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Basic Salt Additives Modulate the Acidic Microenvironment Around In Situ Forming Implants

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Abstract

There is a growing number of protein drugs, yet their limited oral bioavailability requires that patients receive frequent, high dose injections. In situ forming implants (ISFIs) for controlled release of biotherapeutics have the potential to greatly reduce the injection frequency and improve patient compliance. However, protein release from ISFIs is a challenge due to their proclivity for instability. Specifically, factors such as the acidic microclimate within ISFIs can lead to protein aggregation and denaturation. Basic salts have been shown in PLGA microparticle and microcylinder formulations to significantly reduce protein instability by neutralizing this acidic environment. The overall objective of the study was to demonstrate that basic salts can be used with an ISFI system to neutralize the implant acidification. To this end, the basic salts MgCO3 and Mg(OH)2 were added to a protein-releasing ISFI and the effect on drug release, pH, implant swelling, implant diffusivity, and implant erosion were evaluated. Either salt added at 3 wt% neutralized the acidic environment surrounding the implants, keeping the pH at 6.64 ± 0.03 (MgCO3) and 6.46 ± 0.11 (Mg(OH)2) after 28 day compared to 3.72 ± 0.05 with no salts added. The salts initially increased solution uptake into the implants but delayed implant degradation and erosion. The 3 wt% Mg(OH)2 formulation also showed slightly improved drug release with a lower burst and increased slope. We showed that salt additives can be an effective way to modulate the pH in the ISFI environment, which can improve protein stability and ultimately improve the capacity of ISFIs for delivering pH-sensitive biomolecules. Such a platform represents a low-cost method of improving overall patient compliance and reducing the overall healthcare burden.

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Acknowledgments

We would like to thank the Purdue Electron Microscopy Facility and the Purdue MRI Facility for their assistance with SEM and DWI, respectively. We would also like to acknowledge the Summer Undergraduate Research Fellowship (SURF) at Purdue University for E.W.

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Authors and Affiliations

  1. Weldon School of Biomedical Engineering, Purdue University, Martin C. Jischke Hall (MJIS) Rm 3019, 206 S. Martin Jischke Drive, West Lafayette, IN, 47907, USA

    Kelsey Hopkins, Elizabeth Wakelin, Natalie Romick, Jacqueline Kennedy, Emma Simmons & Luis Solorio

  2. Center for Cancer Research, Purdue University, West Lafayette, IN, USA

    Luis Solorio

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  1. Kelsey Hopkins
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  2. Elizabeth Wakelin
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  3. Natalie Romick
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  6. Luis Solorio
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Correspondence to Luis Solorio.

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Hopkins, K., Wakelin, E., Romick, N. et al. Basic Salt Additives Modulate the Acidic Microenvironment Around In Situ Forming Implants. Ann Biomed Eng 51, 966–976 (2023). https://doi.org/10.1007/s10439-022-03109-6

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  • DOI: https://doi.org/10.1007/s10439-022-03109-6

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