The in vitro effects of antibiotics on cell viability and gene expression of equine bone marrow-derived mesenchymal stromal cells

Interactions Between Biologic Therapies and Other Treatment Modalities

Biologic therapies are becoming increasingly utilized by veterinarians. The literature regarding the interaction of biologic therapies with other therapeutics is still in its infancy. Initial studies have examined the effects of exercise, stress, various pharmaceutical interventions, extracorporeal shockwave, therapeutic laser, and hyperbaric oxygen on biologic therapies. Continued research is imperative as owners and veterinarians increasingly choose a multimodal approach to injury and illness. Further, understanding the effects of concurrently administered treatments and pharmaceuticals as well as the health status of the horse is imperative to providing the optimal therapeutic outcome.

Mesenchymal stem cells: A promising antimicrobial therapy in veterinary medicine

Growing antimicrobial resistance (AMR) is a threat to human and animal populations citing the limited available options. Alternative antimicrobial options or functional enhancement of currently available antimicrobials remains only options. One of the potential options seems stem cells especially the mesenchymal stem cells (MSCs) that show antimicrobial properties. These cells additionally have pro-healing effects that may plausibly improve healing outcomes. MSCs antimicrobial actions are mediated either through direct cell-cell contact or their secretome that enhances innate immune mediated antimicrobial activities. These cells synergistically enhance efficacy of currently available antimicrobials especially against the biofilms. Reciprocal action from antimicrobials on the MSCs functionality remains poorly understood. Currently, the main limitation with MSCs based therapy is their limited efficacy. This demands further understanding and can be enhanced through biotechnological interventions. One of the interventional options is the 'priming' to enhance MSCs resistance and specific expression potential. The available literature shows potential antimicrobial actions of MSCs both ex vivo as well as in vivo. The studies on veterinary species are very promising although limited by number and extensiveness in details for their utility as standard therapeutic agents. The current review aims to discuss the role of animals in AMR and the potential antimicrobial actions of MSCs in veterinary medicine. The review also discusses the limitations in their utilization as standard therapeutics.

Toxicity induced by ciprofloxacin and enrofloxacin: oxidative stress and metabolism

Ciprofloxacin (CIP) (human use) and enrofloxacin (ENR) (veterinary use) are synthetic anti-infectious medications that belong to the second generation of fluoroquinolones. They have a wide antimicrobial spectrum and strong bactericidal effects at very low concentrations via enzymatic inhibition of DNA gyrase and topoisomerase IV, which are required for DNA replication. They also have high bioavailability, rapid absorption with favorable pharmacokinetics and excellent tissue penetration, including cerebral spinal fluid. These features have made them the most applied antibiotics in both human and veterinary medicine. ENR is marketed exclusively for animal medicine and has been widely used as a therapeutic veterinary antibiotic, resulting in its residue in edible tissues and aquatic environments, as well as the development of resistance and toxicity. Estimation of the risks to humans due to antimicrobial resistance produced by CIP and ENR is important and of great interest. Moreover, in rare cases due to their overdose and/or prolonged administration, the development of CIP and ENR toxicity may occur. The toxicity of these fluoroquinolones antimicrobials is mainly related to reactive oxygen species (ROS) and oxidative stress (OS) generation, besides metabolism-related toxicity. Therefore, CIP is restricted in pregnant and lactating women, pediatrics and elderly similarly ENR do in the veterinary field. This review manuscript aims to identify the toxicity induced by ROS and OS as a common sequel of CIP and ENR. Furthermore, their metabolism and the role of metabolizing enzymes were reported.

Intra-articular administration of antibiotics in horses: Justifications, risks, reconsideration of use and outcomes

Antibiotics have been injected intra-articularly by equine veterinarians for decades, either prophylactically when other drugs are administered for osteoarthritis or therapeutically to treat septic arthritis. This route of administration has also more recently gained attention in human orthopaedic clinical practice, particularly as an alternative to systemic antibiotic administration to treat infections following prosthetic arthroplasty. While the rationale for injecting antibiotics intra-articularly has been largely focused on achieving high local drug concentrations, there has been relatively little focus on pharmacokinetic parameters of antibiotics administered by this route, or on the potential for local toxicity. The increasing incidence of antibiotic resistance in veterinary and human medicine prompts reconsideration of off-label antibiotic usage and evaluation of evidence-based dosing strategies. The purpose of this review was to summarise the current literature describing intra-articular antibiotic usage, including specific studies where pharmacokinetics, potential safety and toxicity have been evaluated. This review will advance practitioners' understanding of the use of intra-articularly administered antibiotics, including the overall pros and cons of the approach.

Drug Carriers Based on Graphene Oxide and Hydrogel: Opportunities and Challenges in Infection Control Tested by Amoxicillin Release

Graphene oxide (GO) was proposed as an efficient carrier of antibiotics. The model drug, amoxicillin (AMOX), was attached to GO using a peptide linker (Leu-Leu-Gly). GO-AMOX was dispersed in a hydrogel to which the enzyme responsible for releasing AMOX from GO was also added. The drug molecules were released by enzymatic hydrolysis of the peptide bond in the linker. As the selected enzyme, bromelain, a plant enzyme, was used. The antibacterial nature of the carrier was determined by its ability to inhibit the growth of the Enterococcus faecalis strain, which is one of the bacterial species responsible for periodontal and root canal diseases. The prepared carrier contained only biocompatible substances, and the confirmation of its lack of cytotoxicity was verified based on the mouse fibrosarcoma cell line WEHI 164. The proposed type of preparation, as a universal carrier of many different antibiotic molecules, can be considered as a suitable solution in the treatment of inflammation in dentistry.

Pathways involved in pony body size development

BACKGROUND

The mechanism of body growth in mammals is poorly understood. Here, we investigated the regulatory networks involved in body growth through transcriptomic analysis of pituitary and epiphyseal tissues of smaller sized Debao ponies and Mongolian horses at the juvenile and adult stages.

RESULTS

We found that growth hormone receptor (GHR) was expressed at low levels in long bones, although growth hormone (GH) was highly expressed in Debao ponies compared with Mongolian horses. Moreover, significant downregulated of the GHR pathway components m-RAS and ATF3 was found in juvenile ponies, which slowed the proliferation of bone osteocytes. However, WNT2 and PLCβ2 were obviously upregulated in juvenile Debao ponies, which led to premature mineralization of the bone extracellular matrix. Furthermore, we found that the WNT/Ca²⁺ pathway may be responsible for regulating body growth. GHR was demonstrated by q-PCR and Western blot analyses to be expressed at low levels in long bones of Debao ponies. Treatment with WNT antagonistI decreased the expression of WNT pathway components (P < 0.05) in vitro. Transduction of ATDC5 cells with a GHR-RNAi lentiviral vector decreased the expression of the GHR pathway components (P < 0.05). Additionally, the expression of the IGF-1 gene in the liver was lower in Debao ponies than in Mongolian horses at the juvenile and adult stages. Detection of plasma hormone concentrations showed that Debao ponies expressed higher levels of IGF-1 as juveniles and higher levels of GH as adults than Mongolian horses, indicating that the hormone regulation in Debao ponies differs from that in Mongolian horses.

CONCLUSION

Our work provides insights into the genetic regulation of short stature growth in mammals and can provide useful information for the development of therapeutic strategies for small size.

Mesenchymal Stromal Cells as Potential Antimicrobial for Veterinary Use-A Comprehensive Review

The emergence of “superbugs” resistant to antimicrobial medications threatens populations both veterinary and human. The current crisis has come about from the widespread use of the limited number of antimicrobials available in the treatment of livestock, companion animal, and human patients. A different approach must be sought to find alternatives to or enhancements of present conventional antimicrobials. Mesenchymal stromal cells (MSC) have antimicrobial properties that may help solve this problem. In the first part of the review, we explore the various mechanisms at work across species that help explain how MSCs influence microbial survival. We then discuss the findings of recent equine, canine, and bovine studies examining MSC antimicrobial properties in which MSCs are found to have significant effects on a variety of bacterial species either alone or in combination with antibiotics. Finally, information on the influence that various antimicrobials may have on MSC function is reviewed. MSCs exert their effect directly through the secretion of various bioactive factors or indirectly through the recruitment and activation of host immune cells. MSCs may soon become a valuable tool for veterinarians treating antimicrobial resistant infections. However, a great deal of work remains for the development of optimal MSC production conditions and testing for efficacy on different indications and species.

A Survey of Clinical Usage of Non-steroidal Intra-Articular Therapeutics by Equine Practitioners

There are several non-steroidal intra-articular therapeutics (NSIATs) available for use by equine practitioners for the treatment of performance-limiting joint-related pathology. Information is limited on perceived clinical efficacy, recommended treatment protocols, and associated complications. Our objective with this cross-sectional survey was to investigate the current clinical usage of NSIATs by equine practitioners. An electronic cross-sectional convenience survey inquiring about the use of steroidal and NSIATS (platelet-rich plasma, autologous conditioned serum, autologous protein solution, cellular therapies, and polyacrylamide hydrogel) was distributed internationally to equine practitioners. A total of 353 surveys were completed. NSIATs were used by 87.5% of the participants. Corticosteroids and hyaluronic acid remain the intra-articular therapeutic of choice among practitioners, followed by autologous conditioned serum, platelet-rich plasma and autologous conditioned protein. Polyacrylamide hydrogel was the least used. Practitioners were more likely to use NSIATs if their caseload was > 50% equine (P < 0.001), they treated more than 10 horses intra-articularly per month (P < 0.001), and horses treated were considered English sport horses (P = 0.02). Years in practice and practice location did not influence the use of NSIATs. One of the most common reasons why NSIATs were chosen was to treat acute articular pathologies. As survey limitations, answers to questions regarding clinical response and complication rates were based on subjective estimation and practitioners recall, not clinical records. In conclusion, corticosteroids remain the most widely used intra-articular therapeutic. Among the NSIATs, blood-based products are more commonly used by practitioners, followed by cellular and synthetic products. Equine practitioners frequently use NSIATs, choosing to treat acute joint pathology more than previously reported.

Use of in vitro assays to identify antibiotics that are cytotoxic to normal equine chondrocytes and synovial cells

BACKGROUND

Intra-articular (IA) antibiotic usage is prevalent in equine practice. However, recent emergence of antimicrobial resistance prompts re-evaluation of antibiotic selection, particularly when used prophylactically. Furthermore, many commonly used antibiotics exert direct cytotoxicity to equine cells, and appropriate IA doses have not been defined.

OBJECTIVES

To screen antibiotics in vitro as an initial assessment of cytotoxicity against normal equine joint cells in monolayer culture and explant tissues.

STUDY DESIGN

In vitro experimental study.

METHODS

Chondrocytes and synovial cells were harvested from three horses and plated on 24-well plates (100 000 cells/wells in triplicate) for 48 hours prior to addition of antibiotics. Joint cells were exposed to antibiotics (n = 15) at various doses (25-0.39 mg/mL in complete DMEM media) for 24 hours and viability was assessed by trypan blue dye exclusion. The half maximal inhibitory concentration (IC50) was determined for each antibiotic. Cartilage explants were obtained from 3 horses, minced and exposed to antibiotics (n = 5) for 72 hours. Live/dead staining was performed, and fluorescence was visualised using Olympus IX83 spinning disk confocal microscope. Percentage of live vs dead cells was quantified.

RESULTS

Antibiotics from different antimicrobial classes expressed dose-dependent but variable cytotoxicity to equine joint cells in vitro. Aminoglycosides and doxycycline had the lowest IC50 (most toxic). Ampicillin sulbactam, imipenem, tobramycin, ceftiofur sodium and amoxicillin had IC50 > 25 mg/mL for at least one cell line, representing potentially less cytotoxic alternatives.

MAIN LIMITATIONS

Further studies are necessary to extrapolate these in vitro data results to the in vivo joint environment.

CONCLUSIONS

Targeted IA antibiotic therapy would involve selection of the safest antibiotics (highest IC50) with efficacy based on bacterial culture/sensitivity. Antimicrobial selection and evidence-based dosing may minimise damage to native articular cartilage and synovial cells and development of antimicrobial resistance when IA antibiotics are used in equine practice.

Amikacin induces rapid dose-dependent apoptotic cell death in equine chondrocytes and synovial cells in vitro

BACKGROUND

Equine veterinarians frequently inject aminoglycoside antibiotics intra-articularly, either to treat septic arthritis or for prophylaxis with other medications when injecting joints for osteoarthritis. Although aminoglycosides have been demonstrated to be toxic to equine mesenchymal stem cells (MSC), their effects on resident joint cells have not been previously investigated. Moreover, safe and effective intra-articular doses have not been defined.

OBJECTIVES

To determine effects of concentration, duration of exposure, pH and the presence of synovial fluid on the cytotoxic effects of amikacin on equine chondrocytes, synoviocytes and bone marrow- and adipose-derived MSC.

STUDY DESIGN

In vitro experimental study.

METHODS

Four cell types were harvested from three donor horses and plated in triplicate wells for 48 hours prior to the addition of amikacin. The effects of amikacin on cell viability were assessed for different exposure times, concentrations and with pH buffered or unbuffered in media, as well as in the presence of synovial fluid. Cell metabolism/viability was assessed by colorimetric MTT assay. Cell proliferation was assessed by live cell imaging. Cell viability was assessed using trypan blue and dimeric cyanine nucleic acid stain (yoyo-1). To determine the mechanism of cell death, apoptosis was evaluated using Annexin V and 7AAD staining with flow cytometric quantification. Induction of apoptotic cell death pathways was assessed using caspase-3 expression.

RESULTS

Amikacin is cytotoxic to equine joint cells and MSC in a rapid, dose-dependent, pH-independent manner, which occurs primarily by apoptosis. Amikacin cytotoxicity was not mitigated by the addition of synovial fluid in vitro.

MAIN LIMITATIONS

Further studies are necessary to determine whether these in vitro results predict joint injury in live animal models.

CONCLUSIONS

Amikacin at clinically applied doses induces rapid, pronounced cell death of equine joint cells. These findings suggest that amikacin doses currently used intra-articularly should be reconsidered pending in vivo joint titration studies.

Cryopreservation in 95% serum with 5% DMSO maintains colony formation and chondrogenic abilities in human synovial mesenchymal stem cells

Background

Synovial mesenchymal stem cells (MSCs) are an attractive cell source for cartilage and meniscus regeneration. The optimum cryopreservation medium has not been determined, but dimethylsulfoxide (DMSO) should be excluded, if possible, because of its toxicity. The purposes of our study were to examine the possible benefits of higher concentrations of serum and the effectiveness of 100% serum (without DMSO) for the cryopreservation of synovial MSCs.

Methods

Human synovium was harvested from the knees of four donors with osteoarthritis during total knee arthroplasty. Synovial MSCs (8 × 10⁵ cells) were suspended in 400 μL medium and used as a Time 0 control. The same number of synovial MSCs was also suspended in 400 μL α-MEM medium containing 10% fetal bovine serum (FBS) (5% DMSO, and 1% antibiotic), 95% FBS (and 5% DMSO), or 100% FBS (no DMSO) and cryopreserved at − 80 °C for 7 days. After thawing, the cell suspensions (1.5 μL; 3 × 10³ cells) were cultured in 60 cm² dishes for 14 days for colony formation assays. Additional 62.5 μL samples of cell suspensions (1.25 × 10⁵ cells) were added to tubes and cultured for 21 days for chondrogenesis assays.

Results

Colony numbers were significantly higher in the Time 0 and 95% FBS groups than in the 10% FBS group (n = 24). Colony numbers were much lower in the 100% FBS group than in the other three groups. The cell numbers per dish reflected the colony numbers. Cartilage pellet weights were significantly heavier in the 95% FBS group than in the 10% FBS group, whereas no difference was observed between the Time 0 and the 95% FBS groups (n = 24). No cartilage pellets formed at all in the 100% FBS group.

Conclusion

Synovial MSCs cryopreserved in 95% FBS with 5% DMSO maintained their colony formation and chondrogenic abilities to the same levels as observed in the cells before cryopreservation. Synovial MSCs cryopreserved in 100% FBS lost their colony formation and chondrogenic abilities.

Electronic supplementary material

The online version of this article (10.1186/s12891-019-2700-3) contains supplementary material, which is available to authorized users.

Practical considerations for clinical use of mesenchymal stem cells: From the laboratory to the horse

Since the clinical use of mesenchymal stem cells (MSCs) for treating musculoskeletal injuries is gaining popularity, practitioners should be aware of the factors that may affect MSCs from tissue harvesting for MSC isolation to cell delivery into the injury site. This review provides equine practitioners with up-to-date, practical knowledge for the treatment of equine patients using MSCs. A brief overview of laboratory procedures affecting MSCs is provided, but the main focus is on shipping conditions, routes of administration, injection methods, and which commonly used products can be combined with MSCs and which products should be avoided as they have deleterious effects on cells. There are still several knowledge gaps regarding MSC-based therapies in horses. Therefore, it is important to properly manage the factors which are currently known to affect MSCs, to further strengthen the evidence basis of this treatment.

Cell-Based Therapies for Joint Disease in Veterinary Medicine: What We Have Learned and What We Need to Know

Biological cell-based therapies for the treatment of joint disease in veterinary patients include autologous-conditioned serum, platelet-rich plasma, and expanded or non-expanded mesenchymal stem cell products. This narrative review outlines the processing and known mechanism of action of these therapies and reviews current preclinical and clinical efficacy in joint disease in the context of the processing type and study design. The significance of variation for biological activity and consequently regulatory approval is also discussed. There is significant variation in study outcomes for canine and equine cell-based products derived from whole blood or stem cell sources such as adipose and bone marrow. Variation can be attributed to altering bio-composition due to factors including preparation technique and source. In addition, study design factors like selection of cases with early vs. late stage osteoarthritis (OA), or with intra-articular soft tissue injury, influence outcome variation. In this under-regulated field, variation raises concerns for product safety, consistency, and efficacy. Cell-based therapies used for OA meet the Food and Drug Administration’s (FDA’s) definition of a drug; however, researchers must consider their approach to veterinary cell-based research to meet future regulatory demands. This review explains the USA’s FDA guidelines as an example pathway for cell-based therapies to demonstrate safety, effectiveness, and manufacturing consistency. An understanding of the variation in production consistency, effectiveness, and regulatory concerns is essential for practitioners and researchers to determine what products are indicated for the treatment of joint disease and tactics to improve the quality of future research.

Influence of commonly used pharmaceutical agents on equine bone marrow-derived mesenchymal stem cell viability

REASON FOR PERFORMING STUDY

To provide evidence to support recommendations regarding the co-administration of drugs with mesenchymal stem cell (MSC) therapy.

OBJECTIVES

To determine the influence of sedatives, local anaesthetic and corticosteroids on MSC viability and proliferation, in comparison to somatic cells derived from tendon (TDCs).

STUDY DESIGN

In vitro cell culture.

MATERIALS AND METHODS

MSCs (n = 3) and TDCs (n = 2) were cultured in media containing a clinically relevant dose range of xylazine, romifidine, detomidine and butorphanol, mepivacaine, methylprednisolone, or triamcinolone acetonide. Cell viability in suspension culture was assessed at intervals up to 4 h using the trypan blue dye assay. MSCs in monolayer culture were exposed to the highest concentrations of drug and proliferation was measured using the alamarBlue fluorescence assay.

RESULTS

Exposure to romifidine or mepivacaine did not significantly affect viability or proliferation rate of MSCs or TDCs at any of the dosages tested. At the highest concentration of detomidine and butorphanol, MSC viability was significantly reduced compared to controls. Although xylazine exposure caused a significant (P < 0.001), dose-dependent reduction in MSC viability compared to controls, overall population viability remained good. Conversely, both methylprednisolone and triamcinolone resulted in the rapid death of significant numbers of MSCs (P < 0.001).

CONCLUSIONS

Clinicians can sedate horses and administer nerve blocks to assist in intratendinous or intrathecal injection of MSCs with confidence that these drugs will not impact the viability of implanted cells. However, the concomitant use of corticosteroids is likely to have a severely detrimental effect on cell viability and should not be performed. Similarly, steroid administration into the sheath of a damaged tendon is not recommended.

Effect of Antibiotic Class on Stroke Outcome

BACKGROUND AND PURPOSE

Infections are common after stroke and associated with worse outcome. Clinical trials evaluating the benefit of prophylactic antibiotics have produced mixed results. This study explores the possibility that antibiotics of different classes may differentially affect stroke outcome.

METHODS

Lewis rats were subjected to transient cerebral ischemia (2 hours) and survived for 1 month. The day after stroke they were randomized to therapy with ceftiofur (a β-lactam antibiotic), enrofloxacin (a fluoroquinolone antibiotic), or vehicle (as controls) and underwent the equivalent of 7 days of treatment. Behavioral tests were performed weekly until euthanization. In a subset of animals, histology was done.

RESULTS

There were no differences in outcomes at 24 hours or 1 week after stroke among the different groups. At 1 month after stroke, however, performance on the rotarod was worse in enrofloxacin-treated animals when compared with control animals.

CONCLUSIONS

Independent of infection, the antibiotic enrofloxacin was associated with worse stroke outcome. These data echo the clinical observations to date and suggest that the secondary effects of antibiotics on stroke outcome should be considered when treating infection in subjects with stroke. The mechanism by which this antibiotic affects outcome needs to be elucidated.

Isolation of equine multipotent mesenchymal stromal cells by enzymatic tissue digestion or explant technique: comparison of cellular properties

BACKGROUND

The treatment of tendon lesions with multipotent mesenchymal stromal cells (MSCs) is widely used in equine medicine. Cell sources of MSCs include bone marrow, as well as solid tissues such as adipose tissue. MSCs can be isolated from these solid tissues either by enzymatic digestion or by explant technique. However, the different preparation techniques may potentially influence the properties of the isolated MSCs. Therefore, the aim of this study was to investigate and compare the effects of these two different methods used to isolate MSCs from solid tissues.Equine adipose tissue, tendon and umbilical cord matrix served as solid tissue sources of MSCs with different stiffness and density. Subsequent to tissue harvest, MSCs were isolated either by enzymatic digestion with collagenase or by explant technique. Cell yield, growth, differentiation potential and tendon marker expression were analysed.

RESULTS

At first passage, the MSC yield was significantly higher in enzymatically digested tissue samples than in explanted tissue samples, despite a shorter period of time in primary culture. Further analysis of cell proliferation, migration and differentiation revealed no significant differences between MSCs isolated by enzymatic digestion and MSCs isolated by explant technique. Interestingly, analysis of gene expression of tendon markers revealed a significantly higher expression level of scleraxis in MSCs isolated by enzymatic digestion.

CONCLUSIONS

Both isolation techniques are feasible methods for successful isolation of MSCs from solid tissues, with no major effects on cellular proliferation, migration or differentiation characteristics. However, higher MSC yields were achieved in a shorter period of time by collagenase digestion, which is advantageous for the therapeutic use of MSCs. Moreover, based on the higher level of expression of scleraxis in MSCs isolated by enzymatic digestion, these cells might be a better choice when attempting tendon regeneration.

The use of antimicrobial-impregnated PMMA to manage periprosthetic infections: controversial issues and the latest developments

Despite improvements in intraoperative antimicrobial procedures, in surgical techniques and in implant design for joint replacement, periprosthetic infection after arthroplasty is still one of the most challenging problems encountered by orthopedic surgeons. Systemic antibiotics are not sufficiently effective to eradicate such deep infections because of the impaired blood circulation and low antibiotic concentration at the implantation site. As a local drug delivery system, antibiotic-impregnated PMMA (polymethylmethacrylate) bone cements have been widely used for prophylaxis or treatment of deep infections after total joint replacement. However, the effectiveness of antibiotic-loaded PMMA in preventing infections after arthroplasty is still controversial. Furthermore, the outcomes of established deep infections treated with this technique are not consistent. The local use of antibiotics has led to the emergence of antibiotic-resistant bacterial strains and has adverse effects on the function of osteogenic cells. Recently, many efforts have been made to identify new antibacterial agents that can be loaded into PMMA. These antimicrobial agents should exhibit good antibacterial activity against antibiotic-resistant strains and should simultaneously enhance osteointegration between the PMMA and the bone tissue. PMMA loaded with chitosan or chitosan derivatives has been demonstrated to induce improved osteogenic activity and to exhibit antibacterial activity in a preclinical study.

Bactericidal property and biocompatibility of gentamicin-loaded mesoporous carbonated hydroxyapatite microspheres

Implant-associated infection is a serious problem in orthopaedic surgery. One of the most effective ways is to introduce a controlled antibiotics delivery system into the bone filling materials, achieving sustained release of antibiotics in the local sites of bone defects. In the present work, mesoporous carbonated hydroxyapatite microspheres (MCHMs) loaded with gentamicin have been fabricated according to the following stages: (i) the preparation of the MCHMs by hydrothermal method using calcium carbonate microspheres as sacrificial templates, and (ii) loading gentamicin into the MCHMs. The MCHMs exhibit the 3D hierarchical nanostructures constructed by nanoplates as building blocks with mesopores and macropores, which make them have the higher drug loading efficiency of 70-75% than the conventional hydroxyapatite particles (HAPs) of 20-25%. The gentamicin-loaded MCHMs display the sustained drug release property, and the controlled release of gentamicin can minimize significantly bacterial adhesion and prevent biofilm formation against S. epidermidis. The biocompatibility tests by using human bone marrow stromal cells (hBMSCs) as cell models indicate that the gentamicin-loaded MCHMs have as excellent biocompatibility as the HAPs, and the dose of the released gentamicin from the MCHMs has no toxic effects on the hBMSCs. Hence, the gentamicin-loaded MCHMs can be served as a simple, non-toxic and controlled drug delivery system to treat bone infections.

Quaternized chitosan as an antimicrobial agent: antimicrobial activity, mechanism of action and biomedical applications in orthopedics

Chitosan (CS) is a linear polysaccharide with good biodegradability, biocompatibility and antimicrobial activity, which makes it potentially useful for biomedical applications, including an antimicrobial agent either alone or blended with other polymers. However, the poor solubility of CS in most solvents at neutral or high pH substantially limits its use. Quaternary ammonium CS, which was prepared by introducing a quaternary ammonium group on a dissociative hydroxyl group or amino group of the CS, exhibited improved water solubility and stronger antibacterial activity relative to CS over an entire range of pH values; thus, this quaternary modification increases the potential biomedical applications of CS in the field of anti-infection. This review discusses the current findings on the antimicrobial properties of quaternized CS synthesized using different methods and the mechanisms of its antimicrobial actions. The potential antimicrobial applications in the orthopedic field and perspectives regarding future studies in this field are also considered.