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.

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.

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.

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.

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.

Synthetic oral mucin mimic from polymer micelle networks.

Mucin networks are formed in the oral cavity by complexation of glycoproteins with other salivary proteins, yielding a hydrated lubricating barrier. The function of these networks is linked to their structural, chemical, and mechanical properties. Yet, as these properties are interdependent, it is difficult to tease out their relative importance. Here, we demonstrate the ability to recreate the fibrous like network through a series of complementary rinses of polymeric worm-like micelles, resulting in a 3-dimensional (3D) porous network that can be deposited layer-by-layer onto any surface. In this work, stability, structure, and microbial capture capabilities were evaluated as a function of network properties. It was found that network structure alone was sufficient for bacterial capture, even with networks composed of the adhesion-resistant polymer, poly(ethylene glycol). The synthetic networks provide an excellent, yet simple, means of independently characterizing mucin network properties (e.g., surface chemistry, stiffness, and pore size).

Synthesis and characterization of an antibacterial hydrogel containing covalently bound vancomycin.

The release of freely loaded small molecules from biomaterials often exhibits an initial burst, inhibiting the ability of these materials to match drug release with the biomaterial's degradation period. In terms of antibiotic release systems, the remaining vehicle may become a substrate for colonization by bacterial biofilms once the payload is depleted, which can become life threatening. Secondary surgeries are typically performed to remove these empty depots as a means of preventing this type of infection. To maintain the effectiveness of a locally delivered antibiotic without the drawback of a second surgery, we propose a hydrogel drug delivery system in which the drug release rate of vancomycin and degradation rate of the hydrogel are linked via covalent incorporation of vancomycin in the hydrogel backbone. This was achieved through coupling PEG based monomer with vancomycin to create poly(ß-amino ester) chemistry and verified through drug release and matrix degradation studies. Antibiotic release and material degradation were tunable via hydrophobic/hydrophilic content of the hydrogel matrix and extended up to 3 weeks in PBS sink conditions. Covalent addition of vancomycin to the hydrogel polymer backbone was verified through mass spectroscopy and HPLC peak addition, as well as radiotracing of collected HPLC fractions. Bioactivity of released vancomycin was also confirmed alongside the resulting antimicrobial activity of the reacted vancomycin releasate.

Doxycycline administration improves fascial interface in hernia repair.

BACKGROUND: Despite improvements in ventral hernia repair techniques, their recurrence rates are unacceptably high. Increased levels of matrix metalloproteinases (MMPs) and reduced collagen-1 to -3 ratios are implicated in incisional hernia formation. We have recently shown doxycycline treatment for 4 wk after hernia repair reduced MMP levels, significantly increased collagen-1 to -3 ratios, and increased tensile strength of repaired interface fascia. However, this increase was not statistically significant. In this study, we extended treatment duration to determine whether this would impact the tensile strength of the repaired interface fascia. MATERIALS AND METHODS: Thirty-two male Sprague-Dawley rats underwent incision hernia creation and subsequent repair with polypropylene mesh. The animals received either saline (n = 16) or doxycycline (n = 16) beginning from 1 day before hernia repair until the end of survival time of 6 wk (n = 16) or 12 wk (n = 16). Tissue samples were investigated for MMPs and collagen subtypes using Western blot procedures, and tensiometric analysis was performed. RESULTS: At both 6 and 12 wk after hernia repair, the tensiometric strength of doxycycline-treated mesh to fascia interface (MFI) tissue showed a statistically significant increase when compared with untreated control MFI. In both groups, collagen-1, -2, and -3 ratios were remarkably increased in doxycycline-treated MFI. At 6 wk, the doxycycline-treated MFI group showed a significant decrease in MMP-2, an increase in MMP-3, and no change in MMP-9. At 12 wk, MMP-9 showed a remarkable reduction, whereas MMP-2 and -3 protein levels increased in the doxycycline-treated MFI group. CONCLUSIONS: Doxycycline administration results in significantly improved strength of repaired fascial interface tissue along with a remarkable increase in collagen-1, -2, and -3 ratios.

Doxycycline impacts hernia repair outcomes.

BACKGROUND: Incisional hernias occur commonly in up to 20% of all abdominal operations. Incisional hernia formation has been associated with increased levels of matrix metalloproteinases (MMPs), reduced collagen 1, and increased collagen 3 expression. Doxycycline, a nonspecific inhibitor of MMPs, has been shown to beneficially reduce MMP levels in both cancer and aneurysm models. This study evaluates the impact of doxycycline upon MMP expression, collagen subtypes, and hernia repair distraction forces in an animal model of incisional hernia repair. MATERIALS AND METHODS: Twenty-four Sprague Dawley rats underwent incisional hernia creation and subsequent repair with polypropylene mesh. Animals were administered doxycycline or saline daily beginning 1 d prior to hernia repair and survived for 1, 2, or 4 wk. Serum and tissue were evaluated for MMP content and collagen subtyping utilizing enzyme-linked immunosorbent assay and Western blot. Tensiometric properties of the native abdominal wall after hernia repair were measured with an Instron Corp. (Canton, MA) mechanical testing system. RESULTS: There were no differences in control and experimental groups 1 and 2 wk following hernia repair; 4 wk following hernia repair, doxycycline treated animals demonstrated reduced serum MMP-2 and MMP-9 levels, reduced tissue levels of MMP-2, MMP-3, and MMP-9, and increased collagen 1 to 3 ratios. Distraction forces required to disrupt the hernia repair were increased in the doxycycline treated group compared with controls. CONCLUSIONS: Doxycycline administration is associated with improved hernia repair strength with concomitant reduction of MMP levels with increased collagen 1 deposition. Longer term studies are required to better understand the impact of this treatment.

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.

Oriented immobilization of proteins on hydroxyapatite surface using bifunctional bisphosphonates as linkers.

Oriented immobilization of proteins is an important step in creating protein-based functional materials. In this study, a method was developed to orient proteins on hydroxyapatite (HA) surfaces, a widely used bone implant material, to improve protein bioactivity by employing enhanced green fluorescent protein (EGFP) and ß-lactamase as model proteins. These proteins have a serine or threonine at their N-terminus that was oxidized with periodate to obtain a single aldehyde group at the same location, which can be used for the site-specific immobilization of the protein. The HA surface was modified with bifunctional hydrazine bisphosphonates (HBPs) of various length and lipophilicity. The number of functional groups on the HBP-modified HA surface, determined by a 2,4,6-trinitrobenzenesulfonic acid (TNBS) assay, was found to be 2.8 × 10(-5) mol/mg of HA and unaffected by the length of HBPs. The oxidized proteins were immobilized on the HBP-modified HA surface in an oriented manner through formation of a hydrazone bond. The relative protein immobilization amounts through various HBPs were determined by fluorescence and bicinchoninic acid (BCA) assay and showed no significant effect by length and lipophilicity of HBPs. The relative amount of HBP-immobilized EGFP was found to be 10-15 fold that of adsorbed EGFP, whereas the relative amount of ß-lactamase immobilized through HBPs (2, 3, 4, 6, and 7) was not significantly different than adsorbed ß-lactamase. The enzymatic activity of HBP-immobilized ß-lactamase was measured with cefazolin as substrate, and it was found that the catalytic efficiency of HBP-immobilized ß-lactamase improved 2-5 fold over adsorbed ß-lactamase. The results obtained demonstrate the feasibility of our oriented immobilization approach and showed an increased activity of the oriented proteins in comparison with adsorbed proteins on the same hydroxyapatite surface matrix.

Enhanced affinity bifunctional bisphosphonates for targeted delivery of therapeutic agents to bone.

Skeletal diseases have a major impact on the worldwide population and economy. Although several therapeutic agents and treatments are available for addressing bone diseases, they are not being fully utilized because of their uptake in nontargeted sites and related side effects. Active targeting with controlled delivery is an ideal approach for treatment of such diseases. Because bisphosphonates are known to have high affinity to bone and are being widely used in treatment of osteoporosis, they are well-suited for drug targeting to bone. In this study, a targeted delivery of therapeutic agent to resorption sites and wound healing sites of bone was explored. Toward this goal, bifunctional hydrazine-bisphosphonates (HBPs), with spacers of various lengths, were synthesized and studied for their enhanced affinity to bone. Crystal growth inhibition studies showed that these HBPs have high affinity to hydroxyapatite, and HBPs with shorter spacers bind more strongly than alendronate to hydroxyapatite. The HBPs did not affect proliferation of MC3T3-E1 preosteoblasts, did not induce apoptosis, and were not cytotoxic at the concentration range tested (10(-6)-10(-4) M). Furthermore, drugs can be linked to the HBPs through a hydrazone linkage that is cleavable at the low pH of bone resorption and wound healing sites, leading to release of the drug. This was demonstrated using hydroxyapatite as a model material of bone and 4-nitrobenzaldehyde as a model drug. This study suggests that these HBPs could be used for targeted delivery of therapeutic agents to bone.

Animal models for periodontal disease.

Animal models and cell cultures have contributed new knowledge in biological sciences, including periodontology. Although cultured cells can be used to study physiological processes that occur during the pathogenesis of periodontitis, the complex host response fundamentally responsible for this disease cannot be reproduced in vitro. Among the animal kingdom, rodents, rabbits, pigs, dogs, and nonhuman primates have been used to model human periodontitis, each with advantages and disadvantages. Periodontitis commonly has been induced by placing a bacterial plaque retentive ligature in the gingival sulcus around the molar teeth. In addition, alveolar bone loss has been induced by inoculation or injection of human oral bacteria (e.g., Porphyromonas gingivalis) in different animal models. While animal models have provided a wide range of important data, it is sometimes difficult to determine whether the findings are applicable to humans. In addition, variability in host responses to bacterial infection among individuals contributes significantly to the expression of periodontal diseases. A practical and highly reproducible model that truly mimics the natural pathogenesis of human periodontal disease has yet to be developed.

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.

Novel calcium sulfate space-making devices for bone regeneration: a pilot study.

The feasibility of using preformed calcium sulfate (CS) space-making devices (SMDs) for bone regeneration was explored using a rabbit calvarial model. Twenty-four CS devices were fabricated. Twelve of these were SMDs, which consisted of a domed head that served as the actual space-maker, and a stalk or "tail" portion used to affix the device to the bone. A second set of control devices (CDs) was fabricated that consisted of only the tail portion. CDs were made of medical-grade CS, as were 9 of the SMDs. Six of the CS SMDs were loaded with high or low concentrations of simvastatin. The remaining 3 SMDs were made of a CS/bioactive glass composite. One SMD and 1 CD were implanted bilaterally in the parietal bones of 12 New Zealand White rabbits, which were euthanized 8 weeks following surgery. All implants were well tolerated. In all animals, the side receiving the SMD exhibited greater thickness than did the control sites. The addition of simvastatin resulted in a statistically significant difference in calvarial thickness. The CS/bioactive glass composite also yielded encouraging results. The CS resorbable SMDs are worthy of further investigation.

Programmatic effectiveness of a university-based implant training program: long-term, patient-centered outcomes.

The University of Kentucky College of Dentistry established a formal implant program in 1999. The program utilizes a single system (Straumann) and a team concept in which implants are placed by residents in period ontology or oral and maxillofacial surgery and restored by predoctoral dental students. The program features stringent patient inclusion and exclusion criteria, incremental structured learning experiences, formal standardized protocols, and hands-on preclinical learning experiences. The use of a single system simplified training protocols and inventory requirements. Complete and partially edentulous patients requiring single and multiple implants are eligible for the program, although maxillary anterior sites are excluded. There is a formal quality assurance program to assess patient-centered outcomes. The current report includes data for patients who had implants placed in the period from January 2000 through December 2002. During that period, 192 patients received dental implants, of which 116 patients (248 implants) were available for analysis. The mean follow-up was 7.05 years (median = 7.32 years). The implant survival rate was 98.4%, while the success rate was 93.15%. Success was determined by the absence of pain or mobility, as well as self-reported patient satisfaction with function, appearance, and surgical experience.

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.

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.

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.

Alternating release of different bioactive molecules from a complexation polymer system.

Regeneration of bone is driven by the action of numerous biomolecules. However, most osteobiologic devices mainly depend on delivery of a single molecule. The present studies were directed at investigating a polymeric system that enables localized, alternating delivery of two or more biomolecules. The osteotropic biomolecules studied were simvastatin hydroxyacid (Sim) and parathyroid hormone (1-34) (PTH(1-34)), and the antimicrobial peptide cecropin B (CB) was also incorporated. Loaded microspheres were made using the complexation polymer system of cellulose acetate phthalate and Pluronic F-127 (blend ratio, 7:3). By alternating layers of the different types of microspheres, 10-layer devices were made to release CB and Sim, CB and PTH, or Sim and PTH. In vitro experiments showed five discrete peaks for each molecule over a release period of approximately two weeks. MC3T3-E1 osteoblastic cells alternately exposed to the osteotropic biomolecules showed enhanced proliferation and early osteoblastic activity. Alternating delivery of 10nm Sim and either 500pg/ml or 5ng/ml PTH showed additive effects compared to the CB/Sim or CB/PTH devices. These implantable formulations may be useful for alternating delivery of different biomolecules to stimulate concurrent biological effects in focal tissue regeneration applications.