Physicochemical characterization and evaluation of the suspending properties of <i>Citrullus lanatus</i>seed waste composite

Background and aim: Biomaterial composite waste can be processed for application as pharmaceutical excipient. This study was aimed at assessing the suspending properties of Citrullus lanatus seed composite waste, after defatting, in the formulation of metformin suspension.Methods: Defatted dried C. lanatus seed powder was subjected to micromeritics, water-holding and oilholding, viscosity, pH, and microscopy pre-formulation studies. Eleven batches of metformin suspensions (100 ml) were formulated using 1, 2, 4, 6 and 8% w/ v of the composite powder, similar concentration ranges of xanthan gum, and a control batch. The pH, sedimentation volume, and re-dispersion number of the suspensions were determined.Results: Citrullus lanatus seed yielded 56.31% composite powder having Carrs’ index < 11.32, and angle of repose < 39.05. Pre-formulation studies revealed 3.81 g H2O/ g water-holding capacity, and 2.53 g oil/g oil-holding capacity. While pH of the aqueous composite decreased with storage, viscosity increased with concentration (p < 0.05) and remains relatively stable at < 40oC. The TEM and SEM analyses of the composite-metformin blend revealed unique mesh-like and closely packed continuous sheaths. The composite suspension did not thicken on storage, and was not easily re-dispersed especially at higher concentration.Conclusion: Citrullus lanatus seed composite showed good processing qualities, water-holding capacity and oil-holding capacity, passable thermal stability, and limited suspending properties. It demonstrated potential for optimization and for further research as emulsifier, and in combination with pharmaceutical gums as suspending agents.