Visualization of porosity and pore size gradients in electrospun scaffolds using laser metrology.

We applied a recently developed method, laser metrology, to characterize the influence of collector rotation on porosity gradients of electrospun polycaprolactone (PCL) widely investigated for use in tissue engineering. The prior- and post-sintering dimensions of PCL scaffolds were compared to derive quantitative, spatially-resolved porosity 'maps' from net shrinkage. Deposited on a rotating mandrel (200 RPM), the central region of deposition reaches the highest porosity, ~92%, surrounded by approximately symmetrical decreases to ~89% at the edges. At 1100 RPM, a uniform porosity of ~88-89% is observed. At 2000 RPM, the lowest porosity, ~87%, is found in the middle of the deposition, rebounding to ~89% at the edges. Using a statistical model of random fiber network, we demonstrated that these relatively small changes in porosity values produce disproportionately large variations in pore size. The model predicts an exponential dependence of pore size on porosity when the scaffold is highly porous (e.g., >80%) and, accordingly, the observed porosity variation is associated with dramatic changes in pore size and ability to accommodate cell infiltration. Within the thickest regions most likely to 'bottleneck' cell infiltration, pore size decreases from ~37 to 23 µm (38%) when rotational speeds increased from 200 to 2000 RPM. This trend is corroborated by electron microscopy. While faster rotational speeds ultimately overcome axial alignment induced by cylindrical electric fields associated with the collector geometry, it does so at the cost of eliminating larger pores favoring cell infiltration. This puts the bio-mechanical advantages associated with collector rotation-induced alignment at odds with biological goals. A more significant decrease in pore size from ~54 to ~19 µm (65%), well below the minimum associated with cellular infiltration, is observed from enhanced collector biases. Finally, similar predictions show that sacrificial fiber approaches are inefficient in achieving cell-permissive pore sizes.

Baseline HPV prevalence in rectal swabs from men attending a sexual health clinic in Scotland: assessing the potential impact of a selective HPV vaccination programme for men who have sex with men.

OBJECTIVES: A human papillomavirus (HPV) vaccination programme targeted towards men who have sex with men who are disproportionately affected by HPV anogenital infection and related disease was established in Scotland in July 2017. We aimed to establish a baseline HPV prevalence to assess the potential impact of the programme. METHODS: Residual rectal swabs taken in a sexual health clinic (n=1 248) were tested for the presence of HPV and HPV-type prevalence was collated and stratified by age. Prevalence of HPV types included in the quadrivalent and nonavalent vaccines was specifically assessed. RESULTS: 72.8% (95% CI 70.2% to 75.3%) of swabs were positive for HPV with 59.1% (95% CI 56.3% to 61.9%) of samples positive for at least one high-risk type. A least one of HPV 6, 11, 16 and 18 was detected in approximately half of the swabs. HPV prevalence generally increased with age but did not significantly differ between older age groups. The presence of more than one HPV type increased with age and over half of samples had multiple types present. CONCLUSIONS: While HPV prevalence in this population is high, the potential impact of the vaccination programme is substantial given that 50% are not infected with a vaccine type. Defining a preimmunisation baseline in this group will be important for longitudinal monitoring of impact.