Interval delivery of 5HT2A agonists using multilayered polymer films.

There is an urgent unmet medical need to develop therapeutic options for the ~50% of depression patients suffering from treatment-resistant depression, which is difficult to treat with existing psycho- and pharmaco-therapeutic options. Classical psychedelics, such as the 5HT2A agonists, have re-emerged as a treatment paradigm for depression. Recent clinical trials highlight the potential effectiveness of 5HT2A agonists to improve mood and psychotherapeutic growth in treatment-resistant depression patients, even in those who have failed a median of four previous medications in their lifetime. Moreover, microdosing could be a promising way to achieve long-term alleviation of depression symptoms without a hallucinogenic experience. However, there are a gamut of practical barriers that stymie further investigation of microdosing 5HT2A agonists, including: low compliance with the complicated dosing regimen, high risk of diversion of controlled substances, and difficulty and cost administering the long-term treatment regimens in controlled settings. Here, we developed a drug delivery system composed of multilayered cellulose acetate phthalate (CAP)/Pluronic F-127 (P) films for the encapsulation and interval delivery of 5HT2A agonists from a fully biodegradable and biocompatible implant. CAPP film composition, thickness, and layering strategies were optimized, and we demonstrated three distinct pulses from the multilayered CAPP films in vitro. Additionally, the pharmacokinetics and biodistribution of the 5HT2A agonist 2,5-Dimethoxy-4-iodoamphetamine (DOI) were quantified following the subcutaneous implantation of DOI-loaded single and multilayered CAPP films. Our results demonstrate, for the first time, the interval delivery of psychedelics from an implantable drug delivery system and open the door to future studies into the therapeutic potential of psychedelic delivery.

Systems for local, sustained release of zoledronic acid as a potential treatment for metastatic bone disease.

Bone pain is the leading cause of morbidity in patients with metastatic cancer. Systemic administration of zoledronic acid (ZA) decreases skeletally-related events in bone cancer patients but is associated with major side effects. This project investigated two biomaterials, poly(methyl methacrylate) (PMMA) bone cement and poly(lactic-co-glycolic acid) (PLGA), for local ZA delivery. Compressive properties of PMMA samples were tested with increased drug loading, and in vitro ZA release profiles from PMMA cylinders and PLGA films were measured over 8 weeks. The activity of ZA eluted from both materials was evaluated on the RAW 264.7 macrophage cell line. PMMA samples released up to only 17% of incorporated drug, whereas PLGA films released over 95%. A burst profile was observed for PMMA, while ZA release from PLGA exhibited a typical triphasic profile. Drug bioactivity remained above 50% for both materials. Local ZA delivery from these materials may be useful in the treatment of metastatic bone cancer.

Topical vancomycin for treatment of methicillin-resistant Staphylococcus epidermidis infection in a rat spinal implant model.

STUDY DESIGN: Basic science. OBJECTIVE: Investigate the ability of local applicaiton of vancomycin, either in powder form or suspended within poly(lactic-co-glycolic acid) microspheres (MS), to treat infection using a rat spinal model. Surgical site infections (SSIs) are a serious complication after spine surgery and are associated with high morbidity and mortality and often caused my coagulase negative staphylococci. A comprehensive approach to reduce SSIs has been recommended including the use of topical vancomycin. Animal and human studies have shown improved control of infection with local compared to systemic antibiotics. METHODS: K-wires seeded with methicillin-resistant Staphylococcus epidermidis RP62A (MRSE) were treated with vancomycin powder, carboxymethylcellulose sodium salt (CMC) (microsphere carrier), vancomycin powder, blank MS or vancomycin-loaded MS for 24 or 48 h in vitro after which bacteria were enumerated. In addition, a spinal instrumentation model was developed in rats with a bacterial seeded K-wire implanted into the right side of L4 and L5. Rats underwent no treatment or were treated locally with either vancomycin powder, blank MS or vancomycin-loaded MS. After 8 weeks, the K-wire, bone, soft tissue and wire fastener were cultured and results analyzed. RESULTS: Vancomycin powder and vancomycin-loaded MS resulted in significantly fewer bacteria remaining in vitro than did CMC. Vancomycin powder- treated animals' cultures were significantly lower than all other groups (P < 0.0001) with negative culture results, except for one animal. The vancomycin-loaded MS-treated animals had lower bone bacterial counts than the controls (P < 0.0279); blank MS-treated animals had no differences in bacterial densities when compared to non-treated animals. CONCLUSION: Vancomycin powder and vancomycin-loaded MS were active against MRSE in vitro, in a rat MRSE implant model; however, vancomycin MS were inferior to the topical vancomycin powder. Vancomycin powder prevented MRSE infection in a rat spinal implant infection model.

Biodegradable polymerized simvastatin stimulates bone formation.

Previous research from our labs demonstrated the synthesis of polymerized simvastatin by ring-opening polymerization and slow degradation with controlled release of simvastatin in vitro. The objective of the present study was to evaluate the degradation and intramembranous bone-forming potential of simvastatin-containing polyprodrugs in vivo using a rat calvarial onlay model. Poly(ethylene glycol)-block-poly(simvastatin) and poly(ethylene glycol)-block-poly(simvastatin)-ran-poly(glycolide) were compared with simvastatin conventionally encapsulated in poly(lactic-co-glycolic acid) (PLGA) and pure PLGA. The rate of degradation was higher for PLGA with and without simvastatin relative to the simvastatin polyprodrugs. Significant new bone growth at the circumference of poly(ethylene glycol)-block-poly(simvastatin) disks was observed beginning at 4 weeks, whereas severe bone resorption (4 weeks) and bone loss (8 weeks) were observed for PLGA loaded with simvastatin. No significant systemic effects were observed for serum total cholesterol and body weight. Increased expression of osteogenic (BMP-2, Runx2, and ALP), angiogenic (VEGF), and inflammatory cytokines (IL-6 and NF-ĸB) genes was seen with all polymers at the end of 8 weeks. Poly(ethylene glycol)-block-poly(simvastatin), with slow degradation and drug release, controlled inflammation, and significant osteogenic effect, is a candidate for use in bone regeneration applications. STATEMENT OF SIGNIFICANCE: Traditional drug delivery systems, e.g., drug encapsulated in poly(lactic-co-glycolic acid) (PLGA), are typically passive and have limited drug payload. As an alternative, we polymerized the drug simvastatin, which has multiple physiological effects, into macromolecules ("polysimvastatin") via ring-opening polymerization. We previously demonstrated that the rate of degradation and drug (simvastatin) release can be adjusted by copolymerizing it with other monomers. The present results demonstrate significant new bone growth around polysimvastatin, whereas severe bone loss occurred for PLGA loaded with simvastatin. This degradable biomaterial with biofunctionality integrated into the polymeric backbone is a useful candidate for bone regeneration applications.

A rodent model using skeletal anchorage and low forces for orthodontic tooth movement.

INTRODUCTION: Nonhuman animal models have been used extensively to study orthodontic tooth movement (OTM). However, rodent models have disadvantages, including a reported reduction in bone volume during OTM. The purpose of this study was to determine the viability of a skeletal anchorage and the effect of low force (∼3 cN) on interradicular bone volume during OTM. METHODS: Ninety Sprague-Dawley rats were divided into 5 time points. A miniscrew and a nickel titanium coil spring placed a load of 3 cN (experimental) or 0 cN (sham) on the maxillary first molar in a split-mouth design. Displacement of the first molar and bone volume/total volume (BV/TV) in the interradicular region were quantified. RESULTS: The success rate of the miniscrew was 98.9% (89 out of 90). Linear and angular tooth movement increased steadily (mean 0.1 mm/wk, 0.48 mm at 40 days). BV/TV was significantly reduced between the tooth movement and non-tooth movement sides in the 3 cN group: by 13%, 23%, 15%, 23%, and 16% at 3, 7, 14, 28, and 40 days, respectively. CONCLUSIONS: Our model resulted in efficient OTM without skeletal anchorage failure. BV/TV reduction was lower than in previous reports. This novel validated model is likely to be the basis for future studies.

Vancomycin- and Poly(simvastatin)-Loaded Scaffolds with Time-Dependent Development of Porosity.

Biodegradable scaffolds are widely use in drug delivery and tissue engineering applications. The scaffolds can be modified to provide the necessary mechanical support for tissue formation and to deliver one or more drugs to stimulate tissue formation or for the treatment of a specific condition. In the current study, we developed biodegradable scaffolds that have the potential for dual drug delivery. The scaffolds consisted of simvastatin-containing prodrug, poly(simvastatin) entrapped in poly(ß-amino ester) (PBAE) porogen particles and vancomycin encapsulated in poly(lactic-co-glycolic acid) (PLGA) microspheres, which were fused together around the PBAE porogens to create a slow-degrading matrix. Upon hydrolysis, poly(simvastatin) releases simvastatin acid, which has angiogenic and osteogenic properties, while the PLGA microspheres release vancomycin as an antibacterial agent. Degradation of PBAE porogens through hydrolysis of ester linkages led to the development of porosity in a controlled manner and led to water penetration that facilitated hydrolysis of PLGA. Higher porogen loading (~60% by weight) gave rise to ~70% interconnected porosity with pore spacing of ~180 µm. This open volume facilitated simvastatin acid release upon hydrolysis and entrapped vancomycin release via diffusion through and degradation of PLGA. During the study, ~162 µg of simvastatin acid and ~18 mg vancomycin were released from the highest porosity scaffolds. Bioactivity studies showed that released simvastatin acid stimulated preosteoblastic activity, indicating that scaffold fabrication did not damage the polymeric prodrug. Regarding mechanical properties, compressive modulus, failure strain, and failure stress decreased with increasing PBAE porogen content. These dual drug releasing scaffolds with controlled development of microarchitecture can be useful in bone tissue engineering applications.

Reducible disulfide poly(beta-amino ester) hydrogels for antioxidant delivery.

Recently, biomaterials have been designed to contain redox-sensitive moieties, such as thiols and disulfides, to impart responsive degradation and/or controlled release. However, due to the high sensitivity of cellular redox-based systems which maintain free-radical homeostasis (e.g. glutathione/glutathione disulfide), if these biomaterials modify the cellular redox environment, they may inadvertently affect cellular compatibility and/or oxidative stress defenses. In this work, we hypothesize that the degradation products of a poly(ß-amino ester) (PBAE) hydrogel formed with redox sensitive disulfide (cystamine) crosslinking could serve as a supplement to the environmental cellular antioxidant defenses. Upon introduction into a reducing environment, these disulfide-containing hydrogels cleave to present bound-thiol groups, yet remain in the bulk form at up to 66 mol% cystamine of the total amines. By controlling the molar fraction of cystamine, it was apparent that the thiol content varied human umbilical vein endothelial cell (HUVEC) viability IC50 values across an order of magnitude. Further, upon introduction of an enzymatic oxidative stress generator to the cell culture (HX/XO), pre-incubated thiolated hydrogel degradation products conferred cellular and mitochondrial protection from acute oxidative stress, whereas non-reduced disulfide-containing degradation products offered no protection. This polymer may be an advantageous implantable drug delivery system for use in acute oxidative stress prophylaxis and/or chronic oxidative stress cell therapies due to its solid/liquid reversibility in a redox environment, controlled thiolation, high loading capacity through covalent drug-addition, and simple post-synthesis modification which bound-thiols introduce. STATEMENT OF SIGNIFICANCE: In this work, we demonstrate a unique property of disulfide containing degradable biomaterials. By changing the redox state of the degradation products (from oxidized to reduced), it is possible to increase the IC50 of the material by an order of magnitude. This dramatic shift is linked directly to the oxidative stress response of the cells and suggests a possible mechanism by which one can tune the cellular response to degradable biomaterials.

Testing of a bioactive, moldable bone graft substitute in an infected, critically sized segmental defect model.

Large infected bone defects, often resulting from high energy traumas, are difficult to treat due to their variability in complexity and location. Standard treatment for infected bone defects begins with a protocol that includes a series of debridements in conjunction with an extended course of systemic antibiotics. Only after the infection has been eliminated will repair of the defect commence, typically with implantation of autologous bone. To address some of the shortcomings of the standard treatment methods, such as serial procedures, limited grafting material, and the need for a second surgical site for autologous bone, a sequential, dual drug-releasing, moldable, calcium sulfate-based bone graft substitute was developed previously. In the present studies, the effectiveness of the material for treating both the infection with vancomycin and bone defect with simvastatin was evaluated in vivo using a critically sized, infected segmental defect model in rat femurs. Although the infection was not fully eliminated, the local release of vancomycin increased survivorship of infected animals by 464% compared to nontreated controls. Infected animals receiving antimicrobial treatment showed comparable amounts of new bone formation within the defect site when compared to noninfected controls. Incorporating agents capable of disrupting established biofilms into bone graft substitutes may enhance effectiveness in treating a biofilm infection within a bone defect. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1878-1886, 2018.

Biodegradable Simvastatin-Containing Polymeric Prodrugs with Improved Drug Release.

Simvastatin was previously converted to a polymeric prodrug with higher drug loading, but the hydrophobic nature of the poly(simvastatin) component of the block copolymer led to slow release of the drug in vitro. In this study, we hypothesized that degradation could be accelerated by chemically modifying the polymer backbone by introducing glycolide and lactide comonomers. Copolymers were formed by ring-opening polymerization using 5 kDa monomethyl ether poly(ethylene glycol) as the microinitiator in presence of triazabicyclodecene catalyst. In addition to simvastatin, modified reaction mixtures contained lactide or glycolide. Incorporation of the less hydrophobic glycolide comonomer led to in vitro degradation of up to two times greater mass loss, release of up to ~7 times more simvastatin, and a 2-3 times increase in compressive modulus compared to the lactide-containing and parent polymers.

Highly Thiolated Poly (Beta-Amino Ester) Nanoparticles for Acute Redox Applications.

Disulfides are used extensively in reversible cross-linking because of the ease of reduction into click-reactive thiols. However, the free-radical scavenging properties upon reduction are often under-considered. The free thiols produced upon reduction of this disulfide material mimic the cellular reducing chemistry (glutathione) that serves as a buffer against acute oxidative stress. A nanoparticle formulation producing biologically relevant concentrations of thiols may not only provide ample chemical conjugation sites, but potentially be useful against severe acute oxidative stress exposure, such as in targeted radioprotection. In this work, we describe the synthesis and characterization of highly thiolated poly (ß-amino ester) (PBAE) nanoparticles formed from the reduction of bulk disulfide cross-linked PBAE hydrogels. Degradation-tunable PBAE hydrogels were initially synthesized containing up to 26 wt % cystamine, which were reduced into soluble thiolated oligomers and formulated into nanoparticles upon single emulsion. These thiolated nanoparticles were size-stable in phosphate buffered saline consisting of up to 11.0 ± 1.1 mM (3.7 ± 0.3 mmol thiol/g, n = 3 M ± SD), which is an antioxidant concentration within the order of magnitude of cellular glutathione (1⁻10 mM).

Tuning Properties of Poly(ethylene glycol)-block-poly(simvastatin) Copolymers Synthesized via Triazabicyclodecene.

Simvastatin was polymerized into copolymers to better control drug loading and release for therapeutic delivery. When using the conventional stannous octoate catalyst in ring-opening polymerization (ROP), reaction temperatures ≥200 °C were required, which promoted uncontrollable and undesirable side reactions. Triazabicyclodecene (TBD), a highly reactive guanidine base organocatalyst, was used as an alternative to polymerize simvastatin. Polymerization was achieved at 150 °C using 5 kDa methyl-terminated poly(ethylene glycol) (mPEG) as the initiator. ROP reactions with 2 kDa or 550 Da mPEG initiators were also successful using TBD at 150 °C instead of stannous octoate, which required a higher reaction temperature. Biodegradability of the poly(simvastatin) copolymer in phosphate-buffered saline was also improved, losing twice as much mass than the copolymer synthesized via stannous octoate. The three copolymers exhibited modified rates of simvastatin release, demonstrating tunablity for drug delivery applications.

Sequential Release of Multiple Drugs from Flexible Drug Delivery Films.

Sequential release of drugs aligned with the phases of tissue healing could reduce scarring. To achieve this aim, layered film devices comprising cellulose acetate phthalate (CAP) and Pluronic F-127 (Pluronic) were loaded with ketoprofen, quercetin, and pirfenidone. Citrate plasticizers were added to impart flexibility. Release of two or three drugs in sequence over several days was obtained for all multilayered devices tested. Mechanical analysis showed that elongation increased and modulus decreased with increasing plasticizer content. Release profiles can be tailored by order of layers, plasticizer concentration, and drug loaded, making CAP-Pluronic an appealing system for inhibiting scar tissue formation.

Resistance of Mandibular Polyurethane Replicas to Fracture After Removal of Blocks From the Symphysis and Ramus.

BACKGROUND: When block grafts are harvested intraorally, the donor sites may act as stress concentrators and alter the structural integrity of the mandible. PURPOSE: The study aimed to compare displacement and load failure between intact polyurethane mandibular replicas and similar replicas from which blocks were taken at the symphysis or the ramus. It also aimed to identify trends of load failure. MATERIALS AND METHODS: Thirty-five mandibular replicas were tested to failure with an electromagnetic material testing unit. The variables evaluated in this investigation were maximal load, displacement at maximal load, and fracture location. RESULTS: Statistically significant differences in maximal load were detected between groups (P = 0.0008). Differences between fracture locations were also statistically significant (P < 0.0001). The mandibles from which blocks were removed at the symphysis were significantly more likely to break at a lower maximal load than were the control mandibles (P = 0.0010) or the mandibles from which blocks were removed at the ramus (P = 0.0162). They were also more likely than the control group to break at a lower displacement at maximal load (P = 0.0145). CONCLUSIONS: Location of the donor site significantly influences the structural integrity of mandibular replicas. In addition, the donor site significantly affects the location of mandibular fractures.

Combined Effects of Drugs and Plasticizers on the Properties of Drug Delivery Films.

Formation of scar tissue may be reduced or prevented if wounds were locally treated with a combination of molecules tuned to the different healing phases, guiding tissue regeneration along a scar free path. To this end, drug delivery devices made of cellulose acetate phthalate and Pluronic F-127 were loaded with either quercetin or pirfenidone and plasticized with either triethyl citrate (TEC) or tributyl citrate (TBC). Quercetin inhibits oxidative stress, and pirfenidone has been shown to reduce production of pro-inflammatory and fibrogenic molecules. The combined effects of drug and plasticizer on erosion, release, and mechanical properties of the drug delivery films were investigated. TEC-plasticized films containing quercetin released drug at a slower rate than did TBC films. Pirfenidone-loaded films released drug at a faster rate than erosion occurred for both types of plasticizers. Higher plasticizer contents of both TEC and TBC increased the elongation and decreased the elastic modulus. In contrast, increased pirfenidone loading in both TEC and TBC films resulted in a significantly higher modulus, an anti-plasticizer effect. Adding pirfenidone significantly decreased elongation for all film types, but quercetin-loaded samples had significantly greater elongation with increasing drug content. Films containing quercetin elongated more than did pirfenidone-loaded films. Quercetin is over 1.5 times larger than pirfenidone, has water solubility over 12 times lower, and has 6 times more bonding sites than pirfenidone. These differences affected how the two drugs interacted with cellulose acetate phthalate and Pluronic F-127 and thereby determined polymer properties. Drug release, erosion, and mechanical properties of association polymer films can be tailored by the characteristics of the drugs and plasticizers included in the system.

Multifunctional poly(ß-amino ester) hydrogel microparticles in periodontal in situ forming drug delivery systems.

In situ forming implants (ISIs) formed from poly(lactic-co-glycolic acid) (PLGA) have been commercialized for local drug delivery to treat periodontitis, but drug release from these bulk materials is typically subject to an initial burst. In addition, PLGA has inferior material properties for the dynamic mechanical environment of gingival tissue. In this work, poly(ß-amino ester) (PBAE) hydrogel microparticles were incorporated into a PLGA matrix to provide several new functions: mechanical support, porosity, space-filling, and controlled co-delivery of antimicrobial and osteogenic drugs. First, the effects of PBAE microparticles on ISI architecture and material properties throughout degradation were investigated. Second, the influence of PBAE microparticles on drug release kinetics was quantified. Over a 15 d period, ISIs containing PBAE microparticles possessed greater porosity, ranging from 42-80%, compared to controls, which ranged from 24-54% (p < 0.001), and these ISIs also developed significantly greater accessible volume to simulated cell-sized spheres after 5 d or more of degradation (p < 0.001). PBAE-containing ISIs possessed a more uniform microarchitecture, which preserved mechanical resilience after cyclical loading (p < 0.001), and the materials swelled to fill the injected space, which significantly increased interfacial strength in an artificial periodontal pocket (p < 0.0001). PBAE microparticles eliminated the burst of freely-mixed simvastatin compared to 36% burst from controls (p < 0.0001), and high-dose doxycycline release was prolonged from 2 d to 7 d by pre-loading drug into the microparticles. PBAE-containing PLGA ISIs are more effective space-filling scaffolds and offer improved release kinetics compared to existing ISIs used to treat periodontitis.

Doxycycline shows dose-dependent changes in hernia repair strength after mesh repair.

BACKGROUND: Ventral hernia is a commonly occurring surgical problem. Our earlier studies have shown that a 30 mg/kg dose of doxycycline can significantly impact the strength of polypropylene (PP) mesh in a rat hernia repair model at 6 and 12 weeks. The objective of the present study was to investigate the dose dependence of doxycycline treatment on hernia repair strengths in rats. STUDY DESIGN: Fifty-six Sprague-Dawley rats underwent hernia repair with either PP mesh (n = 28) or sutures only (primary; n = 28); both groups were further divided into four doxycycline groups of seven animals each: control (0 mg/kg), low (3 mg/kg), medium (10 mg/kg), and high (30 mg/kg). One day before hernia repair surgery, animals received doxycycline doses by gavage and continued receiving daily until euthanasia. After 8 weeks, rats were euthanized and tissue samples from hernia repaired area were collected and analyzed for tensile strength using a tensiometer (Instron, Canton, MA, USA), while MMPs 2, 3, and 9, and collagen type 1 and 3 were analyzed by western blotting. RESULTS: In mesh-repaired animals, medium and high doxycycline dose repaired mesh fascia interface (MFI) showed significant increase in tensile strength when compared to control. In the primary repaired animals, there was no significant difference in MFI tensile strength in any dose group. In medium-dose MFI, there was a significant reduction in MMPs 2, 3, and 9. In this animal group, MFI showed significant increase in collagen 1 and significant reduction in collagen type 3 when compared to control. CONCLUSION: It is possible to improve the strength of mesh-repaired tissue by administering a significantly lower dose of the drug, which has implications for translation of the findings.

Layer-by-Layers of Polymeric Micelles as a Biomimetic Drug-Releasing Network.

Mucin networks are lubricous biofunctional coats formed through the continuous deposition of mucin glycoproteins. Previously, we demonstrated the synthesis of a mucin mimic using biotinylated-filomicelles crosslinked via streptavidin using a layer-by-layer approach. These networks recreate the fibrous nature of mucin and can serve as a drug-releasing network. In this work, the ability to vary the network properties by blending filomicelles with spherical micelles is demonstrated. In addition, the deposition of a dense polymer coating on the mucin network was shown to act as a barrier to control diffusion and improved the structural stability under simulated oral chemical conditions. These biomimetic coatings can be utilized as a delivery system, providing a tunable drug release for oral applications.

Comparison of sequential drug release in vitro and in vivo.

Development of drug-delivery devices typically involves characterizing in vitro release performance with the inherent assumption that this will closely approximate in vivo performance. Yet, as delivery devices become more complex, for instance with a sequential drug release pattern, it is important to confirm that in vivo properties correlate with the expected "programming" achieved in vitro. In this work, a systematic comparison between in vitro and in vivo biomaterial erosion and sequential release was performed for a multilayered association polymer system comprising cellulose acetate phthalate and Pluronic F-127. After assessing the materials during incubation in phosphate-buffered saline, devices were implanted supracalvarially in rats. Devices with two different doses and with different erosion rates were harvested at increasing times post-implantation, and the in vivo thickness loss, mass loss, and the drug release profiles were compared with their in vitro counterparts. The sequential release of four different drugs observed in vitro was successfully translated to in vivo conditions. Results suggest, however, that the total erosion time of the devices was longer and that release rates of the four drugs were different, with drugs initially released more quickly and then more slowly in vivo. Many comparative studies of in vitro and in vivo drug release from biodegradable polymers involved a single drug, whereas this research demonstrated that sequential release of four drugs can be maintained following implantation. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1302-1310, 2016.

Dependence of macrophage superoxide release on the pulse amplitude of an applied pressure regime: a potential factor at the soft tissue-implant interface.

Failure of soft tissue implants has been largely attributed to the influence of biomaterial surface properties on the foreign body response, but some implant complications, e.g. macrophage accumulation and necrosis, are still not effectively addressed with surface treatments to minimize deleterious biomaterial effects. We explored an alternative explanation for implant failure, linking biocompatibility with implant micromotion-induced pressure fluctuations at the tissue-biomaterial interface. For this purpose, we used a custom in vitro system to characterize the effects of pressure fluctuations on the activity of macrophages, the predominant cells at a healing implant site. Initially, we quantified superoxide production by HL60-derived macrophage-like cells under several different pressure regimes with means of 5-40 mmHg, amplitudes of 0-15 mmHg and frequencies of 0-1.5 Hz. All pressure regimes tested elicited significantly (p < 0.05) reduced superoxide production by macrophage-like cells relative to parallel controls. Notably, pressure-sensitive reductions in superoxide release correlated (r(2) = 0.74; p < 0.01) only with pulse pressures. Based on the connection between superoxide production and cell viability, we also explored the influence of cyclic pressure on macrophage numbers and death. Compared to controls, adherent macrophage-like cells exposed to 7.5/2.5 mmHg cyclic pressures for 6 h exhibited significantly (p < 0.01) reduced cell numbers, independent of cell death. A similar effect was observed for cells treated with 10 U/ml superoxide dismutase. Collectively, our results suggest that pressure pulses are a putative regulator of macrophage adhesion via a superoxide-related effect. Pressure fluctuations, e.g. due to implant micromotion, may, therefore, potentially modulate macrophage-dependent wound healing.

Treating Proximal Tibial Growth Plate Injuries Using Poly(Lactic-co-Glycolic Acid) Scaffolds.

Growth plate fractures account for nearly 18.5% of fractures in children. Depending on the type and severity of the injury, inhibited bone growth or angular deformity caused by bone forming in place of the growth plate can occur. The current treatment involves removal of the bony bar and replacing it with a filler substance, such as a free fat graft. Unfortunately, reformation of the bony bar frequently occurs, preventing the native growth plate from regenerating. The goal of this pilot study was to determine whether biodegradable scaffolds can enhance native growth plate regeneration following a simulated injury that resulted in bony bar formation in the proximal tibial growth plate of New Zealand white rabbits. After removing the bony bar, animals received one of the following treatments: porous poly(lactic-co-glycolic acid) (PLGA) scaffold; PLGA scaffold loaded with insulin-like growth factor I (IGF-I); PLGA scaffold loaded with IGF-I and seeded with autogenous bone marrow cells (BMCs) harvested at the time of implantation; or fat graft (as used clinically). The PLGA scaffold group showed an increased chondrocyte population and a reduced loss of the remaining native growth plate compared to the fat graft group (the control group). An additional increase in chondrocyte density was seen in scaffolds loaded with IGF-I, and even more so when BMCs were seeded on the scaffold. While there was no significant reduction in the angular deformation of the limbs, the PLGA scaffolds increased the amount of cartilage and reduced the amount of bony bar reformation.