The Highly Controlled and Efficient Polymerization of Ethylene.

The highly controlled and efficient polymerization of ethylene is a very attractive but challenging target. Herein we report on a Coordinative Chain Transfer Polymerization catalyst, which combines a high degree of control and very high activity in ethylene oligo- or polymerization with extremely high chain transfer agent (triethylaluminum) to catalyst ratios (catalyst economy). Our Zr catalyst is long living and temperature stable. The chain length of the polyethylene products increases over time under constant ethylene feed or until a certain volume of ethylene is completely consumed to reach the expected molecular weight. Very high activities are observed if the catalyst elongates 60 000 or more alkyl chains and the polydispersity of the strictly linear polyethylene materials obtained are very low. The key for the combination of high control and efficiency seems to be a catalyst stabilized by only one strongly bound monoanionic N-ligand.

Understanding the basis of medical use of poly-lactide-based resorbable polymers and composites - a review of the clinical and metabolic impact.

This review intended to comparatively explain and present the most important medical use and biological impact of poly-lactides and lactide-based composites. The utilization and degradation of compounds based on lactic acid and polylactides is described in detail. Understanding the metabolism and degradation phenomenon and the factors that potentially influence it is key to modulating their properties as well as their characteristics driven from the fabrication procedures and the fields of use. All these are commented according to the clinician's criteria. The current debate on the advantages and shortcomings of various resorbable polymeric materials categories is also analyzed, from the perspective of the users of resorbable polylactide-based biomaterials. The scientific literature comprises either distinct chemical and physical or specific animal or medical description of resorbable materials; so that in compensation, the present review covers all topics for the most appropriate comprehensive update of the reader.

In quest of optimal drug-supported and targeted bone regeneration in the cranio facial area: a review of techniques and methods.

Craniofacial bone structures are frequently and extensively affected by trauma, tumors, bone infections and diseases, age-related degeneration and atrophy, as well as congenital malformations and developmental anomalies. Consequently, severe encumbrances are imposed on both patients and healthcare systems due to the complex and lengthy treatment duration. The search for alternative methods to bone transplantation, grafting and the use of homologous or heterologous bone thus responds to one of the most significant problems in human medicine. This review focuses on the current consensus of bone-tissue engineering in the craniofacial area with emphasis on drug-induced stem cell differentiation and induced bone regeneration.

Conservative treatment and implant rehabilitation of the mandible in a case of craniofacial fibrous dysplasia: a case report.

We present a case of implant rehabilitation of the mandible in a young patient affected by craniofacial fibrous dysplasia. A computed tomography scan showed involvement of the left orbital contour and left maxilla, with total involvement of the mandible. We performed conservative surgical treatment from 2004 to 2011 to reconstruct and recontour the orbital and mandible region. Next, we performed implant rehabilitation of the mandible. This case emphasizes the importance of conservative and nondemolition treatment to obtain excellent functional and esthetic results.

A Closed-Loop Recyclable Low-Density Polyethylene.

Low-density polyethylene (LDPE) is one of the most important plastics, which is produced unfortunately under extreme conditions. In addition, it consists of robust aliphatic C─C bonds which are challenging to cleave for plastic recycling. A low-pressure and -temperature (pethylene = 2 bara, T = 70 °C) macromonomer-based synthesis of long chain branched polyethylene is reported. The introduction of recycle points permits the polymerization (grafting to) of the macromonomers to form the long chain branched polyethylene and its depolymerization (branch cleavage). Coordinative chain transfer polymerization employing ethylene and co-monomers is used for the synthesis of the macromonomers, permitting a high flexibility of their precise structure and efficient synthesis. The long chain branched polyethylene material matches key properties of low-density polyethylene.

SiCN nanofibers with a diameter below 100 nm synthesized via concerted block copolymer formation, microphase separation, and crosslinking.

SiCN fibers with a mean diameter of 50 nm and an aspect ratio of up to 100 are produced in a two-step process by R. Kempe and co-workers. The key step to fabricate the longitudinal and cross-sectional views of the mesofibers shown here is a concerted block-copolymer synthesis, microphase separation, and cross linking at 140 °C followed by pyrolysis at 1100 °C. Inexpensive components like a commercially available silazane and polyethylene are linked. The fibers may find application in electronic devices, as components of ceramic matrix composites, as fiber beds in high-temperature nano-filtering like diesel fine dust removal, or as thermally robust and chemically inert catalyst supports. Furthermore, the SiCN nanofibers introduced on page 984 are a promising alternative to ultrathin carbon fibers, due to their oxidation resistance.

Tailored nanostructuring of end-group-functionalized high-density polyethylene synthesized by an efficient catalytic version of Ziegler's "Aufbaureaktion".

Monoguanidinato titanium complexes are efficient catalysts to make OH end-group-functionalized polyethylene (PE-OH) by a catalyzed version of Ziegler's "Aufbaureaktion". This PE-OH can be structured to mesoporous polyethylene or polyethylene nanofibers/ribbons through diblock copolymer synthesis, microphase separation, and etching of the sacrificial polylactide block.

Elongation and branching of α-olefins by two ethylene molecules.

α-Olefins are important starting materials for the production of plastics, pharmaceuticals, and fine and bulk chemicals. However, the selective synthesis of α-olefins from ethylene, a highly abundant and inexpensive feedstock, is restricted, and thus a broadly applicable selective α-olefin synthesis using ethylene is highly desirable. Here, we report the catalytic reaction of an α-olefin with two ethylene molecules. The first ethylene molecule forms a 4-ethyl branch and the second a new terminal carbon-carbon double bond (C2 elongation). The key to this reaction is the development of a highly active and stable molecular titanium catalyst that undergoes extremely fast ß-hydride elimination and transfer.

A Standardized g-Force Allows the Preparation of Similar Platelet-Rich Fibrin Qualities Regardless of Rotor Angle.

Platelet-rich fibrin (PRF) is an autologous blood concentrate that supports tissue regeneration. The effect of the centrifuge rotor angle in the fabrication of PRF is still not fully elucidated. The hypothesis of this study is: When applying the same g-force (relative centrifugal force [RCF]) and centrifugation time, PRF components and bioactivity are not modified using either a swing-out rotor or a fixed angle rotor. For this purpose, peripheral blood samples (from five donors) were used to gain solid (710 ×g, 8 min) and liquid (44 ×g, 8 min) PRF matrices using three different centrifuges (one fixed angle as a control and two different swing-out rotor centrifuges). The physical characteristics of the solid PRF were measured to evaluate the clot formation and cellular distribution. The liquid PRF was used to evaluate the cell number, bioactivity, and influence on primary human osteoblasts (pOBs) and primary human fibroblasts (pHFs) in vitro. Solid PRF clots were significantly larger in the group of fixed rotor centrifuges compared with either of the two evaluated swing-out rotor centrifuges. No differences were observed when evaluating the cellular distribution within the solid PRF. No statistically significant differences were documented in the cell's density in liquid PRF samples (platelets, lymphocytes, neutrophils, eosinophils, and basophils) among the differently gained PRF samples. No statistically significant differences were documented for the released growth factors (vascular endothelial growth factor, epidermal growth factor, and transforming growth factor beta 1) over 7 days. pOBs and pHFs viability after treatment with PRF conditioned media showed no statistically significant differences between the evaluated groups. However, the number of adherent cells treated with PRF obtained with the use of the fixed angle rotor was significantly higher when compared with those treated with PRF obtained by using the swing-out rotors. The presented results confirm that regardless of the centrifuge rotor used, the components and bioactivity of solid and liquid PRF matrices are modified by the applied RCF and centrifugation time. These findings are of great importance for highlighting the essential role of adapting the centrifugation protocols when using different centrifuges and to correctly report the used centrifugation protocols in scientific research to allow for reproducible results. Impact statement Platelet-rich fibrin (PRF) is prepared from autologous peripheral blood and is widely applied in research and clinical treatments. The centrifugation parameters used during the preparation of PRF directly influence its components and bioactivity. By using a standardized protocol, the present study demonstrated that adapting various centrifuges to a standardized relative centrifugal force and centrifugation protocol resulted in reproducible PRF matrices with similar bioactivity, regardless of the centrifuge rotor angle. These findings underline the necessity to carefully adapt and correctly report the used centrifuge and centrifugation protocols in scientific research to allow reproducible results.

Degradation of low-density polyethylene to nanoplastic particles by accelerated weathering.

When plastics enter the environment, they are exposed to abiotic and biotic impacts, resulting in degradation and the formation of micro- and nanoplastic. Microplastic is ubiquitous in every environmental compartment. Nevertheless, the underlying degradation processes are not yet fully understood. Here, we studied the abiotic degradation of commonly used semi-crystalline, low-density polyethylene (LDPE) in a long-term accelerated weathering experiment combining several macro- and microscopic methods. Based on our observations, the degradation of LDPE proceeds in three stages. Initially, LDPE objects are prone to abrasion, followed by a period of surface cracking. A large number of secondary particles with a high degree of crystallinity are formed, with sizes down to the nanometer scale. These particles consist of highly polar oligomers leading to agglomeration in the final stage. We therefore suppose that weathered microplastic and nanoplastic particles will attach to colloidal environmental matter. This offers an explanation for the absence of free nanoplastic particles in natural samples.

Highly active titanium-based olefin polymerization catalysts bearing bulky aminopyridinato ligands.

A series of titanium complexes have been prepared using either salt metathesis or amine elimination reactions. Reacting the potassium salt of Ap*H {Ap*H = N-(2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)pyridin-2-yl]amine} (1) with [TiCl(4)(THF)(2)] results in the formation of a nucleophilic ring-opening product of the coordinated tetrahydrofuran (THF) ligand [Ap*TiCl(2)(OC(4)H(8)Cl)] (7). Alkylation with benzylmagnesium chloride gave rise to the corresponding benzyl complex [Ap*TiBn(2)(OC(4)H(8)Cl)] (8). However, THF ring opening was overcome by adopting an amine elimination route instead of salt metathesis. Mono(aminopyridinato)titanium trichloro complexes were prepared in high yields using [(CH(3))(2)NTiCl(3)], together with the corresponding sterically demanding aminopyridine as the starting material. The synthesized complexes could then be alkylated selectively. These complexes were characterized by spectroscopic methods, and their behavior in olefin polymerization and copolymerization of ethene and propene was explored. These mono(aminopyridinato)titanium trichloro complexes are less active if activated with methylaluminoxane (MAO). However, the activity increases strongly if MAO is replaced by d-MAO ("dry methylaluminoxane"). The catalysts show moderate activity toward propene polymerization, while ethylene-propylene copolymers in high-productivity with separated propene units were observed. The catalysts are also highly active in the co- and terpolymerization of 2-ethylidenenorbornene (ENB) with ethylene or ethylene-propylene, together with a very good incorporation of ENB. In all cases, the activity increases with an increase in the steric bulk of the protecting ligand.

Transverse stability of 3-piece Le Fort I osteotomies.

PURPOSE: The transverse dentoalveolar and skeletal stability of multipiece Le Fort I osteotomies with 3 different techniques was investigated. MATERIALS AND METHODS: The records of 87 patients undergoing bimaxillary osteotomies with 3-piece Le Fort I osteotomy were evaluated. According to the surgical technique of maxillary expansion, the subjects were divided into 3 groups: unilateral palatal osteotomy (group A), bilateral palatal osteotomy (group B), and unilateral palatal osteotomy with fixation of the palatal vault with a resorbable plate (group C). In group A palatal bone grafts were used in 9 patients. Posterior-anterior cephalograms and dental casts were taken before surgery (T1), immediately after surgery (T2), and after a follow-up of 12 to 15 months (T3). The skeletal base was measured between the intersections of the lateral contour of the maxillary alveolar process and the lower contour of the maxillo-zygomatic process. Dentoalveolar width was measured between the first premolars and the first molars. According to the magnitude of expansion, the groups were divided into the following subgroups: negative (constriction), 0 to 2 mm, greater than 2 mm to 4 mm, and greater than 4 mm. An analysis of variance with Bonferroni correction was used to compare the demographic and treatment characteristics and the surgical and postsurgical transverse movements of the 3 study groups. The paired t test was run to evaluate the surgical changes (T2 - T1) and the postsurgical stability (T3 - T2). The influence of palatal bone grafts and downgrafting of the maxilla on the amount of relapse was investigated with the unpaired t test. RESULTS: The study variables (T1), the surgical changes (T2 - T1), and the postsurgical changes (T3 - T2) showed no significant differences between the 3 study groups. However, a tendency for less relapse in cases with major expansion was seen in group C. The mean expansion of the entire sample was 2.13 mm at the skeletal base, 1.11 mm in the premolar region, and 1.99 mm in the molar region. Mean relapses of 0.20 mm (9%) at the skeletal base, 0.76 mm (68%) in the premolar region, and 1.20 mm (60%) in the molar region were seen. Palatal bone grafts had no significant effect on the postsurgical changes in group A. Anterior and posterior downgrafting did not result in significantly more relapse. CONCLUSIONS: Surgical expansion of the maxilla provides stable results at the maxillary skeletal base but high relapse rates in the dentoalveolar area. Preoperative orthodontic expansion is one of the main sources of transverse relapse. Fixation of the palatal vault with resorbable plates is a possible technique to improve transverse stability. Larger samples are necessary to provide statistical significance.

Engaging a polylactide copolymer in oral tissue regeneration: first validation of Suprathel® for guided epithelial and osseous healing.

The present study investigated the capacity of Suprathel® (a copolymer membrane, so far validated for skin regeneration) to also regenerate oral tissue - mucosa and bone, by comparing this biomaterial, in a split-mouth rabbit model, to Mucoderm®, a xenogeneic collagen matrix certified for keratinized oral mucosa healing. The clinical reason behind this experimental animal model was to determine whether the benefits of this advanced skin regeneration product (Suprathel®) could be conveyed for future evaluation in clinical trials of oral tissue regeneration in humans. The outcomes of this study validated the use of Suprathel®, a terpolymer of polylactide with trimethylene carbonate and ε-caprolactone, for stimulation of oral epithelium and alveolar bone regeneration in rabbits. Both Suprathel® and Mucoderm® exhibited comparable results and the null hypothesis stating a comparable regenerating effect of these two materials could not be rejected.

Stability of Le Fort I osteotomy in bimaxillary osteotomies: single-piece versus 3-piece maxilla.

PURPOSE: The aim of the present study was to investigate the effect of segmentation on the stability of Le Fort I osteotomies in bimaxillary procedures. PATIENTS AND METHODS: One hundred twenty patients undergoing bimaxillary osteotomies (60 single-piece maxilla, 60 3-piece maxilla) were included in the study. Cephalometric analysis was performed before surgery (T1), immediately after surgery (T2), and after a follow-up of 12 to 15 months (T3). The positional changes of 6 angles (angle of nasion-sella line to A point-nasion line, angle of nasion-sella line to B point-nasion line, angle of nasal line [plane] to nasion-sella line, angle of mandibular line [plane] to nasion-sella line, angle of upper incisor to nasion-sella line, angle of lower incisor to mandibular line [plane]) and 4 maxillary landmarks (upper incisor edge, mesial cusp upper first molar, anterior nasal spine, posterior nasal spine) were measured by superimposition of radiographs. Paired t test was run to evaluate surgical changes (T2-T1) and postsurgical stability (T3-T2). Differences between the 1-piece maxilla group and the 3-piece maxilla group were analyzed with 2-tailed t test. Pearson correlation coefficient was calculated to determine relations among the magnitude of maxillary advancement, superior and inferior repositioning and postsurgical changes of angle of nasion-sella line to A point-nasion line, and the respective landmarks. RESULTS: The study variables (T1), surgical changes (T2-T1), and postsurgical changes (T3-T2) showed no significant differences between groups with single-piece and 3-piece maxilla. However, a tendency for more relapse was observed in the 3-piece maxilla group in the vertical direction. A significant inferior movement of the upper molar (mesial cusp upper first molar) was seen in the single-piece maxilla group (0.5 mm) and the 3-piece maxilla group (0.4 mm). In both groups and all directions, the T2-to-T3 changes had no significant correlation with the T1-to-T2 changes. No differences were observed between superior and inferior repositioning. CONCLUSIONS: Segmentation of the maxilla does not provoke major skeletal or dental instability and should be considered whenever indicated. Adequate bone grafting provides good stability in anterior and inferior repositioning of the maxilla.

Factors for intraoperative blood loss in bimaxillary osteotomies.

PURPOSE: Autologous blood donation is not routinely recommended for all cases of orthognathic surgery. The aim of this study was to evaluate the factors for blood loss during bimaxillary osteotomies that might indicate preoperative blood donation. PATIENTS AND METHODS: In a prospective study, 127 consecutive patients undergoing bimaxillary surgery within a 14-month period were examined for hemoglobin and hematocrit reduction. Possible factors for intraoperative blood loss such as operating time, application of hydroxyethyl starch in segmental osteotomies, experience of the surgeon, and additional procedures (genioplasty, malar osteotomy, iliac crest graft) were statistically analyzed. RESULTS: The experience of the surgeon had no influence on the blood loss. Operating time and Quick value correlated significantly with hemoglobin and hematocrit drop after surgery. There was no difference between 1-piece maxilla cases with or without additional procedures and segmental maxilla cases without additional procedures. Only for the group of patients with segmental osteotomies and additional procedures was a significant higher blood loss found. Two patients (1.6%) received 1 unit of blood. CONCLUSION: For patients undergoing bimaxillary osteotomies with segmentation of the maxilla and additional procedures, a preoperative donation of autologous blood should be considered.

Prevalence of Temporomandibular Disorder Symptoms among Orthognathic Patients in Southern Germany: Retrospective Study.

This study investigated the prevalence of temporomandibular disorder (TMD) among patients before and after orthognathic surgery and assessed the effect of orthognathic surgery on each of the TMD symptoms (clicking, pain, crepitus, and MRI findings). A sample of 100 consecutive patients undergoing bimaxillary surgery for correction of craniofacial deformities (31 male and 69 female), with ages ranging between 17 and 58 years (mean age: 27.7 ± 9.3 years), were interviewed and examined regarding signs and symptoms of TMD. Clinical examination and X-ray and magnetic resonance imaging of the temporomandibular junction were performed at the time of surgery and 1 year thereafter. The prevalence of TMD preoperatively and postoperatively was 35% and 27%, respectively. A high frequency of relief was found in the patients with TMD symptoms (74.3%; 19 (70.3%) of patients had reduced clicking, 7 (87.5%) patients had reduced pain, 4 (100%) patients had reduced crepitus, and 4 (57.1%) patients showed changes in MRI findings), 12 patients who were asymptomatic before surgery developed clicking in TMJ after surgery, 3 developed pain, and 3 developed crepitus. TMD problems can occur in a variety of patients, including those who have facial deformities, and require orthognathic surgery. However, orthognathic surgery may not predictably treat or reduce the symptoms of TMD.

A broadly tunable synthesis of linear α-olefins.

The catalytic synthesis of linear α-olefins from ethylene is a technologically highly important reaction. A synthesis concept allowing the formation of selective products and various linear α-olefin product distributions with one catalyst system is highly desirable. Here, we describe a trimetallic catalyst system (Y-Al-Ni) consisting of a rare earth metal polymerization catalyst which can mediate coordinative chain transfer to triethylaluminum combined with a simultaneously operating nickel ß-hydride elimination/transfer catalyst. This nickel catalyst displaces the grown alkyl chains forming linear α-olefins and recycles the aluminum-based chain transfer agent. With one catalyst system, we can synthesize product spectra ranging from selective 1-butene formation to α-olefin distributions centered at 850 gmol-1 with a low polydispersity. The key to this highly flexible linear α-olefin synthesis is the easy tuning of the rates of the Y and Ni catalysis independently of each other. The reaction is substoichiometric or formally catalytic regarding the chain transfer agent.

A highly efficient titanium-based olefin polymerisation catalyst with a monoanionic iminoimidazolidide pi-donor ancillary ligand.

The titanium complex Cp[1,3-(2',6'-Me2C6H3)2(CH2N)2C=N]Ti(CH2Ph)2, with a monoanionic eta 1-iminoimidazolidide ancillary ligand, is shown to be a highly efficient catalyst for olefin polymerisation when activated with the Lewis acid B(C6F5)3.

Distraction osteogenesis of the mandible: evaluation of callus distraction by B-scan ultrasonography.

INTRODUCTION: Distraction osteogenesis is a new and reliable technique for lengthening of hard and soft tissue in cranio-maxillofacial surgery. Since its first applications, X-rays were often the preferred diagnostic method to monitor this treatment. Apart from adding an additional radiation dose, analysis cannot detect and follow the osteogenic process in the distraction gap on the one hand, nor can it evaluate the soft tissue around the distracted area. In this paper, the authors report their experience with B-scan imaging to control mandibular distraction and to overcome the shortcomings of X-rays analysis. METHOD: Comparison of B-scanning with the traditional X-ray methods was performed in 12 patients. RESULTS: B-scan evaluation appeared to be a precise technique in monitoring the different phases of distraction. It is easy to repeat whenever necessary. Early and late complications of soft tissue healing, movements of the bone segment, as well as the osteogenesis were easily detectable. CONCLUSION: In the authors' opinion B-scan evaluation can play an important role in monitoring distraction osteogenesis.