ABSTRACT
Herein, N-heterocyclic olefins (NHOs) are utilized as catalysts for the ring-opening polymerization (ROP) of functional aliphatic carbonates. This emerging class of catalysts provides high reactivity and rapid conversion. Aiming for the polymerization of monomers with high side chain functionality, six-membered carbonates derived from 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) served as model compounds. Tuning the reactivity of NHO from predominant side chain transesterification at room temperature toward ring-opening at lowered temperatures (-40 °C) enables controlled ROP. These refined conditions give narrowly distributed polymers of the hydrophobic carbonate 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MTC-OBn) (D < 1.30) at (pseudo)first-order kinetic polymerization progression. End group definition of these polymers demonstrated by mass spectrometry underlines the absence of side reactions. For the active ester monomer 5-methyl-5-pentafluorophenyloxycarbonyl-1,3-dioxane-2-one (MTC-PFP) with elevated side chain reactivity, a cocatalysis system consisting of NHO and the Lewis acid magnesium iodide is required to retune the reactivity from side chains toward controlled ROP. Excellent definition of the products (D < 1.30) and mass spectrometry data demonstrate the feasibility of this cocatalyst approach, since MTC-PFP has thus far only been polymerized successfully using acidic catalysts with moderate control. The broad feasibility of our findings was further demonstrated by the synthesis of block copolymers for bioapplications and their successful nanoparticular assembly. High tolerability of NHO in vitro with concentrations ranging up to 400 µM (equivalent to 0.056 mg/mL) further emphasize the suitability as a catalyst for the synthesis of bioapplicable materials. The polycarbonate block copolymer mPEG44-b-poly(MTC-OBn) enables physical entrapment of hydrophobic dyes in sub-20 nm micelles, whereas the active ester block copolymer mPEG44-b-poly(MTC-PFP) is postfunctionalizable by covalent dye attachment. Both block copolymers thereby serve as platforms for physical or covalent modification of nanocarriers for drug delivery.
ABSTRACT
Under mild conditions, PPO-PEO-PPO ("reverse Pluronics") and PBO-PEO-PBO copolyether were generated by way of N-heterocyclic olefin-based organocatalysis. Reverse Pluronics with molar masses > 20 000 g mol-1 could be synthesized with excellent control (DM ≤ 1.03) and were converted into (ordered) mesoporous carbons via organic self-assembly to showcase the need for tailor-made copolymer as structure-directing agent.
ABSTRACT
BACKGROUND: Since the first description of the minimally invasive totally gasless video-assisted thyroidectomy (MIVAT) technique in 1998, relatively few studies have evaluated the outcome of this procedure. The authors review their experiences based on a prospective randomized trial comparing the potential advantages of MIVAT over conventional thyroidectomy. METHODS: Patients undergoing surgery for either thyroid nodule or diffuse thyroid disease with hyperthyroidism were randomly selected for either MIVAT or conventional thyroidectomy. The exclusion criteria specified nodules larger than 35 mm, thyroid lobe volume greater than 20 ml, thyroiditis, and previous neck irradiation or surgery. Operative time, postoperative complications, and cosmetic results were evaluated using both a verbal response scale and a numeric scale. RESULTS: Both the MIVAT group and the conventional thyroidectomy group included 15 patients. No significant differences were noted between the two groups in terms of age, sex, or indication for operation. The mean operative times were 65.5 +/- 18 min. for MIVAT and 43.3 +/- 14 min. for conventional thyroidectomy (P = 0.001). No postoperative complications were detected in either group. The cosmetic results, evaluated by both verbal response and numeric scales, were respectively as follows: MIVAT (3.7 +/- 0.2 and 7.9 +/- 1.2) and conventional thyroidectomy (2.3 +/- 0.7 and 4.9 +/- 1.3). The differences significantly favored MIVAT (P = 0.028 and P = 0.015, respectively) despite the small number of patients enrolled in this study, and consequently, its limited statistical power. CONCLUSION: Although the complications are comparable between the two approaches, conventional thyroidectomy involves less operative time. However, MIVAT offers distinct advantages to selected patients in terms of very good to exellent cosmetic results and reduced postoperative distress.
Subject(s)
Hyperthyroidism/surgery , Thyroidectomy/methods , Video-Assisted Surgery/methods , Adult , Aged , Esthetics , Female , Humans , Male , Middle Aged , Minimally Invasive Surgical Procedures , Postoperative Complications , Prospective Studies , Treatment OutcomeABSTRACT
Minimally invasive video-assisted thyroidectomy (MIVAT) was published in 1998. In this paper authors describe their initial experiences with this new technique, which is the first publication in their country on this topic based on authors knowledge. Ten patients were selected for MIVAT. Selection criteria were nodule size less than 30 mm, thyroid lobe volume less than 20 ml, no thyroiditis, no previous neck surgery or irradiation. The procedure was carried out through a 20-25 mm central incision above the sternal notch. Dissection was performed under endoscopic vision, using endoscopic, some special and conventional instruments. Authors performed 1 total thyroidectomy, 6 lobectomies, 2 lobectomies with subtotal resection on the opposite side, and 1 resection of thyroid isthmus. Mean operative time was 77 minutes. No conversion to open procedure was performed. No recurrent laryngeal nerve palsy or postoperative hypocalcemia were observed postoperatively. The mean hospital stay was 2 days. The cosmetic result and the postoperative distress were considered very good by the patients. The authors conclude that MIVAT is a safe and feasible procedure. The indications are limited, but in this small group of patients offer excellent cosmetic results with less postoperative distress.
Subject(s)
Thyroidectomy/methods , Video-Assisted Surgery/methods , Adult , Female , Humans , Male , Middle Aged , Minimally Invasive Surgical Procedures/methods , Retrospective Studies , Thyroidectomy/adverse effectsABSTRACT
The surgical treatment of ventral hernias has changed in the last decade. Conventional methods involve tightening of the abdominal fascias is the reason for high recurrence rate. While the use of mesh reduces the recurrence rate, it does not change the rate of other complications, in particular, the risk of infection. We report the results of laparoscopic repair of ventral hernias performed in 15 patients (10 female, 5 male). The average age of patients was 59.5 years (39-79). Indications included 7 recurrent incisional hernias (3 patients had second recurrence, 4 patients had first recurrence operated on without mesh in the first operation); 5 patients with primary incisional hernias; and 3 primary umbilical hernias. The mean size of the defect was 66.2 cm2 (16-130 cm2). Average operation time was 101 minutes (64-190 min). In the postoperative period 1 patient developed seroma, and 4 patients developed ileus each was successfully treated conservatively. In one patient a second-look laparoscopy was performed because of neuralgia. Length of hospital stay varied between 3 and 10 days (median: 6 days); the length of follow-up period was 5-22 months (median: 12.4 months). We believe that laparoscopic treatment of ventral hernias reduces the complication rate, and reduces hospital stay.
