In vitro evaluation of a fibrin gel antibiotic delivery system containing mesenchymal stem cells and vancomycin alginate beads for treating bone infections and facilitating bone formation

In vivo hydroxyapatite scaffold performance in infected bone defects

Critically sized bone defects are often compounded by infectious complications. The standard of care consists of bone autografts with systemic antibiotics. These injuries and treatments lead to donor site morbidity, antibiotic resistant strains of bacteria, and often end stage amputation. This study proposes an alternative to the autograft using a porous, hydroxyapatite (HA) scaffold evaluated with and without infection and antibiotics. Twenty-four New Zealand white rabbits received either our HA scaffold or a pulverized autograft (PBA) within a surgically created critical-sized defect in the femur. The two grafts were evaluated in either septic or aseptic defects and with or without antibiotic treatment. The HA scaffolds were characterized with micro computed tomography. Post-euthanasia, micro computed tomography, histology, and white blood cells component analysis were completed. The HA had significantly greater (p < .001) mineralization to total volume than the PBA groups with 27.56% and 14.88%, respectively, and the septic HA groups were significantly greater than the aseptic groups both with and without antibiotics (p = .016). The bone quality denoted by bone mineral density was also significantly greater (p < .001) in the HA groups (67.01 ± 0.38 mgHA/cm³ ) than the PBA groups (64.66 ± 0.85 mgHA/cm³ ). The HA scaffold is a viable alternative to the bone autograft in defects with and without infection as shown by the quality and quantity of bone.

Treatment of open upper limb injuries with infection prevention and negative pressure wound therapy: a systematic review

OBJECTIVE

Open upper limb injuries requiring soft reconstruction can pose a dilemma for trauma surgeons when considering the treatment options. The British Orthopaedic Association and British Association of Plastic, Reconstructive and Aesthetic Surgeons Standard for Trauma (BOAST) have addressed the management of severe open lower limb fractures with the creation of the BOAST 4 guidelines. However, no such gold standard exists for the treatment of open injuries of the upper limb. Furthermore, treatment of these injuries is often more difficult and requires complicated strategies. Since the advent of negative pressure wound therapy (NPWT), there has been an improvement in wound care, though a focused review of its use in wound closure and infection prevention in the upper limb has not been published. We examine wound care management for open upper limb injuries with regard to the dressings applied, NPWT, wound closure and infection prevention.

METHOD

A systematic search of Medline, Cochrane and Google Scholar was performed using the key words. The key word searches were performed by two independent reviewers and 8,792 papers were found. Manuscripts between 1990 and 2010 were included, with the addition of key manuscripts before this date. Each manuscript was assessed by the two authors independently for methodology and validity Results: Approximately 120 manuscripts fulfilled selection criteria examining the influence of NPWT on open upper and lower limb injuries, and those examining infection risk in the same injuries. Of these 120 manuscripts, 28 were suitable for inclusion in the review. The systematic review is presented, allied to the BOAST 4 principles, examining the use of NPWT and the tools available for infection prevention for wounds of the upper and lower limb. The use of NPWT in conjunction with antibiotic-bead therapy improved the way in which open fractures of both the upper and lower limb are treated.

CONCLUSION

Production of guidelines is warranted for the treatment of upper limb injuries. The treatment options available for wound closure and infection prevention that are used in the treatment of open injuries of the lower limb could be adopted to open injuries of the upper limb.

Clinical Applications of Bone Tissue Engineering in Orthopedic Trauma

Purpose of Review

Orthopaedic trauma is a major cause of morbidity and mortality worldwide. Although many fractures tend to heal if treated appropriately either by nonoperative or operative methods, delayed or failed healing, as well as infections, can lead to devastating complications. Tissue engineering is an exciting, emerging field with much scientific and clinical relevance in potentially overcoming the current limitations in the treatment of orthopaedic injuries.

Recent Findings

While direct translation of bone tissue engineering technologies to clinical use remains challenging, considerable research has been done in studying how cells, scaffolds, and signals may be used to enhance acute fracture healing and to address the problematic scenarios of nonunion and critical-sized bone defects. Taken together, the research findings suggest that tissue engineering may be considered to stimulate angiogenesis and osteogenesis, to modulate the immune response to fractures, to improve the biocompatibility of implants, to prevent or combat infection, and to fill large gaps created by traumatic bone loss. The abundance of preclinical data supports the high potential of bone tissue engineering for clinical application, although a number of barriers to translation must first be overcome.

Summary

This review focuses on the current and potential applications of bone tissue engineering approaches in orthopaedic trauma with specific attention paid to acute fracture healing, nonunion, and critical-sized bone defects.

Fibrin-based delivery strategies for acute and chronic wound healing

Fibrin, a natural hydrogel, is the end product of the physiological blood coagulation cascade and naturally involved in wound healing. Beyond its role in hemostasis, it acts as a local reservoir for growth factors and as a provisional matrix for invading cells that drive the regenerative process. Its unique intrinsic features do not only promote wound healing directly via modulation of cell behavior but it can also be fine-tuned to evolve into a delivery system for sustained release of therapeutic biomolecules, cells and gene vectors. To further augment tissue regeneration potential, current strategies exploit and modify the chemical and physical characteristics of fibrin to employ combined incorporation of several factors and their timed release. In this work we show advanced therapeutic approaches employing fibrin matrices in wound healing and cover the many possibilities fibrin offers to the field of regenerative medicine.

Biologically anchored chitosan/gelatin-SrHAP scaffold fabricated on Titanium against chronic osteomyelitis infection

The obstacles faced to treat chronic osteomyelitis infection clinically led to the search for an ideal biomaterial, resulted in combining two major aspects of bone tissue engineering namely surface modified metallic implant and polymer nanocomposite scaffold. In the present study Gelatin - Strontium incorporated Hydroxyapatite (SrHAP) forming HG scaffold, vancomycin loaded chitosan -gelatin polyelectrolyte complex incorporated gelatin-SrHAP, forming HV scaffolds (HV1-0.5wt% and HV2-1wt% vancomycin) were investigated. The HG, HV1 and HV2 scaffolds were successfully fabricated on Cp-Ti through anchoring by treatment with dopamine, which forms a bidentate co-ordination through NH bonding. Interconnected porous morphology of the scaffolds was confirmed, besides the globular Sr-HAP found in HV2 scaffold. The total amount of vancomycin encapsulation for HV1 and HV2 scaffolds were determined to be 47.55±1.6μg and 82.45±3.5μg respectively. Among the scaffolds studied HV2 scaffold were found to have a significant antibacterial activity for both MRSA and MSSA strains compared to Cp-Ti, HG and HV1 scaffolds. The HV2 scaffold also had significantly higher% of cell viability compared to Cp-Ti, HG and HV1 scaffolds. Furthermore, the presence of the drug vancomycin had no toxic effect on the cells, rather it aided in enhanced cell proliferation and spreading.

A review of fibrin and fibrin composites for bone tissue engineering

Tissue engineering has emerged as a new treatment approach for bone repair and regeneration seeking to address limitations associated with current therapies, such as autologous bone grafting. While many bone tissue engineering approaches have traditionally focused on synthetic materials (such as polymers or hydrogels), there has been a lot of excitement surrounding the use of natural materials due to their biologically inspired properties. Fibrin is a natural scaffold formed following tissue injury that initiates hemostasis and provides the initial matrix useful for cell adhesion, migration, proliferation, and differentiation. Fibrin has captured the interest of bone tissue engineers due to its excellent biocompatibility, controllable biodegradability, and ability to deliver cells and biomolecules. Fibrin is particularly appealing because its precursors, fibrinogen, and thrombin, which can be derived from the patient's own blood, enable the fabrication of completely autologous scaffolds. In this article, we highlight the unique properties of fibrin as a scaffolding material to treat bone defects. Moreover, we emphasize its role in bone tissue engineering nanocomposites where approaches further emulate the natural nanostructured features of bone when using fibrin and other nanomaterials. We also review the preparation methods of fibrin glue and then discuss a wide range of fibrin applications in bone tissue engineering. These include the delivery of cells and/or biomolecules to a defect site, distributing cells, and/or growth factors throughout other pre-formed scaffolds and enhancing the physical as well as biological properties of other biomaterials. Thoughts on the future direction of fibrin research for bone tissue engineering are also presented. In the future, the development of fibrin precursors as recombinant proteins will solve problems associated with using multiple or single-donor fibrin glue, and the combination of nanomaterials that allow for the incorporation of biomolecules with fibrin will significantly improve the efficacy of fibrin for numerous bone tissue engineering applications.

Amniotic fluid-derived stem cells mixed with platelet rich plasma for restoration of rat alveolar bone defect

Stem cells isolated from the amniotic fluid have been shown as a promising candidate for cell therapy and tissue engineering. However, the experimental and preclinical applications of amniotic fluid-derived stem cells (AFSCs) in the very field of maxillofacial bone tissue engineering are still limited. In this study, rat AFSCs were successfully harvested and characterized in vitro. The rat AFSCs showed typical fibroblastoid morphology, stable proliferation activity and multi-differentiation potential. Flow-cytometry analysis demonstrated that these cells were positive for CD29, CD44, and CD90, while negative for hematopoietic markers such as CD34 and CD45. The regenerative performance of AFSCs-premixed with platelet rich plasma (PRP) gel in restoration of alveolar bone defect was further investigated using a modified rat maxillary alveolar defect model. Micro-computer tomography and histological examination showed a superior regenerative capacity of AFSCs-premixed with PRP gel at both 4 and 8 weeks after operation comparing with control groups. Moreover, the implanted AFSCs can survive in the defect site and directly participate in the bone tissue regeneration. Taken together, these results indicated the feasibility of an AFSCs-based alveolar bone tissue engineering strategy for alveolar defect restoration.

Nanoparticle-Based Mycosis Vaccine

Many diseases that were considered major affliction of mankind in the past have been successfully eradicated with introduction of appropriate vaccine strategies. In order to expedite new challenges coming up to deal with various infectious diseases, nano-particulate-based subunit vaccines seem to be the demand of ordeal. The nano-vaccines can find better scope for the diseases that were not rampant in the semi-advanced world few years back. For example in present-day circumstances that corroborate with advancement in the field of medical sciences in terms of cancer chemotherapy, organ transplantation, therapy of autoimmune diseases, etc.; along with prevalence of altogether unheard diseases such as HIV infection, people are at risk of infliction with many more pathogens. In this regard, development of an effective prophylactic strategy against many opportunistic infections primarily caused by fungal pathogens needs better understanding of host pathogen relation and role of active immunity against pathogenic fungi. In the present study, we have tried to decipher effectiveness of a nano-sized vaccine delivery system in imparting protection against fungal pathogens.

Fibrin matrices: The versatile therapeutic delivery systems

Fibrin sealants, that have been employed for over a century by surgeons to stop post surgery bleeding, are finding novel applications in the controlled delivery of antibiotics and several other therapeutics. Fibrinogen can be easily purified from blood plasma and converted by thrombolysis to fibrin that undergoes spontaneous aggregation to form insoluble clot. During the gelling, fibrin can be formulated into films, clots, threads, microbeads, nanoconstructs and nanoparticles. Whole plasma clots in the form of beads and microparticles can also be prepared by activating endogenous thrombin, for possible drug delivery. Fibrin formulations offer remarkable scope for controlling the porosity as well as in vivo degradability and hence the release of the associated therapeutics. Binding/covalent-linking of therapeutics to the fibrin matrix, crosslinking of the matrix with bifunctional reagents and coentrapment of protease inhibitors have been successful in regulating both in vitro and in vivo release of the therapeutics. The release rates can also be remarkably lowered by preentrapment of therapeutics in insoluble particles like liposomes or by anchoring them to the matrix via molecules that bind them as well as fibrin.

Nanostructured platforms for the sustained and local delivery of antibiotics in the treatment of osteomyelitis

This article provides a critical view of the current state of the development of nanoparticulate and other solid-state carriers for the local delivery of antibiotics in the treatment of osteomyelitis. Mentioned are the downsides of traditional means for treating bone infection, which involve systemic administration of antibiotics and surgical debridement, along with the rather imperfect local delivery options currently available in the clinic. Envisaged are more sophisticated carriers for the local and sustained delivery of antimicrobials, including bioresorbable polymeric, collagenous, liquid crystalline, and bioglass- and nanotube-based carriers, as well as those composed of calcium phosphate, the mineral component of bone and teeth. A special emphasis is placed on composite multifunctional antibiotic carriers of a nanoparticulate nature and on their ability to induce osteogenesis of hard tissues demineralized due to disease. An ideal carrier of this type would prevent the long-term, repetitive, and systemic administration of antibiotics and either minimize or completely eliminate the need for surgical debridement of necrotic tissue. Potential problems faced by even hypothetically "perfect" antibiotic delivery vehicles are mentioned too, including (i) intracellular bacterial colonies involved in recurrent, chronic osteomyelitis; (ii) the need for mechanical and release properties to be adjusted to the area of surgical placement; (iii) different environments in which in vitro and in vivo testings are carried out; (iv) unpredictable synergies between drug delivery system components; and (v) experimental sensitivity issues entailing the increasing subtlety of the design of nanoplatforms for the controlled delivery of therapeutics.

Microfluidic spinning of fibrous alginate carrier having highly enhanced drug loading capability and delayed release profile

Natural polymer-based drug carriers have been developed for antimicrobial applications but several problems remain with their poor controllability of drug loading and degradation.

Nanoparticulate drug delivery platforms for advancing bone infection therapies

INTRODUCTION

The ongoing surge of resistance of bacterial pathogens to antibiotic therapies and the consistently aging median member of the human race signal an impending increase in the incidence of chronic bone infection. Nanotechnological platforms for local and sustained delivery of therapeutics hold the greatest potential for providing minimally invasive and maximally regenerative therapies for this rare but persistent condition.

AREAS COVERED

Shortcomings of the clinically available treatment options, including poly(methyl methacrylate) beads and calcium sulfate cements, are discussed and their transcending using calcium-phosphate/polymeric nanoparticulate composites is foreseen. Bone is a composite wherein the weakness of each component alone is compensated for by the strength of its complement and an ideal bone substitute should be fundamentally the same.

EXPERT OPINION

Discrepancy between in vitro and in vivo bioactivity assessments is highlighted, alongside the inherent imperfectness of the former. Challenges entailing the cross-disciplinary nature of engineering a new generation of drug delivery vehicles are delineated and it is concluded that the future for the nanoparticulate therapeutic carriers belongs to multifunctional, synergistic and theranostic composites capable of simultaneously targeting, monitoring and treating internal organismic disturbances in a smart, feedback fashion and in direct response to the demands of the local environment.

Establishing a role for vancomycin powder application for prosthetic joint infection prevention-results of a wear simulation study

Topical vancomycin powder (VP) has shown efficacy and safety in decreasing post-operative spine infections. VP use in arthroplasty has not been established. Concerns remain for third-body wear with the addition of crystalline substrate at the implant interface. The study's purpose was to compare wear behavior of CoCr on UHMWPE to identical wear couples with VP. A six-station wear simulator was utilized and cyclic articulations were run for 10 million cycles (Mc). UHMWPE wear was measured using photography, stereomicroscopy, and gravimetric measurement. There were no differences in wear mark length (P = 0.43), width (P = 0.49), or gravimetric wear at 10 Mc (P = 0.98). VP and control groups lost 0.32 and 0.33 mg, respectively. VP may have a role in PJI prevention. A well-designed clinical study is needed.

Local antibiotic delivery by a bioabsorbable gel is superior to PMMA bead depot in reducing infection in an open fracture model

OBJECTIVES

Local delivery allows a high concentration of antibiotics to be achieved in the wound while avoiding the side effects and cost of systemic administration. Beads molded from polymethylmethacrylate cement are commonly used for local antibiotic delivery but are not ideal. The purpose of this study was to determine whether a bioabsorbable gel delivering vancomycin and gentamicin is more effective in reducing infection than beads delivering vancomycin and tobramycin.

METHODS

This study used a segmental defect rat model contaminated with Staphylococcus aureus and treated with clinically relevant local antibiotic doses, delivered by gel or beads. In the gel group, 1 mL of gel containing gentamicin and vancomycin was spread throughout the wound. In the bead group, four 3-mm beads containing tobramycin and vancomycin were placed in the wound, 2 in the defect and 2 in the adjacent tissue envelope, there was also a control group that received no antibiotic treatment. After 14 days, bone and hardware was harvested for separate microbiological analysis.

RESULTS

There was a significantly lower infection rate in groups treated with antibiotics delivered by gel compared with those treated with either antibiotic beads or no antibiotics at all (P < 0.001). Quantitative cultures also demonstrate significantly less bacteria in the wounds treated with the gel than in the control or bead groups (P ≤ 0.004).

CONCLUSIONS

These results suggest that antibiotic delivery by a gel is superior to beads. The authors propose that antibiotic depot by polymethylmethacrylate antibiotic beads is less effective because this method has to rely on diffusion of the antibiotic from the high concentration close to the beads to all regions of the wound.

Effects of using intravenous antibiotic only versus local intrawound vancomycin antibiotic powder application in addition to intravenous antibiotics on postoperative infection in spine surgery in 907 patients

STUDY DESIGN

A prospective randomized controlled trial.

OBJECTIVE

To assess the ability of local vancomycin powder in controlling postoperative infection in spine surgery.

SUMMARY OF BACKGROUND DATA

Despite improvements through the use of prophylactic systemic antibiotics, surgical site infections remain a significant problem in spine surgical procedures. Various retrospective and prospective studies have reported the efficacy of local application of vancomycin powder in reducing the infection in animal and human studies. However, there were no randomized control trials that reported on its efficacy.

METHODS

Prospective randomized controls of 907 patients with various spinal pathologies were treated surgically during a period of 18 months. The control group received standard systemic prophylaxis only, whereas the treatment group received vancomycin powder in the surgical wound in addition to systemic prophylaxis. Patient demographics, comorbidities, level of spinal pathology, estimated blood loss, nutritional status, and hemoglobin were recorded. Incidence of infection was the primary outcome evaluated.

RESULTS

There were 8 infections (1.68%) in the control group (6 instrumented and 2 noninstrumented, 6 deep and 2 superficial) with bacteria cultured in 3 (1 Escherichia coli and 2 Staphylococcus aureus). In the treatment group, 7 infections (1.61%) were observed (6 instrumented and 1 noninstrumented surgical procedures, 6 deep and 1 superficial) with bacteria cultured in 3 (1 Staphylococcus aureus and 2 Klebsiella). No adverse effects were observed from the use of vancomycin powder. Statistically no significant difference was seen in infection rate between the treatment group and control group.

CONCLUSION

The local application of vancomycin powder in surgical wounds did not significantly reduce the incidence of infection in patients with surgically treated spinal pathologies. The use of vancomycin powder may not be effective when incidence of infection is low.

Comparative effectiveness and cost-benefit analysis of local application of vancomycin powder in posterior spinal fusion for spine trauma

Object

Surgical site infection (SSI) is a morbid complication with high cost in spine surgery. In this era of health care reforms, adjuvant therapies that not only improve quality but also decrease cost are considered of highest value. The authors introduced local application of vancomycin powder into their practice of posterior spinal fusion for spine trauma and undertook this study to determine the value and cost benefit of using vancomycin powder in surgical sites to prevent postoperative infections.

Methods

A retrospective review of 110 patients with traumatic spine injuries treated with instrumented posterior spine fusions over a 2-year period at a single institution was performed. One group (control group) received standard systemic prophylaxis only, whereas another (treatment group) received 1 g of locally applied vancomycin powder (spread over the surgical wound) in addition to systemic prophylaxis. Data were collected on patient demographic characteristics, clinical variables, surgical variables, and 90-day morbidity. Incidence of infection was the primary outcome evaluated, and billing records were reviewed to determine total infection-related medical cost (cost of reoperation/wound debridement, medications, and diagnostic tests). The payer's cost was estimated to be 70% of the total billing cost.

Results

A total of 110 patients were included in the study. The control (n = 54) and treatment groups (n = 56) were similar at baseline. Use of vancomycin powder led to significant reduction in infection rate (13% infection rate in the control group vs 0% in the treatment group, p = 0.02). There were no adverse effects noted from the use of vancomycin powder. The total mean cost of treating postoperative infection per patient was $33,705. Use of vancomycin powder led to a cost savings of $438,165 per 100 posterior spinal fusions performed for traumatic injuries.

Conclusions

The use of adjuvant vancomycin powder was associated with a significant reduction in the incidence of postoperative infection as well as infection-related medical cost. These findings suggest that use of adjuvant vancomycin powder in high-risk patients undergoing spinal fusion is a cost-saving option for preventing postoperative infections, as it can lead to cost-savings of $438,165 per 100 spinal fusions performed.

Local sustained delivery of oncolytic adenovirus with injectable alginate gel for cancer virotherapy

Adenoviruses (Ad) have been investigated for their efficacy in reducing primary tumors after local intratumoral administration. Despite high Ad concentrations and repetitive administration, the therapeutic efficacy of Ad has been limited because of rapid dissemination of the Ad into the surrounding normal tissues and short maintenance of Ad biological activity in vivo. To maximize the therapeutic potential of Ad-mediated gene therapeutics, we investigated the efficacy of local, sustained Ad delivery, using an injectable alginate gel matrix system. The biological activity of Ad loaded in alginate gel was prolonged compared with naked Ad, as evidenced by the high green fluorescent protein gene transduction efficiency over an extended time period. Moreover, oncolytic Ad encapsulated in alginate gel elicited 1.9- to 2.4-fold greater antitumor activity than naked Ad in both C33A and U343 human tumor xenograft models. Histological and quantitative PCR analysis confirmed that the oncolytic Ad/alginate gel matrix system significantly increased preferential replication and dissemination of oncolytic Ad in a larger area of tumor tissue in vivo. Taken together, these results show that local sustained delivery of oncolytic Ad in alginate gel augments therapeutic effect through selective infection of tumor cells, sustained release and prolonged maintenance of Ad activity.

Investigation of potential injectable polymeric biomaterials for bone regeneration

This article reviews the potential injectable polymeric biomaterial scaffolds currently being investigated for application in bone tissue regeneration. Two types of injectable biomaterial scaffolds are focused in this review, including injectable microspheres and injectable gels. The injectable microspheres section covers several polymeric materials, including poly(L-lactide-co-glycolide)-PLGA, poly(propylene fumarate), and chitosan. The injectable gel section covers alginate gels, hyaluronan hydrogels, poly(ethylene-glycol)-PEG hydrogels, and PEG-PLGA copolymer hydrogels. This review focuses on the effect of cellular behavior in vitro and in vivo in terms of material properties of polymers, such as biodegradation, biocompatibility, porosity, microsphere size, and cross-linking nature. Injectable polymeric biomaterials offer a major advantage for orthopedic applications by allowing the ability to use noninvasive or minimally invasive treatment methods. Therefore, combining injectable polymeric biomaterial scaffolds with cells have a significant potential to treat orthopedic bone defects, including spine fusion, and craniofacial and periodontal defects.

An anti-infection tissue-engineered construct delivering vancomycin: its evaluation in a goat model of femur defect

A tissue-engineered construct (TEC) has previously been used for treating bone defects due to its strong osteogenic capability. However, transplantation of a TEC involves an open surgery that can cause infection. To overcome the potential risk of infection after TEC transplantation, we designed a system for the controlled release of antibiotics using fibrin gel-coated vancomycin alginate beads (FG-Vanco-AB) that can supply sustained antibiotics at the graft site. A TEC with FG-Vanco-AB was transplanted into critically sized bone defects of the right femur in a goat. As a control, the TEC without FG-Vanco-AB was transplanted into the left femur defect of the same goat. The breakpoint sensitivity of vancomycin for S. aureus (5 mg/L) was used as a known standard. Study results showed that the duration of time with vancomycin concentrations greater than 5 mg/L in the right graft site, blood, and left graft site were 28 days, 7 days, and 2 days, respectively. The bioactivity regarding vancomycin release was analysed by antibiotic disc diffusion. The vancomycin concentration was decreased from the centre of the graft to both ends of the femur. Radionuclide bone imaging showed no significant difference between the right and left TECs at either 28 or 56 days post-operation. Computed tomography and histological observation showed both sides' bone defects were healed by TEC at 112 days post-operation, and there was no significant difference in computed tomography value. These results suggest that FG-Vanco-AB in transplanted bone provided the ability to kill bacteria in local bone tissue while not interfering with the process of bone reconstruction and wound healing.

Anti-infection tissue engineering construct treating osteomyelitis in rabbit tibia

Bone defect complicated by infection remains a major challenge in orthopedic surguries, and bone grafting for primary repair often associates with high failure rate. The rapid progress in the research spectrums of tissue-engineered bone and antibiotic delivery systems bring hope to solve this issue. Herein, we evaluated the local anti-infective and osteogenic potential of an injectable anti-infection tissue-engineered construct, which includes a fibrin gel scaffold and vancomycin alginate beads (Vanco-AB) to form composites, in the treatment of chronic osteomyelitis with bone defect in rabbit tibia. The infected bone defect model of rabbit tibia was established. Then, the bone defects in the proximal tibial metaphysis were implanted with the constructed composites, containing different combinations of mesenchymal stem cells and Vanco-AB. The in vivo capacities of anti-infection and local osteogenesis of the grafts were determined using radiographic assessment, histopathological observation, and microorganism cultures. Results showed that the injectable anti-infection tissue-engineered construct, comprising a fibrin gel scaffold and Vanco-AB led to efficient eradication of bacteria. At 1 and 3 months after transplantation, the radiographic assessment and microbiological examination demonstrated that the sustained antibiotic release by Vanco-AB significantly decreased the Norden scores of osteomyelitis, generated negative results for the presence of bacteria, and reduced the relapse of osteomyelitis. Meanwhile, tissue-engineered construct implanted in one-stage promoted local bone repair and reconstruction, and it exhibited more apparent osteogenic potential, compared to the control group (without Vanco-AB). In conclusion, the current study achieved the primary repair of bone defect with infection, thus providing an alternative treatment strategy for infected bone defect, which occurs commonly in chronic osteomyelitis.

In vitro and in vivo analysis of a biodegradable poly(lactide-co-glycolide) copolymer capsule and collagen composite system for antibiotics and bone cells delivery

The authors investigated poly(lactide-co-glycolide) (PLGA) capsule and collagen composite system for antibiotics and bone cells delivery to treat infected bone defects. Poly(lactide-co-glycolide) was mixed with vancomycin and hot compressing molded to form an antibiotic capsule. Rabbit mesenchymal stem cells (MSCs) were entrapped in collagen gel phase and dispersed throughout the void volume of capsule. In vitro study, the composite systems were cultured in complete or osteogenic medium for 21 days. The profiles of vancomycin released from the systems were evaluated using the high-performance liquid chromatography method. Relative activity of vancomycin against Staphylococcus aureus was determined by an antibiotic disk diffusion method. The expression of osteogenic gene was determined by reverse-transcription polymerase chain reaction. The alkaline phosphatase activity and calcium level of the MSCs were assessed. Analytical results demonstrated that the concentrations of vancomycin eluted from the composite system were above the minimal inhibitory concentration for 21 days. Sample inhibition zone was 10 to 24 mm, and the relative activity was 17.6% to 100%. mRNA of Cbfa1 and osteocalcin were detected, and increased alkaline phosphatase activity and calcium levels were noted. In in vivo investigation, the PKH 26-labeled MSCs and composite systems were implanted in the distal femoral cavities of four rabbits. The local concentration of vancomycin was above the minimal inhibitory concentration for 56 days. Sample inhibition zone was 9 mm to 24 mm, and the relative activity was 11.8% to 100%. Implanted PKH 26-labeled MSCs were identified in the newly formed bony trabeculae in specimens at 2 and 4 months after implantation. The results offer a potential approach to meet clinical requirements in the treatment of infected bone defects.

Stem cell applications in military medicine

There are many similarities between health issues affecting military and civilian patient populations, with the exception of the relatively small but vital segment of active soldiers who experience high-energy blast injuries during combat. A rising incidence of major injuries from explosive devices in recent campaigns has further complicated treatment and recovery, highlighting the need for tissue regenerative options and intensifying interest in the possible role of stem cells for military medicine. In this review we outline the array of tissue-specific injuries typically seen in modern combat - as well as address a few complications unique to soldiers - and discuss the state of current stem cell research in addressing each area. Embryonic, induced-pluripotent and adult stem cell sources are defined, along with advantages and disadvantages unique to each cell type. More detailed stem cell sources are described in the context of each tissue of interest, including neural, cardiopulmonary, musculoskeletal and sensory tissues, with brief discussion of their potential role in regenerative medicine moving forward. Additional commentary is given to military stem cell applications aside from regenerative medicine, such as blood pharming, immunomodulation and drug screening, with an overview of stem cell banking and the unique opportunity provided by the military and civilian overlap of stem cell research.

Reduced surgical site infections in patients undergoing posterior spinal stabilization of traumatic injuries using vancomycin powder

BACKGROUND CONTEXT

Despite improvements through the use of prophylactic systemic antibiotics, surgical site infections remain a significant problem in the treatment of traumatic spine injuries. Infection rates as high as 10% have been reported in this population. The impact on patients and cost of treating such infections is profound. Local delivery of antibiotics has been found to be efficacious in animal and human studies as an adjunct to systemic antibiotics in surgical site infection prophylaxis.

PURPOSE

To evaluate the efficacy of using vancomycin powder in surgical sites to prevent infections.

STUDY DESIGN

Retrospective case review.

PATIENT SAMPLE

Patients who underwent posterior spine fusions for traumatic injuries over a 2-year period at a single academic center.

OUTCOME MEASURES

Clinical outcome determined was the incidence of either superficial or deep postoperative wound infections.

METHODS

A retrospective review of 110 patients with traumatic spine injuries treated with instrumented posterior spine fusions over a 2-year period at a single academic center was performed. One group (control group) received standard systemic prophylaxis only, whereas another (treatment group) received vancomycin powder in the surgical wound in addition to systemic prophylaxis. Patient demographics and perioperative information obtained included history of previous spine surgeries, substance use, diabetes, body mass index, level of injury, presence of neurologic deficit, operative time, and estimated blood loss. Incidence of infection was the primary outcome evaluated.

RESULTS

The control (N=54) and treatment groups (N=56) were statistically similar. A statistically significant difference in infection rate was found between the treatment group (0%) and control group (13%, p=.02) without any adverse events. No adverse effects were noted from use of the vancomycin powder.

CONCLUSIONS

The use of vancomycin powder in surgical wounds may significantly reduce the incidence of infection in patients with traumatic spine injuries treated with instrumented posterior spine fusion. Applying vancomycin powder to surgical wounds is a promising means of preventing costly and harmful postoperative wound infections in high-risk populations.

Biomedical Applications of Biodegradable Polymers

Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. In order to fit functional demand, materials with desired physical, chemical, biological, biomechanical and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications.

Vascular endothelial growth factor release from alginate microspheres under simulated physiological compressive loading and the effect on human vascular endothelial cells

Bone tissue engineering has generated promising results in bone defect repair, but is limited by the inherently poor nutrient supply to nonvascularized tissue-engineered bone grafts. In this study, we investigated the delivery of vascular endothelial growth factor (VEGF) and the effect on in vitro cultured human umbilical vein endothelial cells (HUVECs), in an attempt to provide experimental basis for promoting the vascularization of tissue-engineered bone grafts. A mechanical stimulator was developed to generate a periodic compressive load analogous to goat locomotor characteristics, simulating the mechanical stimulation applied on the fracture ends of the load-bearing bone. Poly-l-lysine-coated VEGF/alginate microspheres were combined with demineralized bone matrices into composites, and the in vitro release of VEGF from these composites was evaluated under periodic compression. The effect of the release media on HUVECs was also investigated. Compression slightly accelerated VEGF release at the early stage (<11 days) compared with noncompressed composites, although the release profiles of the two composite groups were generally similar. The released VEGF promoted HUVEC proliferation. In addition, the periodic compression applied on composites containing both HUVECs and VEGF/alginate microspheres promoted the expression of matrix metalloproteinases-2/9 in HUVECs. This study provides a model for investigating VEGF release under simulated in vivo biomechanical conditions and without the disadvantage of the rapid degradation of VEGF in in vivo investigation of VEGF release. The results also provide important guidelines for future in vivo experiments.

Tissue response to chitosan/γ-PGA polyelectrolyte complex using a rat model

In this study, the in vivo soft tissue response of chitosan/γ-poly(glutamic acid) (γ-PGA) polyelectrolyte complex (PEC) using a rat model was assessed using chitosan as a cationic polyelectrolyte and γ-PGA as an anionic polyelectrolyte; four groups of chitosan/γ-PGA PECs were synthesized according to the molar ratio of amine groups of chitosan to the carboxylic acid groups of γ-PGA. Different soft tissue responses to chitosan/γ-PGA PEC were observed between the epithelium and the muscle. In the epithelium, the wound dressed with chitosan/γ-PGA PEC healed faster than the control, with chitosan attracting polymorphonuclear (PMN) cells and γ-PGA creating a hydrophilic environment. In the muscle, a quantitative evaluation of the tissue response revealed that different degradation phenomena were evoked by different compositions of chitosan/γ-PGA PEC. After implantation for 28 days, the chitosan/γ-PGA PEC with chitosan dominating showed extensive surface erosion and superficial fragmentation surrounded by inflammatory cells, while chitosan/γ-PGA PECs with γ-PGA dominating elicited minimal degradation. These results confirm that the degradation of PECs can be controlled by tailoring the chitosan/γ-PGA PECs for different purposes. It appears that different local tissue conditions in muscle and epithelium may be involved in this difference.

Biodegradable antibiotic delivery systems

Bacterial infection in orthopaedic surgery can be devastating, and is associated with significant morbidity and poor functional outcomes, which may be improved if high concentrations of antibiotics can be delivered locally over a prolonged period of time. The two most widely used methods of doing this involve antibiotic-loaded polymethylmethacrylate or collagen fleece. The former is not biodegradable and is a surface upon which secondary bacterial infection may occur. Consequently, it has to be removed once treatment has finished. The latter has been used successfully as an adjunct to systemic antibiotics, but cannot effect a sustained release that would allow it to be used on its own, thereby avoiding systemic toxicity.

This review explores the newer biodegradable carrier systems which are currently in the experimental phase of development and which may prove to be more effective in the treatment of osteomyelitis.

Uncultured marrow mononuclear cells delivered within fibrin glue hydrogels to porous scaffolds enhance bone regeneration within critical-sized rat cranial defects

For bone tissue engineering, the benefits of incorporating mesenchymal stem cells (MSCs) into porous scaffolds are well established. There is, however, little consensus on the effects of or need for MSC handling ex vivo. Culture and expansion of MSCs adds length and cost, and likely increases risk associated with treatment. We evaluated the effect of using uncultured bone marrow mononuclear cells (bmMNCs) encapsulated within fibrin glue hydrogels and seeded into porous scaffolds to regenerate bone over 12 weeks in an 8-mm-diameter, critical-sized rat cranial defect. A full factorial experimental design was used to evaluate bone formation within model poly(L-lactic acid) and corraline hydroxyapatite scaffolds with or without platelet-rich plasma (PRP) and bmMNCs. Mechanical push-out testing, microcomputed tomographical analyses, and histology were performed. PRP showed no benefit for bone formation. Cell-laden poly(L-lactic acid) scaffolds without PRP required significantly greater force to displace from surrounding tissues than control (cell-free) scaffolds, but no differences were observed during push-out testing of coral scaffolds. For bone volume formation as analyzed by microcomputed tomography, significant positive overall effects were observed with bmMNC incorporation. These data suggest that bmMNCs may provide therapeutic advantages in bone tissue engineering applications without the need for culture, expansion, and purification.

Fibrin as a delivery system for therapeutic drugs and biomolecules

Fibrin is a natural biopolymer involved in the coagulation cascade. It acts as a reservoir for growth factors, cells, and enzymes during wound healing and provides a scaffold for the synthesis of extracellular matrix. Thus, the use of fibrin has expanded in recent years from traditional use as a sealant for surgical applications, to a tissue engineering scaffold capable of providing nature's cues for tissue regeneration. This paper reviews the advantageous biological aspects of fibrin, the history of the scaffold material, and its present role in the delivery of drugs, growth factors, cells, and gene vectors. Examples are given of studies where the structure and form of the scaffold have been manipulated for optimal release of the therapeutic agent, optimal cellular activity, and investigation into stem cell differentiation. It is evident from the body of literature presented that the benefits of fibrin are being exploited for a vast range of tissue engineering applications and that fibrin remains a key scaffold material for the delivery of drugs and biomolecules.

Controlled dynamization to enhance reconstruction capacity of tissue-engineered bone in healing critically sized bone defects: an in vivo study in goats

Tissue-engineered bone (TEB) has shown to be an effective alternative to conventional gold-standard autogenous bone for the repair of critically sized bone defects (CSBD). Moderate axial interfragmentary movement (IFM) has been shown to promote bone healing in conventional models. This study explored the use of IFM to enhance the capacity of TEB in the repair of CSBD using a goat model. CSBD were created in a goat model. Dynamic intramedullary rods designed to supply axial IFMs within 10% of the interfragmentary strain were used to stabilize CSBD goat femur models, whose bone defects were filled with TEB. Bone regeneration was evaluated using radionuclide bone imaging, roentgenographic analysis, periosteal callus area, computed tomography value score, biomechanical analysis, and histological observation. Compared with the static intramedullary rods, the dynamic intramedullary rod group showed an increase in early-stage callus formation and blood supply to the callus tissue, better differentiation of fibrous and cartilaginous tissue into bone tissue, improved strength and stiffness of callus tissue in late-stage healing, and overall better functional recovery of the goat femur. This showed that moderate axial IFM could promote the osteogenesis and reconstruction of TEB in vivo.

Locally-administered antibiotics in wounds in a limb

We used a goat model of a contaminated musculoskeletal defect to determine the effectiveness of rapidly-resorbing calcium-sulphate pellets containing amikacin to reduce the local bacterial count. Our findings showed that this treatment eradicated the bacteria quickly, performed as well as standard polymethylmethacrylate mixed with an antibiotic and had many advantages over the latter. The pellets were prepared before surgery and absorbed completely. They released all of the antibiotic and did not require a subsequent operation for their removal. Our study indicated that locally administered antibiotics reduced bacteria within the wound rapidly. This method of treatment may have an important role in decreasing the rate of infection in contaminated wounds.