Spotlight on naturally absorbable osteofixation devices

Regulating the proinflammatory response to composite biomaterials by targeting immunometabolism

Composite biomaterials comprising polylactide (PLA) and hydroxyapatite (HA) are applied in bone, cartilage and dental regenerative medicine, where HA confers osteoconductive properties. However, after surgical implantation, adverse immune responses to these composites can occur, which have been attributed to size and morphology of HA particles. Approaches to effectively modulate these adverse immune responses have not been described. PLA degradation products have been shown to alter immune cell metabolism (immunometabolism), which drives the inflammatory response. Accordingly, to modulate the inflammatory response to composite biomaterials, inhibitors were incorporated into composites comprised of amorphous PLA (aPLA) and HA (aPLA + HA) to regulate glycolytic flux. Inhibition at specific steps in glycolysis reduced proinflammatory (CD86+CD206-) and increased pro-regenerative (CD206+) immune cell populations around implanted aPLA + HA. Notably, neutrophil and dendritic cell (DC) numbers along with proinflammatory monocyte and macrophage populations were decreased, and Arginase 1 expression among DCs was increased. Targeting immunometabolism to control the proinflammatory response to biomaterial composites, thereby creating a pro-regenerative microenvironment, is a significant advance in tissue engineering where immunomodulation enhances osseointegration and angiogenesis, which could lead to improved bone regeneration.

Role of Implantable Drug Delivery Devices with Dual Platform Capabilities in the Prevention and Treatment of Bacterial Osteomyelitis

As medicine advances and physicians are able to provide patients with innovative solutions, including placement of temporary or permanent medical devices that drastically improve quality of life of the patient, there is the persistent, recurring problem of chronic bacterial infection, including osteomyelitis. Osteomyelitis can manifest as a result of traumatic or contaminated wounds or implant-associated infections. This bacterial infection can persist as a result of inadequate treatment regimens or the presence of biofilm on implanted medical devices. One strategy to mitigate these concerns is the use of implantable medical devices that simultaneously act as local drug delivery devices (DDDs). This classification of device has the potential to prevent or aid in clearing chronic bacterial infection by delivering effective doses of antibiotics to the area of interest and can be engineered to simultaneously aid in tissue regeneration. This review will provide a background on bacterial infection and current therapies as well as current and prospective implantable DDDs, with a particular emphasis on local DDDs to combat bacterial osteomyelitis.

Ultrasound-Activated Bioresorbable Osteosynthesis in the Treatment of Craniosynostosis

ABSTRACT

The purpose of this study is to estimate the incidence of fixation-related complications following ultrasound-activated biodegradable osteosynthesis (UBO) in the treatment of craniosynostosis. The authors searched MEDLINE, PubMed, Embase, Google Scholar, and Cochrane Library from January 2005 to January 2020 for clinical studies reporting the use of UBO for fixation in the treatment of craniosynostosis. The primary outcome was the incidence of fixation-related complications, including unstable fixation; swelling, plate visibility, or palpability; infection; inflammation, sinus formation, and discharge; implant exposure; reoperation or implant removal. The pooled incidence rates were estimated using random-effects models. Of 155 studies identified, 10 were included, representing 371 patients. Forty-six (12.4%) patients presented fixation-related complications. The incidence rates of swelling/visibility/palpability, infection, and reoperation/implant removal were pooled based on the available data. The pooled incidence rate of chronic swelling/visibility/palpability was 0.21 (95% confidence interval [CI], 0.05-0.43). Sensitivity analysis by omitting the outlier study demonstrates that the incidence of swelling/visibility/palpability was 0.07 (95% CI, 0.04-0.11). The pooled incidence rate of infection and reoperation/implant removal was 0.07 (95% CI, 0.01-0.16) and 0.04 (95% CI, 0.01-0.09), respectively. Results show that although UBO can provide stable fixation, chronic swelling/visibility/palpability, infection, and reoperation for removal are not uncommon. Based on the literature, the authors recommend judicious use of UBO in patients with large frontorbital advancement and in the area of the coronal suture or other sites with thin overlying skin/subcutaneous tissue. The high possibility of chronic swelling/palpability/visibility during degradation, needs to be discussed preoperatively.

Three Dimensional Printed Bone Implants in the Clinic

Implants are being continuously developed to achieve personalized therapy. With the advent of 3-dimensional (3D) printing, it is becoming possible to produce customized precisely fitting implants that can be derived from 3D images fed into 3D printers. In addition, it is possible to combine various materials, such as ceramics, to render these constructs osteoconductive or growth factors to make them osteoinductive. Constructs can be seeded with cells to engineer bone tissue. Alternatively, it is possible to load cells into the biomaterial to form so called bioink and print them together to from 3D bioprinted constructs that are characterized by having more homogenous cell distribution in their matrix. To date, 3D printing was applied in the clinic mostly for surgical training and for planning of surgery, with limited use in producing 3D implants for clinical application. Few examples exist so far, which include mostly the 3D printed implants applied in maxillofacial surgery and in orthopedic surgery, which are discussed in this report. Wider clinical application of 3D printing will help the adoption of 3D printers as essential tools in the clinics in future and thus, contribute to realization of personalized medicine.

Histomorphometric Analysis of Poly-L/D-Lactide 96/4 Sutures in the Gastrocnemius Tendon of Rabbits

Background

Common Achilles tendon ruptures are not usually fixed by bioabsorbable sutures due to limitations in their strength retention properties. Modern technology has made it possible to develop bioabsorbable sutures with prolonged strength retention.

Aims

To evaluate histologically tissue reactions of poly-L/D-lactide (PLDLA) sutures implanted in Achilles tendon of rabbits.

Material and Methods

Fifteen rabbits were evaluated at 2, 6 and 12 weeks postoperatively, with five rabbits in each follow-up group. PLDLA monofilament sutures were implanted into the medial gastrocnemius tendon. Polyglyconate monofilament sutures with similar diameter (Maxon® 4–0, Cyanamid of Great Britain Ltd., Gosport, UK) were implanted in the contralateral gastrocnemius tendon. The histology was studied in hard-resin embedded samples. The thickness of the formed fibrous tissue capsule was determined histomorphometrically.

Results

PLDLA led to formation of significantly thinner fibrous tissue capsule than Maxon® sutures of the same diameter. Median thickness (PLDLA vs. Maxon®) at two weeks was 5.26 vs. 13.22μm, at six weeks 11.66 vs. 80.97μm, and at 12 weeks 10.63 vs. 17.59μm (p<0.01).

Conclusions

During the 12 week follow-up period, PLDLA sutures implanted intratendineously formed thinner fibrous capsule than Maxon® sutures of the same diameter. The suture materials were not totally absorbed by 12 weeks.

In vivo analysis of covering materials composed of biodegradable polymers enriched with flax fibers

BACKGROUND

The objective of this study was to investigate the in vivo effect of bioactive composites with poly(lactic acid) (PLA) or polycaprolactone (PCL) as the matrix, reinforced with bioplastic flax fibers, on the surrounding muscle tissue.

METHODS

Materials of pure PLA and PCL and their composites with flax fibers from genetically modified plants producing poly-3-hydroxybutyrate (PLA-transgen, PCL-transgen) and unmodified plants (PLA-wt, PCL-wt) were placed subcutaneous on the M. latissimus dorsi for four weeks.

RESULTS

The analysis of histological samples revealed that every tested material was differently encapsulated and the capsule thickness is much more pronounced when using the PCL composites in comparison with the PLA composites. The encapsulation by connective tissue was significantly reduced around PCL-transgen and significantly increased in the cases of PLA-transgen and PLA-wt. In the collected muscle samples, the measured protein expression of CD45, lymphocyte common antigen, was significantly increased after the use of all tested materials, with the exception of pure PCL. In contrast, the protein expression of caveolin-1 remained unchanged after treatment with the most examined materials. Only after insertion of PLA-wt, a significant increase of caveolin-1 protein expression was detected, due to the improved neovascularization.

CONCLUSION

These data support the presumption that the new bioactive composites are biocompatible and they could be applicable in the medical field to support the regenerative processes.

Bioabsorbable fixation devices in trauma and bone surgery: current clinical standing

Bioabsorbable fixation devices are increasingly used in trauma, orthopedic and craniomaxillofacial surgery. The devices are essentially made of polylactic acid and/or polyglycolic acid polymers. Ultra-high-strength implants are manufactured from such polymers using self-reinforcing techniques. Implants are available for stabilization of fractures, osteotomies, bone grafts and fusions, as well as for reattachment of ligaments, tendons, meniscal tears and other soft tissue structures. As these implants are completely absorbed, the need for a removal operation is overcome and long-term interference with tendons, nerves and the growing skeleton is avoided. The risk of implant-associated stress shielding, peri-implant osteoporosis and infections is reduced. Implants do not interfere with clinical imaging. Current clinical use of bioabsorbable devices is reviewed.

In vivo testing of a bioabsorbable magnesium alloy serving as total ossicular replacement prostheses

Magnesium alloys have been investigated in different fields of medicine and represent a promising biomaterial for implants due to characteristics like bioabsorbability and osteoinduction. The objective of this study was to evaluate the usability of magnesium as implant material in middle ear surgery. Magnesium implants were placed into the right middle ear of eighteen New Zealand White rabbits. Nine animals were euthanized after four weeks and nine animals after three month. The petrous bones were removed and embedded in epoxy resin. The specimens were then polished, stained and evaluated with the aid of a light microscope. The histological examination revealed a good biocompatibility. After four weeks, a beginning corrosion of the implant’s surface and low amount of trabecular bone formation in the area of the stapes base plate was observed. A considerable degradation of implants and obvious bone formation was found three month after implantation. The magnesium alloy used in the present study partly corroded too fast, so that a complete bone reconstruction could not be established in time. The increased osteoinduction on the stapes base plate resulted in a tight bone-implant bonding. Thus, a promising application of magnesium could be a coating of biomaterials in order to improve the bony integration of implants.

Biodegradable Polymers in Bone Tissue Engineering

The use of degradable polymers in medicine largely started around the mid 20^th century with their initial use as in vivo resorbing sutures. Thorough knowledge on this topic as been gained since then and the potential applications for these polymers were, and still are, rapidly expanding. After improving the properties of lactic acid-based polymers, these were no longer studied only from a scientific point of view, but also for their use in bone surgery in the 1990s. Unfortunately, after implanting these polymers, different foreign body reactions ranging from the presence of white blood cells to sterile sinuses with resorption of the original tissue were observed. This led to the misconception that degradable polymers would, in all cases, lead to inflammation and/or osteolysis at the implantation site. Nowadays, we have accumulated substantial knowledge on the issue of biocompatibility of biodegradable polymers and are able to tailor these polymers for specific applications and thereby strongly reduce the occurrence of adverse tissue reactions. However, the major issue of biofunctionality, when mechanical adaptation is taken into account, has hitherto been largely unrecognized. A thorough understanding of how to improve the biofunctionality, comprising biomechanical stability, but also visualization and sterilization of the material, together with the avoidance of fibrotic tissue formation and foreign body reactions, may greatly enhance the applicability and safety of degradable polymers in a wide area of tissue engineering applications. This review will address our current understanding of these biofunctionality factors, and will subsequently discuss the pitfalls remaining and potential solutions to solve these problems.

Preliminary in vitro evaluation of an adjunctive therapy for extremity wound infection reduction: rapidly resorbing local antibiotic delivery

Despite the continuing advances in treatment of open fractures and musculoskeletal wounds, infection remains a serious complication. Current treatments to prevent infection utilize surgical debridement and irrigation, and high doses of systemic antimicrobial therapy. The aim of this work was to evaluate, in vitro, the potential of a fast-resorbing calcium sulfate pellet loaded with an antibiotic. The pellet could be used as an adjunctive therapy at the time of debridement and irrigation to reduce bacterial wound contamination. Small pellets containing a binder and calcium sulfate were engineered to resorb rapidly (within 24 h) and deliver high local doses of antibiotic (amikacin, gentamicin, or vancomycin) to the wound site while minimizing systemic effects. Results from dissolution, elution, and biological activity tests against P. aeruginosa and S. aureus were used to compare the performance of antibiotic-loaded, rapidly resorbing calcium sulfate pellets to antibiotic-loaded crushed conventional calcium sulfate pellets. Antibiotic-loaded rapidly resorbing pellets dissolved in vitro in deionized water in 12-16 h and released therapeutic antibiotic levels in phosphate buffered saline that were above the minimal inhibitory concentration for P. aeruginosa and S. aureus, completely inhibiting the growth of these bacteria for the life of the pellet. Crushed conventional calcium sulfate pellets dissolved over 4-6 days, but the eluates only contained sufficient antibiotic to inhibit growth for the first 4 h. These data indicate that fast-resorbing pellets can release antibiotics rapidly and at therapeutic levels. Adjunctive therapy with fast-acting pellets is promising and warrants further in vivo studies.

Surface characterization and cell response of a PLA/CaP glass biodegradable composite material

Bioabsorbable materials are of great interest for bone regeneration applications, since they are able to degrade gradually as new tissue is formed. In this work, a fully biodegradable composite material containing polylactic acid (PLA) and calcium phosphate (CaP) soluble glass particles has been characterized in terms of surface properties and cell response. Cell cultures were performed in direct contact with the materials and also with their extracts, and were evaluated using the MTT assay, alkaline phosphatase activity, and osteocalcin measurements. The CaP glass and PLA were used as reference materials. No significant differences were observed in cell proliferation with the extracts containing the degradation by-products of the three materials studied. A relation between the materials wettability and the material-cell interactions at the initial stages of contact was observed. The most hydrophilic material (CaP glass) presented the highest cell adhesion values as well as an earlier differentiation, followed by the PLA/glass material. The incorporation of glass particles into the PLA matrix increased surface roughness. SEM images showed that the heterogeneity of the composite material induced morphological changes in the cells cytoskeleton.

Rapid cooling through the glass transition transiently increases ductility of PGA/PLLA copolymers: a proposed mechanism and implications for devices

Heating bioabsorbable plates above T(g) allows for temporary softening to facilitate adaptation to bone. This can, however, transiently alter the mechanical properties, a better understanding of which would provide further insight into the use of these polymers. Two types of unoriented L-lactide/glycolide copolymer wafer specimens (82:18 and 95:5 molar ratios) were heated to 90 degrees C, cooled at various rates, and mechanically tested (three-point bend). Long cooling times ( approximately 8 h) did not change mechanical properties compared to unheated controls, whereas faster cooling rates resulted in increased ductility (50-200% increase in energy to break and peak deformation), however, there was gradual recovery. Under simulated physiological incubation conditions (pH 7.4 buffer, 37 degrees C) partial recovery occurred within 48 h. These results fit well into the theoretical framework of free volume considerations. Following rapid cooling to below T(g), the polymer is not initially at equilibrium, containing excess free volume that contributes to increased molecular mobility and ductile behavior. As equilibrium is approached, free volume decreases and the material behaves as a glassy solid. While there is little clinical consequence as regards internal fixation devices, possible transient changes in permeability and other properties could have implications in drug delivery and other applications.

Poly-L/D-lactide (PLDLA) 96/4 fibrous implants: histological evaluation in the subcutis of experimental design

Poly-L/D-lactide (PLDLA) 96/4 fibrous implants have been introduced to engineer functional fibrous constructions in situ. The current study was undertaken to evaluate the guidance of the fibrous tissue formation and the tissue reaction of porous PLDLA 96/4 scaffolds implanted in subcutaneous tissue. Three various PLDLA 96/4 knitted-mesh scaffolds (Loose, Ordinary, and Dense) were implanted subcutaneously in 32 rats, and followed-up from 3 days until 48 weeks postsurgery. Histological examination showed that PLDLA 96/4 scaffolds provided a structurally supporting element for 48 weeks. They were filled with fibrous tissue by 3 weeks. During the follow-up, loose connective tissue was organized into dense connective tissue with thick collagen bundles. At 48 weeks, no statistically significant difference was found in the amount of loose or dense connective tissue between the scaffold groups of various porosities, although the tendency for higher amounts of loose connective tissue was seen in the Loose type scaffolds. PLDLA filament diameters were 121 mum at 2 weeks, 119 mum at 24 weeks and 116 mum at 48 weeks (P = 0.03 between 2 and 48 weeks). Porous PLDLA scaffold induced fibrous tissue formation in situ. This can be exploited in engineering fibrous tissue constructs in vivo for tissue support or replacement purposes.

An Experimental Study of Heat Adaptation of Bioabsorbable Craniofacial Meshes and Plates

Intraoperative heating of bioabsorbable plates and mesh panels to above the glass transition temperature is commonly performed to assist their adaptation to bone. Some studies suggest that once heat-adapted, such implants under certain conditions tend to partially revert to their preadapted shape, termed a "memory effect." We investigated this phenomenon by using heat-adapted 82:18 poly-L-lactic acid:polyglycolic acid copolymer mesh panel and plate specimens with a glass transition temperature of 57 degrees C. The specimens retained limited malleability even at temperatures as low as 45 degrees C, substantially below the nominal glass transition temperature, as measured by shape relaxation experiments. At 40 degrees C to 42 degrees C, however, shape relaxation was not observed. A three-dimensional synthetic bone construct was also fixated using 90 degrees C heat-adapted plates, then incubated in a 37 degrees C buffer bath for 4 weeks, with periodic measurement of the shape of the construct. No changes in shape were recorded over this interval, suggesting that heat-adapted bioabsorbable implants forming a three-dimensional fixation network with multiple bone fragments cannot independently shape relax with the overall interconnectedness of the network ensuring its stability over time.

Tissue response in the rat and the mouse to degradable dextran hydrogels

Two types of hydroxyethyl-methacrylated dextran (dex-HEMA) hydrogels differing in crosslink density were compared for local tissue responses and degradation characteristics in mice and rats. Implants (1 mm thick, rat: 10 mm diameter, mouse: 6 mm diameter) varying in degree of HEMA substitution (DS5 and DS13, meaning 5 or 13 HEMA groups per 100 glucose units of dextran) were subcutaneously implanted and tissue responses were evaluated at week 2, 6, and 13 after implantation. In the rat after 2 weeks a slight fibrous capsule was formed composed of macrophages and fibroblasts sometimes accompanied by a minimal infiltrate. Small fragments, surrounded by macrophages and giant cells indicated hydrogel degradation. After 13 weeks DS5 implants were resorbed while parts of the DS13 implants were still present. In the mouse a moderate to strong capsule formation was present at 2 weeks accompanied by inflammatory cells (macrophages and polymorphonuclear granulocytes) and debris. Draining lymph node activation was observed. Skin ulceration was present irrespective of the type of implant. Clear differences in the tissue responses between the rat and mouse were noted, as well as between implants of different degree of substitution. Mice showed a more pronounced early inflammatory response compared with rats, whereas the degradation was more complete in rats than in mice. The differences in histology between the hydrogels disappeared over time at 13 weeks after implantation and similar responses were noted for both types of hydrogels. Both in mice and rats the DS5 hydrogels showed a faster degradation rate than the DS13 hydrogels.

Innovation in multifunctional bioabsorbable osteoconductive drug-releasing hard tissue fixation devices

We review in this paper the work performed by our group to develop multifunctional bioabsorbable ciprofloxacin releasing bone implants. Poly lactide-co-glycolide (PLGA 80/20 and polylactide (P(L/DL)LA 70/30) were used. Ciprofloxacin (CF) and bioactive glass (BaG) 13-93 were added. The mixture was then extruded and self-reinforced. CF release, mechanical strength, and the effect on S. epidermidis attachment and biofilm formation were evaluated. In rabbits, tissue reactions were assessed. Pull out strength was evaluated in cadaver bones. CF was released over 44 weeks (P(L/DL)LA) and 23-26 weeks (PLGA). Initial shear strength of the CF screws was 152 MPa (P(L/DL)LA) and 172 MPa (PLGA). Strength was retained for 12 weeks (P(L/DL)LA) and 9 weeks (PLGA). Histologically, CF releasing implants did not show much difference from control plain PLGA screws except for increased giant cells. CF miniscrews had lower pullout strength than the controls, but CF tacks had better values than controls. BaG led to a drop in pullout strength properties. Bacterial growth, attachment and biofilm formation on CF implants was significantly reduced when compared to controls. Accordingly, bioabsorbable multifunctional implants with appropriate CF release, mechanical, and biocompatibility properties are possible to develop and are considered appropriate to apply clinically.

Polymer-based biodegradable drug delivery systems in pain management

Pain is an unpleasant sensory experience commonly produced by damage to bodily tissues and it is one of the most significant public health problems, because 21.5% of the world population is estimated to suffer from pain. It results in a total loss of more than 165 billion US dollars each year in the United States alone. Pain reflects a mixture of various pathophysiologic, psychologic, and genetic contributions. When undertreated, pain usually results in serious immune and metabolic upset. Therefore, it requires wide understanding and intensive effort for a better management. Currently, pain control is limited by the modest efficiency of the used drugs, the serious side effects of these drugs, and the inefficacy of conventional drug administration. By the introduction of the technology of biodegradable controlled-release devices into clinical practice, pain control not only benefits from these novel methods for a better delivery of various drugs, but the side effects of the drugs are reduced because use of the devices improves patient compliance. Biodegradable controlled-release devices are polymer-based devices that are designed to deliver drugs locally in a predesigned manner. Recently, there was a high interest in developing these devices for the delivery of different drugs used for pain control. This paper first highlights the dimensions and basics of the problem of pain. Then, it presents an overview of the biodegradable polymers that are used in drug delivery systems and summarizes the studies carried out on these systems in the field of pain management. We refer to our experience in developing a device for multimodal drug delivery, including the use of nanotechnology. Future perspectives are also presented.

Stability of craniofacial PLLA/PGA copolymer bioabsorbable screws

The behavior of bioabsorbable plates and screws after implantation is a dynamic process that results in dimensional changes of the devices after surgery. Bioabsorbable plates frequently are recognized as changing because of their size, but bioabsorbable screws are less appreciated in this regard. How bioabsorbable screws may change after placement and whether their manufacturing method has an influence on size and shape after implantation needs further study. Using 1.5-mm diameter screws made of an oriented copolymer of 82% poly-L-lactic acid and 18% polyglycolic acid (LactoSorb copolymer), screw dimensions were measured before and after soaking in an in vitro pH 7.4, 37 degrees C buffer environment. After 33 days of exposure to buffer, there were no changes in the physical appearance of the screws, and there was no change in dimensions or shape. The orientation of polymer materials in a bioabsorbable screw device improves its strength and can retard the rate of hydrolysis. However, the residual stresses in oriented screws theoretically can potentiate dimensional shift in the implants during hydrolysis. That such shift did not occur during the early phase of hydrolysis provides further evidence of the mechanism by which these types of screws can maintain biomechanical function throughout the bone-healing phase of the craniofacial skeleton.

The Effect of High Temperature Intraoperative Molding on Bioabsorbable PLLA-PGA Craniofacial Fixation

Bioabsorbable internal fixation has become an established part of the surgeons' armamentarium. There are several unique aspects of bioabsorbable polymers that can enhance their versatility. One of these is the application of heat to adapt the implant. Hot-tip cautery has been used for years to cut and otherwise customize bioabsorbable implants intraoperatively. As the tips of these devices can reach temperatures of over 1,000 degrees C, there is the potential that such practice can modify the degradation properties of these polymers. This study was performed to better understand the extent to which this potential exists. Screw heads of an 82:18 poly-L-lactic acid and poly-glycolic acid copolymer were modified by repeated passage of a hot-tip cautery wire, deforming the hex geometry to that of a ball. There was no significant difference between the glass transition temperature (approximately 59 degrees C) and inherent viscosity (approximately 1.45 dL/g) of treated and untreated screw heads, indicating no overall change in these properties throughout the mass of the screw head. Additionally, these properties were measured and comparisons made between the treated screw heads and untreated plates made of the same polymer during 28-day exposure to an in vitro bath (pH 7.4, 37 degrees C). The glass transition temperature and inherent viscosity exhibited declines during this period, with no significant differences between the two groups. Collectively, these results suggest that hot-tip cautery results in no substantial changes in the degradation characteristics of this polymer.

Self-Reinforced Ciprofloxacin-Releasing Polylactide-Co-Glycolide 80/20 Inhibits Attachment and Biofilm Formation by Staphylococcus Epidermidis

We have observed the efficiency of antibiotic-releasing polylactide-co-glycolide (PLGA) 80/20 in preventing Staphylococcus epidermidis attachment and biofilm formation in vitro. The aim of the present study was to evaluate the effect of self-reinforced (SR) implants with enhanced antibiotic release on bacterial attachment and biofilm formation rates, and also on growth inhibition of Staphylococcus epidermidis. Cylindrical SR-PLGA+AB specimens (length 30 mm, diameter 3 mm) were examined by scanning electron microscopy (SEM) for attachment of S. epidermidis ATCC 35989 on biomaterial surface and formation of biofilm, after incubating with bacterial suspension of ca. 10 cfu/mL for 1, 3, 7, 14 and 21 days. SR-PLGA and SR-PLGA+AB implants were tested on agar plates by measuring the inhibition distance around implants. On the surface of SR-PLGA+AB, at days 1, 3, 7, 14 and 21, the percentage of areas with not a single bacteria attached, was 88.6%, 71.1%, 73.7%, 73.7%, and 68.4%, respectively. On the areas where bacteria were detected, the number of bacterial cells remained low during whole study period, and no significant increase by time was seen. There was no biofilm observed on 97-99% of the examined areas during the whole study period on SR-PLGA+AB. In agar plates, the SR-PLGA+AB showed inhibition of bacterial growth, with (mean) 53.2 mm diameter of inhibition area with peeled implants and 50.5 mm with non-peeled implants. There was no inhibition seen around implants without ciprofloxacin. Bioabsorbable ciprofloxacin-releasing self-reinforced PLGA (SR-PLGA+AB) was superior to plain SR-PLGA in preventing bacterial attachment, biofilm formation, and also the growth of Staphylococcus epidermidis.

Effect of FGF and Polylactide Scaffolds on Calvarial Bone Healing With Growth Factor on Biodegradable Polymer Scaffolds

Repair of bone defects remains a major concern in reconstructive surgery. Synthetic biodegradable polymers have been used as scaffolds for guided bone regeneration. Fibroblast growth factors (FGFs) promote cell growth, differentiation, and tissue maintenance factors. They can stimulate the proliferation of osteogenic cells and chondrocytes, and also promote angiogenesis. Acidic and basic fibroblast growth factors (FGF-1 and FGF-2, respectively) are the best known members of this protein family. To evaluate the healing of experimental bone defects using poly-L/D-lactide (PLDLA) 96/4 scaffolds and FGF-1, 18 adult rats were operated on. A 6-mm diameter critical size defect (CSD) was made in the calvarial bone of each rat. The animals were divided into three treatment groups: 1) Neither scaffold nor FGF was used (control group); 2) scaffold only; and 3) scaffold with FGF-1. Follow-up time was eight weeks. Samples were embedded in methylmethacrylate and 5-microm thick sections from the middle of each specimen were stained with modified Masson-Goldner method. The shape and size of defects were evaluated radiologically. New bone formation was measured histologically and histomorphometrically. Radiologically, in the control group the shape of the defects changed from round to oval and edges were blunt. In the other groups the defects were round with sharp edges. Histomorphometrically, mean surface area of bone trabeculae was 1.05 mm (SD +/- 0.25) in group 1 (no implant), 1.35 mm (SD +/- 0.52) in group 2 (implant) and 0.79 mm (SD +/- 0.34) in group 3 (implant and FGF-1). Histological examinations revealed no or little osteoid in the groups 1 and 2, whereas in the group 3 samples had little or moderate new bone formation. Accordingly, no clear benefit of using knitted PLDLA scaffolds combined with FGF-1 on the healing of calvarial critical size defects in rats could be demonstrated.

Biodegradable polylactide membranes for bone defect coverage: biocompatibility testing, radiological and histological evaluation in a sheep model

Large bony defects often show a delayed healing and have an increasing risk of infection. Several materials are used for the coverage of large defects. These materials must be biocompatible, easy to use, and must have an appropriate stability to present a mechanical hindrance. Aim of this study was to investigate two different biodegradable membranes for defect coverage in a sheep model. Round cranial defects (1.5 cm diameter) were created in sheep. Six different treatments were investigated: defects without membrane, defects covered with a poly(D,L-lactide) or with a 70/30 poly(L/D,L-lactide) membrane and all defects with or without spongiosa filling. The sheep were sacrificed 12 or 24 weeks postoperatively. Bone formation in the defects was quantified by computer-assisted measurements of the area of the residual defect on CT radiographs. Histomorphometry and host-tissue response were evaluated by light microscopy. The biocompatibility was investigated by analyzing the amount of osteoclasts and foreign body cells. Both membranes served as a mechanical hindrance to prevent the prolapse of soft tissue into the defect. The biocompatibility test revealed no differences in the amount and distribution of osteoclasts at the two investigated time points and between the investigated groups. No negative effect on the tissue regeneration was detectable between the investigated groups related to the type of membrane, but a foreign body reaction around the two membrane types was observed. In the membrane-covered defects, the spongiosa showed a progressing remodeling to the native bony structure of the cranium. The groups without spongiosa partly revealed new bone formation, without complete bridging in any group or at any time point. Comparing the 12 and 24 weeks groups, an increased bone formation was detectable at the later time point. In conclusion, the results of the present in vivo study reveal a good biocompatibility and prevention of soft tissue prolapse of the two used membranes without differences between the membranes. An enhanced remodeling of the spongiosa into native bony structures under the membranes was detectable, but no osteopromoting effect was observed due to the membranes.

Síntese, caracterização e degradação " in vitro" do Poli(L-ácido láctico)

O estudo e aplicação de poliésteres bioreabsorvíveis para reparar tecidos danificados tem se mostrado uma área de pesquisa muito promissora. Poli (L-ácido láctico), PLLA, se destaca dentre os poliésteres bioreabsorvíveis, em função de características como biocompatibilidade e bioreabsorção. No entanto, seu alto custo de importação limita a expansão de seus dispositivos no País. Os objetivos deste trabalho foram sintetizar, caracterizar e estudar a degradação in vitro de membranas de PLLA. O polímero foi sintetizado através da abertura do dímero cíclico do ácido láctico, utilizando-se como catalisador Sn(Oct)2. Obteve-se PLLA com altos valores de massa molar (Mw em torno de 10(5) g/mol) e sua estrutura química foi confirmada através de RMN de ¹H e 13C e IR. As propriedades térmicas do PLLA foram estudadas por DSC, sendo verificada uma alta cristalinidade para o material, o que está de acordo com a literatura. O estudo da degradação "in vitro" das membranas do PLLA mostrou um aumento do grau de cristalinidade em função do tempo de degradação.

Tissue restoration after resorption of polyglycolide and poly-laevo-lactic acid screws

Despite worldwide clinical use of bio-absorbable devices for internal fixation in orthopaedic surgery, the degradation behaviour and tissue replacement of these implants are not fully understood. In a long-term experimental study, we have determined the patterns of tissue restoration 36 and 54 months after implantation of polyglycolic acid and poly-laevo-lactic acid screws in the distal femur of the rabbit. After 36 months in the polyglycolic acid group the specimens showed no remaining polymer and loose connective tissue occupied 80% of the screw track. Tissue restoration remained poor at 54 months, the amounts of trabecular bone and haematopoietic elements being significantly lower than those in the intact control group. The amount of trabecular bone within the screw track at 54 months in the polyglycolic acid group was less than in the empty drill holes (p = 0.04). In the poly-laevo-lactic acid group, polymeric material was present in abundance after 54 months, occupying 60% of the cross-section of the core area of the screw track. When using absorbable internal fixation implants we should recognise that the degradation of the devices will probably not be accompanied by the restoration of normal trabecular bone.

Transphyseal bioabsorbable screws cause temporary growth retardation in rabbit femur

A self-reinforced bioabsorbable poly-L-lactide/polyglycolide (SR-PLGA) 80/20 screw 2.0 mm in diameter was implanted transphyseally across the distal growth plate of the right femur in 24 immature rabbits. Radiologic evaluation revealed a mean shortening of 3.1 mm at 3 weeks, 11.1 mm at 6 weeks, 9.3 mm at 24 weeks, 9.0 mm at 48 weeks, and 12.6 mm at 72 weeks compared with the intact contralateral femur. In 13 control rabbits, drilling without screw placement did not cause any statistically significant femoral shortening. Therefore, the transphyseal SR-PLGA 80/20 screw caused growth retardation for 6 weeks postoperatively, after which the normal growth tendency was recovered until the growth plate was closed. The duration of temporary growth retardation correlated with that of strength retention of the SR-PLGA 80/20 copolymer. These findings suggest that SR-PLGA 80/20 screws can be applied in transphyseal bone fixation. The use of bioabsorbable screws for temporary epiphysiodesis seems attractive but requires further study.

Short term in vivo biocompatibility testing of biodegradable poly(D,L-lactide)—growth factor coating for orthopaedic implants

Fracture healing can be stimulated by exogenous application of growth factors. Using porcine and rat models the efficacy of locally delivered IGF-I and TGF-beta1 from an implant coating has been demonstrated. A thin and biomechanical stable biodegradable poly(D,L-lactide) was used to coat implants and serve as a drug carrier. Due to reports of possible foreign body reactions caused by polymer materials in orthopedic surgery, this study investigated the biocompatibility of the polylactide implant coating and the locally released growth factors during the time course of rat tibial fracture healing (days 5, 10, 15, and 28 after fracture). Monocytes/macrophages and osteoclast were detected using an monoclonal antibody against ED1 (comparable to CD68 in mice and human). The antibody ED1 stains monocytes, macrophages and osteoclast in the bone marrow and in the newly formed fracture callus. A moderate density of the monocytes/macrophages was seen in the proximal part of the medullary canal, but almost no cells were detectable in the region distal to the fracture. The amount of stained cells increased during the observation time with a maximum at days 10 and 15 followed by a decrease at day 28. No differences were detectable between the investigated groups from day 5 to 15 post fracture indicating, that the used poly(D,L-lactide) or the incorporated growth factors do not evoke an elevated immunological response compared to the uncoated titanium implant at the investigated time points. A significantly higher amount of ED1 positive cells was measured 28 days after fracture in the control group compared to the groups with the coated implants. In conclusion, no indication of a foreign body reaction due to the use of the polylactide or the growth factors was found indicating a good short-term biocompatibility of this bioactive coating.

Fixation of the chevron osteotomy with an absorbable copolymer pin for treatment of hallux valgus deformity

This study investigated the use of a bioabsorbable pin made of an oriented poly-L-lactic acid/polyglycolic acid (82:18 ratio) copolymer to fix distal chevron osteotomies in 15 patients (18 feet), with an average follow-up of 18 months. This material absorbs faster than poly-L-lactic acid and slower than poly-p-dioxanone, 2 bioabsorbable polymers that have a clinical history in fixation of distal chevron osteotomies. The average intermetatarsal angle significantly decreased from 11.9+/-1.7 degrees to 0.9+/-3.8 degrees (P < .001) while the average hallux valgus angle significantly decreased from 19.4+/-4.7 degrees to 6.2+/-6.4 degrees (P < .001). The preoperative American Orthopaedic Foot and Ankle Society's hallux-metatarsophalangeal-interphalangeal score averaged 44.6+/-15.1, which increased significantly to 87.4+/-14.9 (P < .001) postoperatively. In 1 procedure, a giant cell granuloma developed that was treated with debridement. Overall, these results were comparable to those derived from the use of other methods of fixation used for bunionectomies.

Tissue response to partially in vitro predegraded poly-L-lactide implants

The in vivo local reaction of as-polymerized poly-L-lactide composed of 96% L-lactide and 4% D-lactide (PLA96) was investigated by histology at 2, 13 and 26 weeks after subcutaneous implantation in rats. In order to simulate possible end stage reactions the PLA96 was also predegraded in vitro until approximately 50% weight loss. The local reaction of predegraded PLA (PLA96(168)) was compared to the local reaction of polyethylene (PE) and non-predegraded PLA (PLA96). For PE and PLA96 a mild local reaction was observed at all time points consisting of a minimal layer of macrophage like cells with incidentally multinucleated giant cells at the implant interface, surrounded by a mild connective tissue capsule. For PLA96 at weeks 13 and 26 some minimal alterations in terms of degradation and ingrowth of cells was noted. The in vitro incubation (90 degrees C for 168 h) of PLA96(168) resulted for the thin 0.2 mm samples in complete degradation. Predegraded 0.5, 1.0 and 2.0 mm PLA96(168) samples were implanted and evaluated. The 1.0 and 2.0 mm samples could be evaluated for all time points investigated, but some 0.5 mm PLA96(168) samples were already completely resorbed at week 2 after implantation. In general, responses found for the predegraded PLA96(168) at weeks 2, 13 and 26 were similar with a pronounced macrophage infiltrate containing birefringent material, encapsulation of polymer fragments, and the presence of a debris area consisting of polymer and cellular remnants. In lymph nodes foamy macrophages with birefringent material were only observed in lymph nodes draining sites with predegraded PLA96(168). Immunohistochemistry was performed for further characterization of the cellular infiltrate. At the implant interface of the non-degrading PE and PLA96, ED1 and OX6 (MHC class II) positive cells were identified. In the capsule macrophage like cells expressed all three macrophage markers ED1, ED2, and ED3. CD4 and CD8 positive cells, indicating T helper and T supressor/cytotoxic cells, respectively, could be observed in low numbers, CD4 more than CD8. Both CD4 and CD8 were occasionally observed within the degrading PLA96(168) implant. Polymorphonuclear neutrophilic granulocytes were mainly observed at 2 weeks after implantation. We showed that predegradation could be used as a means to study late tissue reactions to polymers. Complete degradation may be studied with relatively thin implants, but this may lead to rather optimistic interpretation of resorption periods. When materials are intended to be used for screws and/or plates for bone fixation, implants of at least 1.0-2.0 mm thickness should be used as these may show a more realistic representation of the resorption characteristics of the material under investigation.

Use of bioabsorbable osteofixation devices in the hand

Bioabsorbable internal fixation by means of pins, tacks, screws and miniplates offers an alternative to metallic osteofixation for the stabilization of small bone fractures, osteotomies, ligament injuries and fusions in the hand. The advantages of using them include avoidance of metallic-implant-related long-term complications and a secondary removal operation. Currently the most commonly used devices are made of poly L-lactide (PLLA) and copolymers of polylactides (P(L/DL)LA) and polyglycolide (PLGA). In areas of mechanical stress, the use of ultra-high-strength self-reinforced devices is recommended. Biomechanical studies on fresh frozen bones have shown that the fixation rigidity achieved with self-reinforced devices approaches that of metallic osteofixation methods. The reliability of modern implants has been confirmed in several experimental and clinical studies.

Self-reinforced bioabsorbable miniplates for skeletal fixation in complex hand injury: three case reports

We report our preliminary experience with 3 cases in which internal fixation with a self-reinforced poly-l/dl-lactide 70/30 miniplate and 1.5-mm or 2.0-mm screws were used to stabilize an open metacarpal fracture, a metacarpophalangeal arthrodesis in a thumb replantation, and an interposed bone graft for reconstruction of a thumb. Clinical and radiologic follow-up evaluation lasted for 12 to 20 months. Bone healing was uneventful in all 3 cases with no displacement or delayed union. The implants were biocompatible with no clinically manifested foreign body reaction. Because of the self-reinforcing manufacturing technique the plates have metal-like mechanical and handling properties. Complete late resorption makes self-reinforced poly-l/dl-lactide 70/30 miniplating systems an attractive alternative to metallic implants for skeletal stabilization of small bones of the hand.

Local and controlled release of growth factors (combination of IGF-I and TGF-beta I, and BMP-2 alone) from a polylactide coating of titanium implants does not lead to ectopic bone formation in sheep muscle

The osteoinductive potential of growth factors leads not only to a stimulated bone formation in bony tissue but also in extra skeletal tissue. This potential depends on the dosage and potentially on the application method and may limit the clinical use. The aim of the present study was to investigate the potential of IGF-I, TGF-beta1 and BMP-2 released from a newly developed application systems of orthopaedic implants to induce ectopic bone formation in muscles. This bioactive coating showed a stimulating effect on fracture healing in several experimental studies before. Titanium discs were coated on one side with the drug carrier poly(d,l-lactide) (PDLLA), with the carrier plus IGF-I and TGF-beta1 or with the carrier plus BMP-2. The discs were implanted in the Musculus cleidomastoideus of sheep and followed up for 3 months. X-rays were taken after the operation and the day of sacrifice. The muscles plus implant were harvested and prepared for histology. Neither the radiology nor the histology revealed any signs of ectopic ossification in the implant/muscle interface or in a distance to the plate in any group. An influence of the locally applied growth factor, however, was seen in the formation of a soft tissue capsule. Histomorphometric analysis revealed a significantly larger capsule area over the growth factor coated side in comparison to the uncoated side or the pure titanium plate, indicating an effect of the applied growth factors on cells, however, not resulting in osteoinduction in muscle. The result showed that the local and controlled release of growth factors from PDLLA coated implants does not induce ectopic bone formation in sheep muscle and could be used in orthopaedic surgery to increase healing without the risk of ectopic bone formation in the surrounding soft tissue.