

Single MSCs were present in normal bovine SF, and 96% of them were able to expand at least 1 million-fold. These cells were CD271-, multipotential, considerably more clonogenic, and less adipogenic than matched BM MSCs. In both pellet assays and on polyglycolic acid scaffolds, SF clones displayed consistent chondrogenic differentiation, while BM clones were variable. MSCs were present in arthroscopically normal human joints and were increased 7-fold in early OA (P = 0.034). Their numbers correlated with numbers of free microscopic synovial tissue fragments (r = 0.826, P < 0.0001). OA SF had a growth-promoting effect on synovial MSCs.

CONCLUSION

This study confirms the presence of MSCs in normal SF and shows their numerical increase in early human OA. SF MSCs are likely to originate from synovium. These findings provide a platform for the exploration of the potential role of SF MSCs in joint homeostasis and for investigation of their utility in novel joint regeneration strategies.

Mineral fibre analysis and routes of exposure to asbestos in the development of mesothelioma in an English region

OBJECTIVES

To compare the concentrations of inorganic fibres in the lungs in cases of mesothelioma and controls: to determine whether concentrations of retained asbestos fibres differ with the different exposures identified from interview; and to investigate the existence of a cut off point in concentrations of asbestos fibres that indicates occupational exposure.

METHODS

Case-control study; 147 confirmed cases of mesothelioma and 122 controls identified from deaths occurring in four districts of Yorkshire between 1979 and 1991. Surviving relatives were interviewed to determine lifetime exposure history to asbestos. Mineral fibre analysis was carried out on lung tissue from postmortem examinations.

RESULTS

Odds on high concentrations of retained asbestos fibres were greater in cases than controls. After excluding subjects with occupational and paraoccupational exposure, the odds on high concentrations were still greater in cases than controls, but only significantly so for amphiboles. There was only a weak relation between probability of occupational exposure to asbestos and concentrations of retained asbestos fibres, and no significant difference in fibre concentrations was found between subjects who had been exposed to asbestos through different routes: these comparisons were only based on small groups. There was considerable overlap in concentrations of retained asbestos fibres between cases and controls with and without histories of occupational exposure.

CONCLUSIONS

The study has confirmed previous results of higher concentrations of asbestos fibres in cases than controls, and has shown that this is still found in subjects with little evidence of occupational and para-occupational exposure. The overlap in concentrations of retained asbestos for different groups of subjects did not suggest a clear cut of value.

Routes of asbestos exposure and the development of mesothelioma in an English region

OBJECTIVES

To investigate the contribution of exposure to asbestos through different routes in the development of mesothelioma.

METHODS

Case-control study. 185 confirmed cases of mesothelioma and 160 controls were identified, when death had occurred between 1979 and 1991 in four health districts in Yorkshire. The surviving relatives were interviewed to ascertain lifetime exposure to asbestos. Adjusted odds ratios (ORs) of exposure to asbestos (through occupational, paraoccupational, and residential routes) were calculated for cases and were compared with controls.

RESULTS

Likely or possible occupational exposure to asbestos was more common in cases than in controls (OR 5.6, 95% confidence interval (95% CI) 3.1 to 10.1). After excluding those with likely or possible occupational exposure, likely or possible paraoccupational exposure was more common in cases than controls (OR 5.8, 95% CI 1.8 to 19.2). Only six cases of mesothelioma were identified as being solely exposed to asbestos through their residence, compared with nine controls. The OR for residential exposure to asbestos varied between 1.5 and 6.6, depending on which potential industrial sources were included, but the 95% CIs were so wide that slightly reduced or greatly increased odds comparing cases with controls could not be excluded.

CONCLUSION

Study results support previous evidence that occupational and paraoccupational exposure to asbestos is associated with developing mesothelioma. Despite a rigorous search, purely residential exposure seemed to account for only 3% of identified cases. No firm conclusion can be drawn about the risks from residential exposure alone, as many of the study subjects could also have been occupationally or paraoccupationally exposed to asbestos.

Chronic sinusitis and zinc-containing endodontic obturating pastes

Several researchers have reported a link between the development of a solitary antral aspergillus sinusitis and the presence of zinc-containing root canal obturating paste within the antrum. If diagnosed correctly, it is generally accepted that this type of sinusitis can be treated effectively using surgical techniques alone. However, previous reports have shown that this is not always the case and may result in prolonged and inappropriate treatment of the condition. It is hoped that the reported case and literature review will assist both dental and medical practitioners in identifying affected patients and in the subsequent instigation of correct treatment regimes.

Standardized mortality from cervical cancer: a measure of performance?

A retrospective cohort analysis, using data extracted from clinical notes, examined the validity of standardized mortality ratios (SMRs) for cervical cancer as an indicator of the quality of health services by exploring the mortality at five years of patients presenting with cervical cancer, identifying factors associated with survival, and studying the relationship of those factors to SMRs for the disease. The subjects were 1038 women aged 15-64 registered at the Yorkshire Cancer Registry as having invasive cervical cancer between 1979 and 1983. It was found that independent risk factors for mortality within five years of presentation were stage at diagnosis and smoking habit. Method of treatment had an effect that failed to reach statistical significance. Independent risk factors for late stage at presentation were absence of a history of cervical smear and increasing age. Considerable variation remained unexplained in both models. District SMRs were not related to five-year survival, stage at presentation or screening history. SMRs were related to proportions of smokers. It is concluded that SMRs are subject to considerable influence from a range of unidentified factors, as well as identified risk factors. They are too broad an indicator to be a valid measure of health service performance. The health service's ability to reduce case fatality does not outweigh the effects of incidence and severity. Better indicators would be survival to five years of those presenting at stage II or less and distribution of stage at presentation.

Measles/mumps/rubella vaccine (MMR): an audit of Leeds health professionals' knowledge of contraindications and intention to vaccinate assessed by postal questionnaire

An audit of Leeds health professionals' knowledge of valid contraindications to measles/mumps/rubella (MMR) vaccine was undertaken by postal questionnaire, three months after its introduction. The health professional groups were health visitors, clinical medical officers, general practice trainers and general practice vocational trainees. The results indicate that some health professionals would give MMR vaccine to children when it was contraindicated (e.g. to a child receiving chemotherapy or radiotherapy). However, a much greater problem was the number of health professionals stating that they would not vaccinate children with MMR vaccine in clinical situations where there were no valid contraindications to its use. Some health professionals were also applying contraindications to the use of pertussis vaccine to the use of MMR vaccine. The information contained in the Joint Committee on Vaccination and Immunisation handbook Immunisation against infectious disease on contraindications to MMR vaccine use is also reviewed. It is important that false contraindications are not used by health professionals to wrongly deny children the protection provided by MMR vaccine.

The use of the screening technique as a method of rapidly estimating vaccine efficacy

Using measles notification data for the period December 1st, 1987 to May 31st, 1988, in Leeds, an estimation of measles vaccine efficacy is calculated using the screening technique. This is an equation which allows the rapid estimation of vaccine efficacy and is useful in an outbreak situation in deciding whether the proportion of cases with a vaccination history is still compatible with a good overall vaccine efficacy. No vaccine is 100% effective and the screening technique, which uses readily available data, will quickly indicate whether a more detailed epidemiological investigation is required into vaccine failure.

A report of the investigation and control measures instituted after the isolation of toxin-producing Corynebacterium diphtheriae mitis from a child in Leeds

This report describes the control measures instituted and further investigations undertaken after the isolation of toxin-producing Corynebacterium diphtheriae from a throat swab taken routinely from a nine-year-old boy, recently returned from Pakistan, who had been admitted to hospital in Leeds with hepatitis A infection. Four of his siblings were subsequently shown to have identical Corynebacterium diphtheriae on throat swabbing, except that in one child the organism did not produce toxin. All the children were asymptomatic carriers.

The form and presentation of tuberculosis over a 10-year interval in Leeds

Over the 10-year period 1973-82 1958 cases of tuberculosis were notified in Leeds (population 728 000). Records were traced for 1673 patients and analysed for age, race, sex, sputum status, site of tuberculosis, route of diagnosis and occupation. These results are presented. The tuberculosis screening service at the Leeds Chest Clinic diagnosed 172 cases of tuberculosis from 13 794 contacts screened and 41 cases from 12 572 newly arrived immigrants representing 10.3% and 2.4% respectively of the cases for whom records could be traced. Of these cases discovered by the tuberculosis screening service 25 were sputum positive. A further 15 cases were diagnosed from 2638 contacts screened by the static Mass Miniature Unit. The cost of the screening service at the Leeds Chest Clinic is estimated to be a minimum of 2000 pounds for every case of tuberculosis diagnosed.