Preventing Cross-Contamination during Lyophilization: GMP and Occupational Cleaning Requirements for Nonproduct and Indirect Product-Contact Parts.

A detailed overview is provided for the possible patient exposure to highly potent active pharmaceutical ingredients (HPAPIs) from potential cross-contamination through the lyophilization process. The intent of this paper is to raise awareness of the risk(s) to patients and stimulate the implementation of adequate risk-based controls, such as containment process(es), use of adequate surrogates in cleaning validation/verification, and test method-sensitivity-based cleaning validation acceptance conditions. Although lyophilizers are considered to be nonproduct-contact surfaces because their surfaces and fixtures do not usually come into direct contact with the product, product contamination can occur at critical locations within a lyophilizer and/or during the unloading process. Contamination of the air because of released product particles can also create a risk. Therefore, special attention should be paid to HPAPIs, as the permitted daily exposures (PDEs) for patients are particularly low. During a lyophilizer cycle, areas of concern are spreading of the lyophilizer HPAPI powder because of air turbulence, contaminated plates, mechanical transfer systems, and spreading because of damaged vials or contaminated stainless steel or plastic surfaces. Specific considerations for contamination containment for the lyophilizer unloading process are presented. Suggestions are provided for the prevention of patient exposure through cross-contamination via direct-contact areas and prevention of manufacturing personnel exposure via non-direct-contact areas. A surface limit(s) of 1 PDE per square decimeter for nonproduct-contact surfaces inside a lyophilizer is proposed. Risk-based cleaning validation/verification strategies are discussed, with specific consideration of the quality control test method sensitivity expectations and use of suitable surrogates for lyophilized products in the cleaning verification studies.LAY ABSTRACT: This paper provides an overview of important points to consider during the manufacture of highly potent active pharmaceutical ingredients (HPAPI) with the intention to limit patient exposure and/or manufacturing personnel exposure to these highly toxic HPAPIs. HPAPI can potentially be spread during the freeze-drying process (lyophilization) and may cross-contaminate products. Manufacturing personnel and patients taking other freeze-dried products made in the same lyophilizer could be contaminated. It is therefore necessary to implement rigorous contamination controls. Within the lyophilizer, areas of concern are spreading of the lyophilizer HPAPI powder because of air turbulence, contaminated plates, mechanical transfer systems, and spreading because of damaged vials or contaminated stainless steel or plastic surfaces. Cleaning validation/verification studies, intended to demonstrate sufficient cleanability of the freeze-drying process as well as the recommended test method sensitivity to detect these highly toxic HPAPIs, are reviewed. Limits for the relevant production surface areas where cross-contamination and/or personnel exposure (through direct contact) could occur are proposed in this paper.

Probing optical excitations in chevron-like armchair graphene nanoribbons.

The bottom-up fabrication of graphene nanoribbons (GNRs) has opened new opportunities to specifically tune their electronic and optical properties by precisely controlling their atomic structure. Here, we address excitation in GNRs with periodic structural wiggles, the so-called chevron GNRs. Based on reflectance difference and high-resolution electron energy loss spectroscopies together with ab initio simulations, we demonstrate that their excited-state properties are of excitonic nature. The spectral fingerprints corresponding to different reaction stages in their bottom-up fabrication are also unequivocally identified, allowing us to follow the exciton build-up from the starting monomer precursor to the final GNR structure.

Exciton-dominated optical response of ultra-narrow graphene nanoribbons.

Narrow graphene nanoribbons exhibit substantial electronic bandgaps and optical properties fundamentally different from those of graphene. Unlike graphene--which shows a wavelength-independent absorbance for visible light--the electronic bandgap, and therefore the optical response, of graphene nanoribbons changes with ribbon width. Here we report on the optical properties of armchair graphene nanoribbons of width N=7 grown on metal surfaces. Reflectance difference spectroscopy in combination with ab initio calculations show that ultranarrow graphene nanoribbons have fully anisotropic optical properties dominated by excitonic effects that sensitively depend on the exact atomic structure. For N=7 armchair graphene nanoribbons, the optical response is dominated by absorption features at 2.1, 2.3 and 4.2 eV, in excellent agreement with ab initio calculations, which also reveal an absorbance of more than twice the one of graphene for linearly polarized light in the visible range of wavelengths.

Layer resolved evolution of the optical properties of α-sexithiophene thin films.

We report a combined reflectance difference spectroscopy and scanning tunneling microscopy study of ultrathin α-sexithiophene (6T) films deposited on the Cu(110)-(2×1)O surface. The correlation between the layer resolved crystalline structure and the corresponding optical spectra data reveals a highly sensitive dependence of the excitonic optical properties on the layer thickness and crystalline structure of the 6T film.

Stranski-Krastanov growth of para-sexiphenyl on Cu(110)-(2×1)O revealed by optical spectroscopy.

We have studied the growth of para-sexiphenyl (p-6P) on the Cu(110)-(2×1)O surface using reflectance difference spectroscopy (RDS) in combination with scanning tunneling microscopy (STM). The evolution of the optical anisotropy reveals that the growth of p-6P on the Cu(110)-(2×1)O surface at room temperature follows the Stranski-Krastanov growth mode with a two monolayer thick wetting layer. During all stages of growth, the p-6P molecules are well orientated with their long molecular axis aligned parallel to the Cu-O rows along the [001] direction of the Cu(110) substrate. The high packing density of the p-6P molecules in the first and second monolayer evidenced by RDS and STM is believed to be responsible for the switch from layer-by-layer to three-dimensional island growth.