Trends in the prevalence of cerebral palsy in Northern Ireland, 1981-1997

We describe trends in the prevalence of cerebral palsy (CP) by birth weight group, and in the severity of motor impairments and presence of associated intellectual impairment, in Northern Ireland from 1981 to 1997 (n=909; 510 males, 399 females; total population 415 936 live births) using data from a population-based register of CP. Children with suspected CP or who died before 1 year of age and those with CP of postneonatal origin were excluded. Prevalence of CP was 2.2 per 1000 live births without significant change over time. Among very-low-birthweight (<1500g) live births, prevalence was 44.5 per 1000 (95% confidence interval 32.3–59.8) from 1994 to 1997, with evidence of a statistically significant decline in prevalence since the mid- to late 1980s accompanied by a decrease in the severity of motor impairment and likelihood of intellectual impairment. Among moderately-low-birthweight (1500–2499g) children there was weaker evidence of a peak prevalence in the late 1980s. Prevalence among normal-birthweight infants did not change significantly, but outcome in terms of severity of motor impairment and intellectual impairment improved in the 1990s. Occurrence of bilateral spasticity from 1994 to 1997 was associated with greater severity and likelihood of intellectual impairment for normal-birthweight individuals than for low- or very-low-birth weight individuals.

The modification of PLA and PLGA using electron-beam radiation

The degradable polymers polylactide (PLA) and polylactide-co-glycolide (PLGA) have found widespread use in modern medical practice. However, their slow degradation rates and tendency to lose strength before mass have caused problems. The aim of this study was to ascertain whether treatment with e-beam radiation could address these problems. Samples of PLA and PLGA were manufactured and placed in layered stacks, 8.1 mm deep, before exposure to 50 kGy of e-beam radiation from a 1.5 MeV accelerator. Gel permeation chromatography testing showed that the molecular weight of both materials was depth-dependent following irradiation, with samples nearest to the treated surface showing a reduced molecular weight. Samples deeper than 5.4 mm were unaffected. Computer modeling of the transmission of a 1.5 MeV e-beam in these materials corresponded well with these findings. An accelerated mass-loss study of the treated materials found that the samples nearest the irradiated surface initiated mass loss earlier, and at later stages showed an increased percentage mass loss. It was concluded that e-beam radiation could modify the degradation of bioabsorbable polymers to potentially improve their performance in medical devices, specifically for improved orthopedic fixation.

The determination of optimal processing conditions for PLA and PLA/CaCO3 in twin screw extrusion using DoE and multivariate analysis

Biodegradable polymers, such as PLA (Polylactide), come from renewable resources like corn starch and if disposed of correctly, degrade and become harmless to the ecosystem making them attractive alternatives to petroleum based polymers. PLA in particular is used in a variety of applications including medical devices, food packaging and waste disposal packaging. However, the industry faces challenges in melt processing of PLA due to its poor thermal stability which is influenced by processing temperatures and shearing.
Identification and control of suitable processing conditions is extremely challenging, usually relying on trial and error, and often sensitive to batch to batch variations. Off-line assessment in a lab environment can result in high scrap rates, long lead times and lengthy and expensive process development. Scrap rates are typically in the region of 25-30% for medical grade PLA costing between €2000-€5000/kg.
Additives are used to enhance material properties such as mechanical properties and may also have a therapeutic role in the case of bioresorbable medical devices, for example the release of calcium from orthopaedic implants such as fixation screws promotes healing. Additives can also reduce the costs involved as less of the polymer resin is required.
This study investigates the scope for monitoring, modelling and optimising processing conditions for twin screw extrusion of PLA and PLA w/calcium carbonate to achieve desired material properties. A DAQ system has been constructed to gather data from a bespoke measurement die comprising melt temperature; pressure drop along the length of the die; and UV-Vis spectral data which is shown to correlate to filler dispersion. Trials were carried out under a range of processing conditions using a Design of Experiments approach and samples were tested for mechanical properties, degradation rate and the release rate of calcium. Relationships between recorded process data and material characterisation results are explored.