Sensitivity of Materials in Glass Bioreactors
Cleaning Agents for Glass Reactors, Borosilicate Glass, and Glycol
Glass bioreactors commonly use borosilicate glass, which has structural stability from a thermal expansion coefficient of 3.3 × 10⁻⁶/°C. However, the silica bond in borosilicate glass can be affected by chemicals. For example, cleaners with a basic pH (>9) can break silica bonds, while cleaners with an acidic pH (<5) can break sodium and boron bonds, which cause micro pits. There is an additional hazard from formulated abrasives because they produce micro-scratches that, under operational pressure, can cause micro-scratches to intensify by as much as 70 percent. Data from the industry shows that the use of pH neutral cleaners with a pH between 6-8, can reduce the rate of micro damage to the glass's surface by 40 percent compared to those that are corrosive. pH neutral cleaners can also maintain the glass's optical clarity, and, as a result, reduce the nucleation sites for biofilms and support better cellular economy regulation.
Effects of Thermal Shock and Chemical Action on Microcracks in Borosilicate Glass
Thermal shocks of ±50 °C/min can cause the glass vessels to expand unevenly, which can lead to micro cracks and stress fractures. Chemical aggression coupled with pH bias also affects the silica substrate by providing pH bias so that micro cracks can propagate. With the pH bias, thermal and chemical micro cracks also propagate. When thermal stress couples with chemical stress, cracks can propagate as much as 300 times faster than thermal stress alone. Under these stress-agitation and pressure-cycled environmental conditions, subsurface micro cracks will propagate to a point that will result in the failure of the bioreactor to maintain sterility. By maintaining pH neutral rinsing and a ±5 °C/min temperature control, the service life of a bioreactor can be extended by 60 percent through a reduction in the rate of fractures.
Optimized Cleaning-in-Place (CIP) Protocols for Glass Bioreactors
Nozzle placement, flow velocity (≥1.5 m/s), and turbulence design to eliminate stagnant zones
Optimized Cleaning-in-Place (CIP) protocols for glass bioreactors require consistency and thoroughness to eliminate the design challenges of stagnant zones. Achieving a flow velocity of ≥1.5 m/s will generate sufficient turbulence and shear stress to wash biofilms off surfaces that resist flow and stagnant zones. Nozzle placement should be designed for the bioreactor’s geometry as well. Vertical nozzles ensure flow is dispersed evenly across the surfaces, while angled nozzles direct flow to corners and vertical weld seams. Modeling from CFD shows that a threshold velocity of 1.5 m/s should eliminate 15-25% of the biofilm. Careful placement of the nozzles will elevate the Reynolds number to above 4000, resulting in uniform flow and turbulence across the surfaces.
Temperature ramp control (±5°C/min) during CIP heating/cooling cycles
Careful design will yield a high margin of safety to ensure thermal CIP will be safe for bioreactors. Thermal regulations that dictate the flow and the speed of the thermal CIP will decrease the chances of bioreactor rupture to a high degree, while also allowing for the solubilization of biofilm to occur in a consistent and repeatable manner.
Maintenance Schedules Controlled by Production Rather than Calendar
Cycle count directed inspections according to regulations (USP <1043>, ISO 20957)
Calendar based maintenance schedules do not take into account actual wear that a glass bioreactor has after a bioreactor has undergone a certain number of cycles (i.e. fermentation, SIP, CIP). Like traditional maintenance procedures, usage based inspections suffer from the balancing act of wrong, too early, too late. This subject is addressed in regulatory guidelines: risk assessment of the loss of integrity of equipment is endorsed by USP <1043> and there is a requirement of justification for the intervals of inspections in ISO 20957 and a requirement for a history of mechanical stress from components. The integration of cycle counters, through PLC logging or a sensor based approach, compliance and maintenance of the bioreactor is improved by 30-40% for the replacement of the time based inspections.
Finding Glass Liner Defects Early
Detection of glass integrity Failure: Multiple Mode inspections with exploitation of Photo luminance
The development of microfractures on the glass bioreactor is inevitable. It is of utmost importance that early detection is performed for the integrity of the glass bioreactor. One method is the multiple inspections, which are divided into the following categories.
Haze and/or clouding deficiencies can be seen in the glass after high-intensity lighting is used to illuminate the glass.
Surfaces and subsurfaces can be visualized by Borescope imaging at 360 degrees and up to 50x magnification.
Using Dye-penetrant testing of a fluorescent tracer fluid and UV light to view the testing exploit the service abscess and/or micro nicks to penetrate and identify subsurface and break the surface. These cracks can be sub 0.1 mm size and are virtually non-visible to the naked eye.
Combining all methods results in a 76% reduction in false-negative detection compared to a single-modality check. Rapid does not only help identify and deter contamination from occurring and helps to eradicate service life from the equipment by 3–5 years by not causing unplanned shutdowns. This also complies with the proactive equipment integrity outlined in USP <1043> and Annex 1.
FAQ
Why cleaning agents should be pH-neutral when cleaning borosilicate glass?
Borosilicate glass should not be pH acidic. As a silicate rich glass network, pH-neutral agents (pH 6–8) should not eat away at the silicate network and should optimize the glass sacrosilicate integrity.
What are the effects of temperature ramps on CIP?
Small temperature ramps of controlled temperature (±5°C/min) should not cause thermal stresses due to micro-cracking of the bioreactor glass.
Why maintenance based glass bioreactor cycles?
Maintenance based on cumulative cycle count eliminates unnecessary interactions and optimizes timely maintenance based on operational wear.
How does multi-modal inspection sustain bioreactor quality?
Visual, borescope inspection, and dye-penetrant inspection eliminates the majority of the potential contamination life-cycle by detecting and assessing the integrity of the glass.