Collagen And Elastin-Like Polypeptide Composite Scaffold For Controlled Drug And Protein Delivery

Objectives: Evaluation of compositional factors of collagen density, addition of Elastin-Like Polypeptide (ELP), and chemical crosslinking of collagen to achieve controlled release of doxycycline hyclate and recombinant human Bone Morphogenetic Protein (rhBMP-2).
Methods: Doxycycline hyclate (0.5%) or rhBMP-2 (0.005%) was incorporated into the collagen hydrogel by incubating collagen type I (rat tail tendon, 8.91 mg/mL) in 1N NaOH, sterile DI H₂O, and 10X DMEM at 37°C overnight. ELP or chemical crosslinking agent (ethyl (dimethylaminopropyl) carbodiimide/N-Hydroxysuccinimide) was incorporated into the collagen solution and the hydrogel formation was performed in the same manner as collagen hydrogel to produce ELP-collagen or crosslinked collagen hydrogels. Studied hydrogels were placed onto swabbed petri dishes of Pseudomonas aeruginosa or Streptococcus sanguinis for evaluation of inhibition of bacteria growth. Data shown as mean ± 95% confidence interval with n = 3. Values with p ≤ 0.05 deemed statistically significant.
Results: Doxycycline release showed a bi-phasic release profile with the initial burst of 50% release during the first 24 hours followed by a gradual release of up to 100% release over the seven days. The zones of inhibition confirmed the bacteriostatic effect of the released doxycycline for P. aeruginosa and S. sanguinis. Osteoinductive protein, rhBMP-2, exhibited a nearly linear release profile in all hydrogel compositions. The higher collagen density and incorporation of ELP into collagen scaffolds achieved a significantly four-fold slower rhBMP-2 release (p < 0.05).
Conclusions: Overall, collagen and collagen-ELP scaffolds showed a controlled drug and protein delivery. The bi-phasic release profile of doxycycline can be clinically relevant to prevent post-surgical infection. The released doxycycline from all hydrogels was effective against commonly encountered Gram-negative aerobe and Gram-positive facultative anaerobe. The linear sustained release profile of rhBMP-2 will enhance the osteogenic response of the implanted scaffolds.