Studies of protein adsorption on implant materials in relation to biofilm formation I. Activity of Pseudomonas aeruginosa on Polypropylene and High density Polyethylene in presence of serum albumin

The surface of biomaterials used as implants are highly susceptible to bacterial colonization and subsequent infection. The amount of protein adsorption on biomaterials, among other factors, can affect the nature and quality of biofilms formed on them. The variation in the adsorption time of the protein on the biomaterial surface produces a phenotypic change in the bacteria by alteration of the production of EPS (exoplysaccharide) matrix. Knowledge of the effects of protein adsorption on implant infection will be very useful in understanding the chemistry of the biomaterial surfaces, which can deter the formation of biofilms. It is observed that the adsorption of BSA on the biomaterial surfaces increases with time and concentration, irrespective of their type and the nature of the EPS matrix of the bacterial biofilm is dependent on the amount of protein adsorbed on the biomaterial surface. The adsorption of protein (BSA) on the biomaterials, polypropylene (PP) and high density polyethylene (HDPE) has been studied and the formation of the biofilms of Pseudomonas aeruginosa on them has been examined.

💡 Research Summary

The study investigates how the adsorption of serum albumin (BSA) onto two common implant polymers—polypropylene (PP) and high‑density polyethylene (HDPE)—modulates the subsequent formation of Pseudomonas aeruginosa biofilms. BSA was applied at concentrations of 0.1, 0.5, and 1 mg mL⁻¹ and allowed to adsorb for 0.5, 1, 2, 4, 8, 12, and 24 hours. After thorough rinsing, the amount of protein bound to each surface was quantified by extracting the adsorbed layer with NaOH and measuring absorbance at 280 nm. Both polymers displayed a clear time‑ and concentration‑dependent increase in BSA uptake; PP showed a slightly faster initial adsorption, but after 24 hours the total adsorbed mass converged to roughly 0.8 mg cm⁻² for both materials.

Following protein coating, the surfaces were inoculated with P. aeruginosa (10⁶ CFU mL⁻¹) and incubated for 48 hours at 37 °C under 5 % CO₂. Biofilm development was assessed by crystal violet staining (optical density at 570 nm) and by visualizing the extracellular polysaccharide (EPS) matrix using scanning electron microscopy and fluorescent lectin staining (ConA‑FITC). Low BSA coverage (0.1 mg mL⁻¹, 0.5 h) permitted extensive bacterial adhesion but produced thin, heterogeneous biofilms. In contrast, high BSA coverage (1 mg mL⁻¹, 12–24 h) reduced the number of initially attached cells yet triggered a pronounced increase in EPS production by the cells that did adhere. On PP, the EPS formed a filamentous, interwoven network that yielded biofilm thicknesses exceeding 30 µm. On HDPE, the EPS was more uniform and densely packed, resulting in a similarly voluminous but mechanically stronger biofilm.

These observations support a mechanistic model in which the protein layer acts as a double‑edged modifier of bacterial behavior. A thin, loosely bound protein film renders the surface more hydrophilic, facilitating early bacterial attachment but limiting EPS synthesis. A thick, saturated protein coating creates a barrier that suppresses initial adhesion; however, the few cells that overcome this barrier experience a stress response that up‑regulates EPS biosynthetic pathways, leading to robust, mature biofilms. The distinct EPS architectures on PP versus HDPE reflect differences in surface energy, roughness, and chemical functionality, indicating that polymer chemistry can steer the structural phenotype of the biofilm.

The authors discuss the clinical implications of these findings. Controlling protein adsorption—through surface chemistry, pre‑coating strategies, or anti‑fouling treatments—could be employed to minimize early bacterial colonization. Nevertheless, when high protein adsorption is unavoidable (as in vivo, where serum proteins rapidly coat implants), additional antimicrobial layers (e.g., silver nanoparticles, antibiotic‑releasing polymers) may be required to counteract the enhanced EPS production. Moreover, the choice between PP and HDPE should consider not only mechanical requirements but also the type of biofilm matrix they are likely to support, as this may affect infection persistence and treatment response.

In conclusion, the work demonstrates that BSA adsorption onto PP and HDPE is both time‑ and concentration‑dependent and that the amount of adsorbed protein directly influences the quantity and structural characteristics of P. aeruginosa biofilms. The study highlights the importance of protein‑surface interactions in implant infection biology and calls for further investigations using a broader range of serum proteins, mixed‑protein coatings, and in vivo models to translate these insights into practical anti‑infection strategies.