Amparo María Gallardo-Moreno

Surface damage occurring during surgery can compromise coating integrity, leaving exposed areas susceptible to bacterial colonization. However, the impact of partial coating loss on antibacterial performance has not yet been investigated. In this work, a multifunctional UV-activated coating composed of hydroxyapatite, magnesium phosphate, and zinc oxide (HMZ) was developed and electrodeposited onto AZ31 and MgCa magnesium alloys. Its antibacterial efficacy against Staphylococcus aureus and Escherichia coli was evaluated under three conditions: adhered bacteria, planktonic cells, and biofilm. In the absence of UV activation, coated surfaces exhibited no significant antibacterial activity. In contrast, fully coated and UV-activated surfaces achieved bacterial reductions above 98% in all scenarios. Surfaces with 60% coverage showed antibacterial efficacy equivalent to that of fully coated surfaces, even against established biofilm. Surfaces with 30% coverage also exhibited moderate activity, particularly against adhered and planktonic bacteria. These results demonstrate that full surface coverage is not required to preserve the coating’s antibacterial effectiveness. This strategy provides a clinically relevant solution to maintain antibacterial protection even when coating integrity is compromised.

The development of bioabsorbable biomaterials with surface properties that promote tissue integration while preventing bacterial colonization remains a major challenge in biomedical engineering. In this study, polylactic acid (PLA) films with tailored surface microtopographies were fabricated through a simple and scalable solvent casting approach by incorporating surfactants with different chemical natures: sodium dodecylsulphate (SDS), hexadecyltrimethylammonium bromide (CTAB) and polysorbate 20 (Tween-20, T20). Magnesium particles were also incorporated as a biodegradable antibacterial additive and to improve the mechanical behaviour of PLA. Surface morphology and topography were analyzed by atomic force microscopy and optical profilometry, while wettability and surface free energy were assessed by contact angle measurements. The biological performance of the films was evaluated using Staphylococcus epidermidis adhesion and biofilm formation assays, together with cell viability studies employing HaCaT human keratinocytes.Distinct and reproducible surface microstructures were generated depending on the surfactant employed, including conical protrusions, isotropically distributed microcavities, and spiral-like patterns. Surfactant incorporation reduced bacterial adhesion relative to pristine PLA, an effect further enhanced by magnesium addition, which led to the total inhibition of viable biofilms on CTAB- and SDS-containing samples. In contrast to samples incorporating CTAB or SDS, T20-modified PLA supported keratinocyte adhesion and long-term viability, even in the presence of magnesium. These results establish surfactant-induced microstructuring as a powerful and unexplored strategy for modulating the biological response of PLA, opening new avenues for the design of bioabsorbable biomedical devices for wound healing.

Polylactic acid (PLA) is gaining prominence in biomedical fields due to its favorable physicochemical characteristics, such as biodegradability and biocompatibility. This study investigates the degradation behavior of PLA films fabricated with dimethyl carbonate, a green solvent alternative to traditional chloroform, and sterilized via UV-C irradiation. Two degradation pathways were examined: exposure to ultraviolet radiation (photodegradation) and immersion in a simulated body fluid (m-SBF) buffer (physiodegradation), with and without human supplementation of serum albumin (HSA). Surface properties such as zeta potential, hydrophobicity, surface tension, and chemical composition were evaluated before and after degradation. Prolonged UV-C photodegradation resulted in chemical activation of the surface, which modulated subsequent interactions with the physiological environment. More specifically, an increase of the negative surface charge and a slight reduction of the surface free energy were observed. Photodegradation enhanced subsequent physiodegradation, as evidenced by greater surface polarity and ion adsorption. Immersion in m-SBF led to increased hydrophilicity, while HSA presence during immersion influenced the formation of biointerfacial layers, markedly shifting the surface to a superhydrophilic and nearly neutral electrical state. Analytical techniques such as time-of-flight secondary ion mass spectrometry identified the presence of nitrogen-containing fragments indicative of protein attachment. Notably, UV-C exposure reduced protein adsorption, suggesting changes in surface affinity.

Metal–organic frameworks (MOFs) can be prepared from bioactive molecules, which are released during the degradation of the material in the body. Particularly, MOFs have recently emerged as bisphosphonate (BP) drug delivery systems. In this work, two novel MOFs based on the smallest bisphosphonate medronic acid (MA) and calcium with formulas [Ca­(CH₄O₆P₂)·H₂O] (GR-MOF-23) and [Ca­(CH₄O₆P₂)·CH₃OH] (GR-MOF-24) in aqueous and/or methanolic solutions at room temperature were synthesized and fully characterized. The stability test performed in simulated physiological conditions (a phosphate buffer saline (PBS, pH = 7.4, 10 mM) solution at 37 °C) showed a progressive Ca²⁺ leaching from both GR-MOF-23 and GR-MOF-24, achieving 38.0 ± 2.8 and 35.8 ± 3.9% release of calcium after 1 week of suspension. Interestingly, the recovered solid residues from the stability tests were identified as apatite and calcium phosphate phases, which might facilitate the formation of bone apatite and collagen. The antibacterial activity of GR-MOF-23 and GR-MOF-24 was investigated against Escherichia coli and Staphylococcus aureus, among the most relevant human pathogens, causing a wide variety of infections in bone fracture in osteoporosis and prosthesis. While both materials exhibited bacteria growth inhibition, GR-MOF-24 also showed a bactericide action, likely due to a more progressive release of Ca²⁺, which is the ion related to the improved stability of the biofilm. These innovative materials present exciting opportunities for developing antibacterial surfaces in prosthetics and the treatment of bone fracture infections.

Interest in biodegradable implants has focused attention on the resorbable polymer polylactic acid. However, the risk of these materials promoting infection, especially in patients with existing pathologies, needs to be monitored. The enrichment of a bacterial adhesion medium with compounds that are associated with human pathologies can help in understanding how these components affect the development of infectious processes. Specifically, this work evaluates the influence of glucose and ketone bodies (in a diabetic context) on the adhesion dynamics of S. aureus to the biomaterial polylactic acid, employing different approaches and discussing the results based on the physical properties of the bacterial surface and its metabolic activity. The combination of ketoacidosis and hyperglycemia (GK2) appears to be the worst scenario: this system promotes a state of continuous bacterial colonization over time, suppressing the stationary phase of adhesion and strengthening the attachment of bacteria to the surface. In addition, these supplements cause a significant increase in the metabolic activity of the bacteria. Compared to non-enriched media, biofilm formation doubles under ketoacidosis conditions, while in the planktonic state, it is glucose that triggers metabolic activity, which is practically suppressed when only ketone components are present. Both information must be complementary to understand what can happen in a real system, where planktonic bacteria are the ones that initially colonize a surface, and, subsequently, these attached bacteria end up forming a biofilm. This information highlights the need for good monitoring of diabetic patients, especially if they use an implanted device made of PLA.