(W1030-11-61) Sending Ritonavir to Space and Back – Drug Development Enabled by Specially Designed Hardware to Perform in Microgravity

Purpose: Early proof-of-concept demonstrations conducted on parabolic flights and on extended microgravity platforms such as the International Space Station (ISS) have demonstrated the potential benefits of in-space microgravity crystallization for better understanding of polymorphism and for supporting pathfinding routes towards novel formulations (1-4). However, due to the extensive planning duration, limited resources, and high cost associated with human spaceflight, the benefits of microgravity crystallization have remained inaccessible and ineffective in addressing unmet pharmaceutical needs on Earth. We present an autonomous platform for in-orbit crystallization of APIs. After being launched into orbit via a rocket transporter rideshare, the capsule is deployed into low-Earth orbit to execute the desired crystallization process autonomously in microgravity. After completing the crystallization process, the capsule de-orbits, reenters the atmosphere, and safely lands on Earth. This platform enables high- cadence access to microgravity for the pharmaceutical industry to address crystallization challenges and expand the scope of materials that can be processed in space by avoiding human-operator limitations through autonomous operation. We demonstrate the feasibility of the capsule by successfully crystallizing ritonavir’s metastable Form III (5).

Methods: In-orbit crystallization is performed inside a compact, unmanned capsule with Earth reentry capabilities. The reentry capsule and on-board crystallization hardware were developed internally, shown in Figure 1. Power, communication, and propulsion are provided by a third party. The spacecraft was brought to orbit on a rocket launched June 12^th, 2023. In-orbit crystallization experiments initiated on June 29^th, 2023. The melt temperature was held for 36 minutes at 131 °C +/- 2 °C. The quench from the melt temperature to the growth temperature occurred at a rate of -50.9 °C/min where it reached a temperature of 77.3 °C before stabilizing. The growth phase temperature was set at 80 °C +/- 4.2 °C for 23.97 hours before cooling to 15 °C at a rate of -3.8 °C/min. This profile is demonstrated in Figure 2. The crystallization hardware features three stainless steel sample vials sealed with a stainless-steel screw-on cap.  A PTFE sphere is seated between the cap and the ritonavir Form II powder to enable sealing of the powder under compression. The hardware is controlled with a printed circuit board (PCB) that enables the application of pre-programmed thermal profiles, established from ground-based studies on ritonavir’s metastable Form III (5). Temperature control is achieved through the use of film heaters and a Peltier device in thermal contact with the flight vials via an aluminum heat spreader. The control vials were also placed in the capsule but were thermally isolated from the crystallization hardware. The capsule performed reentry first by undergoing three de-orbit phases followed by separation from the satellite where it began its freefall through the atmosphere and ultimate touchdown. The temperature from separation through touchdown is shown in Figure 3.

Results: Temperature monitoring showed that the flight hardware performed in a near-exact match in terrestrial and in-orbit tests, exhibiting a profile to crystallize the metastable Form III of ritonavir, as shown in Figure 1. The only deviations were that in-orbit cooling stages were consistently faster than terrestrial cooling stages. Throughout reentry from low-Earth orbit, through passing through the planet’s atmosphere, and landing, temperature of the hardware remained stable allowing the crystallized ritonavir and respective controls to be safely recovered upon touchdown. Analysis indicated that all crystallized ritonavir was metastable Form III, and all control vials match that of their prepared form.

Conclusion: Our presented results demonstrate the feasibility of processing pharmaceuticals in microgravity. Autonomous operation and reentry expand access to in-orbit processing of pharmaceuticals. The presented work demonstrates excellent thermal control both in-orbit and throughout recovery. For the thermal profile investigated, the polymorphic outcome for ritonavir crystallized from its melt is unchanged when compared to results on Earth. By demonstrating the feasibility of autonomous reentry working outside of the bounds of the ISS while ensuring drug retrievability, this work shows a path towards in-space processing of pharmaceuticals that enables the development of novel drug products for use on Earth.

References: 1. Y. Zhang, J. Cheng, Y. Glick, G. Samburski, J. Chen, C. Yang, Antisolvent crystallization of L-histidine in micro-channel reactor under microgravity Microgravity Science and Technology 32, 27-33 (2020).
2. S. Amselem Remote controlled autonomous microgravity lab platforms for drug research in space Pharmaceutical Research 36, 183 (2019).
3. M. A. Giulianotti and L. A. Low, Pharmaceutical research enabled through microgravity: Perspectives on the use of the international space station U.S. national laboratory Pharmaceutical Research 37, 1 (2020).
4. P. Reichert, W. Prosise, T. O. Fischmann, G. Scapin, C. Narasimhan, A. Spinale, R. Polniak, X. Yang, E. Walsh, D. Patel, W. Benjamin, J. Welch, D. Simmons, C. Strickland, Pembrolizumab microgravity crystallization experimentation npj Microgravity 5, A28 (2019).
5. S. D. Parent, P. A Smith, D. K. Purcell, D. T. Smith, S. J. Bogdanowich-Knipp, A. S. Bhavsar, L. R. Chan, J. M. Croom, H. C. Bauser, A. McCalip, S. R. Byrn, A. Radocea, Ritonavir form III: A coincidental concurrent discovery Crystal Growth & Design 23, 320-325 (2022).

Acknowledgements: The authors acknowledge the mission operations team at Varda Space Industries and Rocket Lab, Inc. for their work in maintaining the capsule throughout its life cycle. The authors acknowledge Brandon Amat, Tracy Vu, and Kris Stone for their recovery of the capsule and safe retrieval of the experimental vials. The authors acknowledge Aakash Patel for integration and testing support. The authors acknowledge Sarah Parent for her photography of the hardware.


Overview of the in-orbit crystallization hardware. (A) Exploded view of the Varda PCB Stack and API vials. The components are as follows. 1) (3x) 316 Stainless Steel vials each holding ~150 mg of API, sealed with a PTFE ball and spacers. 2) 6061 Aluminum plate heat spreader holding the vials and the resistance temperature detectors (RTDs). 3) Thermal interface material 4) (6x) Kapton film heaters each with a total power of 23 watts 5) (6x) Peltier devices used in both forward bias for cooling and reverse bias for additional heater power 6) PCB 7) (2x) RTDs in heat spreader and 1x RTD on the ballast side of the PCB 8) grounding wires. (B) Picture of the fully assembled Varda PCB Stack.


Comparison of the hardware temperature during the 1-g crystallization of ritonavir and the heat spreader temperature during the in-orbit crystallization of ritonavir.


Timeline of Heat Spreader Temperature Throughout Reentry with Corresponding Images from Capsule. (A) Image and corresponding heat spreader temperature upon capsule separation from the Pioneer satellite. (A-B) Image shows the capsule above Earth independent of the satellite. (B) Image and corresponding heat spreader temperature at the maximum capsule external temperature during reentry. (C) Image and corresponding heat spreader temperature upon capsule touchdown in Utah. (D) Image and corresponding heat spreader temperature at maximum temperature experienced while awaiting recovery.