Search

• α-Olefins are important bulk and fine chemicals employed for the synthesis of plastics, detergent alcohols and lubricants for instance. The synthesis of α-olefins from ethylene, an abundantly available and inexpensive feedstock, is highly attractive, is carried out in megaton scale annually and is a key application of homogenous catalysis. Unfortunately, the synthesis of branched olefins is challenging especially in direct or so call on-purpose synthesis. We recently reported a molecular Ti catalyst (Science 2022) permitting the selective reaction between an α-olefin and two ethylene molecules to overcome this problem. Unfortunately, the synthesis of the Ti pre-catalyst(s) is very challenging preventing easy derivative modifications to fully exploiting the potential of the novel reaction. • We report on an easily accessible zirconium catalyst that permits the co-oligomerization of 1-hexene and ethylene. • We report synthesis and structure of six novel Zr precatalysts. • Some of the Zr catalyst systems introduced here show an extremely high activity in ethylene homo-oligomerization. Selective co-oligomerizations between α-olefins and ethylene are of high interest since they allow to extend the α-olefin scope employing inexpensive and abundantly available ethylene. Here we report on an easily accessible zirconium catalyst that permits the co-oligomerization of 1-hexene and ethylene with an activity of 2200 kg/mol h bar and a co-oligomer selectivity of 65 mol%. In more detail, we report synthesis and structure of six novel Zr precatalysts, their ethylene homo-oligomerization behavior and the co-oligomerization of the most promising of the six precatalysts. Criteria were activity and selectivity (α-value). Some of the Zr catalyst systems introduced here show an extremely high activity in ethylene homo-oligomerization up to 96,600 kg/mol h bar. [ABSTRACT FROM AUTHOR]

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 e-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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A series of tripodal nitrogen containing ligands including amidine and aminopyridines with extra oxazoline functionality were synthesized. The corresponding titanium complexes bearing such ligands were synthesized by diethylamine elimination route. Diethylamidotitanium trichloride [EtNTiCl] reacts with the functionalized anilines, 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-N-(2-fluorophenyl)-aniline (FOxH) and 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-N-(2-methoxyphenyl)aniline (MeOOxH), the amidine(E)-N'-(2,6-diisopropylphenyl)-N-(2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenyl)benzimidamide ( Am OxH), and the aminopyridines N-(2-(4,4-dimethyl-4,5-dihydro oxazol-2-yl)phenyl)-6-(piperidin-1-yl)pyridin-2-amine (ApOxH) and N-(2-(4,4- dimethyl- 4,5-dihydrooxazol-2-yl)phenyl)-6-(2,4,6-triisopropyl phenyl)pyridin-2-amine (Ap*OxH), under diethylamine elimination to form the corresponding titanium trichlorides [FOxTiCl3], [MeOOxTiCl3], [AmOxTiCl3], [ApOxTiCl3] and [Ap*OxTiCl3] in excellent yields. These compounds were characterized by spectroscopic methods, and X-ray crystal structure analysis (selected complexes). Furthermore, their behavior in ethylene polymerization was explored. The complexes show moderate activity towards ethylene if activated with MAO. The observed PEs were analyzed by HT-GPC and were found to be of low molecular weight for the amidinate AmOxTiCl3 but of very high one (Mp up to 3.5 million g/mol) for the aminopyridinate Ap*OxTiCl3 titanium complex. [ABSTRACT FROM AUTHOR]

α-Olefins are very important bulk and fine chemicals and their synthesis from ethylene, an abundantly available and inexpensive feedstock, is highly attractive. Unfortunately, the direct or on-purpose synthesis of olefins from ethylene is limited to three examples, 1-butene, 1-hexene, and 1-octene, all having a linear structure. Herein, the direct synthesis of 3-methylenepentane and 4-ethylhex-1-ene, branched trimerization, and tetramerization products of ethylene, respectively, is reported. Different molecular titanium catalysts, all highly active, with a selectivity toward the formation of the branched ethylene trimer or tetramer, the employment of different activators, and different reaction conditions are the key to selective product formation. The long-time stability of selected catalysts employed permits upscaling as demonstrated for the synthesis of 4-ethylhex-1-ene (52 g isolated, TON(ethylene) 10.7 · 10 6 )., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

The aim of this study was to analyze published works that investigate the in vivo bone regeneration capacity of polymeric membranes loaded with active substances and growth factors. This scoping review's purpose was to highlight the histological and radiological interpretation of the locally produced effects of the polymer membranes studied so far. For the selection of the articles, a search was made in the PubMed and ScienceDirect databases, according to the PRISMA algorithm, for research/clinical trial type studies. The search strategy was represented by the formula "((biodegradable scaffolds AND critical bone defect) OR (polymers AND mechanical properties) OR (3Dmaterials AND cytotoxicity) AND bone tissue regeneration)" for the PubMed database and "((biodegradable scaffolds AND polymers) OR (polymers AND critical bone defects) OR (biodegradable scaffolds AND mechanical properties) AND bone tissue regeneration)" for the ScienceDirect database. Ethical approval was not required. Eligibility criteria included eight clinical studies published between 2018 and 2023. Our analysis showed that polymer membranes that met most histopathological criteria also produced the most remarkable results observed radiologically. The top effective scaffolds were those containing active macromolecules released conditionally and staged. The PLGA and polycaprolactone scaffolds were found in this category; they granted a marked increase in bone density and improvement of osteoinduction. But, regardless of the membrane composition, all membranes implanted in created bone defects induced an inflammatory response in the first phase.

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., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

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.

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.

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 β-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.

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., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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., (Copyright © 2011 American Association of Oral and Maxillofacial Surgeons. Published by Elsevier Inc. All rights reserved.)

Objective: The aim of the present study was to investigate the effect of segmentation and different movements of the segments in LeFort I osteotomies on the bone blood flow (BBF)., Material and Methods: The study sample of the prospective cohort study was composed of subjects scheduled to undergo 3-piece LeFort I osteotomies and simultaneous BSSO for correction of developmental skeletal deformities. The primary predictor variables were: time (T1, before LeFort I osteotomy; T2, after LeFort I osteotomy; T3, after segmentation and fixation of the maxilla) and magnitude of maxillary movement in the sagittal, vertical, and transverse planes measured in millimeters (mm). The subjects were assigned to 2 risk groups (high/low) depending on the amount of the movement. The primary outcome variable was maxillary bone blood flow measured with a laser Doppler at 4 sites: premaxilla, right and left maxillary lateral segments, and the mandible., Results: No significant difference was observed among the 3 maxillary regions. The mean decrease of the maxillary BBF between T1 and T2 as well as the reduction of BBF between T2 and T3 were statistically significant for all regions (P = .028 to P = .005 for T1/T2; P = .003 to P = .028 for T2/T3). No significant difference could be found between the 2 risk groups of maxillary movements., Conclusions: Multisegmental maxillary osteotomies lead to a significant reduction of BBF. Moderate maxillary movements have no significant influence on the blood supply.

Aminopyridinato-ligand-stabilized organoyttrium cations are accessible in very good yield through alkane elimination from trialkyl yttrium complexes with sterically demanding aminopyridines, followed by abstraction of one of the two alkyl functions using ammonium borates. At 80 degrees C and in the presence of small amounts of aluminum alkyl compounds, very high ethylene polymerization activities are observed if very bulky aminopyridinato ligands are used. During these polymerizations a reversible polyethylene chain transfer is observed between the organoyttrium cations and aluminum alkyls. The chain-transfer catalyst system described here is able to produce relatively long-chain (up to 4000 g mol-1) Al-terminated polyethylene with a molecular-weight distribution<1.1. In the synthesis of higher molecular PE a slight increase in polydispersity with increasing chain length (15,600 g mol-1, approximately 1.4) is observed owing to reduced reversibility caused by higher viscosity and precipitation of polymer chains (temperature of 80-100 degrees C).

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.

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.