Enzymatic post-crosslinking of printed hydrogels of methacrylated gelatin and tyramine-conjugated 8-arm poly(ethylene glycol) to prepare interpenetrating 3D network structures.

Methacrylated gelatin (GelMA) has been intensively studied as a 3D printable scaffold material in tissue regeneration fields, which can be attributed to its well-known biological functions. However, the long-term stability of photo-crosslinked GelMA scaffolds is hampered by a combination of its fast degradation in the presence of collagenase and the loss of physical crosslinks at higher temperatures. To increase the longer-term shape stability of printed scaffolds, a mixture of GelMA and tyramine-conjugated 8-arm PEG (8PEGTA) was used to create filaments composed of an interpenetrating network (IPN). Photo-crosslinking during filament deposition of the GelMA and subsequent enzymatic crosslinking of the 8PEGTA were applied to the printed 3D scaffolds. Although both crosslinking mechanisms are radical based, they operate without interference of each other. Rheological data of bulk hydrogels showed that the IPN was an elastic hydrogel, having a storage modulus of 6 kPa, independent of temperature in the range of 10 - 40°C. Tensile and compression moduli were 110 kPa and 80 kPa, respectively. On enzymatic degradation in the presence of collagenase, the gelatin content of the IPN fully degraded in 7 days, leaving a stable secondary crosslinked 8PEGTA network. Using a BioMaker bioprinter, hydrogels without and with human osteosarcoma cells (hMG-63) were printed. On culturing for 21 days, hMG-63 in the GelMA/8PEGTA IPN showed a high cell viability (>90%). Thus, the presence of the photoinitiator, incubation with H2O2, and mechanical forces during printing did not hamper cell viability. This study shows that the GelMA/8PEGTA ink is a good candidate to generate cell-laden bioinks for extrusion-based printing of constructs for tissue engineering applications.

Biocompatibility and degradation comparisons of four biodegradable copolymeric osteosynthesis systems used in maxillofacial surgery: A goat model with four years follow-up.

Applying biodegradable osteosyntheses avoids the disadvantages of titanium osteosyntheses. However, foreign-body reactions remain a major concern and evidence of complete resorption is lacking. This study compared the physico-chemical properties, histological response and radiographs of four copolymeric biodegradable osteosynthesis systems in a goat model with 48-months follow-up. The systems were implanted subperiosteally in both tibia and radius of 12 Dutch White goats. The BioSorb FX [poly(70LLA-co-30DLLA)], Inion CPS [poly([70-78.5]LLA-co-[16-24]DLLA-co-4TMC)], SonicWeld Rx [poly(DLLA)], LactoSorb [poly(82LLA-co-18GA)] systems and a negative control were randomly implanted in each extremity. Samples were assessed at 6-, 12-, 18-, 24-, 36-, and 48-month follow-up. Surface topography was performed using scanning electron microscopy (SEM). Differential scanning calorimetry and gel permeation chromatography were performed on initial and explanted samples. Histological sections were systematically assessed by two blinded researchers using (polarized) light microscopy, SEM and energy-dispersive X-ray analysis. The SonicWeld Rx system was amorphous while the others were semi-crystalline. Foreign-body reactions were not observed during the complete follow-up. The SonicWeld Rx and LactoSorb systems reached bone percentages of negative controls after 18 months while the BioSorb Fx and Inion CPS systems reached these levels after 36 months. The SonicWeld Rx system showed the most predictable degradation profile. All the biodegradable systems were safe to use and well-tolerated (i.e., complete implant replacement by bone, no clinical or histological foreign body reactions, no [sterile] abscess formation, no re-interventions needed), but nanoscale residual polymeric fragments were observed at every system's assessment.

Morphological and biomechanical effects of annulus fibrosus injury and repair in an ovine cervical model.

Tissue engineering repair of annulus fibrosus (AF) defects has the potential to prevent disability and pain from intervertebral disc (IVD) herniation and its progression to degeneration. Clinical translation of AF repair methods requires assessment in long-term large animal models. An ovine AF injury model was developed using cervical spinal levels and a biopsy-type AF defect to assess composite tissue engineering repair in 1-month and 12-month studies. The repair used a fibrin hydrogel crosslinked with genipin (FibGen) to seal defects, poly(trimethylene carbonate) (PTMC) scaffolds to replace lost AF tissue, and polyurethane membranes to prevent herniation. In the 1-month study, PTMC scaffolds sealed with FibGen herniated with polyurethane membranes. When applied alone, FibGen integrated with the surrounding AF tissue without herniation, showing promise for long-term studies. The 12-month long-term study used only FibGen which showed fibrous healing, biomaterial resorption and no obvious hydrogel-related complications. However, the 2 mm biopsy punch injury condition also exhibited fibrotic healing at 12 months. Both untreated and FibGen treated groups showed equivalency with no detectable differences in histological grades of proteoglycans, cellular morphology, IVD structure and blood vessel formation, biomechanical properties including torque range and axial range of motion, Pfirrmann grade, IVD height, and quantitative scores of vertebral body changes from clinical computed tomography. The biopsy-type injury caused endplate defects with a high prevalence of osteophytes in all groups and no nucleus herniation, indicating that the biopsy-type injury requires further refinement, such as reduction to a slit-type defect that could penetrate the full depth of the AF without damaging the endplate. Results demonstrate translational feasibility of FibGen for AF repair to seal AF defects, although future study with a more refined injury model is required to validate the efficacy of FibGen before translation.

Orbital floor repair using patient specific osteoinductive implant made by stereolithography.

The orbital floor (OF) is an anatomical location in the craniomaxillofacial (CMF) region known to be highly variable in shape and size. When fractured, implants commonly consisting of titanium meshes are customized by plying and crude hand-shaping. Nevertheless, more precise customized synthetic grafts are needed to meticulously reconstruct the patients' OF anatomy with better fidelity. As alternative to titanium mesh implants dedicated to OF repair, we propose a flexible patient-specific implant (PSI) made by stereolithography (SLA), offering a high degree of control over its geometry and architecture. The PSI is made of biodegradable poly(trimethylene carbonate) (PTMC) loaded with 40 wt % of hydroxyapatite (called Osteo-PTMC). In this work, we developed a complete work-flow for the additive manufacturing of PSIs to be used to repair the fractured OF, which is clinically relevant for individualized medicine. This work-flow consists of (i) the surgical planning, (ii) the design of virtual PSIs and (iii) their fabrication by SLA, (iv) the monitoring and (v) the biological evaluation in a preclinical large-animal model. We have found that once implanted, titanium meshes resulted in fibrous tissue encapsulation, whereas Osteo-PMTC resulted in rapid neovascularization and bone morphogenesis, both ectopically and in the OF region, and without the need of additional biotherapeutics such as bone morphogenic proteins. Our study supports the hypothesis that the composite osteoinductive Osteo-PTMC brings advantages compared to standard titanium mesh, by stimulating bone neoformation in the OF defects. PSIs made of Osteo-PTMC represent a significant advancement for patients whereby the anatomical characteristics of the OF defect restrict the utilization of traditional hand-shaped titanium mesh.

Synthesis and characterization of rGO-graft-poly(trimethylene carbonate) for nerve regeneration conduits.

Graphene-graft-polymer has been used to improve the compatibility between graphene and a polymer matrix, and to further enhance electrical, mechanical and biological properties of polymer/graphene composites. In this study, poly(trimethylene carbonate) (PTMC) was successfully grafted onto graphene surface via 'grafting from' method. Reduced graphene oxide (rGO) initiator was synthesized by azido ethanol reaction with graphene oxide (GO) at high temperature. This resulted in thermal reduction of the GO and stable hydroxyl groups on the graphene surface. Subsequently, rGO initiator was used for the ring-opening polymerization of TMC monomer. rGO-graft-PTMC composites with PTMC molecular weights of 430, 480, 2150 and 7030 g mol-1 were successfully synthesized using different amounts of TMC. Single layer graphene nanosheets remained after graft polymerization by this method. rGO-graft-PTMC dispersions in chloroform were stable. The rGO-graft-PTMC composites with PTMC molecular weights of 430-7030 g mol-1 had electrical conductivities ranging from 0.2 to 0.016 s cm-1. To investigate the biocompatibility of rGO-graft-PTMC, PTMC-based films containing rGO-graft-PTMC were prepared and used in cell culturing experiments. The composite films showed good biocompatibility with PC12 neuronal cells. It is concluded that rGO-graft-PTMC composite is a promising material for the preparation of nerve regeneration conduits.

A Zebrafish Embryo Model for In Vivo Visualization and Intravital Analysis of Biomaterial-associated Staphylococcus aureus Infection.

Biomaterial-associated infection (BAI) is a major cause of the failure of biomaterials/medical devices. Staphylococcus aureus is one of the major pathogens in BAI. Current experimental BAI mammalian animal models such as mouse models are costly and time-consuming, and therefore not suitable for high throughput analysis. Thus, novel animal models as complementary systems for investigating BAI in vivo are desired. In the present study, we aimed to develop a zebrafish embryo model for in vivo visualization and intravital analysis of bacterial infection in the presence of biomaterials based on fluorescence microscopy. In addition, the provoked macrophage response was studied. To this end, we used fluorescent protein-expressing S. aureus and transgenic zebrafish embryos expressing fluorescent proteins in their macrophages and developed a procedure to inject bacteria alone or together with microspheres into the muscle tissue of embryos. To monitor bacterial infection progression in live embryos over time, we devised a simple but reliable method of microscopic scoring of fluorescent bacteria. The results from microscopic scoring showed that all embryos with more than 20 colony-forming units (CFU) of bacteria yielded a positive fluorescent signal of bacteria. To study the potential effects of biomaterials on infection, we determined the CFU numbers of S. aureus with and without 10 µm polystyrene microspheres (PS10) as model biomaterials in the embryos. Moreover, we used the ObjectJ project file "Zebrafish-Immunotest" operating in ImageJ to quantify the fluorescence intensity of S. aureus infection with and without PS10 over time. Results from both methods showed higher numbers of S. aureus in infected embryos with microspheres than in embryos without microspheres, indicating an increased infection susceptibility in the presence of the biomaterial. Thus, the present study shows the potential of the zebrafish embryo model to study BAI with the methods developed here.

Fabrication of poly (trimethylene carbonate)/reduced graphene oxide-graft-poly (trimethylene carbonate) composite scaffolds for nerve regeneration.

One of the key challenges for neural tissue engineering is to exploit functional materials to guide and support nerve regeneration. Currently, reduced graphene oxide (rGO), which is well-known for its unique electrical and mechanical properties, has been incorporated into biocompatible polymers to manufacture functional scaffolds for nerve tissue engineering. However, rGO has poor dispersity in polymer matrix, which limits its further application. Here, we replaced rGO with rGO-graft-PTMC. The rGO-graft-PTMC was firstly prepared by grafting trimethylene carbonate (TMC) oligomers onto rGO. Subsequently, PTMC/rGO-graft-PTMC composite fibrous mats were fabricated by electrospinning of a dispersion of PTMC and rGO-graft-PTMC. The loading of rGO-graft-PTMC could reach up to 6 wt% relative to PTMC. Scanning electron microscopy images showed that the morphologies and average diameters of PTMC/rGO-graft-PTMC composite fibrous mats were affected by the content of rGO-graft-PTMC. Additionally, the incorporation of rGO-graft-PTMC resulted in enhanced thermal stability and hydrophobicity of PTMC fibers. Biological results demonstrated that PC12 cells showed higher cell viability on PTMC/rGO-graft-PTMC fibers of 2.4, 4.0 and 6.0 wt% rGO-graft-PTMC compared to pure PTMC fibers. These results suggest that PTMC/rGO-graft-PTMC composite fibrous structures hold great potential for neural tissue engineering.

Osteogenic magnesium incorporated into PLGA/TCP porous scaffold by 3D printing for repairing challenging bone defect.

Bone defect repair is a challenging clinical problem in musculoskeletal system, especially in orthopaedic disorders such as steroid associated osteonecrosis (SAON). Magnesium (Mg) as a biodegradable metal with properly mechanical properties has been investigating for a long history. In this study, Mg powder, poly (lactide-co-glycolide) (PLGA), ß-tricalcium phosphate (ß-TCP) were the elements to formulate a novel porous PLGA/TCP/Mg (PTM) scaffolds using low temperature rapid prototyping (LT-RP) technology. The physical characterization of PTM scaffold and Mg ions release were analyzed in vitro. The osteogenic and angiogenic properties of PTM scaffolds, as well as the biosafety after implantation were assessed in an established SAON rabbit model. Our results showed that the PTM scaffold possessed well-designed bio-mimic structure and improved mechanical properties. Findings of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and micro-computed tomography (micro CT)-based angiography indicated that PTM scaffold could increase blood perfusion and promote new vessel ingrowth at 4 weeks after surgery, meanwhile, a plenty of newly formed vessels with well-architective structure were observed at 8 weeks. Correspondingly, at 12 weeks after surgery, micro-CT, histological and mechanical properties analysis showed that PTM could significant enhance new bone formation and strengthen newly formed bone mechanical properties. The mean bone volume in PTM group was 56.3% greater than that in PT group. Biosafety assessments from 0 to 12 weeks after implantation did not induce increase in serum Mg ions concentration, and immune response, liver and kidney function parameters were all at normal level. These findings suggested that the PTM scaffold had both osteogenic and angiogenic abilities which were synergistic effect in enhancing new bone formation and strengthen newly formed bone quality in SAON. In summary, PTM scaffolds are promising composite biomaterials for repairing challenging bone defect that would have great potential for its clinical translation.

A drug eluting poly(trimethylene carbonate)/poly(lactic acid)-reinforced nanocomposite for the functional delivery of osteogenic molecules.

BACKGROUND: Poly(trimethylene carbonate) (PTMC) has wide biomedical applications in the field of tissue engineering, due to its biocompatibility and biodegradability features. Its common manufacturing involves photofabrication, such as stereolithography (SLA), which allows the fabrication of complex and controlled structures. Despite the great potential of SLA-fabricated scaffolds, very few examples of PTMC-based drug delivery systems fabricated using photo-fabrication can be found ascribed to light-triggered therapeutics instability, degradation, side reaction, binding to the macromers, etc. These concerns severely restrict the development of SLA-fabricated PTMC structures for drug delivery purposes. METHODS: In this context, we propose here, as a proof of concept, to load a drug model (dexamethasone) into electrospun fibers of poly(lactic acid), and then to integrate these bioactive fibers into the photo-crosslinkable resin of PTMC to produce hybrid films. The hybrid films' properties and drug release profile were characterized; its biological activity was investigated via bone marrow mesenchymal stem cells culture and differentiation assays. RESULTS: The polymer/polymer hybrids exhibit improved properties compared with PTMC-only films, in terms of mechanical performance and drug protection from UV denaturation. We further validated that the dexamethasone preserved its biological activity even after photoreaction within the PTMC/poly(lactic acid) hybrid structures by investigating bone marrow mesenchymal stem cells proliferation and osteogenic differentiation. CONCLUSION: This study demonstrates the potential of polymer-polymer scaffolds to simultaneously reinforce the mechanical properties of soft matrices and to load sensitive drugs in scaffolds that can be fabricated via additive manufacturing.

Microstructured Photo-Crosslinked Poly(Trimethylene Carbonate) for Use in Soft Lithography Applications: A Biodegradable Alternative for Poly(Dimethylsiloxane).

Photo-crosslinkable poly(trimethylene carbonate) (PTMC) macromers were used to fabricate microstructured surfaces. Microstructured PTMC surfaces were obtained by hot embossing the macromer against structured silicon masters and subsequent photo-crosslinking, resulting in network formation. The microstructures of the master could be precisely replicated, limiting the shrinkage. Microstructured PTMC was investigated for use in two different applications: as stamping material to transfer a model protein to another surface and as structured substrate for cell culture. Using the flexible and elastic materials as stamps, bovine serum albumin labelled with fluorescein isothiocyanate was patterned on glass surfaces. In cell culture experiments, the behavior of human mesenchymal stem cells on nonstructured and microstructured PTMC surfaces was investigated. The cells strongly adhered to the PTMC surfaces and proliferated well. Compared to poly(dimethylsiloxane) (PDMS), which is commonly used in soft lithography, the PTMC networks offer significant advantages. They show better compatibility with cells, are biodegradable, and have much better mechanical properties. Both materials are transparent, flexible, and elastic at room temperature, but the tear resistance of PTMC networks is much higher than that of PDMS. Thus, PTMC might be an alternative material to PDMS in the fields of biology, medicine, and tissue engineering, in which microfabricated devices are increasingly being applied.

Comparison of Poly(l-lactide-co-ɛ-caprolactone) and Poly(trimethylene carbonate) Membranes for Urethral Regeneration: An In Vitro and In Vivo Study.

Urethral defects are normally reconstructed using a patient's own genital tissue; however, in severe cases, additional grafts are needed. We studied the suitability of poly(l-lactide-co-ɛ-caprolactone) (PLCL) and poly(trimethylene carbonate) (PTMC) membranes for urethral reconstruction in vivo. Further, the compatibility of the materials was evaluated in vitro with human urothelial cells (hUCs). The attachment and viability of hUCs and the expression of different urothelial cell markers (cytokeratin 7, 8, 19, and uroplakin Ia, Ib, and III) were studied after in vitro cell culture on PLCL and PTMC. For the in vivo study, 32 rabbits were divided into the PLCL (n = 15), PTMC (n = 15), and control or sham surgery (n = 2) groups. An oval urethral defect 1 × 2 cm in size was surgically excised and replaced with a PLCL or a PTMC membrane or urethral mucosa in sham surgery group. The rabbits were followed for 2, 4, and 16 weeks. After the follow-up, urethrography was performed to check the patency of the urethra. The defect area was excised for histological examination, where the epithelial integrity and structure, inflammation, and fibrosis were observed. There was no notable difference on hUCs attachment on PLCL and PTMC membranes after 1 day of cell seeding, further, the majority of hUCs were viable and maintained their urothelial phenotype on both biomaterials. Postoperatively, animals recovered well, and no severe strictures were discovered by urethrography. In histological examination, the urothelial integrity and structure developed toward a normal urothelium with only mild signs of fibrosis or inflammation. According to these results, PLCL and PTMC are both suitable for reconstructing urethral defects. There were no explicit differences between the PLCL and PTMC membranes. However, PTMC membranes were more flexible, easier to suture and shape, and developed significant epithelial integrity.

The zebrafish embryo as a model to quantify early inflammatory cell responses to biomaterials.

To rapidly assess early inflammatory cell responses provoked by biomaterials in the full complexity of the living organism, we developed a zebrafish embryo model which allows real time analysis of these responses to biomaterial microspheres. Fluorescently labeled microspheres with different properties were injected into embryos of selected transgenic zebrafish lines expressing distinct fluorescent proteins in their neutrophils and macrophages. Recruitment of leukocytes and their interactions with microspheres were monitored using fluorescence microscopy. We developed a novel method using ImageJ and the plugin ObjectJ project file "Zebrafish-Immunotest" for rapid and semi-automated fluorescence quantification of the cellular responses. In the embryo model we observed an ordered inflammatory cell response to polystyrene and poly (ε-caprolactone) microspheres, similar to that described for mammalian animal models. The responses were characterized by an early infiltration of neutrophils followed by macrophages, and subsequent differentially timed migration of these cells away from the microspheres. The size of microspheres (10 and 15 µm) did not influence the cellular responses. Poly (ε-caprolactone) microspheres provoked a stronger infiltration of neutrophils and macrophages than polystyrene microspheres did. Our study shows the potential usefulness of zebrafish embryos for in vivo evaluation of biomaterial-associated inflammatory cell responses. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2522-2532, 2017.

Poly(trimethylene carbonate)-based composite materials for reconstruction of critical-sized cranial bone defects in sheep.

PURPOSE: The use of ceramic materials in repair of bone defects is limited to non-load-bearing sites. We tested poly(trimethylene carbonate) (PTMC) combined with ß-tricalcium phosphate or biphasic calcium phosphate particles for reconstruction of cranial defects. MATERIALS AND METHODS: PTMC-calcium phosphate composite matrices were implanted in cranial defects in sheep for 3 and 9 months. Micro-computed tomography quantification and histological observation were performed for analysis. RESULTS: No differences were found in new bone formation among the defects left unfilled, filled with PTMC scaffolds, or filled with either kind of PTMC-calcium phosphate composite scaffolds. Porous ß-TCP scaffolds as control led to a larger amount of newly formed bone in the defects than all other materials. Histology revealed abundant new bone formation in the defects filled with porous ß-TCP scaffolds. New bone formation was limited in defects filled with PTMC scaffolds or different PTMC-calcium phosphate matrices. PTMC matrices were degraded uneventfully. New bone formation within the defects followed an orderly pattern. CONCLUSIONS: PTMC did not interfere with bone regeneration in sheep cranial defects and is suitable as a polymer matrix for incorporating calcium phosphate particles. Increasing the content of calcium phosphate particles in the composite matrices may enhance the beneficial effects of the particles on new bone formation.

Synthetic Biodegradable Hydrogels with Excellent Mechanical Properties and Good Cell Adhesion Characteristics Obtained by the Combinatorial Synthesis of Photo-Cross-Linked Networks.

Major drawbacks of synthetic hydrogels are their poor mechanical properties and their limited ability to allow cell attachment and proliferation. By photo-cross-linking mixtures of dimethacrylate-functionalized oligomers (macromers) in a combinatorial manner in solution, synthetic hydrogels with high water uptake and the remarkable ability to promote cell adhesion and proliferation were prepared. A total of 255 different networks based on poly(trimethylene carbonate) (PTMC)-, poly(d,l-lactide) (PDLLA)-, poly(ε-caprolactone) (PCL)- and poly(ethylene glycol) (PEG) macromers were synthesized simultaneously and screened for their ability to allow the adhesion of human mesenchymal stem cells (hMSCs) in a high throughput-like manner. Of these networks, several hydrogels could be identified that were able to take up large amounts of water while at the same time allowed the adhesion of cells. By synthesizing these hydrogel networks anew and analyzing the cell adhesion and proliferation behavior of human mesenchymal stem cells to these synthetic hydrogels in more detail, it was confirmed that mixed-macromer hydrogel networks prepared from equal amounts of PTMC-dMA 4k, PDLLA-dMA 4k, PCL-dMA 4k, PEG-dMA 4k, and PEG-dMA 10k and hydrogel networks prepared from PTMC-dMA 4k, PDLLA 4k, PEG-dMA 4k, PTMC-dMA 10k and PEG-dMA 10k were highly hydrophilic (water uptake was respectively 181 ± 2 and 197 ± 18 wt % water) and allowed very good cell adhesion and proliferation. Furthermore, these networks were extremely resilient in the hydrated state, with tearing energies of respectively 0.64 ± 0.34 and 0.27 ± 0.04 kJ/m(2). This is much higher than other synthetic hydrogels described in literature and close to articular cartilage (1 kJ/m(2)).

A new poly(1,3-trimethylene carbonate) film provides effective adhesion reduction after major abdominal surgery in a rat model.

BACKGROUND: Postoperative adhesions remain a major clinical problem after abdominal surgery. We evaluated the efficacy of a new poly(trimethylene carbonate) (PTMC) film as an antiadhesive material. In many abdominal operations, there is an increased risk of fecal contamination; the risk of (increased) infection in presence of PTMC film was studied in 2 additional animal models. METHODS: A validated rat adhesion model with peritoneal ischemic buttons was used to compare the new PTMC film with a hyaluronate carboxymethylcellulose (HA-CMC) sheet, icodextrin solution, and a control group. Primary endpoint was occurrence of adhesions at the ischemic buttons after 14 days in 44 rats (n = 11 per group). To evaluate potential risks associated with the film, both an anastomotic leakage model and a cecal ligation and puncture model were used. Kruskal-Wallis tests with subsequent Mann-Whitney tests were used to detect differences between groups. RESULTS: PTMC film showed a significant reduction in the amount of adhesions (median, 0.5 buttons) compared with control group (median, 4 buttons; P < .001) and icodextrin group (median, 4.5; P < .001). The amount of adhesions was similar to the HA-CMC group (median, 2; P = .04). The presence of the film did not increase the risk of anastomotic leakage or bacterial growth in a contaminated environment. CONCLUSION: The presence of a PTMC film leads to a significant reduction in the amount of adhesions after 14 days in an ischemic button rat model. Furthermore, this film was found to be safe in an animal model, even in complex abdominal operations with an increased risk of fecal contamination.

Antimicrobial delivery systems for local infection prophylaxis in orthopedic- and trauma surgery.

Infectious complications occur in a minor but significant portion of the patients undergoing joint replacement surgery or fracture fixation, particularly those with severe open fractures, those undergoing revision arthroplasty or those at elevated risk because of poor health status. Once established, infections are difficult to eradicate, especially in the case of bacterial biofilm formation on implanted hardware. Local antibiotic carriers offer the prospect of controlled delivery of antibiotics directly in target tissues and implant, without inducing toxicity in non-target organs. Polymeric carriers have been developed to optimize the release and targeting of antibiotics. Passive polymeric carriers release antibiotics by diffusion and/or upon degradation, while active polymeric carriers release their antibiotics upon stimuli provided by bacterial pathogens. Additionally, some polymeric carriers gelate in-situ in response to physiological stimuli to form a depot for antibiotic release. As antibiotic resistance has become a major issue, also other anti-infectives such as silver and antimicrobial peptides have been incorporated in research. Currently, several antibiotic loaded biomaterials for local infection prophylaxis are available for use in the clinic. Here we review their advantages and limitations and provide an overview of new materials emerging that may overcome these limitations.

A combined biomaterial and cellular approach for annulus fibrosus rupture repair.

Recurrent intervertebral disc (IVD) herniation and degenerative disc disease have been identified as the most important factors contributing to persistent pain and disability after surgical discectomy. An annulus fibrosus (AF) closure device that provides immediate closure of the AF rupture, restores disc height, reduces further disc degeneration and enhances self-repair capacities is an unmet clinical need. In this study, a poly(trimethylene carbonate) (PTMC) scaffold seeded with human bone marrow derived mesenchymal stromal cells (MSCs) and covered with a poly(ester-urethane) (PU) membrane was assessed for AF rupture repair in a bovine organ culture annulotomy model under dynamic load for 14 days. PTMC scaffolds combined with the sutured PU membrane restored disc height of annulotomized discs and prevented herniation of nucleus pulposus (NP) tissue. Implanted MSCs showed an up-regulated gene expression of type V collagen, a potential AF marker, indicating in situ differentiation capability. Furthermore, MSCs delivered within PTMC scaffolds induced an up-regulation of anabolic gene expression and down-regulation of catabolic gene expression in adjacent native disc tissue. In conclusion, the combined biomaterial and cellular approach has the potential to hinder herniation of NP tissue, stabilize disc height, and positively modulate cell phenotype of native disc tissue.

Low-intensity pulsed ultrasound (LIPUS) and pulsed electromagnetic field (PEMF) treatments affect degeneration of cultured articular cartilage explants.

PURPOSE: Articular cartilage has some capacity for self-repair. Clinically used low-intensity pulsed ultrasound (LIPUS) and pulsed electromagnetic field (PEMF) treatments were compared in their potency to prevent degeneration using an explant model of porcine cartilage. METHODS: Explants of porcine cartilage and human osteoarthritic cartilage were cultured for four weeks and subjected to daily LIPUS or PEMF treatments. At one, two, three and four weeks follow-up explants were prepared for histological assessment or gene expression (porcine only). RESULTS: Non-treated porcine explants showed signs of atrophy of the superficial zone starting at one week. Treated explants did not. In LIPUS-treated explants cell clusters were observed. In PEMF-treated explants more hypertrophic-like changes were observed at later follow up. Newly synthesized tissue was present in treated explants. Gene expression profiles did indicate differences between the two methods. Both methods reduced expression of the aggrecan and collagen type II gene compared to the control. LIPUS treatment of human cartilage samples resulted in a reduction of degeneration according to Mankin scoring. PEMF treatment did not. CONCLUSIONS: LIPUS or PEMF prevented degenerative changes in pig knee cartilage explants. LIPUS reduced degeneration in human cartilage samples. LIPUS treatment seems to have more potency in the treatment of osteoarthritis than PEMF treatment.

Biodegradable elastomers for biomedical applications and regenerative medicine.

Synthetic biodegradable polymers are of great value for the preparation of implants that are required to reside only temporarily in the body. The use of biodegradable polymers obviates the need for a second surgery to remove the implant, which is the case when a nondegradable implant is used. After implantation in the body, biomedical devices may be subjected to degradation and erosion. Understanding the mechanisms of these processes is essential for the development of biomedical devices or implants with a specific function, for example, scaffolds for tissue-engineering applications. For the engineering and regeneration of soft tissues (e.g., blood vessels, cardiac muscle and peripheral nerves), biodegradable polymers are needed that are flexible and elastic. The scaffolds prepared from these polymers should have tuneable degradation properties and should perform well under long-term cyclic deformation conditions. The required polymers, which are either physically or chemically crosslinked biodegradable elastomers, are reviewed in this article.

Thermoresponsive copolymer brushes possessing quaternary amine groups for strong anion-exchange chromatographic matrices.

A thermoresponsive copolymer incorporating a quaternary amine group, poly(N-isopropylacrylamide-co-3-acrylamidopropyl trimethylammonium chloride (APTAC)-co-tert-butylacrylamide), was conjugated to the surface of silica beads through surface-initiated atom transfer radical polymerization. Prepared copolymer- and copolymer brush-modified beads were characterized by CHN elemental analysis, X-ray photoelectron spectroscopy, gel permeation chromatography, and observation of phase transition profiles. Phase transition profiles of the prepared copolymer indicated that 5 mol % APTAC is suitable for enabling thermally modulated property changes in the copolymer. Chromatographic elution behaviors of adenosine nucleotides and proteins were observed using prepared beads as chromatography matrices. Higher retention time of adenosine nucleotides and strong protein adsorption behavior were observed compared with those on beads with tertiary amine groups, because of the strong basic properties. Therefore, copolymer brush modified beads will be useful as thermoresponsive ion-exchange chromatographic matrices.